An assessment of the performance of semiconductor gas sensors as gas chromatographic detectors.

Four types of commercially available n-type semiconductor gas sensors (three tin oxide types: T.G.S.711, T.G.S.812 and International Sensor Technology methane sensor, and one ferric oxide type: Matsushita L.P.G. sensor) were evaluated as gas chromatographic detectors in the G.C. analysis of mine air samples. A 1.5 meter x 4 millimeter stainless steel column packed with active carbon type 208C (60-72 B.S.mesh) at 40 G was used; to separate hydrogen, carbon monoxide and methane using purified air as carrier gas. Optimum operating conditions for the T.G.S.711 sensor: heater voltage 6.5 volts DC, purified air carrier gas at 20 cnrminuteand operational amplifer circuitry (LM 741), provided good sensitivity and acceptable peak symmetry, although some skewness of peaks was still evident. A preliminary assessment of the performance of these sensors was made for the analysis of some lower hydrocarbon gases (C[1]-C[3]) using a 1.5 meter x 4 millimeter stainless steel column packed with activated alumina (60-80 B.S.mesh) at 60 C. Lower limits of detection achieved were 0.002 ppm for hydrogen and 0.01 ppm for other gases, with a useful working range up to 100 ppm. An interesting finding was that carrier gases containing lower levels of oxygen gave an enhanced response in terms of peak height. It was concluded that the use of semiconductor gas sensors as G.C. detectors provided a simple and convenient method of assessing the characteristics of this type of sensor and might be employed to elucidate the mechanism of response, which is still in question.