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A simple and selective method was developed for the preconcentration, separation, and determination of trace amounts of As(III) in an aqueous solution by solid phase extraction combined with graphite furnace atomic absorption spectrometry. Activated carbon (AC) was modified by sodium diethyldithiocarbamate (NaDDTC) and then used as a new, stable and easily prepared solid sorbent in a mini column for the extraction of As(III) in aqueous solution. Factors influencing the sorption and desorption of As(III), such as volume and concentration of eluent, sample pH, flow rate and effect of interfering ions on the recovery of As(III) have been systemically investigated. At pH 2.0 As(III) could be adsorbed quantitatively by NaDDTC-AC, and then eluted completely with 2 mL of 3.0 mol·L−1 HNO3. The amount of eluted As(III) was measured using graphite furnace atomic absorption spectrometry. The detection limit of As(III) was 0.04 ng·mL−1 with enrichment factor of 100 and the relative standard deviation (RSD, n=8) was 1.58% at 10 ng·mL−1 level.

A simple and sensitive method using mini-column packed with multi-walled carbon nanotubes (MWCNTs) combined with graphite furnace atomic absorption spectrometry (GFAAS) for preconcentration and determination of ultra trace amounts of As(III) in an aqueous medium is proposed. The procedure is based on the solid phase extraction of the As(III)-sodium diethyldithiocarbamate (As-NaDDTC) chelate on MWCNTs. Various parameters such as the effect of pH, eluent type and volume, amount of sorbent, and matrix effects on the quantitative recoveries of analyte ions were evaluated. It was found that sorption is quantitative and desorption occurs with 4.0 mL of 3.0 mol L−1 HNO3 in acetone. The limit of detection of the method was 0.008 ng mL−1 for GFAAS with enrichment factor of 125 and the relative standard deviation (RSD) 0.97% (n = 8, C = 10 ng mL−1). This method has been applied to the determination of ultra trace As(III) in water and rice plant and its ash successfully.