Sodium dodecyl sulfate concentration

GL 19] ]R 9] ]P 20] The rate of reaction is proportional to decreasing surfactant (sodium dodecyl sulfate) concentration [63]. No change in the enantiomeric excess was observed. These results are an indication of operation in a chemical regime. 

Figure 12.12b illustrates the application of gel electrophoresis to protein characterization. In this illustration a cross-linked polyacrylamide gel is the site of the electrophoretic migration of proteins that have been treated with sodium dodecyl sulfate. The surfactant dissociates the protein molecules into their constituent polypeptide chains. The results shown in Figure 12.12b were determined with well-characterized polypeptide standards and serve as a calibration curve in terms of which the mobility of an unknown may be interpreted to yield the molecular weight of the protein. As with any experiment that relies on prior calibration, the successful application of this method requires that the unknown and the standard be treated in the same way. This includes such considerations as the degree of cross-linking in the gel, the pH of the medium, and the sodium dodecyl sulfate concentration. The last two factors affect the charge of the protein molecules by dissociation and adsorption, respectively. Example 12.5 considers a similar application of electrophoresis. 

Figure 17B. The sodium dodecyl sulfate concentration at different heights for the conditions in Fig. 16. The interface was initially between layers 3 and 4.

Figure 2.5 shows the value of 0 for different sodium dodecyl sulfate concentrations. At a critical concentration, the cmc, the increases sharply. The cmc can be calculated as ... 

Figo 6o Dependence of the particle number N on sodium dodecyl sulfate concentration [SDS] in aqueous phase polymerization of MMA at various monomer concentrations. N denotes the number of particles per liter of reaction mixture. Initial monomer concentrations, [M]o, are O 0.0038, 0.019, O 0.035, 0.0571, 0o0761,... 

For initiation in micelles, the emulsifier concentration must exceed the cmc. The classical concept of the cmc is that it represents that concentration at which micelles form at higher concentrations, more micelles form, and at lower concentrations, no micelles are present. The cmc is usually determined by the inflection point in some physical property measured as a function of emulsifier concentration. Figure 1 shows a schematic illustration of the variation of conductivity k, turbidity t, equivalent conductivity X, surface tension y, and osmotic pressure tt with sodium dodecyl sulfate concentration (18). All five parameters show an inflection point at ca. 8mM, which is the most common value of the cmc, and all five curves are consistent with the concept of micelles forming above ca. 8mM and not forming at lower concentrations. Recent measurements of the partial specific volume of sodium lau-ryl sulfate solutions (19), however, suggest that aggregates of lauryl sulfate ions are present of concentrations well below the cmc. 

Figure 1 Schematic illustration of variation of conductivity, turbidity, equivalent conductivity, surface tension, and osmotic pressure with sodium dodecyl sulfate concentration (18).

Neelson et al. [92] followed the effect of emulsifier (sodium dodecyl sulfate) concentration on the decomposition rate of initiator and the rate of polymerization. The decomposition rate of potassium peroxodisulfate increased with increasing the emulsifier concentration. For example, with increasing [SDS]/(mol dm ) 0, 1.74, 3.47, 6.95, 13.89, and 24.3 increased kj x 10 /s 2.9, 3.6, 12.3, 16.9, and 21.9 (50 °C, [VC] = 11.5 moldm ). For the catalitic decomposition of peroxodisulfate caused by emulsifier the authors derived the following semiempirical expression... 

Decomposition of peroxodisulfates in the aqueous sodium dodecyl-sulfate solutions (below and above CMC) with and without poly(vinyl chloride) particles and/or vinyl chloride monomer was investigated by Georgescu et al. [94, 95]. They also observed the increase of peroxodisulfate decomposition in the presence of emulsifier (Fig. 4). In contrast, the decomposition rate decreased with increasing particle concentration. The dependence of the initial decomposition rate of potassium peroxodisulfate vs the emulsifier concentration is described by a curve with a maximum at CMC. The catalyzed decomposition of initiator was ascribed to the interaction of initiator with free emulsifier molecules or with emulsifier micelles. The effect of particles was ascribed to the decrease of the water-soluble fraction of emulsifier caused by adsorption of emulsifier on the polymer particle surface. The relationship of the decomposition rate constant vs the emulsifier (sodium dodecyl sulfate) concentration with and without poly(vinyl chloride) particles is described by a curve of the same shape but with different absolute values of k ka is lower in the presence of PVC particles (Fig. 4). The most intensive decomposition of initiator occurs at concentrations close to the CMC. Decomposition of peroxodisulfate recorded with vinyl chloride and poly(vinyl chloride) is faster than in pure water and slower than in emulsifier solutions. Variations in the decomposition rate results from the... 

