Micellar HPLC chromatography

Figure 15.4 Separation of mixtures of beta-blockers by using micellar HPLC, employing the following mobile phases (a) 0.12M SDS, 5% propanol, 0.5% tiiethylamine (b) 0.06 M SDS, 15% propanol (c) 0.1 IM SDS, 8% propanol. Adapted from Journal of Chromatographic Science, 37, S. Carda-Broch et al., Analysis of urine samples containing cardiovascular drugs by micellor liquid chromatography with fluorimetric detection , pp. 93-102, 1999, with permission from Preston Publications, a division of Preston Industries, Inc.

Pluym et al. compared the use of CE to that of HPLC in chemical and pharmaceutical quality control. They stated that CE could be considered as a complementary technique to HPLC because of its large separation capacity, its simplicity, and its economical benefits. Jimidar et al. decided that CE offers high separation efficiency and can be applied as an adjunct in HPLC method validation. Mol et al. evaluated the use of micellar electrokinetic chromatography (MEKC) coupled with electrospray ionization mass spectrometry (ESI—MS) in impurity profiling of drugs, which resulted in efficient separations. 

Versatility of CE separation modes zone electrophoresis (CZE), micellar electrokinetic chromatography (MEKC), gel electrophoresis (CGE), isotachophoresis (CITP), isoelectric focusing (CIEF), capillary electrochromatography (CEC, a hybrid with HPLC), and last but not least Affinity CE (ACE)... 

Micellar etectrokinetic chromatography electrophoresis with micelles acting as pseudostationary phase Capillary electrochromatography similar to HPLC, except mobile phase is driven by electroosmosis instead of pressure... 

The scope of this review is limited to the hop-borne a- and /3-acids and to products derived from them that have appreciable commercial relevance. Thus, the liquid chromatography of the iso-a-acids and their chemically modified counterparts as well as of the hulupones will be considered. By far the major focus here will be HPLC analyses, but other methodologies that have been applied (countercurrent distribution, gas chromatography, supercritical-fluid chromatography, thin-layer chromatography, and micellar electrokinetic chromatography) will also be briefly considered. 

Excellent chromatographic performance using micellar electrokinetic chromatography (MEKC) has been demonstrated for the a-, / -, and iso-a-acids. Thus the six major components of a mixture of a- and /3-acids can be baseline resolved within 10 minutes (47). Similarly, the six major iso-a-acids can be baseline resolved within 20 minutes (48). De Keukeleire presented MEKC separations of the p- and tetrahydroiso-a-acids that compared well with conventional HPLC analyses (17). 

Capillary electrochromatography (CEC) is a rapidly emerging technique that adds a new dimension to current separation science. The major "news" in this method is that the hydrodynamic flow of the eluting liquid, which is typical of HPLC, is replaced by a flow driven by electro-endoosmosis. This increases considerably the selection of available separation mechanisms. For example, combinations of traditional processes such as reversed-phase- or ion-exchange- separations with electromigration techniques are now possible. Also, CEC is opening new horizons in the separation of non-polar compounds, and thus represents an alternative to the widely used micellar electrokinetic chromatography. 

CRM for road dust (BCR-723) containing 81.3 2.5 Jg/kg Pt, 6.1 1.9 ig/ kg Pd, and 12.8 1.3 Jg/kg Rh, was introduced [49, 228]. It is widely used for quality control of results obtained in the analysis of environmental materials (e.g., airborne particulate matters, dusts, soils, and sediments). Comparison of results obtained using different analytical procedures and interlaboratory studies are recommended when there is a lack of suitable CRM (e.g., in examination of clinical samples). The use of standards based on real matrices (e.g., saliva, plasma, ultrafiltrates, and lung fluids) instead of synthetic solutions is recommended in such analyses. Difficulties with the identification and quantification of different metal species in examined samples make the reliability of results of great importance. The use of various instrumental techniques for examination of particular samples can be helpful. The application of chromatography, mass spectrometry, and electrochemistry [199] HPLC ICP MS and HPLC MS/MS [156] ESI MS and MALDI [162] micellar electrokinetic chromatography, NMR, and MS [167] AAS, ESI MS, and CD spectroscopy [179] SEC IC ICP MS and EC ESI MS [180] and NMR and HPLC [229] are examples of such approaches. 

A promising alternative to HPLC and TLC is micellar electrokinetic chromatography (MEKC). Pietta et al. (1998a) used a 25 mM tetraborate buffer containing 30 mM sodium dodecyl sulfate (SDS) at pH 8.6 for the separation of CADs. The separation was completed within 20 min with good resolution. The advantage to this method is that the cost of operation is less than HPLC, because organic solvents are not needed. 

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... 

Mesoporous MSU-X silica was synthesized with a two-step pathway, that allowed us to get a high control degree on both the final material shape and the porous size distribution. These materials were developed and tested for separating applications, including HPLC chromatography and ultrafiltration membranes. Both applications show that the specific structure of the Micellar Templated Structures exhibits a new behavior in the separation applications, compared with other materials. They are explained by the combined effect of the silica nature and the specific cylindar pore shape. 

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