Ion Chromatography−Photodiode Array UV−Visible Detection of Cr(III) Hydrolytic Polymerization Products in Pure and Natural Waters

Abstract

Hydrolytic polymerization of Cr(III) aqua ions was investigated in pure Milli-Q water and in surface waters, using Sephadex column fractionation followed by nonsuppressed ion chromatography (IC) with UV detection at λ 462 nm. Pure and natural waters spiked with 0.04 M Cr(III) were fractionated on Sephadex columns into four fractions using eluents with increasing ionic strength. Fractions were analyzed for total Cr by atomic absorption, and recoveries ranged from 94 to 101%. Fractions representing monomeric and low oligomeric Cr (III) species were subjected to IC using a low-capacity mixed resin column and a mobile phase consisting of 2 M NaClO₄/0.02 M HClO₄ at pH 4.50. Monomeric Cr(III) species were detected in the IC chromatograms of the freshly prepared Cr(III) solution with capacity factors (k‘) ranging from 0.05 to 0.40. In the 3-days-aged samples, dimeric and trimeric peaks with k‘ = 1.09 and 1.70, respectively, were detected. Monomeric, dimeric and trimeric Cr(III) peaks collected from the IC preparative experiments were scanned between λ 200 and 600 nm, using a photodiode array detector. The UV−visible spectral characteristics of the monomer, dimer, and trimer confirmed their identities. The trimeric Cr(III) peak was more predominant in the IC chromatograms of the surface water and accounted for 6.5−35.9% of the total Cr(III) in the samples.