Fig. 11-15. Variation with time of aqueous sodium dodecyl sulfate solutions of various concentrations (from Ref. 54). See Ref. 56 for later data with highly purified materials.

Fig. XIII-9. The dependence of the flotation properties of goethite on surface charge. Upper curves are potential as a function of pH at different concentrations of sodium chloride lower curves are the flotation recovery in 10 M solutions of dodecylammo-nium chloride, sodium dodecyl sulfate, or sodium dodecyl sulfonate. (From Ref. 99.)...

In a series of experiments at 60 C, the rate of polymerization of styrene agitated in water containing persulfate initiator was measuredt for different concentrations of sodium dodecyl sulfate emulsifier. The following results were obtained ... 

If the coupling component is not ionic, however, more dramatic effects occur, as found by Hashida et al. (1979) and by Tentorio et al. (1985). Hashida used N,N-bis(2-hydroxyethyl)aniline, while Tentorio and coworkers took 1-naphthylamine and l-amino-2-methylnaphthalene as coupling components. With cationic arenediazo-nium salts and addition of sodium dodecyl sulfate (SDS), rate increases up to 1100-fold were measured in cases where the surfactant concentration was higher than the critical micelle concentration (cmc). Under the same conditions the reaction... 

It can be seen that the solubility in water of sodium dodecyl sulfate is around 30%. However, the triethanolamine salt is still more soluble and forms clear solutions at 40% concentration. Figure 3 shows plots of the solubility of sodium alcohol sulfates with alkyl chains from Cn to C18 vs. temperature. As expected, the solubility decreases as the number of carbon atoms in the alkyl chain increases [80]. 

The curve shown in Fig. 6 for sodium dodecyl sulfate is characteristic of ionic surfactants, which present a discontinuous and sharp increase of solubility at a particular temperature [80]. This temperature is known as the Krafft temperature. The Krafft temperature is defined by ISO as the temperature [in practice, a narrow range of temperatures] at which the solubility of ionic surface active agents rises sharply. At this temperature the solubility becomes equal to the critical micelle concentration (cmc). The curve of solubility vs. temperature intersects with the curve of the CMC vs. temperature at the Krafft temperature. 

The influence of the presence of alcohols on the CMC is also well known. In 1943 Miles and Shedlovsky [117] studied the effect of dodecanol on the surface tension of solutions of sodium dodecyl sulfate detecting a significant decrease of the surface tension and a displacement of the CMC toward lower surfactant concentrations. Schwuger studied the influence of different alcohols, such as hexanol, octanol, and decanol, on the surface tension of sodium hexa-decyl sulfate [118]. The effect of dodecyl alcohol on the surface tension, CMC, and adsorption behavior of sodium dodecyl sulfate was studied in detail by Batina et al. [119]. 

Figures 12 and 13 show plots of the surface tension of sodium dodecyl ether (1 EO) sulfate and sodium dodecyl sulfate (2 EO) sulfate vs. their bulk concentration in distilled water and in sodium chloride solutions of 0.1 and 0.5 M total ionic strength at 10, 25, and 40°C [125].

FIG. 10 Surface tension vs. surfactant concentration for sodium dodecyl sulfate and sodium dodecyl ether (m EO) sulfates at 25 °C [124],... 

FIG. 11 Surface tension vs. log surfactant concentration for (O) sodium decyl ether (2 EO) sulfate, (A) sodium dodecyl sulfate, (A) sodium dodecyl ether (1 EO) sulfate, ( ) sodium dodecyl ether (2 EO) sulfate, and ( ) sodium tetradecyl ether (2 EO) sulfate at 25 °C [94]. 

