Flow injection spectrophotometric determination of reducing sugars using a focalized coiled reactor in a domestic microwave oven

A flow injection (FI) spectrophotometric procedure for determining reducing sugars content in sugar cane juices using a focalized PTFE coiled reactor positioned at the output antenna of a domestic microwave oven at 700 W is proposed. In this system, sample solution converge to 1.0 mol l−1 NaOH and 5.2 mmol l−1 K3Fe(CN)6 solutions previously mixed and the decrease of hexacyanoferrate(III) concentration was monitored at 420 nm. Under best analytical conditions, there was a direct relationship between absorbance decrease and reducing sugar content (fructose plus glucose concentrations) in the concentration range from 50 to 1200 μmol l−1 with a detection limit of 15 μmol l−1. The relative standard deviations (rds) were less than 1.4% for ten injection of 400 and 800 μmol l−1 fructose solution and the analytical frequency was 70 h−1. A paired t-test showed that all results obtained for sugar cane juices using this FI procedure and the Somogyi–Nelson batch procedure agree at the 95% confidence level.