Comparison of PCB analysis by GC Electron Capture Detection and GC-MS Selective Ion Monitoring Analytical Methods

Transcription

1 Comparison of PCB analysis by GC Electron Capture Detection and GC-MS Selective Ion Monitoring Analytical Methods Robert K. Johnston, Ronald Gauthier, William Wild, Jr. Space and Naval Warfare Systems Center, San Diego, CA Fredrick Newton*, Henry Camp, Stephanie Roy, Linda Cook Arthur D. Little, Cambridge, MA Alan Roberts URS Grenier, Denver, CO Diane Luszniak, Dale Hoover Axys Analytical, Sidney, BC *Current Address Battelle Ocean Sciences, Carlsbad, CA Presented at the Society of Environmental Toxicology and Chemistry 22 nd Annual Meeting in North America, Changing Environmental Awareness: Societal Concerns and Scientific Responses, Platform Session Persistent, Bioaccumulative, and Toxic Chemicals (PBTs) in Aquatic Ecosystems, 15 November 2001, Baltimore Convention Center, Baltimore, Maryland. Author to whom correspondence should be addressed: 1

2 Introduction PCB Methods Used Precision MDL Study Accuracy Analysis of Standard Reference Materials 1944 Sediment 1974a Mussel Tissue Results Comparison of Results in Fish Tissue Summary ABSTRACT Different analytical methods were used to analyze PCB congeners, homologues, and Aroclors in deep sea sediment and black cod samples from off the coast of California and in vermillion snapper, white grunt, and black sea bass samples from coastal waters off South Carolina. Sediment and black cod samples were analyzed for PCBs by both Gas Chromatography Electron Capture Detection (ECD) and GC-MS in Selected Ion Monitoring Mode (SIM) methods. The fish samples from South Carolina were analyzed by high resolution GC-MS (Method 1668) and by SIM. For each method the samples were processed in the same manner for sample preparation, extraction, and fractionation, only the injection and quantification procedures differed. For the ECD method, samples were analyzed for 26 congeners and 8 Aroclors. For SIM and Method 1668 data on 26 (or 31) congeners, 10 homologues, and 8 Aroclors were obtained. For fish tissue samples, the methods resulted in similar detection limits, had similar accuracy for standard reference materials, and obtained similar results for field samples analyzed by both methods. Based on the highly significant regression between the sum of congeners measured by ECD (sumecd) and sum of homologues measured by SIM (TOTALPCB), TOTALPCB could be predicted by ΣECD with a high degree of confidence. Sediment samples showed similar distributions of congeners measured by both methods. The fish samples analyzed by SIM and Method 1668 showed similar results for TOTALPCB but there were differences in sensitivity and abundance of individual congeners. The results of the study were used to assess the potential ecological and human health risk of PCB contamination in the food chain. Keywords: PCB, GC-MS, ecological risk assessment, human health risk assessment 2

3 PCB Methods Used 8081M - PCB Congener - GC- Electron Capture Detection (ECD) 26 congeners Sediment Fish Tissue Arthur D. Little, Cambridge, MA 680M-GC/MS- Selective Ion Monitoring (SIM) 31 congeners 10 homologues Total PCBs Sediment Fish Tissue Arthur D. Little, Cambridge, MA EPA METHOD 1668A High Resolution GC/MS 31 congeners 10 homologues Total PCBs Fish Tissue Axys Analytical, Sidney, BC For each method the samples were processed in the same manner for sample preparation, extraction, and fractionation, only the injection and quantification procedures differed. 3

4 Precision MDL Study for Fish Tissue 4

5 ppb dry weight MDL Study for Fish Tissue (Haddock) MDL Study for Fish SIM ECD SIM MDL - ECD MDL - 0 Congener Number Number of Chlorines The MDL study was performed on spiked samples of fish tissue. Bars are average and standard deviation of 8 repeated measurements. Detection limits were similar for both methods. 5

6 Accuracy Analysis of Standard Reference Materials 1944 Sediment ECD SIM 1974a Mussel Tissue ECD SIM 1668 Standard Reference Materials (SRMs) were obtained from the National Institute of Standards and Technology (NIST). The Certificate for the SRMs have certified values for analytes that have been obtained from two or more independent analytical techniques and reference values for noncertified analytes. Reference values are noncertified values that are the best estimates of the true values; however, the values do not meet NIST criteria for certification and are provided with associated uncertainties that may reflect only measurement precision, may not include all sources of uncertainty, or may reflect a lack of sufficient statistical agreement among multiple analytical methods (NIST 1999). SRMs were included in each analytical batch as part of each laboratory s QA/QC procedures. 6

7 SRM Results for Sediment (1) Sediment SRM 1944 DO21 ECD DO24 ECD DO21 SIM DO24 SIM ng/g dry weight PCB Congener Green error bars are certified (or reference) values ±95% confidence interval for Standard Reference Material (SRM) 1944 New York/New Jersey Waterway Sediment (NIST 1999a). Red points are for replicate ECD analyses and blue points are for replicate SIM analyses. 7

