A gas monitoring system for ethylene oxide sterilizers with constant sample flow through a microwave cavity spectrometer.

This paper reports a measurement system for monitoring the gas concentrations of ethylene oxide (EO) within sterilizers. It samples gas from the sterilizer chamber at a constant flow into a microwave cavity spectrometer. The pressure in the cavity of the spectrometer is linearly proportional to that in the sterilizer chamber, hence the partial pressure (i.e. gas concentration) of the EO gas is linearly proportional to that in the chamber. Measurement of the gas concentration in the chamber can therefore take place without the need to monitor and interpret the chamber pressure. As a consequence the reliability of the sterilization process may be improved, thus enabling a reduction in the in-chamber concentration of EO during sterilization and, hence, EO residues. The microwave cavity spectrometer operates under conditions of power saturation, and there is a good linear correlation between the output signal and the concentration of EO in the gas cell (to within a standard error of 4%).