Trace Measurements of Ethylene Oxide Using Cavity-enhanced Absorption Spectrometry near 3066 cm–1

Abstract

Ethylene oxide (EtO) is a key carcinogen that is widely used in chemical manufacturing and biotechnology industries. Recent work has suggested that permissible exposure limits for EtO be reduced from 1 -5 ppm to sub-ppb levels. Such new standards will require new methodologies that are capable of measuring EtO with the requisite precision. In this paper, we demonstrate a new analyzer based on cavity-enhanced absorption spectrometry that utilizes a broad EtO absorption feature near 3066 cm -1 . A fit function is developed that includes water, methane, and EtO absorbances and accounts for absorption both inside and outside the cavity. A methane standard is used to determine the cavity gain factor, and the EtO absorbance spectrum is empirically determined. The final system shows excellent linearity from 0 -909 ppb EtO (R 2 ~0.9999) with a measurement precision of better than ±1 ppb (1σ, 60 seconds) that improved to ±0.5 ppb (1σ, 15 minutes). Deliberate ambient EtO releases demonstrate the instrument's utility in rapidly detecting hazardous conditions. Further work will include improving the measurement precision and directly comparing the system to EPA Method TO-15.

Ethylene Oxide in Southeastern Louisiana’s Petrochemical Corridor: High Spatial Resolution Mobile Monitoring during HAP-MAP

“…Several in situ optical instruments have been recently developed that enable EtO detection in real-time. 8,24,25 Most of these new techniques have sub-1 ppb precision at relatively short averaging periods (1 s to 1 h) and are increasingly being applied to measure EtO in both background and near-source environments. [7][8][9]15 Given that 100-in-one million elevated cancer risk corresponds to a lifetime exposure concentration of 10.9 ppt, high accuracy and precision measurements of EtO are needed to pinpoint risks posed to populations.…”

“…The landscape for assessing ambient EtO levels, however, is changing. Several in situ optical instruments have been recently developed that enable EtO detection in real-time. ,, Most of these new techniques have sub-1 ppb precision at relatively short averaging periods (1 s to 1 h) and are increasingly being applied to measure EtO in both background and near-source environments. − , Given that 100-in-one million elevated cancer risk corresponds to a lifetime exposure concentration of 10.9 ppt, high accuracy and precision measurements of EtO are needed to pinpoint risks posed to populations. The fast time-response of these instruments offers the possibility for assessing the spatial patterns of ambient EtO concentrations via mobile monitoring, a practice that is somewhat common for certain pollutants, particularly some criteria air pollutants and others related to traffic (see Wang et al and references therein), but is far less common for air toxics. , …”

Ethylene Oxide Monitor with Part-per-Trillion Precision for In-Situ Measurements

“…Several additional in-situ instruments for the detection of EtO have been developed recently. Gupta et al (2022) describe a cavity-enhanced absorption spectrometry method with precision < 1 ppb (1 sigma, 60 seconds) and 0.5 ppb (1 sigma, 15 minutes). Picarro, Inc. (2021) has publicized cavity ringdown spectroscopy (CRDS) instruments with detection limits of 0.1 -0.25 ppb (3 sigma, 300 seconds) depending on instrument model.…”