Melting & Dropping Point

Transcription

1 Melting & Dropping Point Melting Point Dropping Point Softening Point Performance Verification Automated Melting & Dropping Point Analysis A Comprehensive Textbook

2 Content Content 1. Introduction 4 2. The Melting Point General Considerations Automatic Melting Point Determination: The METTLER TOLEDO MP Excellence Instrument Line Automatic Melting Point Determination: The Measurement Principle Pharmacopeia Melting Point Transmission Intensity Curve Thermodynamic Melting Point Application Tips & Hints for Accurate Melting Point Determination Instrument Calibration and Adjustment Quick and Reliable Sample Preparation: The Capillary Filling Tool Melting Point Capillary Sample Preparation Sample Preparation: Bad Example Sample Preparation: Good Example Sample Measurement Tips & Hints Melting Point Standards Overview Melting Point Measurement Results 18 4 Melting Point Workflow Support by LabX PC Software Melting Point Workflow Integration and Support by LabX Melting Point Screening Supported by LabX 21 5 Fundamentals of Dropping & Softening Point Determination General Consideration Automatic Dropping and Softening Point Determination: The METTLER TOLEDO DP Excellence Instrument Line Automatic Dropping and Softening Point Determination: The Unique Detection Principle Automated Dropping Point Measurement by Video Based Image Analysis Automated Softening Point Measurement by Video Based Image Analysis International Dropping and Softening Point Standards 25 6 Application Tips & Hints for Accurate Dropping & Softening Point Determination Instrument Calibration and Adjustment Sample Preparation DP Excellence Accessory Box Efficient and Reliable Sample Preparation: The Sample Preparation Tool DP Excellence Sample Holder and Standard Compliant Cups Solid Samples Lubricant Greases Bitumen, Pitch 33 2

3 6.2.7 Resins, Rosins Waxes Liquid Samples or Samples that Require Cooling Prior to Measurement 35 7 Dropping and Softening Point Measurement Results Dropping Point of Edible Oils and Fats Measured on DP90 Excellence Dropping Point of Fats and Waxes Measured on DP70 Excellence Dropping Point of Lubricant Greases Softening Point of Bitumen Softening Point of Resins 41 8 Performance Verification with MP VPac Ready-to-use Kit of Traceable Reference Substances Do-it-yourself Service Reference Substances 42 9 More Information 43 3

4 Introduction 1. Introduction In order to characterize a material aside from chemical analysis, primarily physical methods allow us to differentiate between, identify and classify substances or to provide descriptions of quality. The thermal characteristics of a substance or mixture of substances, such as melting point, provide valuable and accessible information in this respect. The melting point is the temperature at which the solid phase changes to the liquid state. Such accurate data is associated with the equally important, but more empirical, thermal characteristic: dropping or softening point of industrial or naturally-occurring products. These empirical values are dependent on the measurement method used and thus require a sensible standardized procedure. The exact thermal characteristics of almost all pure organic and inorganic substances, however, can be found in comprehensive tables. For almost 5 decades METTLER TOLEDO has provided instrumental solutions for the automatic determination of the thermal values melting point, dropping and softening point. The melting point and Dropping Point Excellence line, METTLER TOLEDO s latest release of compact instruments for thermal characterization, support the complete analytical workflow with innovative solutions. These are highlighted in this guideline in addition to fundamental knowledge about melting, dropping and softening point determination and practical application tips for daily use. 4

5 2. The Melting Point 2.1 General Considerations Determination of melting point is one of the oldest methods of identification and testing, particularly for organic substances. Melting point is easy to determine and, since it is a numerical property, can be conveniently tabulated and classified. Since melting point is highly dependent on purity, it can also be used for evaluating the quality of substances. Pure crystalline substances change to the liquid state at a precisely defined temperature, which is specific for each crystalline material. Crystalline and molten states of the same material can only exist at the same time at the melting point. Automatic melting point determination methods make use of these phenomena, which become visible during the change in aggregate state. Pure substances melt at a highly-defined temperature whereas impure, contaminated substances generally exhibit a large melting interval. The temperature at which all material of a contaminated substance is molten is usually lower than that of a pure substance. This behavior is known as melting point depression and can be used to obtain qualitative information about the purity of a substance. 2.2 Automatic Melting Point Determination: The METTLER TOLEDO MP Excellence Instrument Line The Melting Point Excellence instrument portfolio consists of three compact models for automatic melting point determination: the MP50, the MP70 and the MP90. Each comes with a color touchscreen for intuitive and efficient operation. The user interface follows the established One Click philosophy that is common for all instruments in METTLER TOLEDO s analytical instrument portfolio. The MP50 Excellence measures the melting point of up to four samples at the same time from ambient temperature to 300 C maximum. The melting point or melting range measurements are performed in the pharmacopeia mode, which means that the furnace temperature is recorded. The transmission curves are evaluated with fixed, noneditable parameters to obtain either melting point or melting range. The MP50 comes with one method template. Based on this template, a maximum of 12 different melting point determinations can be set up and started via Shortcuts on the touch screen. Method parameters cannot be edited once they are stored. Furthermore, the MP50 does not provide a database for reference substances or automatic calibration routines. The latter must be performed manually. Temperature accuracy specifications over the whole measurement range are outstanding and superior to any competitor instrument. Black and white melting point videos can be recorded up to a maximum length of 60 min per individual measurement and up to a total recording time of 60 min. For documentation purposes the MP50 provides GLP-compliant printouts with the compact USB-P25 printer from METTLER TOLEDO. The MP70 Excellence measures the melting point of up to four samples at a time from ambient temperature to 350 C. Melting point and melting range measurements are performed in the pharmacopeia mode, as in the MP50. In addition, melting point furnace temperatures can be corrected automatically to obtain the thermodynamic melting point. Melting curves can be evaluated with editable parameters allowing flexible adaptation to the melting properties of the substance; decomposing, subliming or colored substances can be accurately tested. Five ready-to-use METTLER TOLEDO 5

6 The Melting Point methods come with the instrument, containing optimized parameters to immediately start calibration measurements with METTLER TOLEDO reference substances. The MP70 can stores up to 20 editable methods which can be started via ShortCuts. The melting point values of five METTLER TOLEDO reference substances are stored in the instrument. These values are used to validate the calibration by comparing them with the actual measurement and storing them for a subsequent adjustment, if required. Transcription errors are thus avoided and the instrument's temperature adjustment is greatly facilitated. Temperature accuracy specifications are identical to that of the MP50. Melting point videos can be recorded in color up to a maximum length of 60 min per individual measurement and up to 300 min total recording time. The MP70 and MP90 allow video storage on an SD card inserted into the instrument. For documentation purposes the MP70 provides GLP compliant printouts with the compact USB-P25 printer from METTLER TOLEDO. Comprehensive printouts including result data, transmission curves and melting point video snapshots can be stored as pdf files or printed on a network printer. Last but not least, the MP70 can be connected to LabX PC software that provides, amongst many other features, complete instrument control based on automatically processed methods, secure data storage, and result validation. The MP70 instrument can be integrated into a PC software network together with other analytical instrument solutions from METTLER TOLEDO. The MP90 Excellence is the high-end model of the MP Excellence instrument line. It includes all MP70 features plus a higher temperature range of up to 400 C. 6 capillaries can be measured at the same time. Up to 60 methods and up to 100 reference substances can be stored. The MP90 is designed for varied and high sample throughput and high automation demands. 2.3 Automatic Melting Point Determination: The Measurement Principle The determination of melting point is usually performed in glass capillaries with an internal diameter of approx. 1 mm and a wall thickness of mm. The finely ground sample is placed in the capillary tube to a filling level of 2 3 mm and heated in an appropriate furnace. The melting process is visually inspected. This method is required in many local pharmacopeias. Moistening Point Sintering Point Collapse Point A Meniscus Point B Clear Point C The Japanese Industrial Standard 'JIS K 0064' from 1992 shows a comprehensive illustration of different stages of the melting process of a solid crystalline substance inside a capillary. We focus on the distinct stages 'Collapse point', 'Meniscus point' and 'Clear point and label them A, B and C. The Collapse point «A» shows the substance mostly solid and a small amount of molten material. At the meniscus point «B» most of the substance is molten but some solid material is still present. At point C, the clear point, the substance is completely molten. Obviously the temperature increases between points A and C. At the melting point not only the aggregate state changes; quite a lot of other physical characteristics also change significantly. Amongst these are the thermodynamic values, specific heat capacity, enthalpy, and rheological properties such as volume or viscosity. Last but not least, the optical properties birefringence 6

