VISIBLE DIODE-LASER INDUCED FLUORESCENCE DETECTION IN LIQUID-CHROMATOGRAPHY AFTER PRECOLUMN DERIVATIZATION OF THIOLS

New cyanine labels containing only a single active group for the chemical derivatization of thiols were synthesized in order to apply visible diode laser induced fluorescence (DIO-LIF) detection in conventional-size liquid chromatography (LC). 2-Mercaptobenzothiazole (MBT) was selected as test compound. The most appropriate label was CY5.4a-IA, a sulfonated dicarbocyanine with a iodoacetamide reactive group. The detection limit of labeled MBT in the LC-DIO-LIF system was 8 X 10(-12) M. The detection limit of MBT was 1 x 10(-9) M; lower concentrations are not labeled quantitatively. The injection repeatability was 1.0% (n = 6), the reaction repeatability was 3.0% (n = 6), and linearity was observed from 2.5 X 10(-9) to 1.0 x 10(-5) M. As an example, MBT-spiked river water and urine samples were derivatized with CY5.4a-IA and analyzed by LC-DIO-LIF. Hardly any interference was found. The method compares very favorably with existing techniques.