Determination of trace inorganic anions in seawater by capillary zone electrophoresis with artificial seawater as background electrolyte

Abstract

We describe capillary zone electrophoresis (CZE) for the determination of trace inorganic anions in seawater. Bromide, nitrite, and nitrate were simultaneously determined using artificial seawater as the background electrolyte (BGE) without the interference of a high concentration of chloride in seawater. The proposed method was also applied to other environmental water samples, such as river water and rainwater samples, because the method was not affected by the salinity of samples. Then, highly sensitive CZE for nitrite and nitrate was established using transient isotachophoresis (TITP) as an on-line concentration procedure. The limits of detection (LODs) for nitrite and nitrate were 2.7 and 3.0 μg/l, respectively, at a signal-to-noise ratio of three. The values of the relative standard deviation (RSD) of the peak area for nitrite and nitrate were 2.0 and 0.75%, respectively, when the nitrite concentration was 0.05 mg/l and that of nitrate was 0.5 mg/l. The RSDs of the peak height were 4.4 and 2.3%. The RSDs of the migration time for these ions were 0.19 and 0.17%. The proposed method was applied to the determination of nitrite and nitrate in MOOS-1, a proposed certified reference material for nutrients in seawater distributed by the National Research Council of Canada (NRC, it is now sold as a seawater certified reference material for nutrients). The results for nitrite and the sum of nitrite and nitrate almost agreed with assigned tolerance intervals that were determined by NRC. Analytical results for nitrite and nitrate in coastal seawater samples taken from the surface and the seabed around the coastal area of Osaka Bay agreed with those obtained by naphthylethylenediamine spectrophotometry. In addition, another TITP-CZE method using phosphate as the terminating ion was developed for the simultaneous determination of iodide and iodate in seawater. The LODs for iodide and iodate were 4.0 and 5.0 μg/l. The RSDs of the peak area, peak height, and migration time for iodide and iodate were 2.9, 1.3, 1.0 and 2.3, 2.1, 1.0%, respectively. © 2005 The Japan Society for Analytical Chemistry.