New approach for detection of chromate ion by preconcentration with mixed metal hydroxide coupled with fluorescence sensing of copper nanoclusters

The authors describe a two-step strategy for in-situ dispersive solid phase extraction (is-dSPE) of Cr(VI) ion (chromate) prior to its determination by using copper nanoclusters capped with 4,6-diamino-2-mercaptopyrimidine (DAMP-CuNCs) as a fluorescent probe. By emulating the formation of layered double hydroxides and taking advantage of their compositions, the extraction of chromate is accomplished by rapidly dispersing a suspension of mixed hydroxides of Mg2+ and Al3+ into the sample solution. After enrichment, chromate is directly quantified through selective quenching of the fluorescence of DAMP-CuNCs. This results from an inner filter effect caused by chromate only, while other anions have no effect. Under optimized conditions, the method has a linear response in the 1-7 mu M chromate concentration range, and the lower limit of detection is 0.31 mu M. The is-dSPE has improved detection sensitivity and has provided a highly selective response. It was successfully applied to the determination of chromate in (spiked) water samples, and the results agreed well with data obtained by ICP-OES.