Cryogenic trapping with a packed cold finger trap for the determination and speciation of arsenic by flow injection/hydride generation/atomic absorption spectrometry

Abstract

An innovative analytical system based on the combination of cryogenic trapping and unambiguous gas chromatographic separation performed within a packed cold finger trap (PCFT) has been developed here. In this hydride generation-packed cold finger trap-atomic absorption spectrometric (HG-PCFT-AAS) system, the carrier gas (He) and heating voltage were optimized from a complete factorial experiment and in accordance with a base-line resolution (R_S > 1.4) between monomethylarsonic acid (MMA) and dimethylarsenic acid (DMA); the sheath gas argon (Ar) flow rate, on the other hand, was optimized from a single factorial experiment to obtain the highest signal-to-noise (S/N) ratio. Here, for MMA and DMA analysis, compromised levels of the parameters for hydride generation were determined from an L₁₆(4)⁵ orthogonal array experimental design following the principle of the larger-is-better S/N ratio. The hydride evolution after the addition of a citrate buffer was employed to selectively measure arsenite (As^III). With an atomic absorption spectrometer (AAS) serving as the detector, the limits of detection were 0.9, 0.8, 0.5, and 0.6 ng for As^III, As^V (arsenate), MMA and DMA, respectively. The results of the application of the method in freshwater and seawater showed spike recovery ranges from 82∼113% and relative standard deviation of triplicate analysis ranges from 3∼10%, depending on the arsenic species. Accuracy of the established method was also validated by analyzing two standard reference materials, NASS-5 and SLEW-3, in which two arsenic species, As^III and As^V, are detected.