7 reflection and light transmission change. Compared to other physical values the change in light transmission can easily be determined and can therefore be used for melting point detection. Capillary with sample Window Reflection light source Furnace Transmission light source Camera system Powdered crystalline materials are opaque in the crystalline state and transparent in the liquid state. This distinct difference in optical properties can be measured in order to determine the melting point by recording the percentage of light intensity shining through the substance in the capillary, the transmittance, in relation to the measured furnace temperature. In the METTLER TOLEDO melting point instruments MP50, MP70 and MP90, a red LED is used as the transmission light source which shines through holes inside the furnace in the lower region of the capillary. The transmitted light is recorded by a video camera. As required by pharmacopeias, METTLER TOLEDO melting point instruments provide visual inspection of the melting process. White LED light shines on the furnace. The reflected light is recorded by a video camera and 6.5 magnification allows clear observation of even dark-colored substances. The video camera serves as an artificial eye and also allows visual determination of the melting point, if required by the SOP. Furthermore, the complete melting process is recorded and can be viewed later, when required. Typical Light Intensity (Transmittance) in % Furnace Temperature In this diagram an overlay of several melting point curves is shown. The same substance was distributed amongst six capillaries and measured with an MP90 Excellence melting point instrument. The rise in transmittance is distinct and sharp and almost identical for each of the six simultaneously measured capillaries. This result reflects crystallinity, purity and careful and correct sample preparation. Once the whole substance has melted the transmittance curve flattens at a distinct point to a constant, usually high, level. At this point no further change in transmittance is recorded. The transmission mode recording used in the MP Excellence instrument line provides the most accurate determination of the melting process. Between ambient temperature and 200 C a temperature accuracy of ±0.2 C is achieved. Up to 400 C an accuracy of ± 0.5 C is achieved. These values are unsurpassed in automatic melting point determination. 7

8 The Melting Point 2.4 Pharmacopeia Melting Point This time vs. temperature diagram illustrates the conditions in a furnace during melting point determination. The red dotted line represents the linear increase of the furnace temperature (in this case a constant heating rate of 1 C/min was applied). The temperature of the sample (black solid line) lags behind the furnace temperature and cannot be measured directly due to technical reasons. To do so would require the thermocouple to be inserted into the capillary containing the sample. A significant part of the heat transmitted from the oven to Temperature (T) T Pharma = T C T B T A Start of melting (collapse point) Meniscus point Furnace Temperature Sample Temperature End of melting (clear point) Time (t) melt the sample would first heat up the thermocouple itself. As a consequence, the measured temperature would be higher than the actual melting temperature and therefore be wrong. Melting point determination starts at a predefined temperature close to the expected melting point. The black solid line represents the temperature of the sample. At the beginning of the melting process, both sample and furnace temperatures are identical; the furnace and sample temperatures are thermally equilibrated beforehand. The sample temperature rises proportionally to the furnace temperature. We have to bear in mind that the sample temperature increases with a short delay which is caused by the time needed for heat transmission from the furnace to the sample. While heating up, the furnace temperature is always higher than the sample temperature. At a certain point the furnace heat melts the sample inside the capillary. The sample temperature remains constant until the whole sample is molten. We identify different furnace temperature values T A, T B and T C which are defined by the respective melting process stages: collapse point, meniscus point and clear point. The sample temperature inside the capillary rises significantly once the sample is completely molten. It increases parallel to the furnace temperature showing a similar delay as in the beginning. Measuring in the pharmacopeia mode means that the furnace temperature is measured rather than the sample temperature. The pharmacopeia mode neglects that the furnace temperature is different (higher) during the heating process than the sample temperature. The furnace temperature remains uncorrected in comparison to the sample temperature, which cannot be measured directly. The difference between furnace and sample temperature depends on: A faster heating rate means a bigger difference between furnace and sample temperature. Heat transmission between furnace and sample, influenced by the setup of the system, i.e. the oven architecture. Heat capacity, an important sample-specific thermodynamic value. Influences of sample mass and wall thickness of the glass capillaries are comparatively minor, but should not be neglected, especially if high-precision measurements are being compared. The following important points should be remembered: Melting points determined according to the pharmacopeia mode are, effectively, higher than the true melting point because the furnace continues to heat up while the sample is still melting. The melting temperature is not measured directly at the sample but outside the capillary in the furnace. Results depend strongly on the heating rate, the higher the heating rate the higher the observed melting point temperature. We note the start of the melting process as T A and the end of the melting as T C. 8

9 2.5 Transmission Intensity Curve Let's apply these facts to our familiar melting point curve. Furnace temperature at point A, the collapse point or melting start, is evaluated at 5% transmittance threshold level. This is a default parameter used in the MP Excellence instruments. It is fixed in the MP50 and variable in the MP70 and MP90. The furnace temperature at point B, the meniscus point, is evaluated when the transmittance curve is as close as possible to its steepest increase, by default at 40%. This value can be varied in the MP70 and MP90, not in the MP50. Typical Light Intensity (Transmittance) in % C - End of melting (corresponds to clear point) the light intensity remains approximately constant. slope dependent (default 0.4%/s), can be varied in MP70/90. B - Melting point (corresponds to meniscus point). default at 40% transmittance (threshold), can be varied in MP70/90. A - Start of melting (corresponds to collapse point). Furnace Temperature default at 5% transmittance, can be varied in MP70/90. The furnace temperature at the melting end, point C, is evaluated when the transmittance remains approximately constant. By default, a slope value of 0.4% transmittance per second is used. This value can be varied in the MP70 and MP90, but not in the MP50. In order to determine the melting point, points B and C are used for evaluation. Evaluation of the melting point at threshold level B yields precise melting points because the increase of the transmittance curve is very steep. If the transmittance does not increase above the preset threshold value B, due to decomposition or inclusion of air bubbles in the molten substance, point C can be used for evaluation. In pure, crystalline substances the temperature difference between points B and C does not differ significantly due to the steep rise of the transmittance curve. Melting point determination according to pharmacopeia means that the end of melting, the clear point C where the substance is completely molten, must be used for temperature determination. The slope criteria used in the MP Excellence instruments ensure that the melting point is evaluated correctly and precisely. Points A and C can be used to determine the melting range. Melting range determination is applied to characterize substances that show a relatively broad melting range. It is also required by pharmacopeias such as the United States Pharmacopeia. The pharmacopeia's requirements for melting point determination at a glance: use capillaries with outer diameters ranging from mm and wall thicknesses from mm. Apply a constant heating rate of 1 C/min. If not otherwise stated, in most pharmacopeias temperature at the end of melting is recorded at point C when no solid substance is left. The recorded temperature represents the temperature of the heating stand, which can be an oil bath or a metal block, in which the thermocouple is positioned. In the previous section we noted a dependency on the applied heating rate. As a consequence, all measurements including calibration and adjustments are only comparable if the same heating rate is applied for all such measurements. 9

10 The Melting Point 2.6 Thermodynamic Melting Point In order to evaluate the thermodynamic melting point, the sample temperature must be known. As this temperature cannot be measured directly for technical reasons, an indirect method is used to obtain this value. The pharmacopeia melting point is therefore corrected to the thermodynamic value by subtracting the pharmacopeia (furnace) temperature value with a thermodynamic correction. The absolute value of this correction depends on the heating rate and the instrument used. Temperature (T) T Pharma = T C Furnace Temperature Sample Temperature Time (t) T Pharma : Temperature of the furnace at the corresponding melting point Let's compare pharmacopeia with b: Heating rate [ C/min] thermodynamic melting point f i : Thermodynamic factor [(min/ C) 1/2 ] evaluation. Pharmacopeia defines the end of melting as the melting point. The exact melting point value provided, however, depends on the heating rate. The thermodynamic melting point value, on the other hand, is the physically correct melting point. This value does not depend on heating rate or other parameters. This is a very useful value as it allows melting points of different substances to be compared independently of experimental setup. T B T A T Thermo Thermodynamic Correction Start of melting (collapse point) Meniscus point T Thermo = T Pharma(b)-f i (b) 1/2 T Thermo : Thermodynamic temperature (Sample Temperature) End of melting (clear point) The quantitative relationship between pharmacopeia and thermodynamic melting point is given in the above equation. The thermodynamic melting point is obtained by subtracting the mathematical product of a thermodynamic factor f and the square root of the heating rate from the pharmacopeia melting point. The thermodynamic factor is an empirically determined instrument-specific factor that depends on the status of the melting point process, either point A, B or C, and other parameters such as: The fusion heat of the sample Thermal conductivity of both sample and glass capillary Sample preparation/packing method Furnace structure Sample mass Status of the melting process defined by A (f A = 0.2), B (f B = 1.5) and C (f C = 2.0) As the majority of all samples measured are organic substances, a good approximation of the average fusion heat is 150 J/g. Careful sample preparation is imperative to obtaining accurate transmission curves that can be reliably and correctly evaluated. Once the appropriate mode is selected in the method, the MP70 and the MP90 Excellence perform the thermodynamic correction automatically. If required, an MP50 user may calculate the thermodynamic melting point manually using the above formula with the given f-factors and the applied heating rate. The following example calculation illustrates the thermodynamic correction of the measured furnace temperature: The pharmacopeia melting point of benzoic acid was determined at a heating rate of 1 C /min to be C Point B was used for evaluation of the melting point curve The thermodynamic melting point of benzoic acid is calculated by: T Thermo = C = C 10

