SPECTROPHOTOMETRIC FLOW INJECTION DETERMINATION OF TOTAL REDUCING SUGARS IN TOBACCO BASED ON OXIDATION BY FERRICYANIDE AND FORMATION OF PRUSSIAN BLUE

Abstract

Using the Prussian blue (ferric ferrocyanide) color reaction, a simple and sensitive flow injection spectrophotometric method for the determination of total reducing sugars in tobacco is proposed. At a temperature of 110°C, sucrose was on-line hydrolyzed to reducing sugars quantitatively in 0.5 moll−1 HCl. The reducing sugars were oxidized by alkaline potassium ferricyanide solution with equal reaction rates for glucose and fructose. The produced ferrocyanide reacted with ferric nitrate to form Prussian blue, which was detected spectrophotometrically at 690 nm for evaluation of the total reducing sugars. Using a merging zone manifold and alkaline citrate solution as carrier, the precipitation of Prussian blue on the system tube was effectively prevented. The detection limits and linear ranges were 0.1mg l−1 and 0.5–15 mg l−1 for glucose, and 0.4 mg l−1 and 0.5–20 mg l−1 for fructose, respectively. The sampling rate was 40 per hour. The proposed method was applied to determine total reducing sugars in tobacco.