Piezoelectric crystal sensor for the determination of formaldehyde in air.

Formaldehyde in air was detected and assayed with a piezoelectric quartz crystal coated with a 7,10-dioxa-3,4-diaza-1,5,12,16-hexadecatetrol/chromotropic acid solution. Water vapor and several gaseous interferents were removed by passing the sampling stream through a column of anhydrous magnesium perchlorate. The response curves were linear in the concentration ranges 0.4-4.5 and 0.4-3.6 ppm v/v CH(2)O with and without the scrubber column, respectively. A single coating was used for 12 days (500 assays) without significant loss in sensitivity. With a single-point daily recalibration, the useful lifetime of the coating is about 2 months.