Enzymatic determination of glucose in milk samples by sequential injection analysis

The present work describes a comparative study involving two sequential injection enzymatic procedures for the spectrophotometric determination of glucose in milk samples. The determinations were based on the use of the enzymes, glucose oxidase and peroxidase, in solution or immobilized, and 4-aminophenazone and phenol as chromogenic reagents. In the first procedure, 8.4 IU of glucose oxidase and 0.5 IU of peroxidase were consumed in each determination. In the second procedure, 107 IU of glucose oxidase and 105 IU of peroxidase, immobilized in glass beads, were sequentially packed into the same reactor. The reactor allowed us to perform about 600 continuous determinations with no activity loss. The proposed systems allowed the determination of glucose up to 120 mg L(-1) in milk samples with a precision, considering the RSD (%) values, lower than 3.5%. The results obtained for the two systems were comparatively evaluated against a routine enzymatic method, showing a relative deviation of less than 3%.