Colorimetric speciation analysis of chromium using 2-thiobarbituric acid capped silver nanoparticles

In the present work, 2-thiobarbituric acid (TBA)-capped silver nanoparticles (AgNPs) have been introduced as a novel nanoprobe in the construction of a sensitive and selective colorimetric sensor for Cr(iii) and Cr(vi) ions. Cr(iii) can be linked to TBA on the AgNP surface via -N or -OH groups and form a bridge between two or more AgNPs causing their aggregation. This phenomenon leads to a dramatic color change in TBA-AgNPs from yellow to pinkish red. UV-Vis spectrophotometry, FT-IR and transmission electron microscopy (TEM) were utilized for quantitative analyses, characterization of modified AgNPs and determination of the interaction mechanism of TBA-AgNPs - Cr(iii). The color change depended on the concentration of Cr(iii) and the ratio of UV-Vis absorption intensity at 520 nm to that at 418 nm (A520/A418) was linearly proportional to the concentration of Cr(iii) from 0.012 to 3.25 mg L-1 (LOD = 8.4 µg L-1). To eliminate or reduce the interference of other cations in Cr(iii) determination, EDTA was used as a masking agent at pH 6.5. Moreover, the developed method was used for the determination of Cr(vi) in the presence of ascorbic acid (AA) (as a reducing agent) in the concentration range of 0.20 to 1.40 mg L-1. The proposed probe was successfully applied for the determination of Cr(iii) and Cr(vi) in cement factory wastewater.