Course Outline. in Soil/Sediment&WasteSediment&Waste by. Overview of VOCs Analysis Sample Collection VOCs Analysis

Transcription

1 Determination of Volatile Organic Compounds in Soil/Sediment&WasteSediment&Waste by Headspace Technique.( ) MS (Environmental Toxicology) The University of Michigan, USA Phaitoon_m@yahoo.com Mobile: Course Outline Overview of VOCs Analysis Sample Collection VOCs Analysis 2 1

2 References METHOD 5021A (Revision 1, June 2003) VOLATILE ORGANIC COMPOUNDS IN VARIOUS SAMPLE MATRICES USING EQUILIBRIUM HEADSPACE ANALYSIS METHOD 5000 (December 1996) SAMPLE PREPARATION FOR VOLATILE ORGANIC COMPOUNDS METHOD 5035A CLOSED-SYSTEM PURGE-AND-TRAP AND EXTRACTION FOR VOLATILE ORGANICS IN SOIL AND WASTE SAMPLES 3 References METHOD 8000C (Revision 3, March 2003) DETERMINATIVE CHROMATOGRAPHIC SEPARATIONS METHOD 8015D (Revision 4, June 2003) NONHALOGENATED ORGANICS USING GC/FID METHOD 8260C (Revision 3, August 2006) VOLATILE ORGANIC COMPOUNDS BY GAS CHROMATOGRAPHY/MASS SPECTROMETRY (GC/MS) 4 2

3 VOCs Laboratory 3.4 Laboratory for VOCs analysis should be completely free of solvents Special precautions must be taken to determine methylene chloride. The analytical and sample storage area should be isolated from all atmospheric sources of methylene chloride, otherwise random background levels will result SW-846 Method VOCs Laboratory all GC carrier gas lines and purge gas plumbing should be constructed of stainless steel or copper tubing Methylene chloride will permeate through polytetrafluoroethylene (PTFE)tubing 343L Laboratory workers clothing - Solvent Extraction SW-846 Method

4 EQUIPMENT AND SUPPLIES 7 Headspace System holding samples at elevated temperatures and establishing a reproducible equilibrium between a wide variety of sample types and the headspace accurately transferring a representative portion of the headspace into a gas chromatograph fitted with a capillary column 8 4

5 Headspace Containers Clear glass, 22-mL soil vials with a PTFE-lined septum Prior to use, wash the vials and septa with detergent solution, then rinse with tap water followed by distilled water. Dry the vials and septa in an oven at 105 C for 1 hour, then remove and allow to cool. Store in an area free of organic solvents. 9 Field Sampling Equipment Water Samples Clear or amber 40 ml vials with screw-cap PTFE lined vials (for water samples only). 10 5

6 Field Sampling Equipment Soil Samples Soil sampler which delivers at least 2 g of soil is necessary, e.g., Purge-and-Trap Soil Sampler Model 3780SPT (Associated Design and Manufacturing Company) or equivalent An automatic syringe or bottle-top dispenser calibrated to deliver 10.0 ml of matrix modifier solution, e.g., Automatic Vaccinator Model C1377SN (NASCO) or equivalent 11 5 GRAM SOIL SAMPLER 12 6

7 10 GRAM SOIL SAMPLER 13 EasyDraw Syringe & PowerStop Handle 14 7

8 Terra Core Soil Sampler 15 Field Sampling Equipment Soil Samples Crimping tool for headspace vials. If using screw-top vials, this is not needed. VOA vials or 60-mL VOA vials with PTFEfaced septa and crimp seal caps or screw-top caps. These vials will be used for sample screening, high concentration analysis (if needed) and dry weight determination 16 8

9 Miscellaneous Equipment Crimping tools For the preparation p of blanks, standards and water samples Syringes Automatic syringe calibrated to deliver internal standards and surrogate analyte 5-mL glass hypodermic syringes with Luer-Lock tip 17 REAGENTS & STANDARDS Organic-Free Reagent Water Methanol - Pesticide quality Calibration spiking solutions Internal and surrogate standards Matrix Modifying Solution 18 9

