Ethylene Oxide Measurments By Method TO-15 - US EPA

Ethylene Oxide Measurementsby TO-15 MethodEPA/OAQPS/AQADAmbient Air Monitoring Group1

Outline EtO basics and background information EtO analytical specifics using TO-15 method EtO co-elutions and issues with target ion forquantitation Method improvements for EtO analysis Summary Next steps2

EtO physical chemical properties Chemical formula: C2H4O Chemical structure: Molar mass:44.052 g/mol Vapor pressure: 1095 mmHg @20oC Boiling point: 10.4oC3

EtO Methodological Challenges Standard Stability Primary and secondary source EtO standards procurementNATTS TAD Method Sensitivity Specificity (Co-elution)4

GC/MS systemTO-15 Method Preconcentrator Capillary column Mass spectrometer5

EtO Measurement by GC/MS and TO-15 Full spectrum scan Lower analytical sensitivityand efficiency Less uncertainty with fullspectrum informationcollected for compoundidentification Selected ionmonitoring(SIM) Higher analyticalsensitivity and efficiency(desired lower MDL) Uncertainties andlimitations due to decreasedcollected spectrainformation (possibleinterferant)6

Example GC/MS running conditionsVOC analytical system:Entech 7200Preconcentrator;Agilent 6890 GC/FIDcoupled withan Agilent 5975 MS;SIM P-2019.pdf

Target ion for quantitationSource: https://webbook.nist.gov/ Target ion 29 or 44 Issues discovered Qualifying ions: 15, 42, 438

Method Detection Limit Determination Over the course of three different dates Prepare minimum of 7 different spiked canisters at a concentrationbelow the calibration curve Prepare minimum of 7 different method blank canisters Analyze the prepared spiked and method blanks using establishedmethod Determine the MDLsp and MDLb Assign the laboratory MDL as the greater of these EPA’s contract lab analyzed blank and spiked EtO canisters at 0.10ppbfor MDL Determined MDLs on 3 systems: 0.025-0.061ppb EtO 100-in-1-million cancer risk level: 0.011ppb9

Retention time shiftGradual retention time shift as concentrations increase0.25ppb2.50ppb0.50ppb1.00ppb5.00ppb 0.1minPeak retention time shift and tailing effect: Polar analyte by a nonpolar column10

Co-elution evaluationsPotential interference analytes: Acetaldehyde Methanol Trans-2-butene11

Trans-2-butene mass spectrum4156Source: https://webbook.nist.gov/Shared common fragment ions which are major/minor ions for EtO: 15, 29;42, 4312

Issues with ion 29 for quantitation13

EtO Measurement Technical tion indicators Retention times differencewithin 0.1min Biased high flag--LK415614

Unresolved peaks/beyond separation2915 Unresolved peaks Non-negligible Contributionto ion 29 from Trans-2-butene No clear inflection to splitpeaks Co-elution flag--BH415615

Issues with ion 44 for quantitation16

Issues with ion 44-Example 1442915 Example samplespectra andchromatogramsIon 44 not ideal forquantitation Ion 44 – a lump andunresolved peak Ion 44 Abundanceratio to ion 29extremely high 4x ICAL17

Issues with ion 44-Example 2442915 Ion 44 not ideal forquantitation Baseline for ion 44noisy and not on areasonable flat base Difficult forsoftware toaccurately integrate Suspected leaks orCO2 managementissues18

EtO Identification criteriaNATTS TAD19

EtO Identification issues Retention timedeviation Qualifier ionabundance ratiooutside of 30% Misidentified asEtO byChemstation20

EtO Identification issues-ND Softwareinappropriately assignsample as non-detect;peak not recognized Peak rejectionthreshold set too high Obvious ion 29 Adopt S/N toolpeak; Need to review S/N 3; When manually chromatograms andintegrated,spectra by analystEtO 0.23ppb21

Method improvements for EtOmeasurements by TO-1522

Method Improvement for EtO Co-elutions Adjust chromatographic parameters Choose different target ion for quantitation and identification Change oven temperature program Ramp more slowly Begin at sub-ambient temperature Increase temperature around EtO elution window– mightmake peak shape sharper Change column Increase polarity of stationary phase (e.g., DB-624 column) https://www.restek.com/ezgc23

Improved CO2/water managementand ion 44 peaks442915 Ion 44 as target ion Baseline for ion 44improved EtO ion 44 peakdistinct and clearshaped Ion 44 absent fromtrans-2-butene24

EtO Co-elutionImprovementLonger non-polarcolumn—DB-1 100mEtO Better separation for EtO andco-elutions May alter retention order Longer running time persample25Source: Apel-Riemer

EtO Co-elution ImprovementSlightly polar columnDB-624 Better separation for EtOand co-elutions Altered retention order May reduce performancefor other target analytes26

EtO TO-15 Method Evaluations Determine method detection limit (MDL) Determine the MDLspike and MDLblank Verify canister cleanliness Evaluate EtO stability in canisters Canister zero stability checks Canister known standard stability checks Verify sampling unit cleanliness Zero air challenge Known standard challenge27

Summary EtO measurements can achieved by typical TO-15method setup, however with limitations MDL not as low as desired even with SIM Slight retention time shift and observed tailing on typicalnonpolar column used Lower MDL and consistent retention time could beachieved by a polar column, but performance of a few lowMW analytes reduced28

Summary Issues with the most abundant ions for quantitation Ion 29—co-elutions (one identified as trans-2-butene) Monitor additional ions 41 and 56 to aid EtO identification andquantitation, however may reduce sensitivity Co-elution indicator—shoulder peak or inflection Appropriate data qualifiers(e.g., LK and BH) Ion 44—CO2 or water management issues Leak checks Optimize pre-concentrator settings Assess appropriate peak rejection threshold Review chromatograms and spectra for properidentification29

Next steps—EtO research EPA ORD started study on EtO stability in cylinders EtO calibration standards from vendors who supply EtO,concentration from 100ppb to 100ppm range A blend of EtO with stable SF6 to monitor concentration ratiosover time by FTIR EPA ORD lab will further investigate co-elutions with EtO Two GC systems set up with TO-15 capability Typical GC/MS coupled with nonpolar column GC/TOF-MS coupled with slightly polar DB-624 column Analyze samples from subset of NATTS/UATMP sites withobserved EtO co-elution to identify interferants30

Next Steps—Proficiency Tests Battelle to conductEtO methoddemonstration byevaluating spikedcanisters with EtOand 15 other VOCs First PT VOCsamples expected –3rdQ 2019 VOC PT anticipatedto increase to everyquarter Non-NATTS labs canopt in31

Thanks!Questions?32

EtO co-elutions and issues with target ion for quantitation Method improvements for EtO analysis Summary . Determined MDLs on 3 systems: 0.025 -0.061ppb EtO 100-in-1-million cancer risk level: 0.011ppb. Retention time shift. 0.25ppb. . integrated, EtO 0.23ppb 21. Method improvements for EtO measurements by TO-15. 22.