Separation and Determination of Chromium(VI), Molybdenum(VI) and Vanadium(V) in Steel Using Capillary Ion Electrophoresis with Direct UV Detection

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Abstract
The application of capillary ion electrophoresis to the separation and determination of chromium (VI), molybdenum (VI) and vanadium (V) with direct on-column UV detection at 254 nm is described. Using a cathodic injection and anodic detection scheme, Cr(VI), Mo(VI) and V(V) were separated in about 4 min in a fused silica capillary column, with a phosphate buffer of pH 12.0, at an applied voltage of 15 KV, followed by direct UV detection. An electro-osmotic flow modifier, namely a cetyltrimethylammonium bromide (CTAB), is necessary to shorten the migration times of these ions. Incorporating citrate into the electrophoretic buffer markedly improves the sensitivity and efficiency. The influence of several experimental parameters on both sensitivity and efficiency was investigated. Linearity of calibration graphs is observed for about three orders of magnitude with sub-ppm detection limits. The applicability of the method to the analysis of steel samples is demonstrated. The peak response is strongly dependent upon ionic strength of sample solution and appropriate measurers, such as standard addition, must be used to account for differences in standard and sample conductance.