Micellar electrokinetic chromatography development

A variety of formats and options for different types of applications are possible in CE, such as micellar electrokinetic chromatography (MEKC), isotachophoresis (ITP), and capillary gel electrophoresis (CGE). The main applications for CE concern biochemical applications, but CE can also be useful in pesticide methods. The main problem with CE for residue analysis of small molecules has been the low sensitivity of detection in the narrow capillary used in the separation. With the development of extended detection pathlengths and special optics, absorbance detection can give reasonably low detection limits in clean samples. However, complex samples can be very difficult to analyze using capillary electrophoresis/ultraviolet detection (CE/UV). CE with laser-induced fluorescence detection can provide an extraordinarily low LOQ, but the analytes must be fluorescent with excitation peaks at common laser wavelengths for this approach to work. Derivatization of the analytes with appropriate fluorescent labels may be possible, as is done in biochemical applications, but pesticide analysis has not been such an important application to utilize such an approach. 

Micke, G. A., Fujiya, N. M., Tonin, F. G., de Oliveira Costa, A. C., and Tavares, M. F. M. (2006). Method development and validation for isoflavones in soy germ pharmaceutical capsules using micellar electrokinetic chromatography. /. Pharm. Biomed. Anal. 41(5), 1625—1632. 

Dedicated applications of capillary zone electrophoresis (CZE) coupled to MS are discussed, particularly in the field of drug analysis. Development of other capillary-based electrodriven separation techniques such as non-aqueous capillary electrophoresis (NACE), micellar electrokinetic chromatography (MEKC), and capillary electrochromatography (CEC) hyphenated with MS are also treated. The successful coupling of these electromigration schemes with MS detection provides an efficient and sensitive analytical tool for the separation, quantitation, and identification of numerous pharmaceutical, biological, therapeutic, and environmental compounds. 

The early phase of development can be characterized by a transfer of concepts from conventional CE to the planar format, such as capillary gel electrophoresis, micellar electrokinetic chromatography, sample stacking and pre- and postcolumn sample derivatization. Emphasis was laid on the demonstration of the specific advantages mainly from the separation science point of view. With only very few exceptions, detection has received much less attention yet. LIF detection with confocal imaging has been used in most of the early work owing to its high sensitivity and its relatively easy implementation. If not explicitly mentioned otherwise, all experiments described in the following sections were carried out with LIF detection [28,29]. 

Chromatographic and related electrophoretic methods for the separation of transition metal complexes or their ligands were reviewed . Micellar electrokinetic chromatography (MEKC) presents a new development in the field of capillary zone electrophoresis (CZE). The use of micellar solutions expands the application of CZE to electronically neutral solutes, as well as charged ones. Thus, electrically neutral / -diketonates Cr(dik)3, Co(dik)3, Rd(dik)3, Pt(dik)2 and Pd(dik)2 were separated by CZE in micellar solutions of sds. A linear log-log relationship was found between the distribution coefficient and the partition coefficient of the complex between dodecane and water, which was used for prediction of both the distribution coefficients and the migration times of different metal complexes . 

Various papers related to the simultaneous determination of creatinine and uric acid can be found in the hterature. Several authors have developed capillary zone electrophoresis (CZE) methods for simultaneous analysis of these compounds in urine. The CE analysis of these renal markers offers some advantages when compared with chromatography, such as shortened separation time, reduced reagent consumption, and increased resolution. Capillar micellar electrokinetic chromatography has been applied to the simultaneous separation of creatinine and uric acid in human plasma and urine. However, chromatographic techniques are widely accepted for the determination of these compounds. Reversed-phase and ion... 

Capillary electrophoresis (CE) is a powerful separation technique. It is especially useful for separation of ionic compounds and chiral mixtures. Mass spectrometry has been coupled with CE to provide a powerful platform for separation and detection of complex mixtures such as combinatorial libraries. However, the full potential of CE in the application of routine analysis of samples has yet to be realized. This is in part due to perceived difficulty in the use of the CE technique compared to the more mature techniques of HPLC and even SFC. Dunayevskiy et al. [136] analyzed a library of 171 theoretically disubstituted xanthene derivatives with a CE/ESI-MS system. The method allowed the purity and makeup of the library to be determined 160 of the expected compounds were found to be present, and 12 side products were also detected in the mixture. Due to the ability of CE to separate analytes on the basis of charge, most of the xanthene derivatives could be resolved by simple CE-MS procedures even though 124 of the 171 theoretical compounds were isobaric with at least one other molecule in the mixture. Any remaining unresolved peaks were resolved by MS/MS experiments. The method shows promise for the analysis of small combinatorial libraries with fewer than 1000 components. Boutin et al. [137] used CE-MS along with NMR and MS/MS to characterize combinatorial peptide libraries that contain 3 variable positions. The CE-MS method was used to provide a rapid and routine method for initial assessment of the construction of the library. Simms et al. [138] developed a micellar electrokinetic chromatography method for the analysis of combinatorial libraries with an open-tube capillary and UV detection. The quick analysis time of the method made it suitable for the analysis of combinatorial library samples. CE-MS was also used in the analysis... 

To date, the use of chemometrics for method development and robustness testing has been published for all areas of CE, including capillary zone electrophoresis (CZE), capillary electrokinetic chromatography (EKC) using chiral selectors for enantioseparations, micellar electrokinetic chromatography (MEKC), and microemulsion electrokinetic chromatography (MEEKC). A comprehensive description can be found in Chapters 5 and 13 as well as in recent reviews (6-11). Several monographs on chemometrics in analytical chemistry have been published such as References 12-14. This chapter will... 

FIGURE 15.1. Schematic representation of the steps underlying QSRR development in micellar electrokinetic chromatography. 

Several modes of CE have been described in the literature over past decade [6, 7], The most common are open tubular or capillary zone electrophoresis (CZE), micellar electrokinetic chromatography (MEKC), microemulsion elec-trokinetic chromatography (MEEKC), capillary electrochromatograpy (CEC), capillary gel electrophoresis, capillary isoelectric focusing and capillary iso-tachophoresis. Three recent reviews by Watzig [113], Tagliaro etal. [114] and Riekkola etal. [115] summarise the current method development options available to manipulate selectivity. In pharmaceutical analysis, CZE, MEKC, MEEKC and CEC are commonly used. 

Mohna, M. and Silva, M., Micellar electrokinetic chromatography current developments and future. 

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