Surfactants weakly acidic

The titration must be done with alcoholic acid or alkali, and is best done potentiometrically with an autotitrator. Next best is manual potentiomet-ric titration, but it is satisfactory to use indicators, methyl orange or bromophenol blue for the low-pH end-point and phenolphthalein for the high-pH end-point. The information obtained is often a useful crosscheck on the mass balance in the analysis of an unknown, but it can also help in the analysis of WW amphoterics, which contain appreciable amounts of non-surfactant weak acids and bases. 

Mooney et al. [70] investigated the effect of pH on the solubility and dissolution of ionizable drugs based on a film model with total component material balances for reactive species, proposed by Olander. McNamara and Amidon [71] developed a convective diffusion model that included the effects of ionization at the solid-liquid surface and irreversible reaction of the dissolved species in the hydrodynamic boundary layer. Jinno et al. [72], and Kasim et al. [73] investigated the combined effects of pH and surfactants on the dissolution of the ionizable, poorly water-soluble BCS Class II weak acid NSAIDs piroxicam and ketoprofen, respectively. 

Consequently, the SDS microemulsion system is the best model for indirect measurement of log Pow. However, this is valid only for neutral solutes. We reported that the relationship between MI and log Pow for ionic solutes is different from that for neutral solutes (49). This would be caused by the ionic interaction between ionic solutes and the ionic microemulsion as well as ionic surfactant monomer in the aqueous phase. Kibbey et al. used pH 10 buffer for neutral and weak basic compounds and pH 3 buffer for weak acidic compounds (53). Although their purpose was to avoid measuring electrophoretic mobility in the aqueous phase, this approach is also helpful for measuring log Pow indirectly. 

Polymeric reversed phase resins are synthesized from divinylbenzene with styrene, methylstyrene or other styrenic monomers. Divinylbenzene is the major component and provides crosslinking. These resins are macroporous, and the surface area is usually in excess of 300 m2 / g. This surface area provides the adsorptive surface for retention of hydrophobic species. These resins can be used for matrix elimination of surfactants, weak carboxylic acids, fats, proteins, etc. 

The effect of various surfactants, the cationics-eetyl trimethyl ammonium bromide (CTAB), and cetyl pyridinium chloride (CPC), the anionic-sodium lauryl sulfate (SLS), and the nonionic-polysorbate 80 (Tween 80), on the solubility and ionization constants of some sparingly soluble weak acids of pharmaceutical interest was studied (Gerakis et al., 1993). Benzoic acid (and its 3-methyl-, 3-nitro-, and 4-tert-butyl-derivatives), acetylsalicylic acid, naproxen, and iopanoic acid were chosen as model drugs. The cationics, CTAB and CPC, were found to considerably increase th< ionization constant of the weak acidS Ka ranged from-0.21 to-3.57), while the anionic, SLS, showed a negligible effect and the nonionic, Tween 80, generally decreased the ionization constants Solubility of the acids increased in aqueous micellar and in acidiLed micellar solutions. 

After dyeing, the liquor is usually drained off the material is rinsed and then washed off with addition of a surfactant. The washing intensity depends on the substantivity of the dye hydrolysate. With alkali-sensitive vinylsulfone dyes, soaping at the boil must be carried out in a neutral or weakly acidic liquor to prevent cleavage of the dye-fiber bond. 

In the dyeing process, the dyeing bath is made weakly acidic (pH 4.5-5). The process is started at 20-45 °C, followed by heating at a rate of l°C/min and dyeing at near boiling temperature. Aftertreatment (soaping) is performed with a nonionic surfactant and sodium bicarbonate or ammonia at 95 °C. 

When an inorganic phosphate buffer or sodium hydroxide is present, without imidazole, only weakly acidic phenol of pKa 11.6 can be detected. Since the phenolic group is adjacent to anionic sulfonates of the AOT, ionization is weakened. / -Nitrophenol in the water pool is influenced primarily by electrostatic interaction between molecular imodazole (Im) and the anionic surfactant group. When excess imidazole (but not methanol or n-butanol) is added to the water pool, a fraction of the interfacial /mitrophenol is displaced into the water pool. 

For waste management purposes, various solvent extraction processes primarily for the removal of Cs and °Sr from alkaline or weak acidic solutions have been developed on bench scale as well as on pilot scale [35,36]. Di-2-ethylhexyl phosphoric acid/kerosene system with Span 80 surfactant showed promise for the pertraction of °Sr from aqueous solutions. 

Polysorbates are stable to electrolytes and weak acids and bases gradual saponification occurs with strong acids and bases. The oleic acid esters are sensitive to oxidation. Polysorbates are hygroscopic and should be examined for water content prior to use and dried if necessary. Also, in common with other polyoxyethylene surfactants, prolonged storage can lead to the formation of peroxides. 

