Determination of carbon monoxide in ambient air using piezoelectric crystal sorption detection

Abstract

A new piezoelectric quartz crystal (PQC) sorption detector was developed to monitor carbon monoxide (CO) at sub-ppm level in ambient air. Out of the 28 coating materials studied, the palladium(II) acetamide complex with a 1:10mole ratio of Pd(II) to acetamide was found to be the best. The detection is based on a non-reversible gas/coating interaction with sensitivity depending on gas flowrate. For 5-15min exposure at a flowrate of 50ml/min, the working ranges were found to vary from 0.7 to 40ppm (total exposure from 8 to 160μg CO) and detection limits (S/N=2) from 0.7 to 2ppm CO (total exposure to 8μg CO). The repeatability at 10ppm CO was 11.8% (R.S.D. for n=3). The sensor lifetime was found dependent on exposure up to 160μg CO or not exceeding 1000Hz accumulative shift of frequency to avoid saturation of active sites at the crystal surface. No interference to CO detection was found for H 2, H 2S, SO 2, NO 2, CO 2, HCHO, gasoline and water vapors at concentrations much higher than ambient air. Compared to existing CO monitor, the PQC detector developed has advantages of adequate selectivity, high sensitivity, fast response and a much lower detection limit for detecting CO at sub-ppm levels. However, it is limited by the total exposure to a maximum of 160μg CO that restricts its application to intermittent monitoring of low CO concentration. The present work has demonstrated the advantages of using strong non-reversible interaction to enhance PQC sensitivity, as the total exposure can be adjusted easily by a suitable control of the gas flowrate. © 2002 Elsevier Science B.V. All rights reserved.