11 3. Application Tips & Hints for Accurate Melting Point Determination 3.1 Instrument Calibration and Adjustment If we want to make sure that the melting point instrument is providing the correct results, we need to verify its measurement accuracy. In the previous chapter we learned that we cannot measure the sample temperature directly using a certified thermometer. Therefore, in order to check the temperature accuracy, we use reference substances ideally with certified temperature values. Thus, we can compare nominal values including tolerances with actual measured values. If calibration fails, which means if the measured temperature values do not match the range of the certified nominal values of the respective reference substances, we need to adjust the instrument. Calibration prior to adjustment X X X Adjustment with new offset and slope values derived from the correction curve. Calibration after adjustment X Correction curve Measured value Certified T-range of reference substance Measured value Certified T-range of reference substance New slope and offset values to adjust the furnace temperature are calculated from the correction curve (see illustration), which is obtained by linear regression. Apply the same heating rate every time, especially when pharmacopeia melting points are compared. The melting point instrument should be calibrated with at least one reference substance melting point lying within the required temperature range. Adjust the instrument with at least two reference substances that encompass the whole melting range required. Check the new adjustment with a different reference substance than the one used for adjustment. We highly recommended that you use METTLER TOLEDO reference substances for calibration and adjustment purposes of MP Excellence instruments. Each reference substance comes with a certificate and both nominal pharmacopeia and thermodynamic melting points written on the label. The substances are securely identified with two barcodes showing the filling code and lot number. Quality of the substances is guaranteed and is monitored by DSC measurements. The following table provides an overview of METTLER Toledo reference substances. Reference substance MP pharmacopeia (1 C/min) MP thermodynamic Benzophenone 49.8 ± 0.2 C 47.8 ± 0.2 C Vanillin 83.7 ± 0.2 C 81.7 ± 0.2 C Benzoic acid ± 0.2 C ± 0.2 C Saccharin ± 0.3 C ± 0.3 C Potassium nitrate ± 0.3 C ± 0.3 C 11

12 Melting Point Determination MP Excellence instruments leave the factory having been adjusted using METTLER TOLEDO reference substances. A three-point calibration with benzophenone, benzoic acid and caffeine is performed, followed by an adjustment. The adjustment is then verified by calibration with vanillin and potassium nitrate. If USP, WHO, Chinese or other reference substances are required the instrument may need to be adjusted with these substances. Prior to this special adjustment a calibration is recommended. The linearity of the MP furnace is very stable and therefore reliable. In order to ensure measurement accuracy it is recommended that the furnace is calibrated with certified reference substances on a regular basis, for example once a month. Let us now consider the melting point of a reference substance measured under identical conditions in two different melting point instruments with different furnace structures. In the thermodynamic mode the certified temperature value does not depend on the furnace structure, whereas in the pharmacopeia mode the furnace structure will affect the value given. As a result, each certified temperature value must clearly reveal the measurement mode and, particularly in the pharmacopeia mode, must state the heating rate applied for the measurement. Each of the MP Excellence line models of METTLER TOLEDO is based on the same furnace structure. Therefore, the certified temperature values in the pharmacopeia mode are valid for all models, providing that the same heating rate is applied for the measurement. As a consequence, for each METTLER TOLEDO reference substance three different temperature values are given: one for the thermodynamic melting point which is identical for both the FP and the MP instruments, and two for the pharmacopeia melting points of the MP instrument and the FP instrument, respectively. If we compare the current MP Excellence line with its predecessor, the FP81, we notice that there is a difference in the deviation of the furnace temperature to the sample temperature. This is due to the different furnace layouts of the instruments, which have a different effect on heat transfer to the sample. As a result, different thermodynamic f factors are used to correct the furnace temperature to the sample temperature in the FP model. Temperature (T) T Pharma, MP = T C, MP T Pharma, FP = T C, FP T A, MP T A, FP Start of melting (collapse point) Furnace Temperature Sample Temperature FP Sample Temperature MP End of melting (clear point) Time (t) 12

13 3.2 Quick and Reliable Sample Preparation: The Capillary Filling Tool The capillary preparation tool is a very simple-to-use mechanical device that allows efficient and reliable sample packing. It serves a fourfold purpose: 1. Convenient carriage of up to six melting point capillaries. Upfront sample preparation and secure storage prior to analysis are facilitated. 2. Small portions of the powdered substances can easily be taken from the mortar for stepwise filling of the capillary. 3. The peg-like design of the tool allows the capillaries to be bounced on a hard surface in order to compress the powdered sample in the bottom of the capillary. 4. Capillary transfer into the furnace is easy: simply position the capillaries in the tool above the appropriate holes of the furnace and release. The capillary tool is perfect for performing the sample preparation task effectively and efficiently. It is part of the MP accessory box that contains other useful accessories for reliable and repeatable sample preparation. The MP accessory box is part of the standard delivery of the MP90 and is a highly recommended optional accessory for MP50 and MP70 instruments. It contains 150 melting point capillaries, three METTLER TOLEDO certified reference substances (benzophenone, benzoic acid, saccharin), agate mortar and pestle, tweezers and spatula, and 5 capillary tools. 5 capillary filling tools Spatula, tweezers Mortar, pestle 150 capillaries Reference substances: benzophenone, benzoic acid, saccharin 13

14 Melting Point Determination 3.3 Melting Point Capillary Sample Preparation The sample preparation process is illustrated in the following photo sequence. All tools shown in the pictures are part of the MP accessory box. Whenever possible, finely grind a small portion of the sample in a mortar. Do not collect the sample with the open end of the capillary directly from the bottle without prior grinding. Such collected crystals may be too coarse and will lead to air bubble inclusion in the melt. A finely-ground sample will easily fall to the bottom of the capillary. There is no need to press it into the capillary with a steel rod or similar device. Six capillaries are prepared simultaneously for measurement in the MP90 Excellence instrument. The capillary filling tool can perfectly assist the filling as the empty capillaries are securely held in the peg-like grip. Collecting a small sample portion from a mortar is easily done with the assistance of the tool. Apply a stepwise filling of the capillary using a small quantity at a time. The small amount of sample at the top of the capillaries is then moved down to the closed end of the capillary by free bouncing of the capillaries on the table several times. This action packs the sample tightly down into the capillary bottom. It is imperative to let the capillaries loosely bounce instead of pushing them against the surface. The 'bouncing effect' causes tight packing of the substance and avoids the inclusion of air. Filling height can be checked with the engraved ruler on the capillary filling tool. Generally filling height should not exceed 3 mm. If exceeded, the probability of bubble formation during the melting process becomes likely, which disturbs the transmission light recording. If the filling height is less than 3 mm, the holes that guide the transmission light to the capillary may not be completely covered with sample after completion of the melting process as the substance may collapse considerably while liquefying. If the hole is not completely covered the transmittance rise at the melting point will not be pronounced and may not rise above the threshold level B. 14

15 3.4 Sample Preparation: Bad Example The above screenshots of a melting point process video show an unsuccessful attempt to achieve accurate results. The first screenshot reveals the melting process close to the collapse point. We observe a filling height higher than 3 mm inside the capillary and too coarse crystals that start to liquefy at the surface. At the collapse point in screenshot 2 we observe air bubble inclusion in capillaries #3 and #4. Air is trapped at the bottom of the capillary and cannot escape because it is blocked by the coarse crystals above. Close to the meniscus point, crystals fall into the melt and trap air bubbles, which is particularly visible in capillaries #3 and #4. At the clear point, air bubbles are visible in capillaries #1 and #4. In capillary #2 some crystals are present and in capillary #3 a clear melt is observed. In this melting process we can see inhomogeneous melting disturbed by air bubble formation resulting from overfilling and insufficient sample grinding. Both are the result of poor sample preparation. Capillary #1 Capillary #2 Capillary #3 Capillary #4 The events observed in the melting point video show clear effects in the above transmission curves. In capillary 1, air bubbles trapped in the region of the transmission light hole in the furnace significantly diminish the increase in transmittance while the substance melts. The default point B threshold level of 40% may therefore be too high and melting point cannot be evaluated. The transmittance curves of capillaries #2 and #3 seem to be sufficiently successful as the rise in transmittance easily passes the 40% threshold level. However, some small irregularities in transmittance at the beginning of the melting may negatively affect repeatability. In the transmittance curve of capillary #4 a pronounced shoulder is observed prior to the final increase. This may be due to the premature melting of finely ground crystals before the bulk material consisting of coarse crystals melts. A delayed increase above the threshold value B or a higher C temperature may result. This negatively affects accuracy. 15