10 Matrix Modifying Solution Add 180 g of ACS NaCl to 500 ml of reagent water. Mix well until all components are dissolved Analyze a 10.0 ml portion from each batch to verify that the solution is free of contaminants. Store in a sealed bottle in an area free of organic chemicals at 4 CC 19 Chemical Preservatives Acidic or basic Chosen based on analytes of interest should be mixed with sample at time of sampling The matrix modifying solution may not be appropriate for soil samples having high carbon content (>1%) 20 10

11 Basic preservatives addition of 100 mg of ACS grade trisodium phosphate dodecahydrate (Na 3 PO 4.12H 2 O) to either a 22 ml headspace vial or a 40 ml water sample vial will raise the ph above water sample Acidic preservative 2-3 drops of 6N hydrochloric acid (HCl) should be added to a 40 ml vial For soil sample 1 gram of solid, ACS grade sodium bisulfate (NaHSO4) should be added to each 22 ml vial 22 11

12 SAMPLE COLLECTION Chapter 4 Organic Analytes, Sec. 4.1 and Method 5035, Appendix A for general sample collection information. 23 SAMPLE COLLECTION METHOD 5035A CLOSED-SYSTEM PURGE-AND-TRAP AND EXTRACTION FOR VOLATILE ORGANICS IN SOIL AND WASTE SAMPLES Appendix A 24 12

13 Water Sample Collection Collected and stored with minimum headspace and the diameter of any bubble caused by degassing upon cooling the sample should not exceed 5-6 mm. When a bubble is present and if any evidence of leakage is found, the sample can be considered corrupted and should be discarded 25 Water Sample Collection Fill the 40 ml vial and chemically preserve the sample if necessary, ensure that there is no headspace in the vial, and seal. At least two vials should be collected per sample, and more may be necessary for duplicate analyses and MS/MSD analyses. The transfer of the sample into a headspace vial and the addition of matrix modifier and standards shall be performed in the laboratory 26 13

14 Soil Sample Collection Two procedures include the addition of a matrix modifying solution in the field while the third procedure does not. Soil samples containing over 1% organic carbon may yield low recoveries when the matrix modifying solution is used. The matrix modifying solution may not be appropriate for these samples 27 Soil Sample Collection The choice is based on field conditions, organic carbon content of the soil, the specific volatile analytes of interest, and the intended use of the analytical results. Whichever alternative is used, collect 3 or 4 vials of sample from each sampling point to allow for sample reanalyses if necessary. In addition, separate portions of sample are taken for dry weight determination and for high concentration analysis (if necessary) 28 14

15 Soil Sample Collection Soil Samples: Procedure 1 Without addition of modifying solution & standards Used for high concentrations (> 200 g/kg) Using soil sampler, add 2-3 cm (2 g) of soil sample to a tared 22-mL headspace vial and seal immediately with the PTFE side of the septum facing toward the sample. The samples should be introduced into the vials gently to reduce agitation which might drive off volatile compounds 29 Soil Sample Collection Soil Samples: Procedure 2 (+modifying solution) Using soil sampler, add 2-3 cm (2 g) of soil sample to a tared 22-mL headspace vial containing 10.0 ml of matrix modifier or reagent water and seal immediately with PTFE side of the septum facing toward the sample. The samples should be introduced into the vials gently to reduce agitation which might drive off volatile compounds 30 15

16 Soil Sample Collection Soil Samples: Procedure 3 Same as procedure 2 but adding modifying solution in the field 31 Soil Sample Collection Fill a 40- or 60-mL VOA vial with soil from each sampling point to use for dry weight determination, sample screening, and high concentration analysis (if necessary) 32 16

17 Quality Control Field duplicate Trip blank Field blank Equipment rinsate Temperature blank Matrix spike and matrix spike duplicate 5035A Appendix A 33 Field duplicate A field duplicate may be prepared at a frequency of one per day per matrix The field duplicate is an independent sample which is collected as close as possible to the same point in time and space as the primary field sample. Field duplicates are used to estimate the reproducibility (precision) of the sampling process 34 17

