Long‐chained gemini surfactants for semipermanent wall coatings in capillary electrophoresis of proteins

Abstract

In this paper, we presented the first example of using gemini surfactants as semipermanent coatings in CE for protein separation. These coatings are based on the self-assembly of a series of cationic gemini surfactants, alkanediyl-alpha,omega-bis(dimethylalkylammonium bromide) (m-s-m), on the capillary wall. The coatings can keep stable for a long time without surfactant in the buffer, e.g., after the surfactants were removed from the buffer, the reversed EOF only decreased by 3.6 and 3.9% for 18-2-18 and 16-2-16 coatings over 60 min under continuous electrophoretic conditions. The coating stability increased with the alkyl chain length m. The double long chains of geminis (m > or = 14) yielded a good coating stability; meanwhile, the spacer group acted as an EOF modifier. Thus, this bifunctional surfactant coating provided a new buffer-independent method for EOF control. For 18-s-18 series, the best coating stability and largest EOF were obtained at s = 10. Ranging s from 3 to 10 yielded a linear fine-tuning of EOF and thereby allowed the adjustment of the protein apparent mobility. Highly efficient separation (>500 000 plates/m) was achieved with all the 18-s-18 coatings. Excellent run-to-run and day-to-day reproducibility (RSD of migration time </=0.7 and 4.3% for run-to-run and day-to-day assays, respectively) and fine recoveries (97.5-100.1%) of the protein samples indicated that the gemini semipermanent coatings were quite effective for the wall adsorption suppression of proteins.

Use of gemini surfactants as semipermanent capillary coatings in aqueous‐organic solvents for capillary electrophoretic separation of inorganic anions

“…Taking s 5 4 and 10 as examples, with MeOH concentration ranging from 0 to 40% v/v, the decrease of EOF magnitude of 18-4-18 coating (4.9-17.6%) is obviously larger than that of 18-10-18 coating (2.3-12.3%) after 60 min electrokinetic rinsing. This result is consistent with that obtained in aqueous buffer [20]. The reason may be related to the packing of gemini surfactant coatings on the capillary surface [20,43]: the long spacer length may allow the gemini molecules to interdigitate to a larger degree to reach the maximum chain-chain interaction, and thus yielding a more denser packing of coating and a better coating stability than the short spacer length; the densest packing is achieved at s 5 10.…”

“…This is because the high pH promotes the ionization of surface silanols, and thereby enhances the electrostatic interaction between the capillary wall and the gemini surfactant coating. The similar phenomenon was also observed in previous reports using semipermanent coatings in aqueous media [20,46]. …”

“…diyl-a,o-bis(dimethyloctadecylammonium bromide) (18-s-18), the coatings turned from dynamic to semipermanent, which allowed the separation to be performed without the surfactant in buffer [20]. These semipermanent coatings have shown good stability, e.g.…”

“…Recently, Liu et al reported that cationic gemini surfactants were good capillary coating materials for separation of proteins in aqueous media [18][19][20]. Particularly, when using long-chained gemini surfactant alkane- Sep. Sci 2009, 32, 4148-4154 4148 diyl-a,o-bis(dimethyloctadecylammonium bromide) (18-s-18), the coatings turned from dynamic to semipermanent, which allowed the separation to be performed without the surfactant in buffer [20]. These semipermanent coatings have shown good stability, e.g.…”

“…highly hydrophobic compounds [17]. Recently, Liu et al reported that cationic gemini surfactants were good capillary coating materials for separation of proteins in aqueous media [18][19][20]. Particularly, when using long-chained gemini surfactant alkane-…”