Buffered surfactant solutions

Figure 13. Plot of log C,/Co against time as a function of surfactant concentration, S. Decomposition in buffered surfactant solutions pH = 11.62 temperature =49.7°C.

Figure 16. Dependence of the saturated solubility of Co (III) (acac), Wf, in buffered surfactant solutions on the surfactant concentration. The concentration of Co (III) (acac)s soluble in the true aqueous phase, Wx, is illustrated by the dotted line. Wn is the concentration of Co(III) (acac), soluble in the surfactant micelles. The pH values are as follows A, 11.62 +, 10.84 , 10.28 and 0.9.56.

The effect of concentration of cationic (cetylpyridinium chloride, CPC), anionic (sodium dodecylsulfate, SDS) and nonionic (Twin-80) surfactants as well as effect of pH value on the characteristics of TLC separ ation has been investigated. The best separ ation of three components has been achieved with 210 M CPC and LIO M Twin-80 solutions, at pH 7 (phosphate buffer). Individual solution of SDS didn t provide effective separation of caffeine, theophylline, theobromine, the rate of separ ation was low. The separ ation factor and rate of separ ation was increase by adding of modifiers - alcohol 1- propanol (6 % vol.) or 1-butanol (0.1 % vol.) in SDS solution. The optimal concentration of SDS is 210 M. 

The method for creating acceptor sink condition discussed so far is based on the use of a surfactant solution. In such solutions, anionic micelles act to accelerate the transport of lipophilic molecules. We also explored the use of other sink-forming reagents, including serum proteins and uncharged cyclodextrins. Table 7.20 compares the sink effect of 100 mM (5-cyclodextrin added to the pH 7.4 buffer in the acceptor wells to that of the anionic surfactant. Cyclodextrin creates a weaker sink for the cationic bases, compared to the anionic surfactant. The electrostatic binding force between charged lipophilic bases and the anionic surfactant micelles... 

Traditionally, components of the NMF are measured following extraction of comeocytes recovered from superficial tape-strippings, or from direct extraction of the skin surface by attaching open-ended chambers to the skin and eluting with small volumes of aqueous buffers or dilute surfactant solutions. By analysing sequential tape strips recovered from the same site profiles of how NMF levels change with depth can be constructed. These profiles indicate that the levels of NMF decline markedly toward the surface of the skin. This is typical of normal skin exposed to routine soap washing where much of the readily soluble NMF is washed out from the superficial SC.83... 

Dissolution of Biotinylated Phospholipid in Nonionic Surfactant Solution. Solutions of the nonionic surfactant octaethylene-glycol mono-n-dodecylether (C12E8) at a concentration of 10-3 M in standard buffer were used to solubilize DMPE-B to obtain solutions of 5 x lO" M and 1.25 X 10" M of the modified phospholipid. The phospholipid was suspended in 100 ml of the C12E8 solutions and the mixture was vigorously stirred with heating to a uniform temperature of 60-70°C for about 45 minutes whereupon all of the DMPE-B was solubilized. Solutions of underivatized phospholipid in C12E8 were prepared in a similar fashion. 

Similar experiments were performed on solutions of avidin and BSA (both 10 6 M) and avidin, BSA, and lysozyme (all 10 M). In the avidin/BSA system, a total of 77% of the original avidin was recovered in resolubilized precipitate, while in the avidin/BSA/lysozyme system, 87% of the original avidin was recovered in resolubilized precipitate. As a control, solutions of myoglobin in buffer (10" M), BSA in buffer (10" M), and BSA plus lysozyme in buffer (both 10 M) were mixed with concentrated surfactant solution to obtain a mixture concentration of 4 x 10 M DMPE-B and 7.5 x 10 5 m C12E8. In each case, no turbidity developed in the solution and no precipitate was obtained upon prolonged centrifugation. Thus, it appears that precipitation is completely restricted to avidin, the protein to which the affinity phospholipid binds specifically. 

Surfactant Chemical Stability. Two approaches were used in assessing surfactant degradation over time. The first consisted of monitoring the pH of surfactant solutions that were in contact with pieces of reservoir rock over several months. Because only commercially available surfactants were tested and almost all of them contained secondary components, the pH data were rather inconclusive. The fact that reservoir solids have some buffering capacity made the interpretation of pH trends even more difficult. 

Park et al (2007) introduced two nonionic surfactants, APG and Brij30, and one anionic surfactant, SDS, to remediate phenanthrene-spiked kaolinite. These authors found that APG produced the highest electroosmotic flow and showed the best removal efficiency among tested surfactant solutions. An electrokinetic test using Brij 30 showed relatively low phenanthrene removal because of low electroosmotic flow, even though the surfactant showed better solubilization than did APG. However, electroosmotic flow using Brij 30 could be enhanced by addition of acetate buffer, thus enhancing removal efficiency. 

Figure 8.2. MEKC separation of some corticosteroids using (A) 50-mM SDS and (B) 50-mM sodium cholate as the surfactant in the run buffer. The solution also contained 25-mM sodium borate pH 9.0. The separation was performed with a 57-cm open tube capillary. The compounds were detected at 200mn.

FIGURE 6.9 Emission spectra of 104 in different surfactant solutions (0.5 mg polymer in phosphate-buffered saline (PBS), 10% w/v surfactant, 385 nm, 25°C) PBS, no surfactant cetylpyridinium chloride (CPC) Triton X-100 (160 mM) Tween 20 (81 mM) and Brij 35 (82 mM). The emission spectra were normalized so that the emission maxima intensities of all the samples are identical. (From Lavigne, J.J., et al., Macromolecules, 36, 7409, 2003. With permission.)... 

Reversed-Phase Liquid Chromatography (RPLC) is an important tool in protein chemistry. Examination of sorption isotherms revealed that alcohohc buffers did not desorb proteins near physiological pH in RPLC systems, while buffers containing a poly(ethoxy alcohol) surfactant did not desorb protein at pH 2, but they did at pH 7 with concentrations of surfactant apparently well above the critical micellar concentration (cmc) [2]. It has been proposed that a necessary condition for the desorption of a protein from a surface is that the surface tension of the solvent falls between that of the protein and the surface [6]. This condition is fiilfilled for many proteins with surfactant solutions near conditions of physiological pH and ionic strength. Therefore, it was expected that separations of proteins could be thieved in these conditions. 

Several variables should be considered in the development of an MLC procedure the nature of surfactmit and modifier, their concentrations, and pH. When a surfactant solution is used as mobile phase, the retention of solutes can be adequately controlled through the addition of a small amount of alcohol, and through variation of pH. The alcohol usually also improves the efficiency of the chromatographic peaks. Other variables that affect the retention and efficiency are temperature and ionic strength. However, most procedures are performed at room temperature, and the ionic strengfti is given by the combination of the surfactant and buffer in the mobile phase, and is not studied as a separate variable. 

Laboratory studies on oil displacement efficiency by surfactant-polymer flooding process have been reported by a number of investigators (1-10). In general, the process is such that after being conditioned by field brine or preflush, a sandstone core or a sandpack is oil-saturated to the irreducible water content. It is then waterflooded to the residual oil level. Finally, a slug of surfactant solution followed by a mobility buffer is injected. 

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