DIRECT DETERMINATION OF TRIMETHYLAMINE IN FISH IN THE FLOW REVERSAL INJECTION MODE USING A GAS EXTRACTION SAMPLING DEVICE

A new method for the direct determination of trimethylamine in fish sa mples is proposed. The method uses a gas extraction sampling device wh ere samples are treated to release gaseous trimethylamine species; the gaseous analyte is then driven to the loop of an injection valve loca ted in a straightforward single-channel manifold, where the flow direc tion is repeatedly reversed (no de-bubbler is needed), and the derivat izing reaction in the carrier solution is monitored in situ with a spe ctrophotometer. A pH indicator (Bromothymol Blue) is used to detect th e amine by a gas-liquid (aqueous) dissolution reaction. Trimethylamine can thus be determined over the range from 0.2 to 10 mu g mL(-1) (3.4 x 10(-6)-1.7 x 10(-4) M), with a relative standard deviation of 2.2% for 5 mu g mL(-1) of the analyte. About 10 determinations per hour can be processed in this way.