8 SRM Results for Sediment (2) DO21 ECD DO24 ECD DO21 SIM DO24 SIM Sediment SRM 1944 ng/g dry weight PCB Congener

9 SRM Results for Sediment (3) Sediment SRM 1944 ng/g dry weight DO21 ECD DO24 ECD DO21 SIM DO24 SIM PCB Congener

10 SRM Results for Tissue (1) 150 ECD n = 5 SIM n = 7 SRM Mussel Tissue 1974a 1668 n = 7 [310] ng/g dry weight PCB Congener Green error bars are certified (or reference) values ±95% confidence interval for Standard Reference Material (SRM) 1974a Organics in Mussel Tissue (Mytilus edulis) (NIST 1999b). The mean and standard deviation were obtained from replicate SRM analyses by ECD (red), SIM (blue), and 1668 (pink). The ECD method had one result off-scale at 310 ng/g for congener 77. For Method 1668 congener 44 coelutes with congeners 47 and 65, and conger 87 coelutes with congeners 108, 119, 86, 97, &

11 SRM Results for Tissue (2) 150 SRM Mussel Tissue 1974a ECD n = 5 SIM n = n = 7 ng/g dry weight PCB Congener For Method 1668, congener 101 coelutes with congeners 90 & 113, and congener 128 coelutes with congener

12 SRM Results for Tissue (3) Hexachlorobiphenyls - SRM Mussel Tissue 1974a 150 ECD n = 5 SIM n = n = 7 ng/g dry weight PCB Congener For method 1668, congener 128 coelutes with congener 166 and congener 138 coelutes with congeners 129, 160, and

13 50 40 SRM Results for Tissue (4) SRM Mussel Tissue 1974a ECD n = 5 SIM n = n = 7 ng/g dry weight PCB Congener For Method 1668, congeners 180 and 183 coelutes with congeners 193 and 185, respectively. 13

14 Comparison of ECD and SIM Results in Fish Tissue 29 fish tissue samples were analyzed by both ECD and SIM methods. 14

15 Congeners in Fish Tissue 30% 25% % of Measured Congeners ECD SIM 20% 15% 10% 5% 0% PCB153 PCB138 PCB118 PCB180 PCB101 PCB187 PCB183 PCB105 PCB128 PCB170 PCB66 PCB87 PCB153 was the most abundant congener measured by both methods. The percent abundance of the congeners measured by both methods was similar. 15

16 ECD vs SIM Congeners PCB153 PCB138 SIM Higher 1:1 ppb dry weight by SIM ECD Higher ppb dry weight by ECD Plot shows the correspondence between both methods for PCB153 and PCB138. The diagonal line represents a 1:1 relationship, below the line represents higher concentrations measured by ECD and above the line represents higher concentrations measured by SIM. 16

17 ECD vs SIM Congeners Cont. 100 ppb dry weight by SIM PCB118 PCB180 PCB101 SIM Higher 1:1 ECD Higher ppb dry weight by ECD Plot shows the correspondence between both methods for PCB118, PCB180, and PCB

18 Regression SECD vs TPCB Fish Fillet Total PCB by SIM (ppb dry weight) % Prediction Interval 95% Conf. Interval of Regression y = 1.96(x) r 2 = Sum of 26 Congeners by ECD (ppb dry weight) Regression for fish tissue between the sum of 26 congeners measured by ECD (ΣECD) and total PCB (TPCB) determined by the sum of homologues measured using SIM. 18

19 Comparison of SIM and 1668 Results in Fish Tissue 61 fish tissue samples ere analyzed by both SIM and 1668 methods. 19

20 SIM and 1668 Congener Results: High PCB Concentrations in Fish FS-09-WG-T SIM ng/g dry weight Plot shows the correspondence of congener concentrations measured by SIM and 1668 for a fish tissue sample with a high concentration of PCBs. 20

21 SIM and 1668 Homologue Results: High PCB Concentrations in Fish FS-09-WG-T SIM ng/g dry weight Mono Di Tri Tetra Penta Hexa Hepta Octa Nona Deca Plot shows the correspondence of homologue concentrations measured by SIM and 1668 for a fish tissue sample with a high concentration of PCBs. 21

22 SIM and 1668 Total PCB Results: High PCB Concentrations in Fish FS-09-WG-T SIM ng/g dry weight Total PCB Plot shows the correspondence of Total PCB measured by SIM and 1668 for a fish tissue sample with a high concentration of PCBs. 22

23 SIM and 1668 Congener Results: Low PCB Concentrations in Fish FS-20-WG-R SIM ng/g dry weight Plot shows the difference in congener concentrations measured by SIM and 1668 for a fish tissue sample with a low concentration of PCBs. 23

24 SIM and 1668 Homologue Results: Low PCB Concentrations in Fish FS-20-WG-R SIM 1668 ng/g dry weight Mono Di Tri Tetra Penta Hexa Hepta Octa Nona Deca Plot shows the difference in homologue concentrations measured by SIM and 1668 for a fish tissue sample with a low concentration of PCBs. 24

