A Simple High Performance Capillary Electrophoretic Method for the Simultaneous Determination of Chromium and Vanadium in Real and Environmental Samples
A very simple, selective and highly sensitive capillary electrophoretic method for the simultaneous determination of chromium(III) and vanadium(V) with Mo(VI)-P(V) reagent has been developed. A Mo(VI)-P(V) reagent reacted with a mixture of trace amounts of chromium(III) and vanadium(V) to form the stable heteropolyanions in 0.1M acetate buffer (pH 2.0) at room temperature (25±5) 0C. Both anionic forms of chromium(III) and vanadium(V) can be determined simultaneously by capillary electrophoresis with direct UV detection at 254nm. The pre-column complex formation reaction is instantaneous and absorbance remains stable for 24h. Linear calibration curves were obtained in the concentration ranges of 0.06 - 60 mgL-1 and 0.05 - 80 mgL-1 of Cr(III) and V(V), respectively; the detection limits were 6.0 g L-1 and 5.0 g L-1 for Cr(III) and V(V), respectively. The influence of several experimental parameters on both sensitivity and efficiency was investigated. The interference from over 60 cations, anions and complexing agents has been studied at 1 mgL-1 of Cr and V, respectively. The unique selectivity and sensitivity of the method allowed its direct application to the determination of Cr and V in complex matrices of certified reference materials and synthetic seawater.. The developed was also used successfully in the determination of chromium and vanadium in environmental waters (tap and lake). The method has high precision and accuracy (s = ±0.02 for 0.5 mg L-1).
Chromium and / or vanadium in trace amounts is important industrially , as a : biological nutrient , epidemiological preventive, toxicant , environmental pollutant  and occupational hazard . Therefore, the accurate determination of the metal at trace and ultra-trace levels is important. Simultaneous determination of chromium and vanadium in complicated matrices is a very difficult task that achieved using sophisticated and / or high cost instruments such as anodic stripping voltammetry with ICP-MS detection , ICP-AES , NAA , HPLC , XRF  and AAS . However, the relatively high costs [7-12], high detection limits [10-12] and poor recoveries and precisions are common disadvantages. Capillary Electrophoresis (CE) is being increasingly applied for the determination of metal ions, primarily because of its great flexibility and easy implementation . Separations of metal ions that exist in a free, uncompleted form are comparatively rare in the practice of CE because the absolute mobility values of most of the metal ions in their free form do not differ enough from one to another to envision electrophoretic separations of practical interest. Obviously, complexation presents the most valuable approach for performing metal speciation and offers a powerful means of manipulation and separation selectively.
The present study was undertaken to apply the Mo(VI)-P(V) reagent method to simultaneous CE determination of chromium(III) and vanadium(V), because their yellow color complexes were kinetically stable and possessed different mobility’s. The method was based on the reaction of non-absorbent Mo(VI) P(V) reagent in 0.1 M acetate buffer of pH 2.0 with Cr(III) and V(V) to produce a highly UV-absorbent yellow complex product, followed by direct measurement of the absorbance in aqueous solution. With suitable masking, the reaction can be made highly selective and the reagent blank does not show any UV-absorbance.