DETERMINATION OF REDUCING SUGARS BY FLOW-INJECTION GRAVIMETRY

A flow injection procedure for gravimetric determination of reducing s ugars was developed. The system was designed to permit the monitoring of an in-line formed suspension. In view of the high density of the pr ecipitate, a product of oxidation of reducing sugars by Fehling reagen t, the Archimedes principle was exploited, so that the precipitate was weighed inside the flowing stream. Sample and reagents were simultane ously injected into two convergent carrier streams flowing through a r eaction coil immersed in boiling water under reflux. The formed precip itate was cooled, accumulated on a sintered glass mini-filter and weig hed. An acidic solution was then injected into both carrier streams to promote in-line solubilization of the precipitate. Characteristics of the filtering device, geometry of the debubbler, flow rates, wash sol ution and possibilities of weighing with the filtering unit on the pla te of the analytical balance or suspended under it were investigated. Furthermore, effects of reagent concentration, temperature, surfactant addition and available time for reaction were studied. The gravimetri c flow injection system was very stable and required only 0.64 g Cu pe r determination. Precipitate drying was not needed. Precise results (r .s.d. usually <0.9%), in agreement with an official titrimetric proced ure, were obtained within 0.20 and 1.00% w/v invert sugar. A new weigh ing was accomplished every sixth minute. (C) 1998 Elsevier Science B.V .