25 SIM and 1668 Total PCB Results: Low PCB Concentrations in Fish FS-20-WG-R SIM 1668 ng/g dry weight Total PCB Plot shows the difference between Total PCB concentrations measured by SIM and 1668 for a fish tissue sample with a low concentration of PCBs. 25

26 Homologue Group Concentrations for FS-04-SB-R Low Concentration Sample pg/g wet weight Cl-1 Cl-2 Cl-3 Cl-4 Cl-5 Cl-6 Cl-7 Cl-8 Cl-9 Cl-10 SIM Detects Detects Graph shows results for detected homologue group totals for split sample results on a low PCB concentration fish sample. The SIM method resulted in detectable levels on only 3 homologue group totals and those concentrations were less than levels detected by the 1668 method. 26

27 Homologue Group Detection Limits for FS-04-SB-R Low Concentration Sample pg/g (wet weight) Cl-1 Cl-2 Cl-3 Cl-4 Cl-5 Cl-6 Cl-7 Cl-8 Cl-9 Cl-10 SIM 1/2 RLs /2 RLs Figure shows the Reporting Limits on each homologue group for both SIM (yellow) and 1668 (blue - can barely see) results. 27

28 pg/g (wet weight) Homologue Group Results for FS-04-SB-R Low Concentration Sample SIM 1/2 RLs SIM Detects 1668 Results /2 RLs Cl-1 Cl-2 Cl-3 Cl-4 Cl-5 Cl-6 Cl-7 Cl-8 Cl-9 Cl-10 Slide shows that for the SIM results, the Reporting Limits for non-detected congeners are very significant relative to the reported detected results whereas for 1668 method the Reporting Limits are much smaller than the detected results. Therefore, the difference in the detected results between the two methods is likely to be the congeners that are present but not detectable by the SIM method. This is only pertinent to the low concentration samples. 28

29 Homologue Group Results for FS-20-WG-T High Concentration Sample pg/g (wet weight) SIM detects 1668 Results SIM 1/2 RLs Cl-1 Cl-2 Cl-3 Cl-4 Cl-5 Cl-6 Cl-7 Cl-8 Cl-9 Cl-10 For high concentration samples such as the one illustrated, the detected concentrations are much greater than the reporting limits for either method and one gets good agreement between the two sets of results. 29

30 1668 Result - Total PCB ng/g (ppb) dry weight PCB Concentrations by SIM and 1668 in Fish Tissue SRM Black Sea Bass Vermillion Snapper White Gunt Standard Reference Material 1974a Mussel Tissue 25% :1 25% SIM Result - Total PCB ng/g (ppb) dry weight Graph shows the correspondence between Total PCB measured by SIM and 1668 for the total range of PCB concentrations. 30

31 1668 Result - Total PCB ng/g (ppb) dry weight SRM Black Sea Bass Vermillion Snapper White Gunt SIM Result - Total PCB ng/g (ppb) dry weight Graph shows the correspondence between Total PCB measured by SIM and 1668 for the lower range of PCB concentrations. For the lower range of PCB concentrations between ppb the SIM method resulted in higher concentrations of Total PCB. Below 20 ppb the 1668 method resulted in higher concentrations of Total PCB. 31

32 Summary Three different PCB methods Each sample was prepared, homogenized, extracted, and fractionated by the same procedure Comparison between ECD and SIM Similar Detection Levels Similar Accuracy for Standard Reference Materials Total PCB could be predicted from the ΣECD congeners with a high degree of confidence Comparison between SIM and 1668 Method 1668 had much lower detection limits Some problem with coelutions for 1668 in comparison to SRM values in mussel tissue SIM tended to overestimate PCB concentrations in samples with low PCBs Overall good similarity among methods References: Arthur D. Little Standard Operating Procedure ADL Determination of PCBs by Gas Chromatography/ Mass Spectrometry In The Selected Ion Monitoring Mode. Date Initiated: July 6, 1999, Revision Number: 00, Revision Date: July 6, Arthur D. Little Standard Operating Procedure ADL Determination Of Chlorinated Pesticides and PCB Congeners By Gas Chromatography-Eclectron Capture Detection (GC/ECD). Date Initiated: April 24, 1992, Revision Number: 05, Revision Date: September 1, National Institute of Standards & Technology Certificate of Analysis Standard Reference Material New York/New Jersey Waterway Sediment. Gaithersburg, MD. Revised Certificate Issue Date: 14 May National Institute of Standards & Technology Certificate of Analysis Standard Reference Material 1974a Organics in Mussel Tissue (Mytilus edulis). Gaithersburg, MD. Revised Certificate Issue Date: 5 May US EPA Method 1668, Revision A: Chlorinated Biphenyl Congeners in Water, Soil, Sediment and Tissue by HRGC/HRMS. EPA-821-R , Office of Water. 32