DETERMINATION OF CHLORIDE, NITRATE, SULFATE, NITRITE, FLUORIDE, AND PHOSPHATE BY ON LINE COUPLED CAPILLARY ISOTACHOPHORESIS-CAPILLARY ZONE ELECTROPHORESIS WITH CONDUCTIVITY DETECTION

Capillary zone electrophoresis (CZE) on-line coupled with capillary isotachophoresis (ITP) in the column-coupling configuration of the separation unit was studied for determination of nitrite, fluoride, and phosphate persent in a large excess of chloride, nitrate, and sulfate. Such distributions of these anions are typical for many environmental matrices, and it is shown that the ITP-CZE tandem enables the ITP determination of the macroconstituents, while ITP-preconcentrated microconstituents cleaned up from the macroconstituents can be determined by CZE with a conductivity detector. This approach was effective when the concentration ratio of macro-microconstituents was less than (2-3) x 10(4). The limits of detection achieved for the microconstituents (200, 300, and 600 pptr for nitrite, fluoride, and phosphate, respectively) enabled their determinations at low parts per billion concentrations in instances when the concentrations of sulfate or chloride in the samples were higher than 1000 ppm. Although in such situations the load capacity of the ITP column was not sufficient to provide the quantitations of the macroconstituents, the ITP sample cleanup enabled the CZE determinations of the microconstituents present in the samples at 10(5)-10(6)-fold lower concentrations. Experiments with samples of such extreme compositions showed that anionic impurities from the ITP electrolyte solutions transferred together with the analytes into the CZE column are probably the main hindrances in extending this dynamic concentration range by decreasing the limits of the detection to a level associated with the noise characteristics of the conductivity detector.