Capillary zone electrophoresis method for the determination of sulfate in concrete

Abstract

A capillary zone electrophoresis (CZE) method for the determination of sulfate in concrete digested with concentrated nitric acid is described. An electrolyte containing 50 mmol l^–1 thiocyanate, 10 mmol l^–1 tris(hydroxymethyl)aminomethane, 2.5 mmol l^–1 tetradecyltrimethylammonium bromide and 140 µg ml^–1 nitrate at pH 9 was used to separate the sulfate in under 12 min without significant interference from the highly acidic sample matrix containing a high level of nitrate. The external standard calibration curve was linear (r²= 99.6%) between 10 and 100 µg ml^–1 and the limit of dectection (3 × baseline noise) was < 4 µg ml^–1. The precisions (s_r) of absolute migration times and corrected peak areas were 1.7%(n= 5) and 3.6%(n= 5), respectively. The concentration of sulfate determined in one sample of concrete using CZE (0.5% m/m) was comparable to that obtained by standard gravimetric analysis (0.6% m/m).