Speciation of arsenic (III) and arsenic (V) based on quenching of CdS quantum dots fluorescence using hybrid sequential injection–stopped flow injection gas–diffusion system

A hybrid sequential injection–stopped flow injection system was developed for the speciation of arsenic based on the quenching of mercaptoacetic acid capped cadmium sulfide quantum dots (CdS–MAA QDs) fluorescence intensity. The analytical procedure involves the generation of arsine from As(III) by sodium borohydride in acetate buffer medium pH 6.0. The generated arsine (donor stream) diffuses across the PTFE membrane of the gas–diffusion unit into an acceptor stream and then interacts with CdS–MAA QDs. Total arsenic was determined after pre-reduction of As(V) to As(III) with 1% (m/v) mercaptoacetic acid. Concentration of As(V) in the sample solutions can be deduced from the difference of total arsenic and As(III). Optimization of the experimental conditions and instrumental parameters were investigated. Under optimal conditions, limits of detection were 20 μg L−1 for As(III) and 40 μg L−1 for As(V). Recoveries in the range 84–103% were obtained from sediment sample.

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► We developed the hybrid SI – stopped FI gas-diffusion system for arsenic speciation.
► Determination was based on the fluorescence quenching of CdS-MAA QDs by arsine.
► Total arsenic was determined after pre-reduction with mercaptoacetic acid.
► As(V) can be deduced from the difference of total arsenic and As(III).