Analyst, December 1996, Vol. 121 1773 biosensor reported for formaldehyde vapour, by Guilbault.14 He detected formaldehyde with a detection limit of 10 ppb, while enzymic methods could detect formaldehyde typically in the ppb range, with one assay reporting a detection limit of 120 ppt v/v. As a demonstration of formaldehyde sensing, this biosensor has been successful. However, further work needs to be carried out to improve the stability of the enzyme, which is poor. When steady-state amperometric responses were used as a measure of ADH biosensor response, a linear response was obtained up to approximately 250 ppm ethanol vapour. This ability of the RMs to concentrate the vapour is ideal for sensing low levels of ethanol, but is not suitable for sensing the high levels of ethanol vapour routinely encountered in everyday applications (100-1 000 ppm).Alternatively, the ADH bio- sensor could be used for measuring ethanol vapour, if the exposure times are short, i.e., the concentration of ethanol partitioned in the gel phase is very low and ADH is not substrate saturated. Enzyme stability remains a major problem owing to the poor stability of ADH. Improvements in enzyme purifica- tion and stabilization would greatly enhance further develop- ment of practical ethanol vapour biosensors. If the problem of biosensor stability (i.e., enzyme stability and gel stability) could be overcome, then this formaldehyde biosensor could successfully compete with conventional meth- ods of formaldehyde detection. 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Paper 61038541 Received June 3,1996 Accepted July 30, 1996 13-14, 574.