Achievements capillary zone electrophoresis

In its simplest form capillary electrophoresis is termed capillary zone electrophoresis . The conditions used in this type of analysis are relatively simple and the mobile phase used consists of a buffer with various additives. Many applications focus on critical separations which are difficult to achieve by HPLC. In many cases it is difficult to explain completely the types of effects produced by buffer additives. 

Nitroaromatic explosives and other nitrated organic explosives are under the normal conditions neutral compounds and therefore cannot be separated directly by capillary zone electrophoresis (CZE) technique. Another separation vector must be introduced in order to achieve the resolution between the solutes. Micellar electrokinetic chromatography (MEKC) is typically employed on microchip scene for separation of nitroaromatic explosives. 

Although methods based on capillary zone electrophoresis have not achieved the popularity of HPLC methods, a few studies have been reported. The defining characteristics of these are summarized in Table 5. 

Direct control of the EOF in capillary zone electrophoresis can be obtained by using an external electric field. The EOF may be increased, decreased, or even reversed in the fused silica capillaries by the application of a separate potential field across the wall of the capillary. Further, the zeta potential can be changed at any time during the analysis to achieve innovative separation results. 

Although in some instances it is possible to determine low concentrations of inorganic anions by capillary zone electrophoresis [24], problems arise when the concentrations of the sample constituents vary considerably. This is due to the fact that the determination of microconstituents may require the sample load to have an impact on both the migration velocities and the resolution of analytes [25], The use of indirect detection, as preferred in the case of inorganic anions [24,26] is also less capable of achieving adequate load capacities. 

An approach suitable for drug screening alternative to MEKC was proposed by Chee and Wan (1993), who used capillary zone electrophoresis (CZE) with 50 mAf phosphate buffer pH 2.35 in a 75 / m i.d. (60 cm long) bare silica capillary. In 11 minutes, they achieved the separation of 17 basic drugs of potential forensic interest methapyrilene, brompheniramine, amphetamine,... 

Capella-Peiro et al. (28) used a 3 full factorial design to optimize the capillary zone electrophoresis (CZE) separation of a group of seven antihistamines (brompheniramine, chlorpheniramine, cyproheptadine, diphenhydramine, doxylamine, hydroxyzine, and loratadine). In this case, critical parameters such as pH (a concentration of 20 mM phosphate was kept constant in all the experiments) and the applied voltage were studied to evaluate their effect on the resolution and efficiency. Maximum response was achieved at pH 2.0 and an applied voltage of 5 kV. After a repeatability study to check the precision of the electrophoretic method, as well as a suitable calibration, the usefulness of this optimized method was demonstrated through the determination of the listed histamines in pharmaceuticals, urine, and serum samples (recoveries were in agreement with the stated contents). Urine samples were diluted and directly injected in the CE system, while serum samples were previously extracted by means of a solid-phase extraction (SPE) procedure. 

CEC is a hybrid separation technique that combines capillary HPLC (50-pm capillary diameter) with capillary zone electrophoresis, and its main advantage is the enormous number of theoretical plates that can be achieved. This is a result of the uniform, plug-like flow that electro-endoosmosis generates and the fact that this allows the use of very small particles (3 pm diameter). The technology is at an early stage of development (as there are problems inherent in packing columns of such small particle size f9J), but has already resulted in efficiency values of up to 387,000 theoretical plates per meter (10). 

SPE followed by CZE/UV and optimized capillary zone electrophoresis (CZE) with ESI-MS detection was used to determine monosulfonated (Mordant Yellow 8) and a series of disulfonated azo dyes (Acid Red 1, 13, 14 and 73, Mordant Red 9, Acid Yellow 23 and Acid Blue 113) quantitatively in spiked (3 mg T of each compound) groundwater samples and industrial effluents [423]. Azo dyes besides pesticides and herbicides were determined by ion trap MS interfaced by a commercial ESI to the LC-device. By adjusting the repeUer voltage (in-source CID) and doing MS/MS in the ion trap for [M-i-H] ions CID spectra were obtained. With onhne ESI-LC-ITMS, detection limits of O.l-l.O ng could be easily achieved. IT-MS/MS and ESI-CID data were provided and compared [424]. ESI was used for coupling CZE and MS or LC and MS to analyse SPE concentrated sulfonated azo dyes and LAS in industrial effluents. CZE-MS offered higher separation power and... 

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