16 Melting Point Determination 3.5 Sample Preparation: Good Example These video screenshots show an ideal melting process, easily achieved with the MP instruments if the major issues regarding capillary overfilling and insufficient sample grinding are avoided. In the first screenshot we observe a homogeneously distributed filling height of 3 mm or slightly less in all four capillaries. The substance is finely ground into small crystallites. At the collapse point in the second screenshot there is no inclusion of air bubbles, evident in all four capillaries. Close to the meniscus point in the third screenshot we do not observe any issues caused by bubble entrapment, premature or inhomogeneous melting. At the clear point all four capillaries contain a bubble-free molten substance that completely covers each of the four transmission holes. Capillary #1 Capillary #2 Capillary #3 Capillary #4 The respective transmission curves of each capillary reveal an almost ideal S-shaped form. Each of the transmission curves can be precisely evaluated at all three points A, B or C. Accurate results contributing to an accurate main value without any outliers and excellent repeatability are achieved. Let's summarize the following points of this chapter: It is not difficult to prepare samples for melting point analysis correctly. Only the most important errors, overfilling and insufficient sample grinding, need to be avoided and success is ensured. Correct sample preparation requires a maximum of 2 min for sample grinding and capillary filling. During preparation the method can be started at the MP instrument to heat the furnace up to the required start temperature. The time invested in correct sample preparation definitely pays off, as the measurement does not need to be repeated. 3.6 Sample Measurement Tips & Hints Colored or decomposing samples (azo benzene, potassium dichromate, cadmium iodide) or samples that show a tendency to include air bubbles in the melt (urea) may require either the lowering of threshold value B or usage of the C value as the evaluation criteria because the transmission increase will not be so high during the melting. Samples that decompose (sugar) or sublime (caf feine): seal the capillary with a flame. The volatile components produce an overpressure inside the closed capillary that inhibit further decomposition or sublimation. Heating rate: Usually 1 C /min. For highest accuracy and non-decomposing samples use 0.2 C/min. With substances that decompose, 5 C/min; for exploratory measurements 10 C/min. Start temperature: min before the expected melting point (3 to 5 times the heating rate). End temperature: A successful measuring curve requires an end temperature that is approx. 5 C above the expected event. Otherwise use the method parameter 'stop at event' to terminate the temperature program automatically as soon as all samples are completely melted. 16

17 All MP Excellence instruments provide the option of manually terminating the test without losing the recorded data. The MP70 and MP90 methods also include a stop at event parameter that terminates the melting point test as soon as all capillaries have passed the pre-defined threshold value B. Both termination possibilities save time and make melting point analysis very efficient. Use the thermodynamic melting point if SOP and instrument (MP70/90 only) permit it. The thermodynamic melting point is the physically correct melting point and is not dependent on instrument parameters. Incorrect sample preparation may result in transmission curves that do not exceed the 40% threshold value of point B. It is recommended that you either reduce the threshold value or use the C point for evaluation. Point C is independent of the threshold level (MP70/90 only). In pure, crystalline substances the respective temperature values of points B and C are usually very close. This means a temperature difference of 0.2 C or less. This difference is within the measurement uncertainty and therefore the respective temperature values can be regarded as equal. Note: the C point can be thermodynamically corrected. In the MP70/90 instruments the melting point can be evaluated both in pharmacopeia and thermodynamic mode. The melting range can only be evaluated in pharmacopeia mode. Note: Thermodynamic correction of the melting range requires LabX TV PC software. The MP50 only has one method template (manual method) with fixed method parameters for melting point and melting range determination in pharmacopeia mode. Use melting point capillaries from METTLER TOLEDO as these are very precisely manufactured and ensure highly accurate and repeatable results. If capillaries of other vendors are used, the instrument should be calibrated and, if required, adjusted using these capillaries. 3.7 Melting Point Standards Overview The following table provides an overview of the melting point standards that are important for melting point determination. The individual standards specify the measurement parameters, the experimental setup (e.g. heating medium; oil bath or furnace), the capillary dimensions and the detection of the melting point event. Some of the pharmacopeias offer their own reference substances that are recommended for use in the calibration/adjustment of the instrument. The instruments of the MP Excellence line fully comply with these standards. Name Detection point Heating rate [ C/min] Own references substances US Pharmacopeia USP 37-NF32 <741> Melting range: Evaluation of collapse and clear point 1 Yes, 6, range C British Pharmacopeia Meniscus point 1 No Japanese Industrial Standard K 0064 Japanese Pharmacopeia 16 th edition Clear point 1 No Chinese Pharmacopeia Clear point 0.2 C/min and 1 C/min Yes, 12, range C International Pharmacopeia (WHO) Melting point: Evaluation of clear point 1 Yes, 12, range C European Pharmacopeia 8 th edition 8.2 chapter Clear point 1 No ASTM D (2004) Clear point 1 ± 0.2 C/min No 17

18 Melting Point Determination 3.8 Melting Point Measurement Results The following tables include melting point test results of reference substances from two different suppliers, USP and WHO, that were measured with an MP90. For each reference substance, the measurement was obtained by taking the mean value of six capillaries. The results reveal the excellent measurement accuracy and repeatability that can be achieved with MP Excellence instruments. The basis of these measurements is careful sample preparation which can easily be achieved using the capillary filling tool described in Section USP References USP reference substances USP specifies that the measured melting range must a) lie within the specified minimum and maximum temperatures (e.g C for vanillin), and b) must not be broader than the specified admissible values (e.g. 1.5 C for vanillin). So, the permitted measured melting range for vanillin could be , C etc. Name of USP reference substance Assigned MR [ C] Measured MR [ C] Repeatability min/max admissible range min/max range [ C] Vanillin T A: 0.13 T C: 0.05 Phenacetin T A: 0.05 T C: 0.00 Sulfanilamide T A: 0.23 T C: 0.05 Sulfapyridine T A: 0.05 T C: 0.04 Caffeine T A: 0.07 T C: 0.07 MR: Melting range, Repeatability: 6 capillaries Six capillaries of each USP reference substance were measured simultaneously and the respective transmission curves were evaluated in the melting range mode, meaning the default parameters of points A and C were used. Conclusions The accuracy and repeatability of the results obtained from the MP90 are excellent. With each of the tested reference substances a melting range smaller than the admissible reference value was reached. The absolute melting range values were all within the specification temperatures. Hence, the MP90 instrument is ideally suited to determine melting points according to USP. 18

19 3.8.2 WHO References WHO reference substances are specified with a maximum permissible temperature range, in the same way as the METTLER TOLEDO reference substances. The melting point criterion is the clear point C, when all solid material has been transformed into the liquid state. WHO reference substances Name of WHO reference substance Assigned MR [ C] Measured MR [ C] Repeatability [ C] Azobenzene 69.0 (± 0.4) 69.0 T C: 0.22 Vanillin 83.2 (± 0.6) 83.3 T C: 0.17 Acetanilide (± 0.3) T C: 0.09 Phenacetin (± 0.3) T C: 0.15 Sulfapyridine (± 1.2) T C: 0.10 Saccharin (± 0.5) T C: 0.09 MR: Melting range, Repeatability: 6 capillaries Conclusions The MP90 achieved excellent results also with the WHO reference substances. The melting points of all tested references were within specifications. The achieved repeatability was far better than the assigned values. Thus, the MP90 is best suitable to measure melting points following WHO guidelines. 19

20 Workflow Support by LabX 4 Melting Point Workflow Support by LabX PC Software LabX PC software integrates almost the complete laboratory instrument portfolio of METTLER TOLEDO including analytical balances, density meters, refractometers, titrators and melting point instruments MP70 and MP90. Integration with LabX means that each analytical workflow performed on the each instrument is controlled by LabX. Results are securely stored in the LabX database, which can be archived or restored when required. Like the common OneClick interface of the METTLER TOLEDO instruments, LabX provides a unique interface for all integrated instruments on the PC. Beyond instrument and data management, LabX manages instrument users based on a comprehensive management system complying with all FDA requirements. Measurement tasks can be scheduled and issued to the relevant instrument according to the lab's schedule. The operator has the appropriate user rights to work at the specific instrument. LabX supports efficient workflow execution on various different analytical instruments from METTLER TOLEDO and facilitates data management by centralized storage and full 21CFR part 11 compliant audit trail. 4.1 Melting Point Workflow Integration and Support by LabX Let us now investigate how LabX supports the melting point workflow performed on an MP70 or MP90 Excellence system. We structure the MP workflow in three phases: pre-measurement, measurement and postmeasurement. In the pre-measurement phase, compared to the instrument LabX provides almost unlimited possibilities regarding storage and management of reference substances used for calibration or adjustment. Each reference substance can be tracked with lot number and expiry date. Any calibration and adjustment performed on the instrument is stored and available for inspection. This supports a continuous monitoring of the instrument which is imperative for accurate and reliable measurements. In the measurement phase LabX provides a graphical method editor where the complete workflow can be easily programmed and visualized. Messages containing SOP excerpts can be included in the workflow and displayed on the instrument terminal. This is highly beneficial as the operator may not often work with the MP instrument and may operate many different instruments in the lab. Such dedicated support directly at the measurement location is extremely valuable and helps to avoid errors. Pre-Measurement Measurement Post-Measurement LabX supports MP automation possibilities that cannot be achieved on the instrument alone. There are, for instance, screening melting point tests, e.g. mixed melting point determination according to USP in order to determine the purity of a sample, etc. The product-oriented approach allows us to use a single method for a multitude of samples that require only minor modifications of dedicated method parameters. In the post-measurement phase after measurement completion the results are immediately evaluated against predefined nominal values or tolerances. Statistical evaluation can easily be programmed to detect outliers. Based on the outcome, the operator is prompted whether to repeat the measurement or not. A very comprehensive report editor allows to create customized reports based on pre-defined report templates that can be printed on pdf or network printers. Each result is securely stored in the LabX database including a fully 21 CFR part 11 compliant audit trail and is available for backup or archiving whenever required. The result data representation in LabX leaves nothing to be desired. Both melting point video and transmission curve are presented at a glance. That is not possible at the stand alone instrument. The melting point process can be post-analyzed by simultaneous playback of both transmission curve and video. In the graph a moving cursor indicates the current melting process status in real time. All evaluated data are displayed clearly in the table underneath. The user is thoroughly informed. 20

