Abstract
Abstract Chemical speciation of arsenic compounds in human urine is an interesting and important topic because the distribution of different arsenicals in human urine is considered highly related to certain disease and occupational exposure. It has long been realized that the determination of total arsenic concentration is insufficient for clinical and environmental considerations. Generally, the most common analytical methodology to approach As speciation is the hyphenation of a powerful separation technique with a sensitive and selective detector. The direct coupling of high-performance liquid chromatography (HPLC) with inductively coupled plasma mass spectrometry (ICP-MS) seems to be one of the most common approaches for this speciation in a variety of samples. Although ICP-MS is a very powerful technique for trace and isotopic analysis, molecular ion interferences caused by the presence of argon or chlorine which can still disturb the measurement of arsenic isotopes. There were several papers reported that the coupling of hydride generation techniques with ICP-MS is suitable to overcome some of the ICP-MS measurement problems. Greater sensitivity can be attainable because of the improved analyte delivery efficiency and removal of sample matrix. Up to now, chemical hydridization methods are frequently employed to interface chromatographic separation and instrument detection. In view of the inferiority in converting monomethylarsenic acid (MMA), dimethylarsenic acid (DMA) and As(V) into gaseous hydride by chemical methods, a new on-line oxidation technique utilizing HPLC-UV/nano-TiO2 photocatalysis device coupled with hydride generation-ICP-MS for the speciation of arsenic species is developed. In this study, As(III), MMA, DMA and As(V) were separated using anion-exchange chromatography column. After the chromatographic separation, on-line oxidation of arsenic species into As(V) by UV/nano-TiO2 photocatalysis device were investigated. To optimize the oxidation efficiency, the effects of particle size and crystal types of titanium oxide were investigated. Additionally, owing to the hydridization efficiency of As(III) is the best by NaBH4, a pre-reductant（Na2S2O4）was also employed to convert the resultant As(V) to As(III) prior to chemical hydridization step. By way of the use of proposed procedure, the detection limits of As(III), MMA, DMA and As(V) are 0.37、0.18、0.17 and 0.22 ug/L, respectively. The stability of this method can be controlled down to approximately 10 % in 360 min continuous measurement. To evaluate the applicability of proposed method, in-situ and continuous monitoring of the dynamic variation of arsenic species in spiked human urine has been performed by in vitro mode. Base on the achieved analytical results, it indicated that the proposed microdialysis-microbore HPLC- UV/nano-TiO2 photooxidation-pre-reducation- HG-ICPMS hyphenated system is a feasible approach for in vivo tracking the dynamic variation of different arsenic species in living animal.