Pressurized capillary electrochromatography

Applied pressure during CEC can decrease the separation time [30]. In this study the pressurized capillary electrochromatography (pCEC) coupled to NMR separated and identified a mixture of unsaturated fatty acid esters. The analysis time has been reduced by factor of 10 compared to nonpressurized CEC. 

P. Gfrorer, L.-H. Tseng, E. Rapp, K. Albert, and E. Bayer, Inflnence of pressnre upon coupling pressurized capillary electrochromatography with nuclear magnetic resonance spectroscopy. Anal. Chem. 73 (2001), 3234-3239. 

Wu, X., et al., Rapid separation and determination of carbamate insecticides using isocratic elution pressurized capillary electrochromatography, Electrophoresis, 27, 768, 2006. 

Wu, J.T., et al.. Protein digest analysis by pressurized capillary electrochromatography using an ion trap storage/reflectron time-of-flight mass detector. Anal. Chem., 69, 2908,1997. 

Liu, S., et al.. On-line coupling of pressurized capillary electrochromatography with end-column amperometric detection for analysis of estrogens. Electrophoresis, 26, 2342, 2005. 

Nagaraj, S. and Karnes, H.T., Visible diode laser induced fluorescence detection of doxorubicin in plasma using pressurized capillary electrochromatography, Biomed. Chromatogr, 14, 234, 2000. 

Rapp, E., Jakob, A., Schefer, A. B., Bayer, E., and Albert, K., Sphtless on-hne coupling of capiUary high-performance liquid chromatography, capillary electrochromatography and pressurized capillary electrochromatography with nuclear magnetic resonance spectroscopy. Anal. Bioanal. Chem., 376, 1053, 2003. 

Huang P, Jin X, Chen Y, Srinivasan JR, Lubman DM (1999) Use of a mixed-mode packing and voltage tuning for peptide mixture separation in pressurized capillary electrochromatography with an ion trap stor-age/reflection time-of-flight mass spectrometer detector. Anal Chem 71 1786-1791... 

Lin X, Wang J, Li L, Wang X, Lu H, Xie Z (2007) Separation and determination of five major opium alkaloids with mixed mode of hydrophilic/cation-exchange monolith by pressurized capillary electrochromatography. J Sep Sci 30(17) 3011—3017... 

A new analytical method, pressurized capillary electrochromatography (pCEC) with AD using 1.5 mm reversed phase nonporous silica packed columns has been developed for the rapid separation and determination of four Sudan dyes in hot chili [36]. The influence of several experimental parameters on the retention behavior has been investigated. The electrochemical oxidation of Sudans I-FV separated by pCEC can be reliably monitored with a carbon electrode at 0.95 V (vs. Ag/AgCl). Fast and efficient separation of the analytes was achieved within 7 min by pCEC under the optimum conditions. To evaluate the feasibility and reliability of this method, the proposed pCEC-AD method was further demonstrated with hot chili samples spiked with Sudan dyes. 

Capillary Electrochromatography Another approach to separating neutral species is capillary electrochromatography (CEC). In this technique the capillary tubing is packed with 1.5-3-pm silica particles coated with a bonded, nonpolar stationary phase. Neutral species separate based on their ability to partition between the stationary phase and the buffer solution (which, due to electroosmotic flow, is the mobile phase). Separations are similar to the analogous HPLC separation, but without the need for high-pressure pumps, furthermore, efficiency in CEC is better than in HPLC, with shorter analysis times. 

Monolithic columns, formed from the co-polymerization of divinylbenzene and vinylbenzyl chloride or styrene, were observed to be resistant to bubble formation.11 Application of pressure in electrochromatography, discussed below, also reduces bubble formation. A massively parallel detector capable of scanning up to 1000 capillaries using planar confocal fluorescence has been used for DNA sequencing.1213 Recovery of fluorescence following pho-tobleaching has been used to measure DNA mobility in agarose gel.14... 

I.S. Krull, R.L. Stevenson, K. Mistry and M.E. Swartz, Capillary Electrochromatography and Pressurized Flow Capillary Electrochromatography, HNB Publishing, New York, NY (2000). 

Pressurization of the vials at both the inlet and the outlet ends of the CEC capillary column packed with particles to about 1.2 MPa is required to prevent formation of bubbles that lead to a noisy baseline. Typically, equal pressure of an inert gas such as nitrogen is applied to both vials to avoid flow that would otherwise occur resulting from the pressure difference. Hydraulic pressure applied only at the inlet end of the capillary column is occasionally used in pressure-assisted electrochromatography [38,39]. 

Krull IS, Stevenson R, Mistry K, Schwarz ME (2000) Capillary electrochromatography and pressurized flow capillary electrochromatography an introduction. HNB Publishing, New York... 

Nakashima, R., Kitagawa, S., Yoshida, T, and Tsuda, T. (2004). Study of flow rate in pressurized gradient capillary electrochromatography using splitter and separation of peptides using an amide stationary phase. J. Chromatogr. A 1044, 305—309. 

Zheng, J., and Shamsi, S. A. (2006). Capillary electrochromatography coupled to atmospheric pressure photoionization mass spectrometry for methylated benzo[a]pyrene isomers. Anal. Chem. 78, 6921-6927. 

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... 

In addition to high-performance liquid chromatography (HPLC), the chiral resolution using CMPAs was also carried out by supercritical fluid chromatography (SFC) [91] and capillary electrochromatography (CEC) [92-98]. Salvador et al. [91] used dimethylated /1-cyclodextrin as the mobile phase additive on porous graphite carbon as the solid phase for the chiral resolution of tofizopam, warfarin, a benzoxazine derivative, lorazepam, flurbiprofen, temazepam, chlorthalidone, and methyl phehydantoin by SFC. The authors also studied the effect of the concentration of dimethylated /1-cyclodextrin, the concentration of the mobile phase, the nature of polar modifiers, outlet pressure, and the column temperature on the chiral resolution. 

Electrodriven separations, such as capillary electrophoresis (CE) and capillary electrochromatography (CEC), are based on the different electrophoretic mobilities in an electric field of the molecules to be separated. They provide a higher separation efficiency then conventional HPLC since the electrophoretic flow (EOF) has a plug-flow profile. Whereas the mobile phase in CE is driven only by the electro-osmotic flow, it is generated in CEC by a combination of EOF and pressure. CEC has a high sample capacity which favours its hyphenation with NMR. 

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