21 4.2 Melting Point Screening Supported by LabX The task is to efficiently and accurately determine the melting point of an unknown substance. This could be a daily task in a test lab environment. LabX enables the workflow in the following way: in the first step the melting point of an unknown substance is screened with a fast heating rate (5 10 C /min). Based on the result, start and end temperature will be calculated. In the second step, the data is used together with a slower heating rate (1 C /min or less) to more accurately determine the melting point of the unknown substance. We can think of this method as an automatic learning method for melting point determination. The advantages are obvious: only one method is required to cover two steps for a variety of substances, including comprehensive SOP guidance displayed on the MP touchscreen. The resulting benefits are: Fast and accurate determination The user works entirely at the MP instrument The user is guided through the process by appropriate messages on the MP touchscreen Method maintenance complexity is greatly reduced as there is only one method for a variety of samples required. All data are securely stored in the LabX database This is a good example of melting point workflow support enabled by LabX. It serves as one of many examples of how LabX can enable or facilitate automatic melting point determination and therefore augments the various possibilities of the MP Excellence line in a beneficial and secure way. 21

22 The Dropping & Softening Point 5 Fundamentals of Dropping & Softening Point Determination 5.1 General Consideration Synthetic but also naturally-occurring products, which are important raw materials for various industry segments, do not show a defined melting point. They include ointments, synthetic and natural resins, edible fats, greases, waxes, fatty acid esters, polymers, asphalt and tars. These materials gradually soften as the temperature rises and melt over a relatively large temperature interval. Generally the dropping or softening point test is one of the few easily achievable methods available to thermally characterize such materials. To ensure comparable results, standardized test equipment and conditions, as well as appropriate sample preparation, are required. 5.2 Automatic Dropping and Softening Point Determination: The METTLER TOLEDO DP Excellence Instrument Line METTLER-TOLEDO s Dropping Point Excellence instrument line consists of two compact models for automatic dropping or softening point determination: The DP70 and the DP90. Each comes with a color touchscreen for intuitive and efficient operation. The user interface follows the established One Click philosophy that is common for all instruments of the METTLER TOLEDO Analytical instrument portfolio. The DP70 Excellence instrument provides reliable video-based technology for automatic dropping and softening point determination in the range of room temperature to a maximum of 400 C. Two samples can be measured at a time and the mean value is automatically evaluated and clearly displayed on the touch screen. Dropping or softening point tests are videorecorded and stored on the SD card inserted in the instrument. The videos can be viewed at any time required. Thanks to the One Click philosophy, the operation of the instrument is very simple. 5 pre-tested METTLER TOLEDO methods are stored, which can be used for convenient and secure temperature calibration and adjustment purposes using METTLER TOLEDO reference substances without any parameter modification. Furthermore, they serve as templates for specific method development for automatic dropping and softening point determination. A maximum of 60 methods can be stored and started with OneClick with up to 12 ShortCuts displayed on the touch screen. A storage capacity of up to 100 reference substances provides the basis for a comprehensive library of commercially available or own reference substances that are used for calibration and adjustment. The temperature accuracy is outstanding (±0.2 C and up to 400 C ±0.5 C) and unmatched by any other instrument. The built-in user management prevents errors due to unauthorized operation. Results are stored in the instrument and are available for outlier exclusion immediately after test completion. Test results are documented as GLP-compliant printouts on the USB P25 compact strip printer from METTLER TOLEDO or as comprehensive printouts including method, calibration and video snapshots on network printers. In addition, test results can be stored as pdf files in network printer layout on an USB stick, on the SD card, or transferred via ftp for remote storage on a PC. The DP70 comes with an accessory box that includes innovative tools for accurate and repeatable sample preparation. The DP90 Excellence from METTLER TOLEDO consists of a control unit with a touch screen interface and an external measuring cell that can be placed inside a refrigerator or a freezer or, if required, under a fume hood. Depending on the cooling device, the DP90 enables dropping point tests in the range of 400 C to -20 C. The measuring cell can also be placed remotely from the control unit, under a fume hood for example, if samples that decompose are being tested. The DP90 offers the same features as the DP70 in respect of measurement accuracy, operation and result documentation. 22

23 5.3 Automatic Dropping and Softening Point Determination: The Unique Detection Principle The dropping and softening point measurement principle is based on a unique automatic video image analysis that allows direct insight into the dropping or softening point process. Because the measurement is recorded it can be viewed at any time after completion. So, clear evidence what is happening during and after measurement is obtained and replay of the measurement for post-investigation at any time is possible. Reliable results of high accuracy and precision are obtained and, thanks to its flexibility, more application fields can be covered. The majority of instruments on the market provide either observation with manual operation or automation without visual observation such as the FP83HT predecessor of the DP Excellence line. The image analysis technology was published as patent EP from the European Patent Office in The layout of the furnace and the video image analysis respectively allow two samples to be measured simultaneously. The FP83HT predecessor and many other instruments in the market do not offer this. The sample throughput and thus the efficiency are doubled and, if two identical samples are analyzed, a double determination with an averaged result is obtained. This saves time and costs and improves measurement reliability. 5.4 Automated Dropping Point Measurement by Video Based Image Analysis Dropping point (DP) cup, with a 2.8 mm orifice, containing sample in the oven DP Video camera LED light source Online, video-based digital image analysis used in the DP70 Evaluation area: rectangle in top half of picture Detection occurs when drop has passed through the rectangle Generally, the dropping point is the temperature at which the first drop of the molten substance precipitates from a standardized vessel with a defined orifice under controlled test conditions in a furnace. Manual methods obviously require the visual inspection of the dropping point process, which is a tedious process as the attention of an operator is required for a quite a long time to continuously watching the test process. The drop point is a suddenly occurring event, as the liquefied drop is accelerated by gravity as it escapes the cup. Once this happens the operator needs to quickly note the temperature. In summary, manual dropping point testing is a timeconsuming, error-prone process that is strongly influenced by operator bias. If human observation is replaced with a device that records and evaluates the dropping point event automatically, the quality of the result would be greatly improved. In the Dropping Point Excellence instruments from METTLER TOLEDO, a white balanced LED light is shone on the test assembly, which consists of the cup and holder inside the furnace. The reflection is recorded by a video camera. The entire drop point test is video-recorded and image analysis is used to detect the first drop that escapes the sample cup when it passes through a virtual white rectangle located underneath the cup orifice. While detecting this, the furnace temperature is measured and recorded at a resolution of 0.1 C. 23

24 The Dropping & Softening Point This unique detection principle has proven to be very sensitive and reliable. Because the entire process is video recorded, the drop point test can be observed live during the test on the instrument's terminal and repeated at any time after completion. As two samples can be tested in one run the DP Excellence system provides high test efficiency. The picture shows a screenshot of a liquefied lubricant grease dropping at 276 C. 5.5 Automated Softening Point Measurement by Video Based Image Analysis Softening point (SP) cup with 6.35 mm orifice containing sample in the oven 19 mm SP Video camera Online, video-based digital image analysis used in the DP70 Evaluation area: rectangular area including stepping line Detection occurs when stepping line reaches defined distance LED light source The softening point test is used to test substances that only soften or partially melt with increasing temperature. Substances such as resins, rosins or bitumen/asphalt, pitch and tars are typical examples. Softening point tests require a dedicated sample cup with a 6.35 mm orifice in the bottom, which is wider than that of a dropping point cup. In order to enforce the precipitation of the softened sample from the cup when heated, the sample is weighted with a ball of standardized dimensions made of stainless steel (for resins) or lead (for bitumen). Once the sample softens and extends down far enough to reach a 19 mm distance from the cup orifice, the furnace temperature is recorded as the softening point temperature of the sample. The METTLER TOLEDO DP Excellence instruments enable automatic detection of the softening point temperature using video-based image analysis. In the video, the leading edge of the softened sample is marked with a stepping line. Once the stepping line has passed a virtual line that is located 19 mm below the cup orifice the corresponding furnace temperature is measured and recorded at a resolution of 0.1 C. Like in the dropping point test, the entire process is video recorded. It can be observed live and repeated at any time after completion. Two samples can be run simultaneously. The softening point detection principle was also patented due to its technical uniqueness. The picture shows a screenshot of a softened bitumen sample at 55 C that has just passed the 19 mm detection line. 24

