SENSITIVE AND SELECTIVE METHOD FOR DIRECT DETERMINATION OF NITRITE AND NITRATE BY HIGH-PERFORMANCE CAPILLARY ELECTROPHORESIS

In this paper a sensitive and selective method for the direct determin ation of nitrite and nitrate by highperformance capillary electrophore sis (HPCE) is described. Separation conditions are optimized using a s tatistic orthogonal design. Optimization results suggest that the effe cts of several experiment factors on the separation follow the order: cetyltrimethylammonium bromide (CTAB) concentration > buffer pH approx imate to buffer concentration > run voltage. The results also suggest that better separation could be achieved at relatively low electric fi eld (10 kV/50 cm). Nitrite, nitrate, and bromide (an internal standard ) are well separated in the optimized buffer 20 mmol/l of tetraborate plus 1.1 mmol/l of cetyltrimethylammonium chloride (CTAC). HPCE separa tion at a CTAC concentration of 1.1 mmol/l is considered to involve an ion-pair association mechanism. The specificity and quantitation-incl uding calibration range, reproducibility, and minimum detection limit are examined. Finally, the method was used to analyze samples such as tap or river water, a large amount of nitrate in the water does not in terfere with the determination of a small amount of spiked nitrite.