18 Trip blank at a frequency of one per day of sampling Prepared using reagent water transported to the site. accompany the field samples throughout all sample collection and transport operations. This blank will not be opened during sampling activities and will be used to assess sample contamination originating from sample transport, shipping, or site conditions. 35 Field blank Conversely is prepared on-site during the sample collection activities using the same reagent water source used to prepare the trip blank. The field blank should be collected and preserved in the same manner as the environmental samples. The results from this analysis are used to assess sample contamination originating predominantly from field sampling conditions 36 18

19 Equipment Blank (rinsate) Collected from sample collection devices used for each distinct sample matrix. Obtained either prior to or during sample collection activities. The results from these analyses are used to assess possible sample contamination from sampling equipment. 37 Temperature blank Prepared with a water-filled vial or a suitable thermometer, should be included with each cooler of samples designated for transport. Upon sample receipt, laboratory will use the temperature blank or thermometer to determine the internal temperature of each cooler Acceptable temperatures are 4 ± 2 C Cfor refrigerated aqueous and solid samples and < -7C for frozen solid samples 38 19

20 Matrix spike/matrix spike duplicate Matrix spikes are aliquots of environmental samples to which known concentrations of certain target analytes have been added before sample manipulation from the preparation, cleanup, and determinative procedures have been implemented 39 # Samples per sampling point Two(2) 40-mL VOA vials for direct vapor partitioning measurement. These are needed for the most sensitive measurements - one is kept in reserve for any necessary repeat analysis. The upper concentration value of the vapor partitioning method s calibration range limits the usability of these direct measurements 40 20

21 # Samples per sampling point One(1) 40-mL VOA vial for methanol extraction of soil aliquot prior to vapor partitioning Once a methanol extract is obtained, an aliquot of this extract is diluted fifty-fold (50) or more with water and is tested by vapor partitioning as a water matrix. The 50-fold dilution is necessary to minimize interferences in vapor partitioning measurements of water matrices. Methanol extracts have no upper limit of measured VOC concentration since the extract can be subaliquoted for different dilutions 41 # Samples per sampling point One (1) 60-mL VOA vial for any percent moisture determination to report VOC results on a moisture corrected basis, if necessary

22 # Samples per sampling point VOA vials for any QC audits such as duplicates, matrix spikes, etc 43 Field Blanks If matrix modifying solution is not added in the field field blank should be prepared by adding 10.0 ml of organic-free reagent water to a clean vial and immediately sealingthe vial. If matrix modifying solution is to be added in the field, prepare a field blank by adding 10.0 ml of matrix modifying solution plus internal standards to a clean vial 44 22

23 Sample Storage Store samples at 4 C until analysis All samples should be analyzed within 14 days of collection or sooner if labile compounds are target analytes See more detail in Method 5035 Appendix A Table A-1 45 Sample Preservation Techniques 46 23

24 Sample Preservation Techniques 47 Sample Preservation Techniques 48 24

25 Sample Preservation Techniques 49 Sample Preservation Techniques 50 25

26 Water Sample Preparation Pipette 5 ml of the matrix modifier solution into a headspace vial Place septum and crimp top onto the vial, tare and record the weight 51 Water Sample Preparation Withdraw 5 ml sample with gas tight syringe thru septum of sample vial Place sample underneath the top level of matrix modifier in the headspace vial Inject the entire aliquot into the headspace vial and immediately seal the vial 52 26

27 Soil Analysis Method Low concentration method 0.5 to 200 g/kg g High concentration method > 200 g/kg 53 Soil Sample Preparation Low concentrations (0.5 to 200 g/kg), Sample in HS Vial & not adding water nor matrix modifier Unseal the vial, rapidly add 10.0 ml of matrix modifying solution, and immediately reseal the vial Inject each headspace vial with internal standards and surrogates Weigh the sealed vial and its contents to 0.01 g Mix the samples (on a rotator or shaker) for at least 5 min 54 27