25 5.6 International Dropping and Softening Point Standards The following table provides a detailed overview of the softening and dropping point standards that are used to test raw materials and final products in the petrochemical industry. The ASTM D3104 and D3461 standards, which are called Softening Point according to Mettler or Mettler cup & ball, are based on the automatic softening point detection principle with the METTLER TOLEDO instruments described in the previous sections. In the D3104 standard, no extra weighting of the sample in the cup is required whereas in the D3461 standard a lead ball of specified dimensions is required to force the sample to flow from the cup. In both cases the test is performed in a furnace and the softening point temperature is detected and recorded automatically. The ASTM D36 and ISO EN1427 methods specify the softening point test according to the ring and ball method. In contrast to the METTLER TOLEDO standards, a different test setup including liquid-medium bath heating is used. The ASTM D556 and ISO EN2176 are the basis for lubricant grease dropping point testing, using either a liquid medium bath or an aluminium furnace block heating. In both cases the sample needs to be prepared in the dropping point cup according to an exactly specified procedure, which we will investigate later. In both standards, the dropping point event is detected manually. The IP 396 standard adheres to these standards in respect of sample preparation, but is based on a dual heating ramp procedure and automatic dropping point event detection. ASTM D3104 ASTM D3461 ASTM D36 ISO EN1427 ASTM D556, ISO EN2176 ASTM D2265 IP 396 Test principle Softening Point Mettler Softening Point Mettler Cup & Ball Softening Point Ring & Ball Dropping Point Dropping Point Dropping Point Samples Pitch Bitumen/Pitch Bitumen Lubricating Grease Lubricating Grease Lubricating Grease Sample Holder Cup, 6.35 mm orifice Cup, 6.35 mm orifice Ring,15.9 mm Cup, 2.8 mm orifice Cup, 2.8 mm orifice Cup, 2.8 mm orifice Heating method Furnace Furnace Water, Glycerol, Ethylene glycol Oil bath Aluminium block Furnace Additional weight None Lead ball, 0.32 inch,3.2g Steel ball, 9.5 mm, 3.5 g None None None Repeatability 0.5 C 0.5 C 1.2 / 2.0 C 7 C >6 C 6 C (DP=220 C) Reproducibility 1.5 C 1.5 C / C 13 C >9 C 16 C (DP=220 C) T range C C C C C C The DP Excellence instruments allow fully automated dropping point detection of lubricant grease exactly according to the requirements of the IP 396 standard. In all standards, the value range for repeatability and reproducibility are given, which serve as a guideline for assessing the result quality. In the bitumen/pitch/asphalt standards these specifications have a narrow tolerance range, whereas in the lubricant grease standards the tolerance ranges are wider. This is due to the fact that the sample integrity of the grease is destroyed during the heating procedure, especially if temperatures above 200 C are required. 25

26 The Dropping & Softening Point The following table provides an overview of the standards used in the chemical, food & beverage, pharmaceutical and cosmetics industry. The ASTM D6090 standard is based on METTLER TOLEDO instruments and specifies the requirements for automatic softening point determination of resins. The test procedure and detection principle is almost identical to that described in the previous ASTM D3461 standard. One important difference is that a steel ball instead of a lead ball is used to weight the sample in the cup. The ASTM D6493 specifies the softening point test of resins according to the Ring & Ball method, which is almost identical to the ASTM D36 standard shown in the previous slide. The AOCS Cc18-80 standard specifies the automatic dropping point detection of edible fats & oils using a dropping point instrument from METTLER TOLEDO. This standard also applies to samples with dropping points below ambient temperature. The ASTM D3954 standard is also specified on an earlier METTLER TOLEDO dropping point instrument and is used for automatic dropping point tests of waxes. The European Pharmacopeia B standard is analogous, however, the repeatability specifications are narrower. Last but not least, the ASTM D127 describes the manual procedure for dropping point testing of waxes. Many laboratories still follow this standard. Test principle ASTM D6090 Softening Point Mettler ASTM D6493 Softening Point Ring & Ball AOCS Cc18-80 Dropping Point Mettler ASTM D3954 Dropping Point Mettler Ph. EUR , B Dropping Point ASTM D127 Dropping Point Samples Resins Resins Edible oils and fats Sample Holder Heating method Cup,6.35 mm orifice Furnace Ring, 15.9 mm Water, Glycerol, Silicone oil Cup, 2.8 mm orifice Waxes Waxes Waxes Cup, 2.8 mm orifice Cup, 2.8 mm orifice Furnace Furnace Furnace Water Cup, 2.8 mm orifice Additional weight Steel ball, 8.7 mm, 2.77 g Steel ball, 9.5 mm, 3.5 g None None None None Repeatability C C 1.5 C 0.5 C 0.3 C 1.0 C Reproducibility C C 1.6 C 1.5 C not specified 1.2 C T range C C C C C C To summarize, in total there are 5 international standards based on automatic dropping or softening point determination on METTLER TOLEDO instruments (ASTM D3104, D3461, D3954, D6090, AOCS Cc 18-80) The Ring & Ball method is the alternative to the Mettler cup and ball test for bitumen/asphalt/pitch or resin testing. 26

27 6 Application Tips & Hints for Accurate Dropping & Softening Point Determination 6.1 Instrument Calibration and Adjustment If we want to make sure that our dropping point instrument functions correctly, we need to verify its measurement accuracy. This procedure is called calibration and in the following section valuable tips and hints are given to help perform the calibration correctly. As with melting point instruments, in dropping point instruments the sample temperature cannot be measured directly by the use of a certified thermometer. This would falsify the measurement as a significant portion of the heat transferred from the furnace to melt the sample would be used instead to heat the thermo element. In order to check temperature accuracy we use reference substances and compare their nominal values, including tolerances, with the measured values. If the calibration fails, i.e. if the measured temperature values are outside the values of the certified reference substance, the instrument needs to be adjusted. METTLER TOLEDO reference substances such as benzophenone, vanillin, benzoic acid and potassium nitrate provide certified temperature values that can be used for temperature calibration of the DP70 and DP90 furnaces. Caffeine and saccharine cannot be used as they do not drop properly. It is highly recommended that METTLER TOLEDO reference substances are used for calibration and adjustment purposes of DP Excellence instruments. The substances are securely identified with two barcodes showing the filling code and lot number. The quality of the substances is guaranteed and is monitored by DSC measurement. The DP70 and DP90 Excellence instruments include an automatic procedure that compares the measured value with the nominal value. The basis for comparison is the thermodynamic melting point of the calibration substance that is detailed on the corresponding certificate and includes measurement uncertainty. The thermodynamic melting point is the physically correct melting point temperature of the actual sample, not the furnace temperature, and is independent of the experimental setup. The dropping point of a reference substance is not equal to the thermodynamic melting point as the measured temperature is actually the furnace temperature and not the sample temperature. Therefore, the furnace temperature value needs to be adjusted using a correction value, which is stored for each reference substance in the instrument. 27

28 Dropping & Softening Point Determination The correction factor is substance-specific and heatingrate dependent. It corrects the measured furnace temperature to the thermodynamic melting point of the relevant substance. The correction factors in the table are valid for a heating rate of 0.2 C/min. Reference substance Correction factor [ C] Benzophenone -1.2 Vanillin -1.5 Benzoic acid -1.4 Once this is done, the basis for calibration, i.e. the comparison between measured and nominal temperature values is given. Furthermore the correction Potassium nitrate -1.4 factor takes into account the viscosity of the molten reference sample that drops from the cup, which has an influence on the dropping point temperature. The correction factors have been determined empirically by comparing the furnace temperature dropping point with the known thermodynamic melting point of the reference substance. The correction factor should not be applied to samples whose thermodynamic melting point is not known, which is the case if we consider typical samples that are usually tested with dropping or softening point. If the calibration fails, i.e. if the measured values of the reference substance are not within the nominal temperature values, the instrument issues a warning. The instrument then needs to be adjusted. 28

29 6.2 Sample Preparation DP Excellence Accessory Box The DP accessories box is included in the standard delivery of the DP70 and DP90. It provides useful accessories for reliable sample preparation: The DP sample preparation tool that enables efficient and clean filling of up to 4 dropping and softening point cups with liquid or solid substances, including a handle to place or remove the tool's plate into an oven or a refrigerator Two tamping rods to press ground solid samples into dropping or softening point cups 2 softening and 2 dropping point cups made of chromium-plated brass 2 stainless steel balls according to ASTM D cup lids with vent hole to close the sample-containing cup 6 glass cups for collection of liquefied or softened samples during the respective tests Sample carrier that holds two dropping or softening point cups with glass collectors and cup lids A stand that holds two sample carriers A spatula to transfer the sample into a cup or to remove excessive sample A rod to remove excessive lubricant grease from a dropping point cup according to the procedure specified in ASTM D556 Benzoic acid reference substance for calibration of the instrument Cup lids Handle Cups Spatula and rod Balls Collector glass Sample preparation tool Tamping rod Reference substance Benzoic acid Stand Sample carrier 29

