Multisyringe flow injection lab-on-valve systems coupled to hydride generation atomic fluorescence spectrometry for on-line bead-injection preconcentration and determination of total inorganic arsenic in environmental waters

In this work, the third generation of flow injection analysis, that is, the so-called micro-Lab-on-Valve (LOV) approach, is hyphenated for the first time to atomic fluorescence spectrometry (AFS) for the separation, preconcentration and monitoring of hydride forming elements. A multisyringe flowing stream network is assembled for accurate handling of solutions and on-line post column derivatization of the eluate for the generation of the volatile species. The potential of the new hyphenated technique for environmental assays was ascertained via the determination of ultratrace levels of total inorganic arsenic in freshwaters. The method involves the preconcentration of arsenate(V) at pH 10 on a renewable anion exchanger, namely Q-Sepharose, packed in a LOV micro-column. The analyte species is afterwards stripped out, and concurrently pre-reduced, by a 0.25 mL of eluent containing 6 mol L-1 HCl and 10% KI. The eluate merges downstream with a defined plug of sodium tetrahydroborate (0.3% w/v) for generation of arsine, which is subsequently quantified by AFS. An oxidation agent, namely 2x10-6 M potassium permanganate, was employed for the quantitative oxidation of As(III) to As(V) in the samples before loading into the multisyringe flow system. The flow system facilitates on-column reduction with no need for application of programmable stopped-flow. Yet, the high electrolyte concentrations and extreme pH conditions for elution prevents the sorbent to be re-used, so that maximum benefit can be taken from the application of the bead disposal strategy. The proposed procedure is characterized by a high tolerance to interfering hydride forming elements. In fact, ratios of Se(IV) to As ≤ 5000 and Sb(V) to As ≤ 250 are tolerated at the 10% interference level. Under the optimized experimental conditions, a detection limit (3σ) of 0.02 ng mL-1 and a precision better than 6.0% at the 0.1 g L-1 level were obtained for the bead-injection mode whenever the loading sample volume was affixed at 3.0 mL. The procedure was validated by the determination of arsenic in certified reference materials of variable matrix complexity (TMDA-54.3 and LGC-CA010). No significant differences were found between the experimental results and the certified values at a significance level of 0.05.