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Evaluation of Sample Pretreatment Procedures for the Determination of Phthalate Esters in Child Care Products and Children’s Toys by GCMS

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The Consumer Product Safety Improvement Act of 2008 (CPSIA-USA) requires testing of child care products and toys in the US for specific phthalate esters by GCMS. The CPSC test method specifies solvent …

The Consumer Product Safety Improvement Act of 2008 (CPSIA-USA) requires testing of child care products and toys in the US for specific phthalate esters by GCMS. The CPSC test method specifies solvent extraction and subsequent GCMS analysis for specific phthalate esters. In this study, analysis by pyrolysis GCMS was investigated as a technique to simplify sample preparation and improve analytical precision.

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  • 1. Evaluation of Sample Pretreatment Procedures for theDetermination of Phthalate Esters in Child CareProducts and Children’s Toys by Gas Chromatography/ Mass Spectrometry (GCMS)Richard Whitney, PhD, Nicole Lock, Jiarui “Jerry” Wang, Zhuangzhi“Max” Wang, PhD, Clifford M. Taylor, Laura Chambers, ShimadzuScientific Instruments, Columbia, MD, USA, 800-477-1227,www.ssi.shimadzu.com
  • 2. Introduction (1)The Consumer Product Safety Improvement Act of 2008 (CPSIA-USA) requires testing of child careproducts and toys in the US for specific phthalate esters by GCMS. The CPSC test method specifiessolvent extraction and subsequent GCMS analysis for specific phthalate esters. In this study, analysis bypyrolysis GCMS was investigated as a technique to simplify sample preparation and improve analyticalprecision. The analyses were conducted on a Shimadzu GCMS-QP2010 Ultra equipped with a Frontier PY-2020is pyrolyzer, shown in the figure below.The CPSC test method also specifies GCMS analysis in the SIM mode to monitor for low-intensity ions thatare unique to specific phthalate esters. Full-scan mass spectra are extremely valuable in makingunequivocal qualitative identification of specific phthalate isomers, however. Operation of the massspectrometer in the FASST (Scan/SIM) mode allows concurrent acquisition of full-scan and SIM massspectral data, without sacrificing sensitivity of SIM analysis.Significant interferences, particularly terephthalate esters, are frequently present in real-world samples. Analternate chromatographic column (RXI-17Sil MS) provides excellent chromatographic resolution of bis(2-ethylhexyl) terephthalate, a common interference, from the regulated phthalate esters.Acceptable method performance is achieved for calibration and control samples, but difficulties have beenencountered in obtaining reproducible results for real-world samples using the sample extraction procedurein the CPSC method. Using the sample extraction procedure, analyses of replicate aliquots (50mg ofpolymer) of a sample known to contain target phthalate esters were conducted to evaluate methodreproducibility. Results indicate that instrument precision is good; variability in results was previouslyassumed to be related to inhomogeneity of the polymer.
  • 3. Introduction (2)Pyrolysis at relatively low temperature (“thermal extraction”) was investigated as a sample introductiontechnique; pyrolysis offers the advantage of eliminating the time-consuming sample pretreatmentprocedure. It was anticipated that smaller (1mg) aliquots may show even more disparity in results thanthose observed with liquid extraction because sample homogeneity may be accentuated. However,improved precision was observed with replicate samples analyzed using pyrolysis relative to that obtainedfrom replicate extractions. To further evaluate the effect of polymer homogeneity on the analytical precision,the sample was homogenized by cryogenic milling. Replicate analyses of the homogenized sample showedfurther improved precision relative to pyrolysis of the intact sample. Frontier PY-2020is Shimadzu GCMS-QP2010 Ultra
  • 4. Analytical Conditions GC Conditions The GC is operated in the splitless mode, using a RXI-5MS 30M x 0.25mm x 0.25µ capillary column (Restek), as specified by the CPSC method. Analysis using a RXI-17Sil MS 30M x 0.25mm x 0.25µ capillary column (Restek) is conducted using the same chromatographic conditions. MS ConditionsThe MS is operated in the EIScan/SIM (“FASST”) mode, toprovide optimum sensitivity while stillproviding full-scan mass spectra forunequivocal qualitative identification. 4
  • 5. Chromatography of Phthalate EstersRXI-5MS Column 30M x 0.25mm x0.25µ (Restek Corp) Diisononyl phthalate and diisodecyl phthalate appear as multiple chromatographic peaks 1 - Benzyl Benzoate (IS) 2 - Dibutyl Phthalate 6 3 - Butyl Benzyl Phthalate 4 - Diethylhexyl Phthalate 4 5 - Di-n-octyl Phthalate 5 6 - Diisononyl Phthalate 3 7 7 - Diisodecyl Phthalate 1 2 5
