Detecting trace-level concentrations of volatile organic compounds with metal oxide gas sensors

We are studying the reactions of metal oxide semiconductor gas sensors to hazardous volatile organic compounds (VOCs) at concentrations in the lower ppb and even sub-ppb range with and without interfering gases. For these measurements a gas mixing apparatus was realized providing concentrations from some ten ppt to some hundred ppb in a non-varying carrier gas stream. First results show high sensitivity (relative change in conductance) of a commercial thick film sensor, for example approx. 15 % for 500 ppt benzene and 137 % for 40 ppb naphthalene, also in the presence of ethanol (2 ppm) as interfering gas. The absolute change of conductance of the sensor for naphthalene is constant with and without interfering gas.