Selective determination of four arsenic species in rice and water samples by modified graphite electrode-based electrolytic hydride generation coupled with atomic fluorescence spectrometry.

This work describes a novel non-chromatographic approach for the accurate and selective determining As species by modified graphite electrode-based electrolytic hydride generation (EHG) for sample introduction coupled with atomic fluorescence spectrometry (AFS) detection. Two kinds of sulfydryl-containing modifiers, l-cysteine (Cys) and glutathione (GSH), are used to modify cathode. The EHG performance of As has been changed greatly at the modified cathode, which has never been reported. Arsenite [As(III)] on the GSH modified graphite electrode (GSH/GE)-based EHG can be selectively and quantitatively converted to AsH3 at applied current of 0.4A. As(III) and arsenate [As(V)] on the Cys modified graphite electrode (Cys/GE) EHG can be selectively and efficiently converted to arsine at applied current of 0.6A, whereas monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) do not form any or only less volatile hydrides under this condition. By changing the analytical conditions, we also have achieved the analysis of total As (tAs) and DMA. Under the optimal condition, the detection limits (3s) of As(III), iAs and tAs in aqueous solutions are 0.25µgL(-1), 0.22µgL(-1) and 0.10µgL(-1), respectively. The accuracy of the method is verified through the analysis of standard reference materials (SRM 1568a).

Efficient generation of volatile species for cadmium analysis in seafood and rice samples by a modified chemical vapor generation system coupled with atomic fluorescence spectrometry.

A vapor generation procedure to determine Cd by atomic fluorescence spectrometry (AFS) has been established. Volatile species of Cd are generated by following reaction of acidified sample containing Fe(II) and L-cysteine (Cys) with sodium tetrahydroborate (NaBH4). The presence of 5 mg L(-1) Fe(II) and 0.05% m/v Cys improves the efficiency of Cd vapor generation substantially about four-fold compared with conventional thiourea and Co(II) system. Three experiments with different mixing sequences and reaction times are designed to study the reaction mechanism. The results document that the stability of Cd(II)-Cys complexes is better than Cys-THB complexes (THB means NaBH4) while the Cys-THB complexes have more contribution to improve the Cd vapor generation efficiency than Cd(II)-Cys complexes. Meanwhile, the adding of Fe(II) can catalyze the Cd vapor generation. Under the optimized conditions, the detection limit of Cd is 0.012 µg L(-1); relative standard deviations vary between 0.8% and 5.5% for replicate measurements of the standard solution. In the presence of 0.01% DDTC, Cu(II), Pb(II) and Zn(II) have no significant influence up to 5 mg L(-1), 10 mg L(-1)and 10 mg L(-1), respectively. The accuracy of the method is verified through analysis of the certificated reference materials and the proposed method has been applied in the determination of Cd in seafood and rice samples.