Abstract
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.
Highlights
Chromium is a relatively abundant element in the earth’s crust, existing predominantly as Cr(III) compounds
Selective colorimetric determination of Cr(VI) in the presence of Cr(III) in water samples is based on the variation of LSPR absorption band intensity of Ag/Raff NPs as a result of electrostatic attraction between the negatively charged nanoparticles and the positive Cr(III) ions, produced in situ by chemical reduction of Cr(VI) with ascorbic acid, combined with fast kinetics of Cr(III) coordination to the –OH groups of the capping agent on the nanoparticle surface, causing further the nanoparticle aggregation
The interaction of Ag/Raff NPs with in situ reduced Cr(VI) leads to a color change of Ag/Raff NPs dispersion in the first 5 min of the contact time, which indicates their aggregation with a corresponding decrease of LSPR band intensity and the appearance of a shoulder band at longer wavelengths
Summary
Chromium is a relatively abundant element in the earth’s crust, existing predominantly as Cr(III) compounds. The industrial application of Cr(VI) compounds is still very high, leading to release of toxic Cr(VI) species and calls for strict analytical control of Cr(III) and. Taking into account high oxidation power and chemical activity of Cr(VI) as well as its lower concentrations in comparison with Cr(III) species, the analytical procedures developed should ensure fast determination of Cr(VI) on site, during the sampling process. From such a point of view, the direct methods developed for
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