Electrochromatography pressurized flow

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). 

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

Several different analytical and ultra-micropreparative CEC approaches have been described for such peptide separations. For example, open tubular (OT-CEC) methods have been used 290-294 with etched fused silicas to increase the surface area with diols or octadecyl chains then bonded to the surface.1 With such OT-CEC systems, the peptide-ligand interactions of, for example, angiotensin I-III increased with increasing hydrophobicity of the bonded phase on the capillary wall. Porous layer open tubular (PLOT) capillaries coated with anionic polymers 295 or poly(aspartic acid) 296 have also been employed 297 to separate basic peptides on the inner wall of fused silica capillaries of 20 pm i.d. When the same eluent conditions were employed, superior performance was observed for these PLOT capillaries compared to the corresponding capillary zone electrophoresis (HP-CZE) separation. Peptide mixtures can be analyzed 298-300 with OT-CEC systems based on octyl-bonded fused silica capillaries that have been coated with (3-aminopropyl)trimethoxysilane (APS), as well as with pressurized CEC (pCEC) packed with particles of similar surface chemistry, to decrease the electrostatic interactions between the solute and the surface, coupled to a mass spectrometer (MS). In the pressurized flow version of electrochromatography, a pLC pump is also employed (Figure 26) to facilitate liquid flow, reduce bubble formation, and to fine-tune the selectivity of the separation of the peptide mixture. 

Figure 26 Instrumentation Design for Pressurized Flow Electrochromatography of Peptides...

Two successful approaches of pressurization are known (i) Both the inlet and the outlet buffer vial are constantly pressurized [10-13]. (ii) Pressure can be applied either to the inlet [9,14-18] or the outlet end of the capillary [5,6], This technique is called pressure supported or pressure assisted electrochromatography (other synonyms are pressurized CEC, pressurized flow CEC), pressure electrochromatography (PEC), pseudoelectrochromatography (pEC) or electro-HPLC [9,14,15,19-21]). 

A variation of gradient CEC is pressurized-flow CEC or PEC (pressurized flow electrochromatography). A pump forms the gradient and then allows part of this pressurized flow to pump the mobile phase through the packed bed. In this way, one can perform isocratic or gradient CEC with part of the mobile-phase driving force being pumped, part electrophoretic and part electroosmotic flows [1,8,10]. 

Eimer, T., Unger, K.K., and Van der Greef, J., Selectivity tuning in pressurized-flow electrochromatography, Trends Anal. Chem., 15, 463, 1996. 

Krull, I. S., Stevenson, R., Mistry, K., and Schwarz, M. E. Capillary Electrochromatography and Pressurized Flow Capillary Electrochromatography An Introduction, HNB Publishing New York, 2000. 

Kitagawa, S. Tsuji, A. Watanabe, H. Nakshima, M. Tsuda, T. Pressurized flow-drive capillary electrochromatography using ion exchange resins. J. Micro. Separ. 1997, 9 (5), 347-356. 

Source From Capillary Electrochromatography and Pressurized Flow Capillary Electrochromatography An Introduction ... 

Eimer, T. Unger, K.K. Tsuda, T. Pressurized flow electrochromatography with reversed phase capillary columns. Fresenius J. Anal. Chem. 1995, 352, 649. 

In order to improve robustness and suppress bubble formation [23], pressurized flow generated by an LC pump was introduced as pressurized flow electrochromatography (PEC). Additionally it has a benefit with respect to retention time, since EOF is now superimposed by pressurized flow. Applied voltage and pressure are two tunable parameters for the adjustment of selectivity in PEC [18,66]. Most important, it is amendable for the gradient elution technique similarly to conventional HPLC, hence with PEC the promises of CEC can be fully exploited [67]. 

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. 

DGE a AC AMS APCI API AP-MALDI APPI ASAP BIRD c CAD CE CF CF-FAB Cl CID cw CZE Da DAPCI DART DC DE DESI DIOS DTIMS EC ECD El ELDI EM ESI ETD eV f FAB FAIMS FD FI FT FTICR two-dimensional gel electrophoresis atto, 10 18 alternating current accelerator mass spectrometry atmospheric pressure chemical ionization atmospheric pressure ionization atmospheric pressure matrix-assisted laser desorption/ionization atmospheric pressure photoionization atmospheric-pressure solids analysis probe blackbody infrared radiative dissociation centi, 10-2 collision-activated dissociation capillary electrophoresis continuous flow continuous flow fast atom bombardment chemical ionization collision-induced dissociation continuous wave capillary zone electrophoresis dalton desorption atmospheric pressure chemical ionization direct analysis in real time direct current delayed extraction desorption electrospray ionization desorption/ionization on silicon drift tube ion mobility spectrometry electrochromatography electron capture dissociation electron ionization electrospray-assisted laser desorption/ionization electron multiplier electrospray ionization electron transfer dissociation electron volt femto, 1CT15 fast atom bombardment field asymmetric waveform ion mobility spectrometry field desorption field ionization Fourier transform Fourier transform ion cyclotron resonance... 

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]. 

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. 

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