28 Soil Sample Preparation If the sample was sealed into a headspace vial, the vial simply must be injected with applicable internal standards and surrogates 55 High concentration method for water, soil/sediment and solid waste 56 28

29 High concentration Without the addition of matrix modifying solution or organic-free reagent water to the vial weigh the sample to nearest 0.01 g, add 10.0 ml of methanol to the sample in the tared 22-mL vial, and immediately reseal the vial Proceed to Extraction Procedure 57 High concentration Matrix modifying solution or organic-free reagent water were added to sample vial Transfer ~ 2 g sample from 40- or 60-mL VOA vial into a tared 22-mL sample vial. Immediately add 10.0 ml of methanol to the 22-mL vial & Seal both the 22-mL and the VOA vials Proceed to Extraction Procedure 58 29

30 High concentration Proceed to Extraction Procedure (with adding or no adding of modifying solution) Mix by shaking for 10 min at room temperature. Decant 2 ml of the methanol extract to a screw-top vial with PTFE-faced septa and seal. Withdraw 10 L or appropriate volume and inject into a 22 ml vial containing 10.0 ml of matrix modifying solution and internal standards (if necessary) and surrogates. Analyze by the headspace procedure

31 Calibration Method General calibration procedures Determinative methods and Method specific info on calibration and Std preparation GC methods External standard calibration is preferred b/c of possible interference with internal standards If interferences are not a problem, internal standard calibration is acceptable GC/MS methods normally utilize internal standard calibration 61 METHOD 5000 SAMPLE PREPARATION FOR VOLATILE ORGANIC COMPOUNDS 62 31

32 METHOD 5000 provides specific information pertaining to analyte interferences, preparation of calibration and spiking standards, and specific quality control that should be applied to each preparative method. 63 SAMPLE PREPARATION METHODS FOR VOCs SW-846 METHOD 5000: SAMPLE PREPARATION FOR VOLATILE ORGANIC COMPOUNDS 64 32

33 Stock standards 5.3 Stock solutions may be used as calibration standards (CS) if dilutions are made in a watermiscible solvent. Quality control check sample (QCS) stock concentrate must be prepared independently from CS because it serves as a check on the accuracy of calibration solution. SW-846 Method Purgeable stock standards Place ~ 9.8 ml of methanol in a 10-mL, tared, ground-glass-stoppered volumetric flask. Allow flask to stand, unstoppered, for ~ 10 min or until all alcohol-wetted surfaces have dried. Weigh the flask to the nearest g SW-846 Method

34 Purgeable stock standards Using a 100- L syringe, immediately add two or more drops of assayed reference material to the flask, then reweigh. The liquid must fall directly into the alcohol without contacting the neck of the flask. SW-846 Method Purgeable stock standards Reweigh, dilute to volume, stopper, then mix by inverting the flask several times. Calculate the concentration in milligrams per liter (mg/l) from the net gain in weight SW-846 Method

35 Purgeable stock standards Transfer stock standard solution into a PTFEsealed screw-cap bottle. Store with minimal headspace at -10 C to -20 C and protect from light, or as recommended by the supplier of the standard. SW-846 Method Matrix Spike standards Prepare a matrix spike concentrate by mixing stock standards as previously prepared and diluting with a water-miscible solvent Stock standards are to be independent of the calibration standard SW-846 Method

36 Matrix Spike standards Recommended purgeable matrix spiking solution for Methods 8021 and 8260 Prepare a spiking solution in methanol at a concentration of 25 mg/l 1,1-Dichloroethene, Trichloroethene Chlorobenzene, Toluene, Benzene The spiking concentration employed should correspond to either the applicable regulatory limit or action level for the compound or a concentration in the middle of the calibration range 71 Matrix Spike standards For methods with no guidance, select five or more analytes (select all analytes for methods with five or less) from each analyte group for use in a spiking solution. Where matrix spike concentrations in the sample are not listed, it should be at or below the regulatory limit or action level concentration or 1 to 5 times higher than the background concentration, whichever is greater 72 36

