Cationic surfactants quantification

CE has been used for the analysis of anionic surfactants [946,947] and can be considered as complementary to HPLC for the analysis of cationic surfactants with advantages of minimal solvent consumption, higher efficiency, easy cleaning and inexpensive replacement of columns and the ability of fast method development by changing the electrolyte composition. Also the separation of polystyrene sulfonates with polymeric additives by CE has been reported [948]. Moreover, CE has also been used for the analysis of polymeric water treatment additives, such as acrylic acid copolymer flocculants, phosphonates, low-MW acids and inorganic anions. The technique provides for analyst time-savings and has lower detection limits and improved quantification for determination of anionic polymers, compared to HPLC. 

Preconcentration of Pt and Pd by ion-pairing of the respective chloro-com-plexes with a cationic surfactant (iV(l-carbaethoxypentadecyl)-tri-methylammo-nium bromide, C2iH440NBr/Septonex) with subsequent adsorption on CIS silica gel and elution with ethanol was employed for both ICP-AES and ICP-MS quantification, although the eluent had to be evaporated and the residue transferred into a 0.1 M HCl solution before measurement (Vlasankova et al. 1999). 

LC is a separation technique of great importance for formulations since it allows the quantification of a broad spectrum of compounds from surfactants to minor compounds in matrices of detergents, cosmetic products, and industrial products. LC using UV absorbance detection is used in the determination of anionic surfactants (alkylbenzene sulfonate) and nonionic surfactants (APE) in liquid pesticide formulations cationic surfactants such as cetylpyridi-nium in pharmaceutical tablets and benzalkonium... 

Foam films stabilized by anionic surfactants can be destroyed by the addition of an oppositely charged inorganic species or near-stoichiomeric concentrations of metallic ions to form insoluble salts. For example, fatty acids and their derivatives (tall oil, stearate, etc.) can be precipitated by the addition of calcium, aluminium and zinc salts (forming insoluble salts of the acids). There have been several attempts to relate the defoaming action to the solubility product of the particles. A typical series of results for metal oleates are shown in Figure 8.4. The influence of hydrophobic calcium fatty acid soaps on foaming, and quantification of the data in terms of the solubility product of the calcium and sodium fatty acids have also been reported. Cationic surfactants added to foam stabilized by anionic surfactants could also destroy the foam. Unfortunately, due to the formation of solid contaminants and the adverse consumption of chemicals, precipitation antifoamers are used infrequently in industry. 

So far, a reagent has not been found for cationics which has the advantages of methylene blue for anionics a well-defined, stoichiometric complex, rapid kinetics of ion pair formation, and good sensitivity. These advantages can be obtained if the methylene blue/LAS ion pair is used for an indirect determination of cationics. The cationic surfactant pairs with LAS, displacing the methylene blue, so that the color of the organic phase is indirectly proportional to cationic surfactant concentration. The same principle may be used with quantification of unextracted LAS by UV absorbance measurement of the aqueous... 

A sensitive determination of alkanesulfonates combines RP-HPLC with an on-line derivatization procedure using fluorescent ion pairs followed by an online sandwich-type phase separation with chloroform as the solvent. The ion pairs are detected by fluorescence. With l-cyano-[2-(2-trimethylammonio)-ethyl]benz(/)isoindole as a fluorescent cationic dye a quantification limit for anionic surfactants including alkanesulfonates of less than 1 pg/L per compound for a 2.5-L water sample is established [30,31]. 

Commercial mixtures of surfactants comprise several tens to hundreds of homologues, oligomers and isomers of anionic, nonionic, cationic and amphoteric compounds. Therefore, their identification and quantification in the environment is complicated and cumbersome. The requirement of more specific analytical methods has prompted a replacement of many of the separate steps in traditional methods of analysis, usually non-chromatographic, by chromatographic tools. 

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