30 Dropping & Softening Point Determination Efficient and Reliable Sample Preparation: The Sample Preparation Tool The basis for comparable and reliable results in dropping point and softening point analysis is repeatable sample preparation. With the DP Excellence sample preparation tool this crucial step is perfectly supported: Efficient sample preparation as four cups can be prepared at a time Handling errors are minimized and operational security maximized Contamination of the outer surface of the sample cup is avoided which contributes to result reliability The sample preparation tool was patented in 2013 (EP , European Patent Office). It augments the DP Excellence instruments to a complete system that facilitates and secures the complete analytical workflow in dropping and softening point analysis. The sample preparation tool consists of four pieces: A double-sided base plate that holds four dropping point cups on one side and four softening point cups on the other A support disk with four holes A disk-like funnel for powdered samples A handle to carry the whole tool (not shown in the pictures) Dropping point cups are positioned on the side of the base plate with the deepest indentations. The shallower indentations on the other side of the plate are used for positioning the softening point cups. A support disk is used to fix the cups and to make the upper rim of the cup level with the surface. The support disk therefore serves a threefold purpose: first to prevent the sample from contaminating the outer surface of the cups, second to facilitate the removal of excessive sample, and third to facilitate the complete filling of the sample cup with powdered samples DP Excellence Sample Holder and Standard Compliant Cups Standardized dropping and softening point cups from METTLER TOLEDO are made of chromium-plated brass or aluminium. The experimental setup required for an automatic dropping and softening point test consists of the sample-containing cup, closed with a lid, and a collection glass underneath to collect the liquefied sample. Collection glass Stand Cup Lids Cups DP Sample holder and stand Dropping point cups Softening point cups 30

31 The sample carrier allows the efficient, simultaneous measurement of two samples, which are placed with the sample carrier into the DP furnace. After test completion the sample carrier is removed from the furnace and securely placed on the stand to cool down to ambient temperature. It is then quickly disassembled and the collection glasses are put into the waste with the aluminium dropping or softening point cups. Cup lids prevent discharge of expanding sample, which avoids contamination of the furnace. Tedious and time-consuming work in dropping and softening point analysis involves cleaning the components after completion of the analysis. Unhealthy, nonpolar solvents may be required in order to dissolve the sample residues. The DP Excellence system provides disposable aluminium sample cups and glass sample-collectors that make cleaning unnecessary. The post-treatment process is therefore significantly accelerated and the system is ready for the next measurements within a short time. The DP Excellence solution is therefore much more efficient than other competitor systems that require complete cleaning of the sample holder prior to the next analysis Solid Samples For powdered samples the disk-like funnel is mounted on top of the sample preparation assembly unit which guides the powder into the sample cup underneath. The diameter of the funnel hole corresponds exactly with the aperture of the underlying cup. A small portion of ground sample is filled via the aligned funnel into the cup. The rounded end of the tamping rod is then used to compress the sample in the cup. This procedure is repeated until the cup is completely filled with sample. The flat part of the tamping rod is then used to compress the sample in order to make it level with the surface of the support disk. The hole of the support disk is then turned to the next cup and the filling procedure is repeated. The disk-like funnel enables clean and efficient filling of dropping or softening point cups with ground solid samples. Any contamination of the outside surface of the cup is avoided. After filling, the tool can be easily cleaned and dried in an oven. 31

32 Dropping & Softening Point Determination Lubricant Greases The sample preparation for lubricant grease follows the original specifications described in the ASTM D556 standard, which is also used in the ASTM D2265 and the IP 396 standards. In order to avoid any cross-contamination the dropping point cup should be cleaned with solvents such as toluene, isopropanol or mixtures of both solvents, preferably in an ultrasonic bath. The grease sample is packed into the cup with a spatula that is part of the DP70 and DP90 accessory box. The cup is completely filled with the grease and any excess removed with the spatula. When the cup is full, a metal rod with dimensions corresponding to ASTM D556 is pushed through the grease sample from the smaller opening at the bottom of the cup. The rod should make contact with both the upper and lower peripheries of the cup. By maintaining this contact, the cup is moved down along the rod, turning in a spiral-like movement in order to remove a conical section of the grease. This produces a smooth layer of grease of reproducible thickness inside the cup. It is important that the inner cup walls are completely covered with the lubricant grease otherwise the filling procedure needs to be repeated. As the heat transfer is dependent on the mass of the sample, the mass should be reduced to a reasonable minimum in order to ensure efficient and thorough heat transfer. If the cup was completely filled with sample, a temperature gradient from the cup wall to the middle of the sample would form. This would lead to liquefaction of the part of the substance closest to the cup wall while the central part of the sample remains in the original semi-solid state. As a result, the dropping point temperature would be significantly higher, or even no drop would be formed during heating. 32

33 6.2.6 Bitumen, Pitch The photo sequence illustrates the sample preparation of bitumen for subsequent softening point analyses. Melt the sample in a suitable container (here a brass container) on a hot plate at a temperature not higher than 110 C above the expected softening point. Homogenize the molten sample thoroughly by stirring with a glass rod or similar device. Make sure that the bitumen sample is completely molten and of low viscosity. Use appropriate temperature insulating gloves to handle the container safely. Pour the sample into the ASTM D3461 cups that are positioned in the sample preparation tool with the support disk. The molten sample is guided with the glass rod into the cup to ensure controlled bubble-free filling and to avoid uncontrolled spillage of the hot sample. Let the sample cool down to ambient temperature for at least 30 min. Remove excess sample from the cup with a hot knife that has been heated with a hot blow dryer. This avoids excess mechanical stress being imposed on the sample which would have a negative effect on the repeatability of the results. The sample should be tested within the next 2 hours. Repeated melting of the sample should be avoided, since it will harden the material and increase the softening point. Here, the sample preparation tool helps considerably with filling the dropping point cups. Thanks to the support disk, any outside surface contamination is avoided. Removal of excessive sample from the cup is a very easy and repeatable task because the surface of the support disk is level with the rim of the softening point cup. 33

34 Dropping & Softening Point Determination This photo section illustrates the final steps of sample preparation for softening point testing. The softening point cup containing the sample is removed from the base plate, the ball required to weight the sample is put on top and the cup, with the ball inside, is closed with the lid. Together with the collector glass, which is positioned underneath the softening point cup, the whole assembly is mounted into the sample carrier. If two samples are being analyzed the whole procedure is repeated. The sample carrier containing two samples is then mounted into the DP70 or DP90 furnace Resins, Rosins The procedure described for bitumen sample preparation in chapter can, in principle, also be applied for the preparation of resins. It is recommended that the following points are considered: Make sure that the resin sample is not overheated during the melting. Boiling should definitely be avoided as it affects the sample integrity. Make sure that the resin melt is free of air bubbles. Stir the liquid gently with a rod to ensure homogenization and to remove air bubbles. Liquefied resin solidifies relatively fast. This needs to be considered particularly when transferring the molten sample into the dropping point cups. It is recommended that the whole sample container is heated (in an oven or with the aid of a hot air blower) and that the cups are filled with molten resin as quickly as possible. Avoid excessive overfilling of the sample cup. Once the resin is solidified it is very brittle and removal of excessive sample becomes a tedious task. Remove excessive sample with a hot knife shortly after the sample was poured into the dropping point cup (approx. 2 min). As with the bitumen samples, repeated heating of solidified resin samples should be avoided. 34

35 6.2.8 Waxes In principle, wax samples are prepared like other molten samples. Here we position the dropping point cups in the deeper indentations of the sample preparation base plate using the support disk. The wax sample is melted to 15 to 20 C above the expected melting point on a hot plate in a suitable container here a glass beaker. The molten sample is then carefully poured into the dropping point cup, avoiding the inclusion of air bubbles. As with the bitumen sample, a glass rod may be used in order to guide the molten sample into the cup. Remove excessive sample with the spatula provided in the DP accessory box and allow 2 hours of solidification at ambient temperature before the measurement starts Liquid Samples or Samples that Require Cooling Prior to Measurement The DP90 allows dropping point measurements to a temperature of -20 C. The separate measurement cell including the furnace and the optical detection system can be placed in a refrigerator or a freezer to achieve the required temperature. Liquids such as canola oil or organic solvents such as long alkyl chain alcohols or alkanes having sufficiently high melting points can be solidified and measured. Edible oils and fats with melting points below ambient 35

36 Dropping & Softening Point Determination temperature need to be cooled or frozen prior to dropping point measurement. This can easily be achieved in the respective cooling device together with the separate DP90 measurement cell. The following workflow is recommended for dropping point measurements below ambient temperature. Note: A freezer or refrigerator is denoted as cooling device and abbreviated CD. For initial installation: The DP90 measurement cell and the CD should be at ambient temperature. Then, the DP90 is placed in the CD and cooling is started. The DP90 measurement cell should, preferably, be cooled overnight in the CD. The test equipment (sample carrier, collecting glasses, lids) must be cooled for at least for 1 hour in the CD. The sample preparation tool should already be assembled with sample cups and cooled for at least 1 hour in the CD. Using a disposable pipette, transfer the liquid sample drop-by-drop into the precooled sample cups in the sample preparation tool until the cup is completely full. Allow the sample to solidify for at least 1 hour in the CD. Samples that have low (below 0 C) melting points may need to be cooled for longer. The CD should only be opened, when necessary (e.g. sample preparation, sample carrier exchange). A toploading CD was found to support the workflow best. In the method, the brightness factor should be reduced to 30% in order to cope with any reflection from the sample. All manipulation such as sample carrier (dis)assembly, sample preparation etc. must be done inside the CD in order to avoid thawing and condensation. It is recommended that disposable gloves are used. 36

