Rapid Capillary Electrophoretic Method for Trace Chromium Speciation Using a Zwitterionic Isoelectric Polymer Coated Capillary and Photodiode Array Detection

A capillary electrophoretic method has been developed for the rapid screening of water samples for chromium (III) and chromium (VI). Chromium (III) and (VI) were separated as the anionic species, chromate and chromium pyridinedicarboxylate (CrL 2 -1), utilising simple precapillary complexation with 2,6-pyrinedicarboxylic acid (PDCA). The two species were separated using a 30 mM phosphate buffer (pH 6.4) containing 10 mM of N-carboxymethylated polyethyleneimine (CMPEI) to totally suppress the EOF. The relatively high buffer concentration allowed large sample volumes to be injected electrokinetically without introducing substantial peak broadening. Using a short 31 cm capillary, chromate, excess PDCA and chromium-PDCA were separated in under 2.5 min, without interference from other matrix anions or cations present in nonsaline natural water samples. Photodiode array detection allowed the two chromium species to be simultaneously monitored at their optimum absorbance wavelengths (270 and 370 nm) and allowed enhanced peak identification. Detector response was shown to be linear over the range 0.2-1.6 mg/L and detection limits for both species of 20 μg/L in standard solutions were possible.