Simultaneous determination of NaOH, Na2CO3 and Al2O3 in sodium aluminate solutions by flow injection titration

摘要

A flow injection titration method for simultaneous determination of hydroxide, carbonate and alumina in sodium aluminate solutions was proposed. 150μL sample was injected and firstly reacted with a mixture of methyl orange, phenolphthalein and sulfosalicylic acid, and secondly, a mixture of chlorhydric acid, ammonium fluoride and phenolphthalein. Methyl orange and phenolphthalein in the first are the corresponding indicators for the determination of hydroxide and carbonate; sulfosalicylic acid is both the titrant and masking agent for aluminum. Ammonium fluoride in the second is complexing agent for alumina and makes it release corresponding amounts of hydroxide ion to aluminum; phenolphthalein is the corresponding indicator for the determination of hydroxide, carbonate and alumina. Chlorhydric acid is the titrant agent for the three. The proposed method can be employed to analyze aluminate solutions containing hydroxide 3.1～15.5g/L-1, carbonate 3.1～15.5g/L-1 and alumina 0.51～1.02g/L-1 with a sampling frequency of 30 samples per hour. 0.54% and 0.89% are the RSD of sodium oxide and of alumina respectively (n=11).