Certificate of measurement

Transcription

1 Certificate of measurement 4005 Crab paste Proximates and Elements Certified Reference Material LGC7164 Certified Values Constituent 1 Units Number of laboratories Certified value 2,3 Uncertainty 4 Weight5 (g) k value 4 Moisture g/100 g Nitrogen g/100 g Total fat g/100 g Ash g/100 g Chloride g/100 g Calcium mg/100 g Cadmium mg/kg Copper mg/kg Lead mg/kg Magnesium mg/100 g Manganese mg/kg Phosphorus mg/100 g Potassium mg/100 g Sodium mg/100 g Zinc mg/kg Assessed Values Constituent Units Number of laboratories Assessed Weight5 2,3 Uncertainty4 value (g) k value 4 Arsenic mg/kg Cobalt mg/kg Iron 6 mg/100 g Notes: 1. Cadmium and lead were determined at LGC using isotope-dilution ICP-MS (IDMS). These values were confirmed by the results of the inter-laboratory study (see Additional Information). The values for the remaining constituents were assigned using the results of an inter-laboratory study obtained in different laboratories. 2. Unweighted median value, (for arsenic and cobalt, the unweighted mean value) of the concentration obtained by participant laboratories. Each data set was obtained in a different laboratory. For cadmium and lead, the unweighted mean of 12 replicate measurements was used. 3. The results are traceable to the SI. 4. The uncertainty quoted is the half-width of the expanded uncertainty interval calculated using the coverage factor (k) shown in the table, which gives a level of confidence of approximately 95 %. 5. Weight of material taken for the homogeneity assessment. This represents the minimum weight which should be taken for analysis. 6. Results from the homogeneity, stability and inter-laboratory studies showed occasional high outlying results for iron. Date of Issue: August 2015 (updated October 2017) Signed: Gill Holcombe (Mrs) for the Government Chemist Batch number: 001 Page 1 of 6

2 Indicative Values The following figures have not been certified but are provided for information purposes and should be regarded as indicative values only. Constituent Units Range 1 Aluminium mg/kg 1-4 Chromium mg/kg Mercury mg/kg Nickel mg/kg Selenium mg/kg Tin mg/kg Note: 1. Range of participating laboratory median values Additional Information Inter-laboratory study participants were also asked to analyse the candidate material for cadmium and lead. Constituent Units Number of laboratories Range 1 Cadmium mg/kg Lead mg/kg Note: 1. Range of participating laboratory median values Explanation of Terms The constituent values have been categorised as certified, assessed or indicative depending on the source and spread of the data obtained. The certified values were obtained in one of two ways. For cadmium and lead, the values were calculated following analyses carried out at LGC using IDMS (a definitive method with fully evaluated uncertainty) and are traceable to the primary calibration solutions prepared gravimetrically at LGC from compounds of known certified purity. The remaining certified values were calculated using data obtained from an inter-laboratory study from ten or more participating laboratories. The assessed values were calculated using data obtained in an inter-laboratory study from less than ten participants. Values were classified as indicative where the agreement between the results provided by laboratories was poor, or the number of laboratories reporting data was very small. Material Preparation Brown crab meat purchased from a commercial supplier was blended with small amounts of sodium polyphosphate, sodium chloride and water to a smooth paste. The paste was dispensed into cans as 140 g portions, sealed and then heat treated to ensure sterility. Homogeneity The canned material was tested for between-unit homogeneity by analysing randomly selected samples from across the batch. An uncertainty contribution was calculated to allow for possible inhomogeneity and included in the combined uncertainty. Page 2 of 6

3 Characterisation Cadmium and lead were characterised at LGC using 12 units analysed in duplicate by IDMS. Additional constituents were characterised by means of an inter-laboratory study in which each participating laboratory was asked to carry out 5 replicate measurements on the candidate material supplied. Laboratories were asked to determine moisture, nitrogen, total fat, ash, chloride, calcium, iron, magnesium, phosphorus, potassium, sodium, aluminium, arsenic, cadmium, chromium, cobalt, copper, lead, manganese, mercury, nickel, selenium, tin and zinc. Apart from total fat, where participants were asked to incorporate an acid digestion stage in the analysis, analytical methods were not specified by LGC, although laboratories were strongly encouraged to select wellvalidated methods of known trueness and precision. Details of the analytical methods used for the characterisation of this material are contained in a later section. The assigned values for all constituents, except arsenic and cobalt, are based on the median of the individual laboratory medians, after elimination of technical outliers. The 95 % confidence interval of the median of the laboratory medians was used to calculate the uncertainty arising from the inter-laboratory characterisation exercise. For arsenic and cobalt, the equivalent calculations were carried out using the mean of means instead of the median of medians, after elimination of outlying results. The combined expanded uncertainty for each certified and assessed value (quoted in the tables on page 1) was calculated by combining the inter-laboratory characterisation uncertainty with the uncertainty value calculated from the homogeneity assessment, and expanding using a suitable coverage factor. Stability Previous experience suggests that this material is stable over the anticipated lifetime, however LGC7164 Batch 1 will be subjected to routine stability monitoring under LGC s reference material stability monitoring programme. Purchasers will be informed of any changes that affect the certified and assessed values. Methods used by Participating Laboratories Techniques used in the characterisation of this material are summarised below. Constituent Moisture Nitrogen Total fat Ash Chloride Metals Techniques Used Measured as loss on drying using a variety of conditions. Procedures included microwave drying, freeze drying and hot air oven drying. There were two approaches used by participants. Some used a Kjeldahl method (variety of catalysts) and others used instrumentation based on the Dumas principle. Laboratories used acid hydrolysis followed by solvent extraction (variety of solvents). Laboratories used dry ashing in muffle furnace or microwave ashing. The end temperature varied between 500 C and 550 C. Laboratories employed a variety of methods. Some used a method based on a coulometric titration; others used titration with a colorimetric end point. The preparation procedures included ashing and dissolution, cold or hot water extraction and acid extraction. Laboratories used a variety of methods including ICP-OES and ICP-MS following ashing or acid digestion. Page 3 of 6

