Simultaneous determination of trivalent and hexavalent chromium in environmental waters by ion chromatography with derivatization reagent injection-control technique

A new method for the simultaneous determination of trivalent and hexavalent chromium in environmental waters was developed by ion chromatography with derivatization reagent injection-control technique using 2, 6-pyridine dicarboxylic acid and 1, 5-diphenyl carbonhydrazide after pre-and post-column derivatization. The injection time of 1, 5-diphenyl carbonhydrazide was controlled by six port valve after finishing the trivalent chromium determination, which avoided the interference of 2, 6-pyridine dicarboxylic acid on the trivalent chromium determination and lowered the detection limit of trivalent chromium from 0.17 mg·L -1 to 4.9 μg·L -1 . The parameters such as the detection wavelength, eluent concentration, flow rate of derivation agent and volume of quantitative ring were optimized. The peak area repeatability of 0.72 mg·L -1 Cr(Ⅲ) and 0.24 mg·L -1 Cr(Ⅵ) was 0.34% and 0.65%, respectively, and the detection limit of hexavalent chromium was 3.2 μg·L -1 . Cr(Ⅲ) and Cr(Ⅵ) contents in nine environmental water samples such as polluted wastewater, electroplating wastewater before and after treatment, and river waters were determined by the established method. The spiked recoveries of Cr(Ⅲ) were between 83.7% to 117.0% with spiked levels of 0.02-0.48 mg·L -1 , and the recoveries of Cr(Ⅵ) were between 96.0% to 104.5% with spiked levels of 0.02-0.24 mg·L -1 , respectively.