DIFFERENTIAL DETERMINATION OF ARSENIC(III) AND TOTAL ARSENIC USING FLOW-INJECTION ONLINE SEPARATION AND PRECONCENTRATION FOR GRAPHITE-FURNACE ATOMIC-ABSORPTION SPECTROMETRY

Arsenic(III) can be quantitatively extracted using sodium diethyldithiocarbamate (NaDDTC) as the complexing agent and C18 reversed phase packing as the column material for solid phase extraction. Arsenic(V) must be reduced to its trivalent oxidation state prior to extraction. A mixture of sodium sulphite, hydrochloric acid, sodium thiosulphate and potassium iodide was found to be optimum for on-line reduction. When the sorbent extraction is carried out without and with the addition of the reduction mixture, arsenic(III) and total arsenic can be determined sequentially by graphite furnace atomic absorption spectrometry with detection limits (3-sigma) of 0.32 ng for As(III) and 0.43 ng for total arsenic. A 7.6-fold enhancement in peak area compared to direct injection of 40-mu-l samples was obtained after 60 s preconcentration. Results obtained for sea water standard reference materials, using aqueous standards for calibration, agree well with certified values. A precision of 5.5% RSD was obtained for total arsenic in a sea water sample (1.65-mu-g/l As). Results obtained for synthetic mixtures of trivalent and pentavalent arsenic agreed well with expected values.