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A fast, simple and sensitive method was developed for separation and speciation of Cr species using dispersive solid phase extraction prior determination by ICP-MS. The selective determination of toxic Cr(VI) in surface waters is achieved after separation of Cr(III) by sorption on self-standing chitosan film loaded with silver nanoparticles (CHS-AgNPs). Completely green synthetic procedure was used for the preparation of AgNPs, which includes D-(+) raffinose as a non-toxic, environmentally benign reducing and capping agent and NaOH as a base reaction catalyst. The raffinose-coated Ag NPs were blended with chitosan to form polyelectrolyte complex that was cast into stable self-standing film. The parameters affecting the extraction efficiency (pH, sorption time, sample volume) of nanocomposite film toward Cr(III) and Cr(VI) were carefully optimized. Effective separation of Cr species between solid and liquid phase is demonstrated by simply tuning the pH value of the sample solution. The analytical method developed is validated under optimized conditions-the detection limit of 0.02 μg L-1 and determination limit of 0.06 μg L-1 were achieved for both Cr 2 species; the relative standard deviation varied from 3 to 5% for Cr concentrations in the sample solution over the range 0.05-5 µg L-1. The accuracy is established by analysing certified reference materials.

In this study, a new method for selective determination of Cr(VI) in water samples at pH 4 is presented using raffinose capped silver nanoparticles (Ag/Raff NPs) as an optical sensor. The method is based on the variation of LSPR absorption band intensity as a result of electrostatic interaction between the negatively charged Ag/Raff NPs and positive Cr(III) ions, in-situ produced by chemical reduction of Cr(VI) with ascorbic acid, combined with the fast kinetics of Cr(III) coordination to the –OH groups of the capping agent on the nanoparticle surface, further causing the nanoparticle aggregation. The calibration curve for Cr(VI) is linear in the range 2.5–7.5 μmol L−1, the limit of quantification achieved is 1.9 μmol L−1, and values of relative standard deviation vary from 3 to 5% for concentration level 1.9–7.5 μmol L−1. The interference studies performed in the presence of various metal ions show very good selectivity of Ag/Raff NPs toward Cr(VI) species. The added–found method is used to confirm the accuracy and precision of developed analytical approach.

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