DETERMINATION OF ANIONIC TRACE IMPURITIES IN GLYCEROL BY CAPILLARY ISOTACHOPHORESIS WITH ENLARGED SAMPLE LOAD

Glycerol of different quality classifications served as a model for a neutral excess component in the isotachophoretic determination of low- molecular-mass anionic trace impurities. Potential anionic contaminant s such as nitrate, sulphate, chlorate, nitrite, oxalate, fluoride form ate and phosphate were analysed up to an analyte-to-excess ratio of 1: 4.10(7), thus providing the possibility of checking the sample for the mentioned analytes in the order of 2.5.10(-6)-9.5.10(-6)%. Because we used a column-coupling isotachophoretic instrument the electrolyte sy stem consisted of two different leading electrolytes, one for the pre- separation (10 mmol/l HCl, beta-alanine, pH 3.2) in the first capillar y and one for the final separation (5 mmol/l HCl, 1,3-bis[tris(hydroxy methyl)methylamino]propane, beta-alanine, pH 3.6) in the second capill ary. The terminating electrolyte was citric acid. Due to an increased injection volume of 300 mu l, limits of detection (LODs) in the nanomo lar range were realised by conductivity detection. The developed metho d allows simultaneous analysis without sample preparation and/or preco ncentration within 25 min and is for that reason suitable for in-place process control. (C) 1998 Elsevier Science B.V. All rights reserved.