An instrumental method which closely matches the Lane-Eynon titration is evaluated with microcomputer interfacing for determining reducing sugars by titration into boiling Fehling's solution. Titrations using copper or platinum as indicator electrodes for end point detection gave millivolt changes at the end point, varying from 18 to 220 mV depending on the electrode couple used, and relative standard deviations of 0.44-0.67% for the precision of measured end point volumes. Titration data measured with a copper-platinum electrode couple are acquired in real time for 58 raw sugar samples with reducing sugar content varying from 0.10 to 0.61%. Linear regression correlation of the potentiometric titration data and the standard Lane-Eynon method gives a correlation coefficient of 0.9960.
INT.RODUcTIoN
The principal chemical methods for the determination of reducing sugars (RS) are based upon reducing alkaline solutions of certain metallic salts, a property possessed by all aldehydes and ketones. Although many metallic salts, including those of copper, silver, mercury and bismuth, undergo this type of reaction, copper has been employed most generally in sugar analysis [l]. A large number of methods have been proposed for the determination of reducing sugars. In many routine analytical laboratories, however, particularly in the sugar industry, the Lane-Eynon [2] method is still most commonly used for determining reducing sugars [the percentage of raw sugar content (%RS)] in sugar products. This method is based on the reduction of copper(I1) tartrate in a strongly alkaline medium at a boiling temperature using methylene blue as an indicator. The method requires visual end point detection, which is difficult to observe, especially in dark-colored solutions of raw sugars and other sugar products, such as molasses.
In order to overcome this problem, Coalstad 131 developed an electrometric technique for end point detection using two copper electrodes. Bell et al. [4] and Defrates et al. [5] later used a copper and platinum couple instead of the two copper electrodes employed originally by Coalstad 131. Noakes er al.