Determination of chloride, sulfate and nitrate in drinking water by microchip electrophoresis

We report on a method for simultaneous determination of chloride, sulfate and nitrate in drinking water by microchip electrophoresis. By adjusting a pH value of 4.2 in the aspartate background electrolyte, and by applying separation mechanisms via the ionic strength effect (bis-tris propane) and association equilibria (N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate), a complete resolution of analytes from other co-migrating constituents is accomplished. In addition, isotachophoretic preconcentration of nitrate was implemented directly on the microchip. The ions were detected via conductivity measurements after injecting 900-nL samples. The limits of detection range from 40 to 120 μg L-1. The method displays a high reproducibility of the migration velocities under suppressed hydrodynamic and electroosmotic flow and therefore allows for a precise quantitation of analytes. The total analysis time is <450 s, and the working range is up to 60 mg L-1 for chloride and sulfate, and of up to 20 mg L-1 for nitrate. Filtration and degassing are the only sample treatment steps prior to analysis. The use of an internal standard enabled an easy chip-to-chip transfer of the method.