  • 6. Chromatographic Interferences Interference from non-regulated phthalate esters and related compounds masks trace detection of the regulated phthalate esters. Noteworthy is interference of bis(2-ethylhexyl) terephthalate (a commonly- used, non-regulated plasticizer) with detection of di-n-octyl phthalate; these compounds coelute on the RXI-5MS column and have key mass spectral fragment ions in common (m/z 149, 167, 279).Example of chromatography of Full-scan mass spectra are extremelyequal concentrations of di-n-octyl useful in qualitative identification. SIMphthalate and bis(2-ethylhexyl) data alone would make qualitativeterephthalate. identification difficult in these cases. di-n-octyl phthalate bis(2-ethylhexyl) terephthalate
  • 7. Chromatography on RXI-17Sil MS ColumnBis(2-ethylhexyl) terephthalate (“DOTP”) is well-resolved from the regulatedphthalate esters on an RXI-17Sil MS 30M x 0.25mm x 0.25µ capillary column(Restek), using the same chromatographic conditions as with the RXI-5MS column.(Elution of butyl benzyl phthalate is somewhat later than on the RXI-5MS column.) 1 - Benzyl Benzoate (IS) 2 - Dibutyl Phthalate 3 - Butyl Benzyl Phthalate 4 - Diethylhexyl Phthalate 5 - Di-n-octyl PhthalateDOTP interference is well-resolved from the 6 - Diisononyl Phthalate regulated phthalate esters 7 - Diisodecyl Phthalate 6 1 2 4 3 5 7 7
  • 8. Basic Method PerformanceFundamental method performance is satisfactory: • Good chromatography, with excellent linearity and precision for analytical standards and QC samples • Excellent sensitivity with FASST (Scan/SIM)Issues with method implementation: • Background contamination with phthalate esters from various sources – method blanks are very critical. • Interferences from non-regulated phthalate esters and related compounds – chromatographic and mass spectral interferences with detection and quantitation of regulated phthalate esters. • Disparate analytical results have been obtained in several laboratories. The cause of this disparity was previously assumed to be variable homogeneity of solid samples.
  • 9. Sample Preparation Scheme for ReplicateAnalyses of Intact Vinyl Film Sample9
  • 10. Summary of Replicate Results forExtracted Aliquots Diethylhexyl phthalate Observations / Conclusions600 Std Dev (concentration) Graphical representation of the results show instrument400 precision (Std Dev, shown by the dark blue bars in the200 graphic) is considerably better than precision between Diethylhexyl 0 Phthalate aliquots. 1 2 3 4 Concentration (mg/Kg) Results for dibutyl phthalate and butyl benzyl phthalate Diisononyl phthalate are very low (single digit precision), so results for these Std Dev800 (concentration) analytes are not shown here.600400200 Diisononyl The sample preparation for these analyses was Phthalate 0 Concentration conducted simultaneously by the same analyst, so 1 2 3 4 (mg/Kg) sample preparation technique was not assumed to be the source of disparity of the results Diisodecyl phthalate1200.0 Std Dev (concentration) These results indicate that disparity in results of replicate1000.0 800.0 sample analysis are related to sampling (sample 600.0 400.0 homogeneity) or sample preparation, not poor precision Diisodecyl 200.0 Phthalate and accuracy in the instrumental analysis. 0.0 Concentration 1 2 3 4 (mg/Kg)
  • 11. Solutions for CPSC Method PerformanceIssues CPSC Method Performance Issue Solution Difficulties in qualitative identification Conduct analyses using Scan/SIM of regulated phthalate esters with function (FASST) for unequivocal SIM data. qualitative identification. Low level detection of some analytes Excellent sensitivity is achieved using difficult due to low relative Scan/SIM function (FASST), even for abundance of quantitation ions and analytes with multiple chromatographic multiple chromatographic peaks. peaks (DINP,DIDP). Monitoring of low abundance ions for Use of a convenient software feature to quantitation gives rise to large monitor ion abundance ratios allows variations in relative abundance easy modification of method ratios parameters Chromatographic and spectral One major interfering compound is interferences are encountered from easily resolved by using an RXI-17Sil non-regulated phthalate esters and MS chromatographic column (Restek). terephthalate esters. Disparate results are frequently Results indicate that difficulties are obtained for analysis of replicate related to sampling/extraction rather analyses of solid samples. than analysis. Sample homogenization and analysis of replicate sample aliquots is highly recommended. 11
  • 12. Sample Introduction by Pyrolysis• Sample introduction by low-temperature pyrolysis (“thermal extraction”) was investigated for applicability to this method (pyrolysis is not currently authorized by the CPSC Method): • Pyrolysis has the advantage of greatly simplifying sample pretreatment – significant time savings. • Pyrolysis has traditionally not been considered an accurate quantitative technique.• Pyrolysis conditions were chosen to thermally desorb the phthalate esters while not decomposing the polymer itself.• Conditions for Pyrolysis GCMS (Pyr-GCMS) are similar to those used for analysis of polymer extracts: • Pyrolyzer temperature 325oC; interface temperature 320oC. Sample aliquots (0.4mg) were thermally desorbed for 1.0 min. • A 60M RXI-17Sil MS column was used to optimize separation; the split injection mode was used to optimize sample transfer from the pyrolyzer to the GC; additional sample was added to maintain detection limit. 12 • A single SIM group was monitored to simplify data display.
