Capillary electrophoresis anionic surfactants

Improved resolution of inorganic anions in capillary electrophoresis by modification of the reversed electroos-motic flow and the anion mobility with mixed surfactants,/. Chromatogr. A,... 

High-efficiency separations of FQ-labeled proteins are only achieved in the presence of an anionic surfactant, such as SDS. As a result, capillary isoelectric focusing is not useful for the analysis of these proteins. Instead, we employ capillary sieving electrophoresis and micellar electrokinetic capillary chromatography for our two-dimensional electrophoresis. 

Anions and uncharged analytes tend to spend more time in the buffered solution and as a result their movement relates to this. While these are useful generalizations, various factors contribute to the migration order of the analytes. These include the anionic or cationic nature of the surfactant, the influence of electroendosmosis, the properties of the buffer, the contributions of electrostatic versus hydrophobic interactions and the electrophoretic mobility of the native analyte. In addition, organic modifiers, e.g. methanol, acetonitrile and tetrahydrofuran are used to enhance separations and these increase the affinity of the more hydrophobic analytes for the liquid rather than the micellar phase. The effect of chirality of the analyte on its interaction with the micelles is utilized to separate enantiomers that either are already present in a sample or have been chemically produced. Such pre-capillary derivatization has been used to produce chiral amino acids for capillary electrophoresis. An alternative approach to chiral separations is the incorporation of additives such as cyclodextrins in the buffer solution. 

Micellar electrokinetic capillary chromatography (MECC), in contrast to capillary electrophoresis (CE) and capillary zone electrophoresis (CZE), is useful for the separation of neutral and partially charged species [266,267]. In MECC, a surfactant, usually sodium dodecyl sulfate (SDS), is added to the buffer solution above its critical micellar concentration to form micelles. Although SDS is certainly the most popular anionic surfactant in MECC, other surfactants such as bile salts have proved to be very effective in separating nonpolar analytes that could not be resolved using SDS [268]. 

Baryla, N.E. Lucy, C.A. Simultaneous separation of cationic and anionic proteins using zwitterionic surfactants in capillary electrophoresis. Anal. Chem. 2000, 72 (10), 2280-2289. 

Wu N, Sweedler JV, Lin M. Enhanced separation and deletion of sermn bilirubm species by capillary electrophoresis using a mixed anionic surfactant-protein buffer system with laser-induced fluorescence detection. J Chromatogr B Biomed Appl 1994 654 185-91. 

S. A. Shamsi and N. D. Danielson, Naphthalenesulfonates as electrolytes for capillary electrophoresis of inorganic anions, organic acids, and surfactants with indirect photometric detection. 

Nonaqueous capillary electrophoresis (NACE) involves the separation of analytes in a medium composed of organic solvents. The viscosity and dielectric constants of organic solvents affect both sample ion mobility and the level of EOF. The changes in separation selectivity in nonaqueous conditions contribute to a better separation of some substances that have very small charge-to-mass differences in aqueous phases (linear alkylbenzene sulfonates, or triazines). Further adsorption on the capillary wall and/or ion interactions, which cause solute precipitation (e.g., anionic surfactants with cations), can be avoided using NACE. 

CE is a separation technique that may be an alternative to LC to determine alkyl chain distribution of anionic and cationic surfactants. Most of the studies refer to alkylbenzyldimethylammonium with UV absorbance detection (Figure 2). Other uses of CE include the separation of homologs of anionic surfactants (as AS) and cationic (as alkyltrimethylammonium) by isotachophoresis with conductometric detection and homologs of non-UV absorbing surfactants (AS, alkylsulfonate, alkylsarcosinates and dialkyldimethylammonium) by capillary zone electrophoresis using indirect detection. 

C. Wang, C. A. Lucy, Mixed cationic/anionic surfactants for semipermanent wall coatings in capillary electrophoresis. Electrophoresis, 2004, 25, 825-832. 

P. A. Gallagher, N. D. Danielson, Capillary electrophoresis of cationic and anionic surfactants with indirect conductivity detection,/. Chromatogr., 781, 533, 1997. 

Nakamura, H., Sano, A., and Matsuura, K. 1998, Determination of critical micelle concentration of anionic surfactants by capillary electrophoresis using 2-naphthale-nemethanol as a marker for micelle formation. Anal. Sci. 14, 379. 

Lin, J., Nakagawa, M., Uchiyama, K., and Hobo, T. 2002, Comparison of three different anionic surfactants for the separation of hydrophobic compounds by nonaqueous capillary electrophoresis. Electrophoresis 23, 421. 

Capillary electrophoresis of other anionic surfactants conditions are summarized in Tabled. 

TABLE 4 Capillary Electrophoresis Analysis of Other Anionic Surfactants... 

Surfactants are amphophilic molecules, which consist of a hydrophobic carbohydrate part and a hydrophilic head group. In capillary zone electrophoresis (CZE), different types, i.e., anionic, cationic, but also neutral, tensides are employed. The ability of such molecules to interact with ionic and nonionic species has been used in ion chromatography and, in particular, in SDS-poly-(acrylamide) gel electrophoresis (PAGE) (15). 

The type of electrophoresis we have been discussing so far is called capillary zone electrophoresis. Separation is based on differences in electrophoretic mobility. If the capillary wall is negative, electroosmotic flow is toward the cathode (Figure 26-20) and the order of elution is cations before neutrals before anions. If the capillary wall charge is reversed by coating it with a cationic surfactant (Figure 26-24) and the instrument polarity is reversed, then the order of elution is anions before neutrals before cations. Neither scheme separates neutral molecules from one another. 

Haddad, P. R., Harakuwe, A. H., and Bucbberger, W., Separation of inorganic anionic components of bayer liquor by capillary zone electrophoresis. 1. Optimization of resolution with electrolyte-containing surfactant mixtures, J. Chromatogr. A, 706, 571-578, 1995. 

---