Determination of dissolved copper, nickel and cadmium in natural waters by high-performance liquid chromatography

Abstract

A novel technique has been developed to determine dissolved copper, nickel and cadmium in natural waters, and in particular estuarine and sea-waters, by using high-performance liquid chromatography (HPLC). The main performance criteria were that the method was sensitive, reproducible and interference free. This has been achieved by developing a system whereby the trace metals were initially preconcentrated on a bonded-silica (C₂) guard column coated with an ammonium pyrrolidin-1-yldithioformate (ammonium pyrrolidine dithiocarbamate)–cetyltrimethylammonium bromide ion pair. This selectively removed the trace metals from the sample matrix, thereby excluding potential interferents. After preconcentration the metal–dithiocarbamate complexes were flushed with a modified organic mobile phase from the pre-column onto a C₁₈ reversed-phase analytical column for separation. The complexes were detected by means of a variable-wavelength ultraviolet detector. Performance data were obtained, yielding limits of detecton of better than 0.5 µg l^–1 for copper, cadmium and nickel, for 10 ml sample volumes. The precision was better than 5% relative standard deviation for concentrations in the range 0.5–10 µg l^–1. Once optimized the technique was evaluated by analysing estuarine samples with a variety of salinities and comparing the data with those obtained by an accepted reliable method: chelation–solvent extraction–atomic absorption spectrometry. Results showed that there was no significant difference in the data obtained by the two methods. A single calibration graph could be used for samples of all salinities by using the HPLC method.