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 mu g 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 (r(2) = 99.6%) between 10 and 100 mu g ml(-1) and the limit of dectection (3 x baseline noise) was < 4 mu g ml(-1), The precisions (s(r)) of absolute migration times and corrected peak areas were 1.7% (n = 5) and 3.6% (rt = 5), respectively. The concentration of sulfate determined in one sample of concrete using CZE (0.5% mim) was comparable to that obtained by standard gravimetric analysis (0.6% mim).