  • 13. Polymer Sampling for Pyrolysis Two procedures were used in sampling of the vinyl sheet sample for pyrolysis GCMS analysis; 0.4mg sample aliquots were used for pyrolysis GS analysis: 1. Small circular aliquots of the sample were punched out of the sample directly. 2. The sample was cryogenically milled to a fine mesh and an aliquot was taken for analysis.Aliquots were punched from The sample was cryogenicallythe vinyl sheet at various milled, resulting in a finepositions powder. 0.4mg sample aliquots were taken from the cryogenically milled sample. (Sample cup is 13 also shown.)
  • 14. Calibration Using PYR-GCMS• A six-point internal standard calibration was conducted from 0.25- 20ppm. This calibration range corresponds to the same sample concentration of phthalate esters in the polymer as with the CPSC (solvent extraction) method.• Linearity was R2>0.99 for all of the analytes in both the full-scan and SIM modes.• Example calibration curves are shown below for diisononyl phthalate and diisodecyl phthalate. Area Ratio(x0.1) Area Ratio(x0.1) 5.0 Diisononyl Phthalate 3.0 Diisodecyl Phthalate 4.0 2.5 3.0 2.0 1.5 2.0 1.0 1.0 0.514 0.0 0.0 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Conc. Ratio 0.0 0.5 1.0 1.5 2.0 2.5 3.0 Conc. Ratio
  • 15. Precision of Analytical Standards Results usingPYR-GCMSReplicate analyses for eight runs of analytical standard usingPYR-GCMS show excellent instrumental precision with sampleintroduction by pyrolysis (equivalent precision to liquid injection). Mass chromatograms of Precision for analysis of 8 replicates diisodecyl phthalate for %RSD %RSD analysis of 8 replicates (x10,000) Compound Name Scan SIM 1.1 Dibutyl Phthalate 7.07 5.72 1.0 0.9 0.8 Benzyl Butyl Phthalate 7.42 7.65 0.7 0.6 Diethylhexyl phthalate 5.13 5.04 0.5 0.4 0.3 Di-n-octyl phthalate 4.40 4.88 0.2 0.1 Diisononyl Phthalate 4.12 4.82 13.00 13.25 13.50 13.75 14.00 14.25 14.50 14.75 15.00 15.25 Diisodecyl Phthalate 6.67 6.1315
  • 16. Precision of Real-world Sample Results using PYR-GCMS Replicate injections for eighteen runs of vinyl polymer sample show reasonable instrumental precision with sample introduction by pyrolysis. Precision is improved significantly by homogenization of the sample. Precision for analysis of 18 replicates of vinyl polymer by PYR-GCMS Compound Results for Intact Sample Results for Cryo-milled Sample Mean (mg/Kg) RSD(%) Mean (mg/Kg) RSD(%) Dibutyl Phthalate 10 34 11 11 Diethylhexyl Phthalate 44 32 311* 14 Diisononyl Phthalate 600 43 501 11 Diisodecyl Phthalate 65 35 60 15 *Disparity in results for diethylhexyl phthalate is attributed to possible contamination during sample transport or cryo-milling.16
  • 17. SummaryThe CPSC test method has been demonstrated using Shimadzu GCMS-QP2010S and GCMS-QP2010 Ultra operated in the FASST (Scan/SIM)mode. Acceptable basic method performance was demonstrated: excellentsensitivity, linearity, and precision at low concentrations were attained.Interferences from terephthalate esters (non-regulated compounds withsimilar structures) have been encountered in real-world samples. An alternatechromatographic column (RXI-17Sil MS) was employed to providechromatographic resolution of the interferences from the target phthalateesters.Disparate results have been observed for replicate analyses of real-worldsolid samples. To cast light on this issue, replicate aliquots of a vinyl filmsample were prepared according to the CPSC method and analyzed six timeseach. Replicate analyses of each aliquot showed good statisticalagreement, but disparate results were obtained for each of the samplealiquots. These results originally suggested that disparity in the results can beattributed to homogeneity of solid samples or irregularities in the sampleextraction process.
  • 18. Sample introduction using pyrolysis was demonstrated to be a convenient andreliable analytical procedure for determination of phthalate esters in a vinylfilm sample. Excellent linearity and precision for analytical standards and QCsamples were obtained using pyrolysis for sample introduction. Variableresults were observed for analysis of 0.4mg aliquots punched from the vinylfilm sample, but statistical agreement was better using pyrolysis on the intactsample than that from analysis of replicate extraction aliquots using the CPSCmethod.The vinyl film sample was homogenized using cryogenic milling, resulting in afine powder. It was anticipated that the homogeneous sample would givemore precise analytical results. Indeed, analytical precision was improvedconsiderably using the homogenized sample.