Surface-active agents cationic

The adsorption of small ions (sulfate ions) at the surface of solutions of surface active agents (cationic, anionic, and non-anionic) was measured... 

Soaps of heavy metals have been used but cationic surface-active agents have proved more suitable, notably organic amines of relatively high molecular weight. 

Cationic surface-active agents promote wetting of the sulfur and thereby increase the reaction rate (36). The quahty of the product is improved by using photographic-grade sodium sulfite or bisulfite. Excess sulfur is filtered before evaporation (qv) and crystallization (qv). Evaporation is energy-intensive thus it is important to produce the thiosulfate solution at the highest possible concentration. The purity of the product is typically >99% sulfite and sulfate ate the main impurities. 

Surface-active agents iacrease the conductivity of oils quite significantly (97), and addition of water, probably dissolved at the iaterface with the surfactant, further iacreases the conductivity. Nonionic and cationic surface-active agents are preferred to anionic surface-active agents probably because of their higher solubiHty ia oils and higher hygroscopicity. Many anionic surfactants have adequate antistatic efficiency, but they are used less frequendy. 

Benzyl-derived quaternary ammonium compounds are used widely as cationic surface-active agents and as germicides, fungicides, and sanitizers. Benzyl alcohol is used in a wide spectmm of appHcations including pharmaceuticals and perfumes, as a solvent, and as a textile dye assistant. 

Alkylphosphonates are surface-active agents. But the main use of these substances lies in their ability to form stable complexes with bi- or polyvalent cations. Thus, besides the identification of the P-C bond and the determination of the amount of phosphorus in the molecule by one of the previously mentioned methods, measurement of their sequestering ability is carried out. 

Of the four classes of surface-active agents, however, the cationic compounds arguably play the most important role in an antimicrobial context. 

The surface active agents (surfactants) may be cationic, anionic or non-ionic. Surfactants commonly used are cetyltrimethyl ammonium bromide (CTABr), sodium lauryl sulphate (NaLS) and triton-X, etc. The surfactants help to lower the surface tension at the monomer-water interface and also facilitate emulsification of the monomer in water. Because of their low solubility surfactants get fully dissolved or molecularly dispersed only at low concentrations and at higher concentrations micelles are formed. The highest concentration where in all the molecules are in dispersed state is known as critical micelle concentration (CMC). The CMC values of some surfactants are listed in table below. 

High-performance liquid chromatography has, to date, only found limited applications in the analysis of sludges (aliphatic hydrocarbons, cationic and non-ionic surface active agents, carboxylic acids and cobalamin). 

Spectrophotometric methods have found fairly extensive applications but are limited in sensitivity and specificity (cationic surface active agents,... 

Simms etal. [8] discuss the quantitative determination of cationic surface active agents at the sub-ppb level in sewage sludges using fast atom bombardment mass spectrometry. 

Cationic surfactants are surface-active agents that have one or more functional groups in their molecule that ionise in aqueous solution to produce positively charged organic ions. The most representative cationic surfactants are quaternary ammonium derivatives in which the N atom is bonded to four alkyl groups. For many years, ditallow dimethylammonium chloride (DTDMAC) has been the most widely used product of this family. Its recalcitrance to biodegradation, however, has... 

Surface-active agents used as adjuvants in pharmaceutical preparations to improve drug dissolution may affect the stability of /3-lactams. Thus, the presence of micelles of cetyl(trimethyl)ammonium bromide (CTAB) enhanced up to 50-fold the rate of alkaline hydrolysis of penicillins [140]. In the case of cephalosporins, micelle-promoted catalysis of the intramolecular degradation process (see Sect 5.2.2) was also observed [85][141], It has been proposed that the negatively charged penicillins and cephalosporins are attracted by the cationic micelles. This attraction increases substrate concentration in the micellar phase, in turn accelerating the rate of HO- ion attack. Ion exchange at the micellar surface and electrostatic stabilization of the transition state may also contribute to the increased rate [142][143],... 

Baleux, B. and Caumette, P. (1977) Biodegradation of some cationic surface-active agents. Water Res., 11, 833-841. 

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