Further development of capillary electrophoresis for the quantitative determination of small inorganic anions

Factors influencing the separation and indirect UV absorbance detection of common inorganic anions using capillary zone electrophoresis (CZE) have been investigated. Initially a number of different aspects of indirect background electrolyte (BGE) systems were studied, with the resultant observations indicating the requirements of an 'ideal' BGE system for the separation and detection of common inorganic anions in water samples. In addition to the above the correct use of buffers within BGE used with indirect detection was also investigated in order to improve the robustness of inorganic anion determinations and hence quantitative performance Both commercially available and freshly prepared novel polymeric isoelectric buffer systems were investigated. Following the above investigations, studies of detector performance for indirect detection were earned out In a joint study with workers from the University of Tasmania, the optical charactenstics of on-capillary photometnc detectors for capillary electrophoresis were evaluated and five commercial detectors were compared. Plots of sensitivity (absorbance/concentration) versus absorbance obtained with a suitable testing solution yielded both the linear range and the effective pathlength of each commercial detector. With the above results indicating some room for improvement with certain commercial detectors, the project then focused on the use and characterisation of a UV light emitting diode (LED) based detector. LEDs are known to be excellent light sources for detectors in liquid chromatography and capillary electromigration separation techniques. Here, a UV LED was investigated as a simple alternative light source to standard mercury or deuterium lamps for use in indirect photometnc detection of inorganic anions using a chromate BGE. The noise, sensitivity and linearity of the LED detector were evaluated and all exhibited supenor performance to the mercury light source (up to 70% decrease in noise, up to 26 2% increase in sensitivity, and over 100% increase in linear range). Using the LED detector with a simple chromate/diethanolamine BGE, limits of detection for the common inorganic anions, Cl‘, N03, S042, F and PO^, ranged from 3-14pg/L without using sample stacking. Finally, a useful application of the polymenc isoelectric buffer (mentioned above) was developed The rapid simultaneous separation of Cr(VI) and Cr(lll) - pyndmedicarboxylate complex (pre-capillary complexation) was obtained using a phosphate running buffer (pH 6 2) containing the synthesised polymenc isoelectnc reagent. Excellent peak shapes were obtained, with no sign of interaction of the analytes with the components of the BGE. Photodiode array detection was used, which offered the advantage of peak identification via its UV spectrum and also allowed electropherograms to be recorded at two specific wavelengths, namely 365 nm for Cr(VI) and 260 nm for the Cr(lll) complex, thus eliminating interferences from common matnx anions. Injection conditions were optimised in order to establish detection limits, which were below 0 1 mg/L for standard solutions. Lmeanty and other analytical performance charactenstics were also investigated. Finally, real nver water samples were analysed for the Cr(VI) and Cr(lll) species