37 7 Dropping and Softening Point Measurement Results 7.1 Dropping Point of Edible Oils and Fats Measured on DP90 Excellence This table provides an overview of dropping point test results of edible oils & fats measured on a DP90 Excellence instrument from METTLER TOLEDO. The measured dropping point temperatures range from minus 6 C up to 50 C. Each test was repeated several times in order to achieve a significant repeatability value that could be used for result assessment. Sample Dropping Point [ C] Standard Deviation [ C] Repeatability defined by AOCS Cc [ C] Cocoa butter Palm fat Red palm oil Canola oil Pasteurized butter Margarine Pure ghee Hydrogen. vegetable oil Palm oil transesterified Palm seed oil, refined Rape oil, hydrated Mean value of 4 samples, 2 Mean value of 12 samples, 3 Mean value of 6 samples Conclusions In all cases the achieved standard deviation was below the repeatability required by the AOCS standard. This confirms the high result quality that can be achieved by the automated detection method of the MP Excellence line instruments. It also shows the practical usability of dropping point as a quality control parameter for a large variety of substances. 37

38 Dropping and Softening Point Results 7.2 Dropping Point of Fats and Waxes Measured on DP70 Excellence This table provides an overview of dropping point test results for fats and waxes measured on a DP70 Excellence instrument from METTLER TOLEDO. The measured dropping point temperatures ranged from 38 up to 86 C. Each test was repeated several times in order to receive a significant repeatability value that could be used for result assessment. In almost all cases the achieved standard deviation was below the repeatability value required by the ASTM and pharmacopeia standards. There was only one exception: a white wax sample that passed the repeatability criterion of the 0.5 C ASTM standard only. Sample Dropping Point [ C] Standard Deviation [ C] Ph. Eur Method B Repeatability [ C] ASTM D3954 Hydrated peanut oil Wool wax Vaseline yellow Wax white Wax yellow Mean value of 4 samples, 2 Mean value of 2 samples, 3 Mean value of 3 samples Conclusions The results show the practical usability of dropping point as a quality control parameter for these substances. The automated detection of the MP70 matches with ASTM repeatability requirements. 38

39 7.3 Dropping Point of Lubricant Greases This table provides an overview of dropping point test results for various lubricant grease samples, provided by different vendors and measured on a DP70 Excellence instrument from METTLER TOLEDO. The measured dropping point temperatures ranged from 180 up to 280 C. Each test was repeated several times in order to receive a significant repeatability value that could be used for result assessment. In all cases the achieved standard deviation was far below the maximum permissible repeatability value required by the IP 396 standard. Lubricant producer Number of samples per test Dropping Point IP 396 [ C] Max. temperature difference within test [ C] Max. repeatability IP 396 [ C] Shell Shell Shell Shell Shell Shell Klüber Lubrizol Lubrizol Dropping point measurements and maximum repeatability values according to IP 396 Conclusions The fully-automated dual heating-ramp procedure provided by the DP Excellence dropping point instruments proves to be feasible and achieves high result quality. 39

40 Dropping and Softening Point Results 7.4 Softening Point of Bitumen This table provides an overview of softening point test results of pure, wax-modified and polymer-modified bitumen samples measured on a DP70 Excellence instrument from METTLER TOLEDO. The amount of auxiliary reagent used for modification was in the range of 2 to 4 weight %. The measured softening point temperatures ranged from 50 up to 104 C. Each test was repeated four times in order to achieve a significant repeatability value that could be used for result assessment. In almost all cases the achieved standard deviation was below the strict maximum permissible repeatability value required by the ASTM D 3461 standard. These results show that if bitumen is modified by wax, the softening point temperature increases considerably. Bitumen type Sample Softening Point [ C] Pure Wax-modified (2 4 weight %) Standard Deviation [ C] Repeatability defined by ASTM D3461 [ C] A B C D E A B C D A Polymer-modified (2 4 weight %) B C D Conclusions The fully-automated softening point procedure provided by the DP Excellence dropping point instruments yields high result quality and delivers reliable results to the user. 40

41 7.5 Softening Point of Resins This table provides an overview of softening point test results of various resin and rosin samples provided by different vendors, measured on a DP70 Excellence instrument from METTLER TOLEDO. The measured softening point temperatures range from 60 up to 112 C. Each test was repeated several times in order to achieve a significant repeatability value that could be used for result assessment. Resin/Rosin Nominal value [ C] SP [ C] Standard Deviation [ C] Repeatability defined by ASTM D6090 [ C] Synthetic resin Natural rosin FOR85 (tall oil rosin) FOR90S (tall oil rosin) Colophony SP: softening point 1 Mean value of 4 samples, 2 Mean value of 6 samples Conclusions In all cases the standard deviation achieved with the DP70 instrument was far below the maximum permissible repeatability required by the ASTM D6090. Hence, the DP Excellence line instruments are fully compatible with the ASTM D6090 standard. 41

42 Performance Verification with MP VPac 8. Performance Verification with MP VPac 8.1 Ready-to-use Kit of Traceable Reference Substances Performance verification by temperature calibration is the recommended workflow to ensure faultless routine operation of a melting point instrument and to secure result reliability. The MP VPac provides 3 different certified reference substances in prefilled, sealed capillaries for a simple method of verifying instrument accuracy over the temperature range 40 to 230 C. No sample grinding and time-consuming manual upfront filling of melting point capillaries is required. Just take the pre-filled capillaries and insert them into the MP instrument furnace, as in a normal method. The preprogrammed calibration method can be started directly without any modification. Each of the three reference substances included in the MP VPac comes with a certificate that states the certified temperature value including measurement uncertainty. The purity is routinely checked by DSC measurements. The subsequently measured melting point is therefore a reliable way of checking the temperature accuracy of the instrument and whether an adjustment is required. 8.2 Do-it-yourself Service This is a cost-effective and do-it-yourself service that can be performed on Melting Point Excellence instruments. This service allows you to: Have confidence in the accuracy of your results Control the performance of the melting point system Receive an unbiased and traceable analysis verification Performance verification is recommended after: Setting up an instrument Operational qualification of an instrument Monthly periodic check of the instrument 8.3 Reference Substances The MP VPac contains the following melting point reference substances, each in 50 sealed standard METTLER TOLEDO melting point capillaries. Phenyl salicylate: Thermodynamic melting point: 41.8 ±0.2 C Pharmacopeia melting point (1 C/min heating rate): 43.8 ±0.2 C Benzoic acid: Thermodynamic melting point: ± 0.2 C Pharmacopeia melting point (1 C/min heating rate): ±0.2 C Saccharin: Thermodynamic melting point: ±0.3 C Pharmacopeia melting point (1 C/min heating rate): ±0.3 C 42

43 9. More Information Find more information to the following topics: Presentation of all instruments of the MP and DP Excellence instrument line, including technical information (downloadable product brochures). Comprehensive product movies showing the operation of the MP and DP Excellence line instruments. Good Melting and Dropping Point Practice GMDP : Service product offering supporting the whole life cycle of the MP and DP Excellence instruments, including risk check, downloadable data sheets and application literature. Detailed information about the LabX PC Software for the MP 70 and MP90 Excellence instruments. Useful accessories which support secure and efficient sample preparation for melting, dropping and softening point determination. MPVPac : a unique self service for MP Excellence instrument performance verification based on pre-filled, certified reference substances. Comprehensive on-demand webinars that introduce automatic melting, dropping and softening point determination. A lot of useful application tips & hints and a concluding knowledge-testing quiz are included. Go to Good Melting Point Practice Good Dropping Point Practice 43

44 Good Measuring Practices Five Steps to Improved Measuring Results The five steps of all Good Measuring Practices guidelines start with an evaluation of the measuring needs of your processes and their associated risks. With this information, Good Measuring Practices provide straight forward recommendations for selecting, installing, calibrating and operating laboratory equipment and devices. Guaranteed quality Compliance with regulations, secure audits Increased productivity, reduced costs Professional qualification and training 5 Routine Operation 4 Calibration / Qualification Good Measuring Practices 3 Installation / Training 1 Evaluation 2 Selection Good Melting and Dropping Point Practice Reliable thermal values optimized by GMDP Good Thermal Analysis Practice Fast and secure thermal analysis results with the help of GTAP Learn more about Good Measuring Practices program For more information Mettler-Toledo International Inc Laboratory Division Im Langacher CH-8606 Greifensee, Switzerland Subject to technical changes 09/2014 Mettler-Toledo AG Global MarCom Switzerland