An Improved Wet Digestion Procedure for the Analysis of Total Arsenic in Biological Samples by Direct Hydride Atomic Absorption Spectrophotometry

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Abstract
The presence of dimethylarsinic acid (DMAA) in biological samples can cause an underestimation of total arsenic content when analyzed relative to an inorganic arsenic standard by direct hydride flame atomic absorption spectrophotometry. An acid digestion procedure is described that quantitatively recovers DMAA as well as monomethylarsonic acid, inorganic arsenic(III), and arsenic(V) from aqueous and biological samples. Methylated arsenicals are converted to inorganic arsenic by wet digestion with HNO3, H2SO4, and K2Cr2O7 and subsequently reduced to arsenic(III) with Nal. Arsine is generated with NaBH4 and converted to atomic arsenic following immediate introduction into a nitrogen-entrained air-hydrogen flame. This method produces a linear relationship to absorbance within a mass range of 50 to 300 ng arsenic/arsine reaction. A sensitivity of 2 ng arsenic and a detection limit of 7 ng arsenic/arsine reaction were also obtained. Recovery of DMAA from water, urine, feces, or whole blood ranged from 92 to 105% with a coefficient of variation of 5 to 10%.