Enzyme immobilization on an epoxy matrix. Determination of l-arginine by flow-injection techniques

A continuous-flow procedure is described for the determination of l-arginine, based on its l-arginase catalyzed conversion to l-ornithine and urea. The urea formed is transformed into ammonia which is measured spectrophotometrically (629 nm) through indophenol blue formation. Arginase and urea are covalently immobilized on an epoxy resin and are placed in a 50 × 3 mm i.d. glass column. This enzyme reactor is stable for more than 6 months and retains about 80% of its initial activity after 800 assays. Under the proposed experimental conditions, concentrations of l-arginine > 1.7 μg ml−1 (8 μM) can be determined. The procedure has a linear calibration range between 38 μM and 7.5 mM and a relative standard deviation of 1.8% (12 injections at 50 ppm). Among the 22 amino acids investigated, only l-glycine and l-histidine (≥ 960 μg ml−1) interfere.