Figure 1:\u00a0<\/strong>Using full scan conditions reveals background contamination that could affect ethylene oxide analysis, which is not detected using a targeted SIM cleanliness evaluation.<\/div>
Ethylene oxide is heavily used in chemical manufacturing, and its 2016 classification by the U.S. EPA as a carcinogen [1] has generated debate about safety and exposure levels. With the question of how tightly to regulate emissions being discussed by manufacturers and lawmakers alike, it\u2019s more important than ever to develop accurate and efficient methods for ethylene oxide analysis in ambient air. Applying industrial hygiene procedures is not an ideal approach because they target ethylene oxide alone. Monitoring ethylene oxide along with other volatiles would be much more efficient, and many labs are interested in adding it to standard methods for the collection and analysis of volatiles in ambient air, such as EPA Method TO-15A.<\/p>\n\n\n\n
While researching the use of Method TO-15A for monitoring ethylene oxide, we noticed an issue that the EPA is also now investigating: the potential for positive bias due to ethylene oxide growth in air canisters. Seemingly clean air canisters can develop an ethylene oxide signal that, in worst-case scenarios, continues to increase. This situation is similar to the problematic growth of acrolein in air canisters over time. For ethylene oxide, we have seen an almost six-fold increases in signal after two weeks of storage, and observations like this can make analysts wonder what is happening. The air canisters passed a cleanliness evaluation, so it can\u2019t be that, right? As it turns out, it is easier than you might think to miss relevant air canister contamination given the targeted approach to cleanliness that is often used in standard volatiles methods. <\/p>\n\n\n\n
It is well understood that air canisters must be demonstrated to be free of background contamination, but this can be especially challenging with volatile compounds that are sometimes present in the testing environment itself. For volatiles methods, clean air canisters are usually tested specifically for target analytes present at background contamination levels that might lead to reporting inaccuracies. However, this careful, targeted approach using selected ion monitoring (SIM) can mask clues that an air canister actually may not be suitable for ethylene oxide sampling.<\/p>\n\n\n\n
For example, when performing a routine targeted cleanliness check on an air canister, results like the chromatogram shown in Figure 1A are pretty typical. The background is fairly free of volatile contamination for the ions monitored, even when the fill gas used in the evaluation is humidified air (which is a much harder test than using dry air or a humidified or dry inert gas, such as nitrogen). So, the air canister in Figure 1A would likely pass cleanliness testing requirements and be qualified for ethylene oxide analysis projects. However, when we switch from a targeted cleanliness test that uses the narrow, but sensitive, field of view provided by SIM to a broader scanning method, we now see the presence of nontarget, unidentified contamination (Figure 1B).<\/p>\n\n\n
![\"Comparison](\"https:\/\/ez.restek.com\/images\/cgram\/gc_ar1174.png\" "\\"-\\"")
<\/div>