Assay of fish freshness using trimethylamine vapor probe based on a sensitive membrane on piezoelectric quartz crystal

A trimethylamine (TMA) vapor probe based on the sensitive membrane of chitosan, which encapsulated pimelic acid on piezoelectric quartz crystal has been prepared for the assay of fish freshness. The response of the probe to TMA is rapid and completely reversible at normal temperature and relatively high humidity. The probe has an exponential response to TMA in the concentration range of 5–200 ppm, and the relative standard deviations (R.S.D.) were less than 5% for repeated determinations of 50 ppm TMA within 6 months. The results of fish freshness assay were consistent with those obtained by other methods and the sensory test.