Abstract
The following study evaluated the efficacy of using Nutech’s 8900DS preconcentrator in combination with an analytical system based on a 30 m x 0.32 mm x 1.00 µm Rxi®-5Sil MS column for analysis of VOCs in whole air. Results were assessed based on five criteria outlined for time-integrated, whole air canister sampling in the United States (U.S.) Environmental Protection Agency’s (EPA) Compendium Method TO-15 (Determination of Volatile Organic Compounds [VOCs] in Air Collected in Specially-Prepared Canisters and Analyzed by Gas Chromatography-Mass Spectrometry [GC-MS]). Canister blank concentrations were <0.2 ppbv; the average relative standard deviation (RSD) of calibration relative response factors (RRFs) was 9.31%; average scan and selected ion monitoring (SIM) method detection limits (MDLs) were 0.06 ppbv and 35.9 pptv, respectively; average replicate precision was 4.29% difference; and average audit accuracy for all 65 targeted TO-15 VOCs was -2.82%. These performance levels for VOC analysis of air met all Method TO-15 guidelines and were achieved using a 30 m x 0.32 mm x 1.00 µm Rxi®-5Sil MS column with 16.5 minute GC analysis times (~22 min total sample throughput times).
Introduction
Volatile organic compounds (VOCs) are a class of organic chemicals typically characterized as possessing relatively high vapor pressures at room temperature conditions. Their high vapor pressures result from relatively low boiling points, which cause a large number of molecules to evaporate or sublimate from liquid or solid form, respectively, into the gas phase. VOCs are produced from both primary and secondary sources. Primary sources, either natural or anthropogenic, are directly emitted from the source to the air, while secondary sources result from atmospheric reactions. VOCs are of great interest due to their ubiquitous presence in indoor, outdoor, and personal air, and also because VOCs and their atmospheric reaction products have well known adverse environmental impacts and detrimental human health effects. As a requirement of the Clean Air Act Amendments of 1990, the United States (U.S.) Environmental Protection Agency (EPA) is required to control 189 hazardous air pollutants (HAPs). In accordance, the EPA has generated a Compendium of Methods for the Determination of Toxic Organic (TO) Compounds in Ambient Air. More specifically, Compendium Method TO-15 (Determination of Volatile Organic Compounds [VOCs] in Air Collected in Specially-Prepared Canisters and Analyzed by Gas Chromatography/Mass Spectrometry [GC-MS]) has been developed for the sampling and analytical procedures for the measurement of a subset of 97 VOCs included in the 189 HAPs [1]. Method TO-15 is a “performance-based” guidance document for whole air canister sampling and VOC analysis; therefore, the method has very little information on specific procedures or protocols that must be followed to be method “compliant”. However, section 11.1.1 of Method TO-15 does identify three performance criteria, which should be met for a system to qualify. These criteria are: a method detection limit of ≤0.5 ppbv, replicate precision within 25 percent, and audit accuracy within 30 percent for concentrations normally expected in contaminated ambient air (0.5 to 25 ppbv). However, there are two additional criteria laboratories should be cognizant of that are not clearly outlined in Section 11.1.1 of Method TO-15. Section 8.4.1 (Canister Cleaning and Certification) of Method TO-15 stipulates that any canister that has not tested clean (compared to direct analysis of humidified zero air of less than 0.2 ppbv of targeted VOCs) should not be used. In addition, section 10.5.5 (Technical Acceptance Criteria for the Initial Calibration) of Method TO-15 states that for the initial calibration the calculated percent relative standard deviation (%RSD) for the relative response factor (RRF) for each compound in the calibration table must be less than 30% with at most two exceptions up to a limit of 40%. The following investigation was conducted to evaluate the efficacy of pairing Restek® products with a Nutech 8900DS preconcentrator to meet the five aforementioned criteria of U.S. EPA Compendium Method TO-15. Although 60 m GC columns are typically used for TO-15 VOC analysis, a 30 m column was used here to determine if method criteria could be met with faster analysis times.>> Read the full Application Note here
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