Two-phase derivatization of pentazocine with chloroformate esters and determination by gas chromatography

Two-phase derivatization with chloroformate esters of tertiary amines that contain a phenol group has been studied. The derivatives were analysed by gas chromatography with sensitive and selective detectors. The N,O-bis derivative of pentazocine was formed using an aqueous phase at pH 9.8, with tetrabutylammonium ion for extraction of the phenolate ion as an ion-pair. The organic phase comprised methylene chloride with trichloroethyl chloroformate or ethyl chloroformate. At pH 10.7 the derivative was hydrolysed by hydroxide ions extracted into the organic phase. Hydrolysis also occurred when more lipophilic counter-ions such as tetrapentyl-ammonium ions were used. Two-phase derivatization could also be achieved with toluene or ethyl acetate as the organic phase, although the reaction rate was considerably slower. The method was also applied to the assay of pentazocine in plasma. The best results were achieved after selective extraction of pentazocine from plasma, two-phase derivatization with ethyl chloroformate and determination by mass spectrometry or thermionic detection. The minimum detectable concentration of pentazocine was 10 ng/ml in a 1-ml plasma sample.