Capillary electrokinetics cationic surfactants

Abstract Investigations of alternate adsorption regularities of cationic polyelectrolytes a) copolymer of styrene and dimethylaminopropyl-maleimide (CSDAPM) and b) poly(diallyldimethylammonium chloride) (PDADMAC) and anionic surfactant - sodium dodecyl sulfate (SDS) on fused quartz surface were carried out by capillary electrokinetic method. The adsorption/desorption kinetics, structure and properties of adsorbed layers for both polyelectrolytes and also for the second adsorbed layer were studied in dependence on different conditions molecular weight of polyelectrolyte, surfactant and polyelectrolyte concentration, the solution flow rate through the capillary during the adsorption, adsorbed layer formation... 

In this paper we investigate the process of alternate adsorption of cationic polyelectrolyte and anionic surfactant, structure and properties of adsorbed layers depending on different factors (molecular weight of PE, concentration of polyelectrolyte and surfactant, adsorbed layer formation time, the flow rate of the solution) by measuring potential and streaming current using the capillary electrokinetic method. 

Crosby D, El Rassi Z. Micellar electrokinetic capillary chromatography with cationic surfactants. J Liq Chromatogr 1993 16 2161. 

Micelles and cyclodextrins are the most common reagents used for this technique. Micellar electrokinetic capillary chromatography (MECC or MEKC) is generally used for the separation of small molecules [6], Sodium dodecyl sulfate at concentrations from 20 to 150 mM in conjunction with 20 mM borate buffer (pH 9.3) or phosphate buffer (pH 7.0) represent the most common operating conditions. The mechanism of separation is related to reversed-phase liquid chromatography, at least for neutral solutes. Organic solvents such as 5-20% methanol or acetonitrile are useful to modify selectivity when there is too much retention in the system. Alternative surfactants such as bile salts (sodium cholate), cationic surfactants (cetyltrimethy-lammonium bromide), nonionic surfactants (poly-oxyethylene-23-lauryl ether), and alkyl glucosides can be used as well. 

Gong, M., Wehmeyer, K.R., Limbach, P.A., and Heimeman, W.R., Unlimited-volume electrokinetic stacking injection in sweeping capillary electrophoresis using a cationic surfactant. Anal. Chem., 78, 6035, 2006. 

C.-E. Lin, C.-C. Hsueh, T.-Z. Wang, T.-C. Chiu and Y.-C. Chen, Migration behavior and separation of s-triazines in micellar electrokinetic capillary chromatography using a cationic surfactant,... 

Electrophoretic techniques, mainly capillary zone electrophoresis (CZE) and also capillary iso-tachophoresis (ITP) or micellar electrokinetic chromatography (MEKC) have been used in cosmetic analysis (e.g., determination of cationic surfactants in toiletries, parabens in different cosmetics, fluoride, and polyphosphates in toothpaste, hair dyes, or acid preservatives in cosmetic lotions). However, their use is less extensive than LC, probably because the... 

Therefore, using capillary electrokinetics one can in principle investigate the adsorption of cationic surfactant on a silica surface and explain the results obtained on the basis of Langmuir-type isotherms of adsorption. 

With respect to chromatographic techniques, cationic surfactant micelles have been used as mobile phase additives in the well-known micellar liquid chromatography (MLC) [4]. They have also been employed as pseudostationary phases in micellar electrokinetic capillary chromatography (MEKC) [5]. 

A micellar electrokinetic capillary chromatographic (MECC) method to separate 17 dihydroergotoxines, aci-alkaloids, and oxidation products has been described [103]. The authors used novel cationic dimeric (Gemini) surfactants such as l,3-bis(dodecyl-W,N-dimethyl ammonium)-2-propanol and l,3-bis(te-tradecyl-N,N-dimethyl ammonium)-2-propanol for the separation in less than 8 min. 

---