Dialkyldimethylammonium cationic

Surfactants having two alkyl chains can pack in a similar manner to the phospholipids (see Box 6.4 for examples). Vesicle formation by the dialkyldimethylammonium cationic surfactants has been studied extensively. As with liposomes, sonication of the turbid solution formed when the surfactant is dispersed in water leads ultimately to the formation of optically transparent solutions which may contain single-compartment vesicles. For example, sonication of dioctadecyldimethyl-ammonium chloride for 30 s gives a turbid solution containing bilayer vesicles of 250-450 nm diameter, while sonication for 15 min produces a clear solution containing monolayer vesicles of diameter 100-150 nm. The main use of such systems has been as membrane models rather than as drug delivery vehicles because of the toxicity of ionic surfactants. 

FIGURE 21 Conformation of dialkyldimethylammonium cations, (a) Arrangement with all C—C bonds in trans conformation, (b) with the first C—C bond in gauche conformation so that the surfactants can be densely packed in mono- or bilayers (c). 

Alkyltrimethylammonium and dialkyldimethylammonium cationics are converted by Hoffmann degradation to their alk-l-enes by heating on a water bath for 30 min with potassium t-butoxide in benzene-DMSO (4 1). After extraction and clean-up, the alkenes are separated on a glass column (2m X 3mm i.d.) of 5% SE-30 on Chromosorb W AW-DMCS... 

Copolymerization with other water-soluble monomers is also carried out in a similar manner. Cationic polyacrylamides are obtained by copolymerizing with ionic monomers such as dimethylami-noethyl methacrylate, dialkyldimethylammonium chloride, and vinylbenzyltrimethylammonium chloride. These impart a positive charge to the molecule. Anionic character can be imparted by copolymerizing with monomers such as acrylic acid, methacrylic acid, 2-acrylamido-2-methyl-propanesulfonic acid, and sodium styrene sulfonate. Partial hydrolysis of polyacrylamide, which converts some of the amide groups to carboxylate ion, also results in anionic polyacrylamides. 

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. 

The analysis of solvent and perfumes in formulations is performed by GC. For solvent analysis in surfactants sample pretreatment with organic solvent is used for the separation of inorganic impurities. Regarding surfactants and complementary compounds, applications may be mentioned such as the separation of a hardness agent (sodium laurate) in liquid laundry detergent by GC and the Hofmann degradation and analyses of cationic surfactant of the alkyltrimethyl- and dialkyldimethylammonium type in fabric softener and hair rinse. 

Dialkyldimethylammonium surfactants and specifically DHTDMAC are the cationic surfactants most used, as fabric conditioners. DHTDMAC has been... 

Liu and Ding (2004) developed a method to separate simultaneously four homologues of alkyltrimethylammonium and four of dialkyldimethylammonium with internal standard (octylammonium) and using indirect UV detection. Decylbenzyldimethyl ammonium chloride was used as chromophore and the influence on separation of buffer concentration, pH and organic solvent (methanol and tetrahydrofuran) was studied. Besides, methanol concentration in a sample solution was tested to avoid the formation of micelles and surfactant adsorption onto the capillary. The method was applied to determine cationic surfactants in five hair conditioners, finding only four homologous (Ci2 ig) trimethylam-monium at a total concentration of between 0.14 and 2.15%. In one of them, analysis with... 

The most recent advances in MS, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) were applied in positive ion mode to the analysis of three oral rinse and one commercial disinfectant formulation. In the latter, a complex mixture containing three dialkyldimethylammonium and alkylbenzyl-dimethylammonium (Ciq, C14, Cjs) salts was detected and in three oral rinse, cetylpyri-dinium chloride was the cationic surfactant present. Besides, the dissociation was verified as the mode of ionization of quaternary ammonium under MALDI conditions (Morrow et al, 2001). 

LC-MS was the analytical technique chosen to determine anionic and amphoteric surfactants in shampoos without pre-treatment by Miyamae et al. (2001). Moreover, using this combined technique, these authors determined cationic (dialkyldimethylammonium, alkyltrimethylammonium) and nonionic (amine oxide, fatty amides, polyglycerol alcohols...) surfactants in cosmetic lotions and aeams (Miyamae et al, 2002). 

The Ci4-Ciii dialkyldimethylammonium salts used in fabric softeners for home laundry have poor water solubility. Normal phase chromatography is most conveniently used for the separation of these compounds, especially in environmental matrices. Most often, detection is by conductivity and the cations are isolated and injected as ion pairs. 

Levsen, K., M. Emmrich, S. Behnert, Dialkyldimethylammonium compounds and other cationic surfactants in sewage water and activated sludge, Fresenius Z. Anal. Chem., 1993,346, 732-737. 

The ISO method for determination of cationics gives separate procedures for determination of high and low molecular weight compounds (94,95). Low MW compounds (MW less than about 500) such as alkyltrimethylammonium salts are simply dissolved and titrated as described above. Higher MW compounds, such as dialkyldimethylammonium fabric softeners have poor water solubility and are therefore taken up in isopropanol, diluted with water, and used to titrate a known quantity of anionic surfactant,... 

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