Piezoelectric quartz crystal detection of ammonia using pyridoxine hydrochloride supported on a polyethoxylate matrix

Abstract

The use of a nonylphenoxypolyethoxylate (Antarox CO-880) as a support polymer is confirmed as a means of prolonging the life (to >50 d) of pyridoxine hydrochloride as a sensitive sorbent coating during the piezoelectric crystal detection of ammonia. However, the matrix system incurs possible interference from hydrogen chloride gas although, except for triethylamine, the other gases studied at high levels (sulphur dioxide, nitrogen dioxide, carbon dioxide and hydrogen sulphide) give only a small piezoelectric signal. The extreme sensitivity of the piezoelectric crystal detection of ammonia to below the µg dm^–3 range is inconsistent with the Sauerbrey equation, which normally applies to straightforward deposition on piezoelectric transducers. This is a consequence of the low slopes of the log(frequency decrease)versus log(concentration) graphs. Such slopes can be increased by modifying the syringe dilution procedure, but there are other more intransigent factors involved.