ADSORPTIVE STRIPPING VOLTAMMETRY OF LUMICHROME IN SEA-WATER AT THE STATIC MERCURY DROP ELECTRODE

The adsorptive voltammetric behaviour of lumichrome (7,8-dimethylalloxazine), the main product of riboflavin photolysis, was investigated in sea water. The effect of experimental parameters such as preconcentration time and potential, pH of solution and mass transport conditions on the stripping response are discussed. Sensitive measurements can be achieved after controlled adsorption followed by square wave voltammetry. The stripping peak current was found to be proportional to the bulk concentration of lumichrome. The sensitivity was 5 x 10(-2) nA nM(-1) s(-1), the reproducibility was 6% at a concentration of 3.6 x 10(-9) M lumichrome and the detection limit was 100 pM. Using an accumulation time of 600 s at -0.4 V, this technique allows the direct determination of lumichrome naturally present in raw sea water samples. The value found was about 200 pM. The concentration of lumichrome was also determined in the same samples using liquid chromatography after a solid-phase preconcentration step. Good correlations between voltammetric and chromatographic results were found.