Determination of Glucose in Starch Syrups by Copper Acetate Reagent

Abstract

The Zerban-Sattler modification of the Steinhoff method adopted in Official Method of Analysis of the A. O. A. C. was adapted to microanalysis. Reagents (A) 40 g of CuSO4. 5H2O dissolved in water and made up to 1 liter. (B) 300 g of NaOAc. 3H2O dissolved in water and made up to 1 liter. (C) 200 g of KI dissolved in water and made up to 1 liter. (D) 6N-H2SO4. (E) 12g of KCNS dissolved in water and made up to 100 ml. (F) 1 % soluble starch. (G) 0.02N-Na2S2O3 standard solution. Procedure Introduce 2 ml of (A), 2 ml of (B) and 2 ml of a sugar solution containing 40-180mg of glucose in 100 ml into a glass-stoppered test tube which is 2.5 cm in diameter and 20 cm in length, stopper the test tube, and shake vigorously. Heat the test tube and the contents in briskly boiling water in a water bath for 25 minutes, and then cool in running tap water. Add 1 ml of (C) and 1 ml of (D), shake the mixture well, leave it standing for 3-4 minutes, and titrate with (G). When the solution has turned light yellow in color, add 2 ml of (E) and continue titrating . When the color has again turned light yellow, add 2-3 drops of (F) and titrate until the bluish violet color disappears while recording the total volume (a) in ml . Run a blank test and determine the volume of (G) consumed or (b) in ml . Calculate the amount of glucose (y in mg/100 ml) according to the following equation :y=25.27(b-a)+15.17 A comparison of this method with carbon column chromatography indicates that glucose determined by this method comes out 2-3% higher for acid-hydrolyzed syrups and 4-5 % higher for malt-hydrolyzed syrups ; however, this method is practical because of its simplicity in procedure and calculation .