Capillary zone electrophoresis of inorganic anions with conductivity detection.

A carrier electrolyte system for capillary zone electrophoresis (CZE) resolving chloride, bromide, iodide, fluoride, nitrite, nitrate, sulfate, and phosphate in a hydrodynamically closed separation compartment is described. The carrier electrolyte combines the effects of pH, polyvinylpyrrolidone (PVP) and the counterionic constituent on the effective mobilities of the anions. In 300 microns ID capillary tubes made of fluorinated ethylene-propylene copolymer (FEP), and with detection of analytes with the aid of an alternating current conductivity detector, detection limits in the range of 3-10 ppb could be achieved for 200 nL sample volumes. The separation efficiencies were in the range of 1.5-2.5 x 10(5) theoretical plates per meter for an adequate sample load. The reproducibility was evaluated for two concentration levels. For concentrations close to the limits of quantitation (50-120 ppb), the RSD values ranged from 1.5-12.6%, with the highest scatter for fluoride and phosphate. The RSD values were in the range of 0.4-1.5% for 300-1200 ppb concentrations of the anions. Typical analysis times were 2-5 min, depending on the anion species. A series of water samples (drinking, river, rain) was used to assess the practical applicability of the CZE method. The method is a suitable alternative for the determination of both anionic macro- and microconstituents in water with a good overall selectivity.

Isotachophoretic determination of chromium(VI) at low parts per billion concentrations.

Factors important in the isotachophoretic determination of CrVI at low ppb concentrations were studied. To increase the selectivity of the analysis, the use of photometric detection at a 405 wavelength was preferred. Losses of CrVI due to adsorption were found to be the main potential source of analytical errors at the concentration levels of interest. The presence of sulphate in the sample solution at ca. 10(-4) M concentration eliminated the losses due to adsorption on the walls of the sample handling glassware. In analysis with a low pH of the leading electrolyte, adsorption of CrVI on the walls of the separation compartment also played a role; addition of naphthalene-1,3,6-trisulphonate to the sample solution considerably reduced this disturbance. When the precautions concerning adsorption were taken, the detection limits for CrVI were in the range 4-5 ppb (depending on the pH of the leading electrolyte) for a 30-microliters sample volume. The calibration graphs were linear over the concentration range 10(-7)-5 X 10(-6) M with good correlation coefficients. The reproducibilities of the determinations within this concentration range were 2-3% or better. The practical utility of capillary isotachophoresis in the trace determination of CrVI in drinking water and wastewater samples seems promising.

Photometric detection at 405 nm in trace analysis by capillary isotachophoresis.

The possibilities of photometric detection at 405 nm were investigated for trace isotachophoretic analysis of various ionic constituents. Increased selectivity of the detection enabled, for example, the detection and determination of nitrophenols at 10(-8) M in a 25-microliter sample. 5-Nitrofurylacrylic acid, a wine stabilizer, could be detected with confidence at ca. 0.1 ppm in wine without any sample pretreatment. Approximately 250-fmol amounts of amino acids, labelled with 2,4-dinitrophenyl, were detectable with the technique employed. This is almost three decades lower in comparison to what is achievable with an high resolution universal detector. The adsorption of the analytes in the sample handling devices as well as in the separation compartment were problems in the analysis at this concentration level. The detection limit given above was achieved when these phenomena were suppressed by the addition of naphthalene-1,3,6-trisulphonate or pyrophosphate to the sample solution.