Monitoring of volatile bases in fish sample headspace using an acidochromic dye

The release of volatile amines such as trimethylamine (TMA), dimethylamine (DMA) and ammonia from fish samples has been detected and continuously monitored through changes in the colour of a sensitive acidochromic dye using UV–Vis reflectance spectroscopy. Changes in the colour of the calix[4]arene-based dye immobilised on test paper disks in contact with the headspace of cod and whiting samples could be determined by an increase in absorbance centred on ca. 500–510 nm. Fresh whiting produces larger, and more rapid colour changes than fresh cod, suggesting that the rate of release of volatile bases from whiting is faster. The sensitivity of the dye response can be tuned by varying the ratio of LiClO4 to dye in the dye solution due to the formation of a more acidic Li+–dye complex. Volatile components absorbing at lower wavelengths (below 410 nm) were detected in cod samples but not whiting.