Dispersive liquid-liquid microextraction and microsample injection system coupled with inductively coupled plasma-mass spectrometry for inorganic arsenic speciation in natural waters

A method was developed for inorganic arsenic speciation analysis of water samples by a microsample injection system coupled with inductively coupled plasma mass spectrometry (MIS-ICP-MS) following a validated dispersive liquid-liquid microextraction (DLLME). Prior to DLLME speciation analysis, a simple robust microsample injection system was successfully adapted to ICP-MS. A sampling volume of 90 mu L provided almost the same signals as the signals obtained by means of a conventional continuous nebulization sampling system for the ICP-MS instrument. After DLLME, the final solution was injected into nebulizer of ICP-MS using the microsample injection system. Under the optimized conditions, the analyte from only 5.0mL water sample was concentrated by a factor of 48 with detection limits reaching 0.0031 mu gL(-1) for arsenic. The calibration curve had a linear range of 0.0084-0.0800 mu gL(-1) (r(2)=0.999). The relative standard deviations (RSD, n=6) were <4%. The proposed method was applied to the speciation of inorganic arsenic in various water samples with satisfactory results. The determination of arsenite and total As in river, pond, tap and bottled water samples was acheived by the standard addition method. The recoveries for spiked As(III) and As(V) from understudied water samples were in the range of 95-108%.