Collection of trace heavy metals on dithizone-impregnated admicelles for water analysis

Admicelles formed on alumina were studied from the viewpoint of separation vehicles in trace analysis. Gamma-alumina (1.5 g) was suspended in 30 cm(3) of water and mixed with 10 cm(3) of ammoniacal solution containing 1.5 mg of dithizone and 100 mg of sodium dodecyl sulfate. The mixture was acidified to pH 2, where the anionic surfactant was strongly adsorbed on the positively charged alumina surface to form dithizone-impregnated admicelles. Metal contaminants in the admicelles were thoroughly removed by washing with 4 mol dm(-3) nitric acid. The quantitative adsorption from water was performed at pH 2 - 9 for Cu, pH 3 - 9 for Pb and pH 4 - 9 for Co, Ni and Cd. For seawater, simultaneous collection required adjusting the pH to ca. 8. Humic and fulvic acids did not interfere with the separation. The admicelle column was substantially stable during adsorption and desorption, which allowed the same column to be used at least three times. The proposed method was combined with inductively coupled plasma-mass spectrometry for the analysis of seawater.