Capillary Zone Electrophoresis Method for the Determination of Sulfate in Concrete

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 (sr) 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).