Determination of Trimethylamine in Fish by Pervaporation and Photometric Detection

Abstract

A method for the determination of trimethylamine (TMA) in liquid and solid samples is proposed. The method is based on pervaporation of the analyte and monitoring of the change in colour of a pH indicator (Bromothymol Blue) caused by the basic character of the amine. When applied to liquid samples the method is developed in a continuous manifold into which the sample is injected, transported to the separation module and detected after crossing the hydrophobic membrane and leading to the detector. The linear portion of the calibrations curve thus obtained ranges between 2 and 30 mg l ^-1 of TMA, with an RSD of 4.7% and a sample throughput of 8 s h ^-1 . Integration of leaching and pervaporation occurs when the method is applied to solid samples as the solid is directly weighed in the pervaporator where the reagents for removal of the target analyte are injected. The linear range in this case is 0.1–10 mg g ^-1 , with a similar precision and a sampling rate of 2 h ^-1 . The method was applied to both filtrate extracts of fish muscle and to the direct analysis of fish muscle without pre-treatment and showed excellent agreement with the standard method.