Evaluation Of Chromium Speciation In Wastewater Samples By Ionic Liquid Combined With High Erformance Liquid Chromatography

A simple method has been proposed for the determination of chromium species by high-performance liquid chromatography (HPLC) after preconcentration by the ionic liquid,1-butyl-3-methyimidazoliumhexafluorophosphate ([C4MIM][PF6]). The simultaneous preconcentration of Cr(VI) and Cr(III) in wastewater was achieved with ammonium pyrrolidinedithiocarbamate (APDC) as the chelating agent and the ionic liquid [C4MIM][PF6] as the extractant. Baseline separation of the APDC chelates of Cr(Ⅲ) and Cr(VI) was realised on a RP-C18column using a mixture of methanol-acetonitrile-water (53:14:33, v/v) as the mobile phase at a flow rate of1.0mL·min-1. The influences of pH, reaction time, APDC concentration and metal ion interference on the complexation and extraction were evaluated. Our results showed that when the linear concentration of Cr(VI) and Cr (Ⅲ) ranged from25to200μg·L-1, their linear correlation coefficients were between0.9977and0.9978, their recoveries ranged from91.8%to95.8%and their relative standard deviations (n=3) were between0.31%and1.8%. Common metal ions in water did not interfere with the determination. This method is a simple, fast, accurate, highly stable and selective method and has successfully been applied to the speciation of chromium in wastewater. In addition, heavy metal ions such as Cd", Ni2+, Cu2+and Hg2+in wastewater was detected successfully using similar system. Baseline separation of the APDC chelates of Cd2+, Ni2+, Cu2+and Hg2+was realised on a RP-C18column using a mixture of methanol-acetonitrile-water (14:53:33, v/v) as the mobile phase at a flow rate of1.0mL·min-1. Several variables such as the concentration of APDC, sample pH, water bath temperature and time were also investigated in detail. In the optimum condition, the linear correlation coefficients of Cd2+, Ni2+, Cu2+and Hg2+were0.996‘0.9982with the concentration range of250‘2000μg·L-1. The relative standard deviations of Cd2+, Ni2+Cu2+and Hg2+were1.7%～8.3%, and their recoveries ranged from90.7%to102%. This method has successfully been applied to the detection of Ni2+, Cu2+in water of Ningbo Institute of Technology’s river, providing scientific basis to realize the simultaneous detection of heavy metal ions in water.