Simultaneous and automatic determination of hydroxide and carbonate in aluminate solutions by a micro-titration method

An automatic micro-titration method for the simultaneous determination of h ydroxide and carbonate in sodium aluminate solution is proposed. Thirty mu l of the sample is injected and propelled into a titration cell by a reagen t solution containing sulfosalicylic acid, barium chloride, and phenolphtha lein. Sulfosalicylic acid is both the titrant and the complexing agent for aluminum to prevent the formation of an aluminum hydroxide precipitate, Fir stly, hydroxide is titrated by sulfosalicylic acid to the end point indicat ed by phenolphthalein while carbonate is present as barium carbonate. More reagent solution is gradually added until all the barium carbonate is disso lved. A light-emitting diode and phototransistor-based photometer is employ ed to record the absorbance change during the titration process, from which the end points for both hydroxide and carbonate could be obtained. The pro posed method can be employed to analyze industrial sodium aluminate solutio ns containing 50-300 g 1(-1) hydroxide and 0-50 g 1(-1) carbonate (expresse d as Na2O) with a sampling frequency of 45 samples per hour. The relative s tandard deviations are 0.28% for 170.4 g 1(-1) hydroxide and 0.37% for 35.6 g 1(-1) carbonate (both as Na2O, n=13), (C) 1999 Elsevier Science B.V. All rights reserved.