37 Matrix Spike standards The spiking volume added to water should not exceed 1 ml/l so that the spiking solvent will not decrease purging efficiency 73 Laboratory Control Standard Laboratory Control Standard (LCS) should be spiked at the same concentration as matrix spike (MS) 74 37

38 Initial calibration Prepare five 22-mL vials of Standards and a reagent blank The mixing step is eliminated since no soil is present in the vial 75 Calibration Blank 10.0 ml Modifier in HS vial Inject IS & surrogate underneath modifier level Seal Place in Headspace autosampler Analyse by GC, GC/MS 76 38

39 Calibration Standard Prepare Calibration Standard Spiking solution in Methanol or water Spike not more than 20 ul of Standard per 100 ml water At least 5 level standards needed 77 Calibration Standard Place 10.0 ml Modifier in HS vial Inject IS & surrogate underneath modifier level Spike 1 ul of Spiking solution underneath modifier level Seal Place in Headspace autosampler Analyse by GC, GC/MS 78 39

40 Calibration Standard Prepare 20, 40, 100, 200 & 400 mg/l VOC CS spike solution For water sample CS1 = (20 mg/l)(1 ul)/10.0 ml mod.) = 2 ug/l CS2 = (40 mg/l)(1 ul)/10.0 ml mod.) = 4 ug/l 79 Calibration Standard For water sample CS3 = (100 mg/l)(1 ul)/10.0 ml mod.) = 10 ug/l CS4 = (200 mg/l)(1 ul)/10.0 ml mod.) = 20 ug/l CS5 = (400 mg/l)(1 ul)/10.0 ml mod.) = 40 ug/l 80 40

41 For soil samples CS1 = (20 mg/l)(1 ul)/2 g soil) = 10 ug/kg CS2 = (40 mg/l)(1 ul)/2 g soil) = 20 ug/kg CS3 = (100 mg/l)(1 ul)/2 g soil) = 50 ug/kg 81 Calibration Standard For soil samples CS4 = (200 mg/l)(1 ul)/2 g soil) = 100 ug/kg CS5 = (400 mg/l)(1 ul)/2 g soil) = 200 ug/kg 82 41

42 Headspace operating conditions Depending on Headspace System used Example: Mix samples (on a rotator or shaker) for 2 min. Place the vials in the autosampler carrousel at room temperature. The individual vials are heated to 85 C and allowed to equilibrate for 50 min. Each sample is mixed by mechanical vibration for at least 10 min. during this equilibrium period. Each vial is pressurized with helium carrier gas to a minimum pressure of 10 psi. 83 Headspace operating conditions Example: A representative and reproducible sample of the pressurized headspace is transferred to the GC column through a heated transfer line according to the manufacturer's instructions Proceed with the analysis as per the determinative method of choice 84 42

43 Initial Demonstration of Proficiency Lab must generate data of acceptable accuracy and precision for target analytes in a clean reference matrix Including a combination of the sample preparation method (usually a 5000 series method for volatile organics) and the determinative method (an 8000 series method) 85 Initial Demonstration of Proficiency To evaluate performance of total analytical process, reference samples must be handled in exactly the same manner as actual samples. Use a clean matrix for spiking purposes e.g.,organicfree reagent water for water matrix or sand or soil for the solid matrix. Because of the volatility of these compounds, spike must be introduced directly into the matrix while the matrix is in a sealed container (e.g., a gas-tight syringe or purge device) 86 43

44 Initial Demonstration of Proficiency Preparation of reference samples total volume spiked into sample should be no more than 200 L If method lacks performance data, prepare a reference standard concentrate at such a concentration that the spike will provide a concentration in the clean matrix that is times the MDL for each analyte in that matrix 87 Initial Demonstration of Proficiency Equilibrium headspace by Method 5021 Prepare Spike Stock Standard containing each target analyte at 10 mg/l in methanol For water samples, spike 100 ml of organic-free reagent water with 200 L which provides a 20 g/l concentration in the reference sample. Quickly transfer the spiked water to four vials Analyze replicate aliquots (at least four) of the well-mixed ed reference samples 88 44