SPECIATION AND SIMULTANEOUS DETERMINATION OF ARSENIC(III), ARSENIC(V), MONOMETHYLARSONATE AND DIMETHYLARSINIC BY ATOMIC-ABSORPTION USING INVERSE LEAST-SQUARES MULTIVARIATE CALIBRATION

A direct continuous-how hydride generation atomic absorption spectrome tric method for the evaluation of toxic arsenic compounds such as As(I II), As(V), monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA ) has been developed and mathematically evaluated. The procedure invol ves the differential reduction of the species to their hydride forms. The acid media tested for the differential reduction of species to the hydrides were 6 M, 1 M, and 0.5 M HCl, 1 M HAc and citric/citrate buf fer (pH 2 and 4). In 6M HCl the same signal was obtained from As(III), As(V) and MMA using a 3% (w/v) NaBH4 solution in the working conditio ns defined and KI was not necessary to improve the kinetics of hydride generation from As(V). In the other acid media tested, different effi ciencies were obtained from the species studied depending on the pH, a cid nature and acid concentration and univariate calibration could not be employed. Multivariate calibration by the inverse least squares (I LS) method showed that the proposed method is acceptable for quantitat ive speciation. The detection limits obtained were in all cases equal to or lower than 2.7 ng ml(-1) for As(III), 0.8 ng ml(-1) for As(V), 3 .0 ng ml(-1) for MMA and 4.9 ng ml(-1) for DMA.