Abstract

A four-stage sequential extraction procedure for the speciation of nickel has been applied to ambient aerosol samples. The determination of the soluble, sulfidic, metallic and oxidic Ni fractions in particulate matter was carried out by graphite furnace (electrothermal) atomic absorption spectrometry (ETAAS) and inductively coupled plasma mass spectrometry (ICP-MS). An EDTA solution, a mixture of diammonium citrate and hydrogen peroxide, and a KCuCl₃ solution were used as leaching agents for the determination of the soluble, sulfidic and metallic species, respectively, and nitric acid was used for the determination of oxidic compounds after microwave digestion of particulate matter sampled on filters. A new micro scale filter holder placed in a closed flow injection analysis (FIA) system for use in nickel speciation by means of sequential extraction, and the results of the optimisation of the extraction conditions are described. The temperature program for ETAAS was optimised for all extraction solutions with the aid of temperature curves. Pyrolysis temperatures of 900, 600 and 1000 °C were found to be optimum for EDTA, hydrogen peroxide plus ammonium citrate and KCuCl₃-containing solutions, respectively. Airborne dust was sampled on filters at two locations near to a metallurgical plant in Dortmund, Germany. Concentrations in the low ng m⁻³ range down to the detections limits (0.1–0.3 ng m⁻³) and various nickel species were found to be present in the collected dust. The mean fractions of total nickel (sampling period of one month) were found to contain 36 ± 20% of soluble, 6 ± 4% of sulfidic, 11 ± 15% of metallic and 48 ± 18% of oxidic nickel.