Ethylene oxide monitor with ultra-low limit of detection

The recent decrease of the exposure limits to Ethylene Oxide (EtO) in ambient air to 11 parts per trillion (long-term, 1:10000 risk level) requires advanced technology to monitor EtO. Current methods rely on sample trapping and preconcentration to achieve an acceptable limit of detection (LoD). This approach is susceptible to cross interference from other gaseous volatile organic carbon species. We have developed a (prototype) EtO monitor with ultra-low limit of detection based on sensitive and selective laser-optical measurement technology. Our optical technology is direct, sensitive, and selective in the measurement of EtO without the need for sample collection, preconcentration, or any other sample preparation. Our instrument uses laser spectroscopy and a long-pathlength sample cell to measure absorption spectra of EtO with high precision in real time. We demonstrate that we can measure EtO in ambient air with a 1-sigma precision of <60 ppt (parts per trillion) in 1 second and ~12 ppt for a 2-minute average measurement. We show that with further data averaging we can improve the precision to better than 5 ppt for a 30-minute measurement. We demonstrate that with zero-air measurements every 2 to 3 minutes we are able to accurately measure zero EtO repeatably. This fact, coupled with the high precision, allows us to predict measurement accuracy at low ambient EtO levels. For our instrument, drift at long timescales is very low due to the zero-air measurements, and we expect accuracies below 10 ppt for measurements of 30 minutes or longer. The response of our EtO prototype instrument to changes in EtO concentration is highly linear over several orders of magnitude.