Determination of Available Cobalt in Soils by Flame Atomic Absorption Spectrometry with Cloud Point Extraction

Toxicological studies have shown that available heavy metals is critical for risk assessment purpose since their transformations and potential toxicity depends, not only on total content, but also on the special chemical forms of the heavy metals. It is very difficult to measure heavy metals in soil by direct instrumental analysis due to the low contents of avalaible metals in soil samples and interference components. In the present paper, a novel procedure was proposed for the determination of available cobalt in soils by flame atomic absorption spectrometry with Cloud Point Extraction (CPE). In the proposed approach, 0.1 mol/L hydrochloric acid (HCl) was used as the extraction agent and methyl red as a chelating agent, with Triton X-114 being selected as the surfactant. The method improved the selectivity and sensitivity of determination. Under optimized conditions, the linear range is from 0.10 to 2.00 μg/mL, the detection limit is 0.03 μg/mL, the recoveries of the procedure ranged from 94.0% to 104.0%, and the relative standard deviation is 3.3% (ρ=0.5 μg/mL,n=9). It was found that the proportion of available cobalt is very different in soils from different areas. The contents of available heavy metals better reflected the information concerning the migration ability of heavy metals in soil, occurrence status and risk assessment.