Abstract
A method has been developed for the direct determination of methylated arsenicals [dimethylarsinic acid (DMAA) and methane arsonate disodium salt (MAA-2Na) ] and inorganic arsenicals [arsenite {As(III)} and arsenate {As (V)}] using the graphite-furnace atomic-absorption (GFAA) spectrometry system. A sample solution of a 10μl-aliquot was injected into graphite-furnace (Hitachi model 170-70 spectrometer), then dried at 100 °C for 60 s, charred at 620 °C for 30 s and atomized at 2800 °C for 5 s with measurement at 193.7 nm. Argon was used as the sheath gas of 3.0 l/min and purge of 0.15 l/min. Appreciable different sensitivity among DMAA, MAA, As (III) and As (V) was observed in a distilled water matrix alone. The DMAA absorbance showed the lowest sensitivity is approximately 1/31/4 of that of arsenate showed the highest. A remarkable signal enhancement was produced by adding representative alkali metal (LiNO3), alkaline-earth metals [Mg (NO3)2, Ca(NO3)2, Sr(NO3)2, Ba(NO3)2], iron family metals [Fe(NO3)3, Co(NO3)2, Ni(NO3)2], acids (HNO3, HClO4) and basis (LiOH, NaOH, KOH, RbOH, CsOH). By the addition of these coexisting reagents, especially in DMAA signals, improvement of sensitivity was noted up to (34) times, and the sensitivities of DMAA, MAA, As (III) and As(V) with each equivalent arsenic contents became similar. These coexisting reagents [NaOH, Ni(NO3)2] were applied to the determination of arsenicals in environmental materials (extracts of rat's blood, grape, river water and soil, and TLC extracts of these samples) which were extracted and isolated by a similar method to the previous reports {J. Agric. Food Chem., 26 (2), 505 (1978)}. Since the interference from extracts of grape and soil samples were completely eliminated by the addition of coexisting reagent (NaOH), concentration of arsenicals could be calculated directly from the calibration curve. Recoveries on the presence of coexisting reagent (Ni) of DMAA or MAA-2Na added to various samples were almost quantitative.
