Ion-Chromatographic Determination of Low Concentrations of Nitrate in Solutions of High Salinity

Abstract.

The determination of low concentrations of inorganic anions in water samples of high salinity is one of the most difficult tasks in analytical chemistry. There is, however, an increasing demand for the exact and reliable determination of nutrients even at very low concentration levels in environmental samples of complex composition. We therefore present the development, quality control and application of an easy and rugged method that makes possible the determination of trace amounts of nitrate in solutions with high concentrations of chloride (>30 000 mg L⁻¹) and a hundred-fold excess of bromide ions, based on ion chromatography with UV detection at λ = 210 nm. While chloride ions show no absorbance at this wavelength, a bromide concentration >1500 µg L⁻¹ severely interferes with nitrate determination at the trace level. On the contrary, at nitrate concentrations of >500 µg L⁻¹, this bromide interference becomes negligible. Consequently, to overcome the impact of bromide on the trace level determination of nitrate, all samples are spiked with a definite volume of a nitrate standard solution to obtain an overall nitrate concentration of >500 µg L⁻¹ which allows the exact and reliable determination of nitrate concentrations down to 25 µg L⁻¹. We will report the successful application of the method to samples of high salinity.