Gold nanoparticle capped citrate as a ligand for chromium (III) ion: optimization and its application in contaminated tap water

Citrate-capped gold nanoparticle (GNP) was used as a ligand for chromium chelating, and chromium ions reaction led to GNP aggregation. The color change of GNP by aggregation in the presence of chromium is a simple and rapid colorimetric test for these ions in an aqueous solution. GNP capped citrate was prepared by the citrate method and characterized by TEM, and its particle size was 20 nm. Also, the surface plasmon resonance (SPR) peak was 520 nm. In the presence of chromium ions, the color of GNP at 520 nm was shifted to 650 nm because of aggregation to give a signal as a ratio of A650/520 more than one and proportional with chromium concentration directly. The optimum conditions were studied to obtain the high signal represented by the volume of GNP, reaction kinetic of A650 with time, selectivity, and interferences of Zn(II), Fe(III), Fe(II), Sn(II), Ni(II), Ca(II), Al(III), Sr(II), Cu(II), Mn(II), Co(II), Mg(II), Ag(I), and Pb(II) ions. The calibration curve is linear in the range of 100–500 ppb, and the regression was 0.9951 and applied on tap water chromium ions in the same range in the regression of 0.95. This method was simple, rapid reaction, consumed low volumes of sample, and had low detection limits. It can be recommended as a new method for chromium (III) detection in aqueous solutions.