Sheng, J.J., Kasim, N.A., Chandrasekharan, R. and Amidon, G.L. (2006) Solubilization and dissolution of insoluble weak acid, ketoprofen effects of pH combined with surfactant European Journal of Pharmaceutical Sciences, 29 (3-4), 306. 

The relationship between adsorption of surfactants on the one hand and of small organic molecules on the other has been also studied. At sufficiently high adsorption density, the adsorbed surfactant is able to solubilize water insoluble organic compounds, and this phenomenon is termed adsolubilization. This may result in uptake of certain adsorbates which do not adsorb on the material of interest in the absence of surfactant, Adsolubilization of weak acids and bases is strongly pH dependent and it often shows a maximum at pH close to the pKa of the solute. 

One of the more often used spectrophotometric reagents for gold is p-dimethylaminobenzylidenerhodanine (rhodanine, formula 46.3) [33,60]. The reagent reacts with gold ions in weakly acidic media e.g., 0.1 M HCl) to form a pink-violet complex, which is either stabilized in the aqueous phase, or extracted into a mixture of chloroform and benzene (3+1) or isoamyl acetate. In aqueous-pyridine medium, e = 3.8-IO at 515 nm [60]. Rhodanine and its derivatives were applied for determination of Au and other noble metals in the presence of surfactants [61-63]. 

Monticone, V. et al.. Effect of pH on the coadsorption of weak acids to silica/water and weak bases to alumina/water interfaces as induced by ionic surfactants, Langmuir, 16, 258, 2000. 

Bhowal, A. and Datta, S. (1998). A mathematical model for the analysis of extraction data of weak acids/bases in hquid surfactant membranes. J. Membr. Sci., 139, 103-8. 

With the growth of PTC, various new technologies have been developed where PTC has been combined with other methods of rate enhancement. In some cases, rate enhancements much greater than the sum of the individual effects are observed. Primary systems studied involving the use of PTC with other rate enhancement techniques include the use of metal co-catalysts, sonochemistry, microwaves, electrochemistry, microphases, photochemistry, PTC in single electron transfer (SET) reactions and free radical reactions, and PTC reactions carried out in a supercritical fluid. Applications involving the use of a co-catalyst include co-catalysis by surfactants (Dolling, 1986), alcohols and other weak acids in hydroxide transfer reactions (Dehmlow et al., 1985,1988), use of iodide (traditionally considered a catalyst poison, Hwu et... 

Another serious problem that arises in all C02 floods, and must be considered here, is corrosion. As is well known, solutions of C02 in water dissociate to form carbonic acid. This is a weak acid and does not cause much trouble in fresh water floods. However, in brine instead of pure water, C02 does become much more corrosive, and the particular composition of the brine has a great effect. These difficulties can be made worse by the presence of surfactant that can remove coatings emplaced by corrosion inhibitors. This difficulty could occur in both the injection as well as in the production facilities. In many fields, special metallurgy has been needed in critical elements of the hardware. Not much in the way of general principles can be given, except that, in designing a C02 flood, the modification of existing problems is to be expected. 

Because of the formation of emulsions at phase boundaries for APE surfactants, EEE is limited to the degradation products APs, alkylphenol monoethoxylate to triethoxylate (APE(l-3)) and alkylphenol ethoxy carboxylate (APEC). Dichloromethane and hexane are the solvents commonly used in the extraction of APs and APE(l-3) from liquid samples.For phenolic compounds including BPA, OP, and NP, water samples are often acidified to pH < 4 with hydrochloric acid. Acidification of water samples suppresses the dissociation of phenols and prevents the ionization of the analytes, which increased the efficiency of the extraction. Del Olmo et al. " studied the effect of pH on extraction of BPA using sodium hydroxide and hydrochloric acid for adjustment. The result obtained showed that the extraction efficiency remains constant for pH values lower than 6.5, decreasing sharply for higher values. This behavior agrees with the weak acid nature of BPA. 

Long-chain alkanoic acids have a limited use as surfactants. They are very weak acids having a pH range between 5 and 6. They are soluble in most organic solvents but purely soluble in water. Alkali metals and short-chain amines as counterions yield water-soluble soaps which, as a result of hydrolysis, form with free acids the dispersible 1 1 or 1 2 association complexes, so-called "acid soaps". 

These herbicides, in particular those of the last two groups, rarely penetrate the strictly lipophilic barrier formed by the cuticle they must therefore be distributed, with surfactants and wetting agents, in the form of salts or esters of their parent active ingredients. In fact, they are generally weak acids with intermediate lipophilicity expressed as the... 

---