Application of an external contactless conductivity detector for the analysis of beverages by microchip capillary electrophoresis

Quantitative total ionic analysis of alcoholic and nonalcoholic beverages was performed by microchip capillary electrophoresis with external contactless conductivity detection. An electrolyte solution consisting of 10.5 mm histidine, 50 mm acetic acid, and 2 mm 18-crown-6 at pH 4.1 was used for the determination of NH4+, K+, Ca2+, Na+,and Mg2+. Fast analysis of CI-, NO3-, and SO42- was achieved in 20 mm 2-(N-morpholino)ethanesulfonic acid/histicline electrolyte solution at pH 6.0 and the simultaneous separation of up to 12 inorganic and organic anions was performed in a solution containing 10 mm His and 7 mm glutamic acid at pH 5.75. Limits of detection ranged from 90 to 250 mu g/L for inorganic cations and anions, and from 200 to 2000 mu g/L for organic anions and phosphate. Calibration curves showed linear dependencies over one to two orders of magnitude when the stacking effect was minimized by injecting standard solutions prepared in background electrolyte solutions. Total analysis times of 35 and 90 s were achieved for the determination of 5 inorganic cations and for the simultaneous determination of 12 inorganic and organic anions, respectively, which represents a considerable reduction of analysis time compared to conventional separation methods used in food analysis.