On-line monitoring of galactoside conjugates and glycerol by flow injection analysis Original Research Article

A biosensor attached to a flow injection analysis (FIA) system was developed for the automatic determination of galactoside conjugates and glycerol. The biosensor was based on the enzymatic reaction of galactose oxidase (GalOD) using galactose, raffinose, lactose and glycerol as substrates. GalOD converts galactoside conjugates to galactohexodialdose conjugates and glycerol to glyceraldehyde with formation of hydrogen peroxide and consumption of oxygen. Variation of dissolved oxygen in the carrier was estimated utilizing an amperometric oxygen probe. The FIA system consisted in a multichannel peristaltic pump, an injection valve and an electronic transducer which were controlled by the CAFCA software. Stability of the enzyme and optimal working condition were investigated. Optimum pH for the immobilized enzymes under these experimental conditions was 7.4 and the enzyme retained 80% of the original activity after two months of use. Studies on the dynamical response of the biosensor showed that the elapsed time between two successive injections could be as short as 120 s without signal deterioration when the flow rate was 2 ml/min and 50 μl of injection volume. Sensitivity of the biosensor was higher for galactose followed by raffinose, lactose and glycerol. The sensor showed linear response between 0.2 and 2 mM for galactose, 0.5 and 6 mM for raffinose, 25 and 250 mM for lactose, and 2 and 200 mM for glycerol.