8-Anilino-1-naphthalenesulfonic acid surfactants

A Study of Mixed Aqueous Solutions of Hydrocarbon and Fluorocarbon Surfactants Using 8-Anilino-l-naphthalenesulfonic Acid Ammonium Salt... 

In two-phase systems, however, where surfactant and water can partition between a fluid and a liquid phase, significant pressure effects occur. These effects were studied for AOT in ethane and propane by means of the absorption probe pyridine N-oxide and a fluorescence probe, ANS (8-anilino-l-naphthalenesulfonic acid) [20]. The UV absorbance of pyridine A-oxide is related to the interior polarity of reverse micelles, whereas the fluorescence behavior of ANS is an indicator of the freedom of motion of water molecules within reverse micelle water pools. In contrast to the blue-shift behavior of pyridine N-oxide, the emission maximum of ANS increases ( red shift ) as polarity and water motion around the molecule increase. At low pressures the interior polarity, degree of water motion, and absorbance intensity are all low for AOT reverse micelles in the fluid phase because only small amounts of surfactant and water are in solution. As pressure increases, polarity, intensity, and water motion all increase rapidly as large amounts of surfactant and water partition to the fluid phase. The data indicate that the surfactant partitions ahead of the water thus there is a constant increase in size and fluidity of the reverse micelle water pools up to the one-phase point. An example of such behavior is shown in Fig. 4 for AOT in propane with a total fVo of 40. The change in the ANS emission maximum suggests a continuous increase in water mobility, which is due to increasing fVo in the propane phase, up to the one-phase point at 200 bar. 

Although the very existence of CMC of surfactant dissolved in nonpolar has been questioned, the UV absorption and fluorescence emission measurements of AOT-solubilized solubilizates, such as tert-butylphenol, pyrene, and hemi-Mg salt of 8-anilino-l-naphthalenesulfonic acid, in isooctane provided evidence for the existence of CMC at different values of R = [H20]/[A0T] (with R < 3) and CMC value increases with increase in R. The values of CMC, obtained at different temperatures, were used to calculate standard enthalpy of micellization (AH j°) from Equation 1.13 and standard entropy of micellization (AS j ) from Equation 1.14, and these respective values vary from 38.07 to 44.81 kJ mol and 184.60 to 202.60 JK moE with increase in temperature from 20 to 45°C. The positive AH j values arise mainly from the dismantling of hydrated ions in the quasi-lattice of AOT interior. 

FIA of anionics without a phase separation may be based on the quenching effect of surfactants on the fluorescence intensity of 8-anilino-l-naphthalenesulfonic acid coupled with bovine serum albumin (83). Another method of avoiding a phase separation is to use a surfactant-selective electrode. Since interference is a problem, the surfactant-selective electrode approach is best coupled with online concentration with a reversed-phase column. Such a system has been demonstrated for trace analysis of sodium dodecylsulfate (84). 

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