4 Storage Conditions and Shelf Life The material should be stored at (18 ± 4) C in the original sealed can. If stored under the recommended conditions, the values will remain valid for 12 months from the date of shipment (see page 6). Intended Use For constituents where the assigned value is described as Certified or Assessed, the intended use of this material is for the development, validation, (including the assessment of method bias), and quality control of methods for the analysis of crab and seafood products. Where the assigned value is described as Indicative, the material is suitable for monitoring the performance of a method or analyst, but not suitable for assessing method bias. The material may also be applicable to other similar matrices and procedures where suitable reference materials are not available. Information on how to compare an analytical result with a certified value can be found in ERM application note 1; Instructions for Use (updated May 2016) Open the can carefully immediately prior to analysing the material. On opening the can, you may notice some small white spots which have been identified as crystals of tyrosine, formed naturally on the surface of the product. Using a non-metal spatula, stir gently and transfer the entire contents of the can to a small food mixer, paying particular attention to any liquid that may have separated, and blend thoroughly. Preparation should be carried out as quickly as possible once the can is open to avoid loss of moisture. Transfer to an airtight jar and use immediately. LGC is not responsible for changes that occur during storage of any prepared material. Metrological Traceability For the analytes characterised through the inter-laboratory study, the results are considered traceable to the SI through the physical and chemical standards used by the participants. For cadmium and lead, the results are traceable to the SI through the primary standards used for the calibration of the IDMS analysis. These were SRM 3108 for cadmium (NIST, Gaithersburg, MD, USA) and SRM 981 for lead (NIST, Gaithersburg, MD, USA). Page 4 of 6

5 Participants in the Inter-laboratory Study The number of participants results used in the calculation of the certified values is given in the table on page 1. The following organisations took part in the inter-laboratory exercise: Abu Dhabi Quality and Conformity Council Agrifood Technology Bakkavor Group Brulabo Eurofins Exova Glasgow Scientific Services H J Heinz Foods Ltd Lancashire County Scientific Service LATU Marine Scotland Micro-search National Institute of Health Natural Resources Wales Noon Laboratories NSW Department of Primary Industries Premier Analytical Services Salamon and Seaber Sciantec Analytical Services Silliker SVA Ltd Syni Laboratory Service Ltd Thailand Institute of Scientific and Technological Research West Yorkshire Analytical Services United Arab Emirates Australia Belgium Uruguay Portugal Australia France Iceland Thailand Certification revision In October 2017, an error was identified in the units quoted for iron in the Assessed Values table on page 1. The table was corrected to change the units for iron from mg/kg to mg/100 g. Page 5 of 6

6 Unit Number Date of Shipment Legal notice The values quoted in this certificate are the best estimate of the true values within the stated uncertainties and based on the techniques described herein. No warranty or representation, express or implied, is made that the use of the product or any information, material, apparatus, method or process which is the subject of or referred to in this certificate does not infringe any third party rights. Further, save to the extent: (a) prohibited by law; or (b) caused by a party's negligence; no party shall be liable for the use made of the product, any information, material, apparatus, method or process which is the subject of or referred to in this document. In no event shall the liability of any party exceed whichever is the lower of: (i) the value of the product; or (ii) 500,000; and any liability for loss of profit, loss of business or revenue, loss of anticipated savings, depletion of goodwill, any third-party claims or any indirect or consequential loss or damage in connection herewith is expressly excluded. Production of this reference material and certificate was funded by the National Measurement System. This document may not be published except in full, unless permission for the publication of an approved extract has been obtained in writing from LGC Limited. It does not of itself impute to the subject of measurement any attributes beyond those shown by the data contained herein. Page 6 of 6