Coloration reaction of a crowned 2,4-dinitrophenylazophenol-barium(II) complex with amines and its application to flow injection spectrophotometry

Abstract

The coloration reaction of a crowned 2,4-dinitrophenylazophenol (HCDPA)-Ba^II complex with 28 different amines was examined in a non-aqueous solvent (methanol). The absorbances of the resulting chromogens were measured and it was found that a linear relationship existed between the apparent molar absorptivities (a) of the complexes and the pK_a values of the corresponding amines, and that amines having a large pK_a value gave a large a value. A flow injection spectrophotometric method was developed for the determination of trimethylamine (TMA) with the HCDPA-Ba^II complex as chromogenic reagent. The proposed method is simple and sensitive (0.6–3.0 µg per 50 µl for TMA), and can be applied to the determination of total volatile amines as the content of TMA in fish.