This paper discusses the determination of inorganic ions at low μg L−1 levels by capillary zone electrophoresis (CZE) with electrokinetic injection and indirect UV detection. A 70 cm×75 μm i.d. capillary was used at −25 kV with an electrophoretic buffer of sodium chromate containing percentage levels of 1-butanol, and cetyltrimethylammonium bromide (CTAB) as electroosmotic flow modifier (pH 8). The effects of variables such as the presence of electromigrative additives and precautions taken during the preparation of samples (handling, contamination, etc.) were studied.RSD of SO42−, NO3−, and F− peak areas were <13%; for Cl-they were almost 35% when a 10μg L−1 standard solution was analyzed. The method was used to determine these ions in the secondary circuit of a nuclear power water plant.