The logarithm of the micellar molecular weight (M) and consequently the aggregation number of sodium dodecyl sulfate at 25°C in aqueous sodium chloride solutions is linearly related to the logarithm of the CMC plus the concentration of salt (Cs), both expressed in molar units, through two equations [116]. Below 0.45 M NaCl micelles are spherical or globular, and Eq. (18) applies ... 

The conductivity of sodium dodecyl sulfate in aqueous solution and in sodium chloride solutions was studied by Williams et al. [98] to determine the CMC. Goddard and Benson [146] studied the electrical conductivity of aqueous solutions of sodium octyl, decyl, and dodecyl sulfates over concentration ranges about the respective CMC and at temperatures from 10°C to 55°C. Figure 14 shows the results obtained by Goddard and Benson for the specific conductivity of sodium dodecyl sulfate and Table 25 shows the coefficients a and p of the linear equation of the specific conductivity, in mho/cm, vs. the molality of the solution at 25°C. Micellization parameters have been studied in detail from conductivity data in a recent work of Shanks and Franses [147]. 

Sodium dodecyl sulfate is the universal analytical standard for the determination of anionic and cationic active matter. It is used to determine the analytical concentration factor of the cationic surfactant in the titration of anionic active matter and as titrant to determine the cationic active matter. 

Similarly to quantitative determination of high surfactant concentrations, many alternative methods have been proposed for the quantitative determination of low surfactant concentrations. Tsuji et al. [270] developed a potentio-metric method for the microdetermination of anionic surfactants that was applied to the analysis of 5-100 ppm of sodium dodecyl sulfate and 1-10 ppm of sodium dodecyl ether (2.9 EO) sulfate. This method is based on the inhibitory effect of anionic surfactants on the enzyme system cholinesterase-butyryl-thiocholine iodide. A constant current is applied across two platinum plate electrodes immersed in a solution containing butyrylthiocholine and surfactant. Since cholinesterase produces enzymatic hydrolysis of the substrate, the decrease in the initial velocity of the hydrolysis caused by the surfactant corresponds to its concentration. Amounts up to 60 pg of alcohol sulfate can be spectrometrically determined with acridine orange by extraction of the ion pair with a mixture 3 1 (v/v) of benzene/methyl isobutyl ketone [271]. 

The ion pair extraction by flow injection analysis (FIA) has been used to analyze sodium dodecyl sulfate and sodium dodecyl ether (3 EO) sulfate among other anionic surfactants. The solvating agent was methanol and the phase-separating system was designed with a PTFE porous membrane permeable to chloroform but impermeable to the aqueous solution. The method is applicable to concentrations up to 1.25 mM with a detection limit of 15 pM [304]. 

The protein was purified by a dialysis procedure, denatured and analysed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Western blotting indicated that the protein of interest consisted of two components, one of which increased in concentration as the purification proceeded. The authors initially suggested that this could be due to the presence of a number of species produced by modification of the amino acid side-chains, for example, by glyco-sylation, or by modification of the C- or N- terminus. 

We may contrast this behavior to that found for AOT. As shown in Figure 1, the chromatograms for AOT exhibit sharp fronts and somewhat diffuse tails, intermediate in shape between the symmetrical peaks typical of conventional solutes and the highly asymmetric chromatograms obtained for sodium dodecyl sulfate micelles in water (15). In addition, the concentration dependence of Mp" for AOT is gradual, not abrupt as for lecithin. These differences may be attributed to the lability of the AOT micelles which makes the observed retention time quite sensitive to the initial concentration (12) and leads to broadened chromatograms. 

A further interesting application of CLM involves the fluorescence quenching reaction between (5,10,15,20-tetraphenylporphyrinato) zinc (II) and methylviologen at a dode-cane-water interface. [62] This study demonstrated that the quenching reaction could occur only in the presence of an anionic surfactant, sodium dodecyl sulfate (SDS). The quenching efficiency depended on the concentration of SDS in the aqueous phase with a maximum value of 13.5%... 

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