[Determination of trace cobalt in water samples by graphite furnace atomic absorption spectrometry after cloud point].

In buffer solution of citric acid monohydrate-disodium hydrogen phosphate at pH 5-7.5, cobalt water samples were chelated by 1-(2-pyridylazo)-2-naphthol (PAN) to form Co-PAN. After water-bath at 66 degrees C for two hours, Co-PAN is extracted into Triton X-100 nonionic surfactant phase and separated from bulk water. Extracted cobalt content was measured by graphite furnace atomic absorption spectrometry. The surfactant phase separated was treated with 0.5% HNO3-0.1% Pd(NO3)2 to remove background interference at 1200 degrees C temperature. The pre-concentration of cobalt in water samples permitted the detection of 0.003 microg x L(-1) (10sigma) with the enhancement factor of 100. The recoveries were 90.5%-106%. The proposed method was applied to the determination of cobalt in water samples and satisfactory results were obtained.