Surfactant-containing mobile

Examination of equations 5, 6, and 7 reveals that retention can be controlled by variation of the surfactant micelle concentration, variation of pH (for ionizable species), and by manipulation of the solute-micelle binding constant (K. ) which, in turn can be influenced by additives (salt, alcohol referto data on DDT, Table VI) or the type (charge and hydrophobicity) of micelle-forming surfactant employed (refer to data in Table VII for 1-pentanol). Table VIII summarizes some of the factors that influence retention for surfactant-containing mobile phases and compares the effect of changes in these factors upon the retention behavior observed in both micellar liquid and ion-pair chromatography (81). 

The main disadvantages of micellar chromatography are the observed diminished chromatographic efficiency, higher column back pressure, and in preparative work, the need to separate the final resolved analyte from the surfactant (95) (a later section of this review will discuss this latter problem and its resolution in further detail). The higher column back pressure and part of the decreased efficiency stem from the fact that surfactant-containing mobile phases are more viscous compared to the usual hydro-organic mobile phases employed in conventional RP-HPLC (refer to viscosity data in Table X)... 

Summary of Some Selected Separations Reported which have Utilized Surfactant-Containing Mobile Phases ... 

J.F. Clos and J.G. Dorsey, Enhanced Stability of Electrochemical Detection with Surfactant Containing Mobile Phases in LC and Flow-Injection Analysis, Anal. Lett., 23 2327 (1990). 

Surface active electrolytes produce charged micelles whose effective charge can be measured by electrophoretic mobility [117,156]. The net charge is lower than the degree of aggregation, however, since some of the counterions remain associated with the micelle, presumably as part of a Stem layer (see Section V-3) [157]. Combination of self-diffusion with electrophoretic mobility measurements indicates that a typical micelle of a univalent surfactant contains about 1(X) monomer units and carries a net charge of 50-70. Additional colloidal characterization techniques are applicable to micelles such as ultrafiltration [158]. 

While mechanistic simulators, based on the population balance and other methods, are being developed, it is appropriate to test the abilities of conventional simulators to match data from laboratory mobility control experiments. The chapter by Claridge, Lescure, and Wang describes mobility control experiments (which use atmospheric pressure emulsions scaled to match miscible-C02 field conditions) and attempts to match the data with a widely used field simulator that does not contain specific mechanisms for surfactant-based mobility control. Chapter 21, by French, also describes experiments on emulsion flow, including experiments at elevated temperatures. 

Early researchers sought to choose appropriate surfactants for mobility control from the hundreds or thousands that might be used, but very little of the technology base that they needed had yet been created. Since then, work on micellar/polymer flooding has established several phase properties that must be met by almost any EOR surfactant, regardless of the application. This list of properties includes a Krafft temperature that is below the reservoir temperature, even if the connate brine contains a high concentration of divalent ions (i.e., hardness tolerance), and a lower consolute solution temperature (cloud point) that is above the reservoir temperature. 

Countercurrent chromatography can be used to extract and to concentrate, in a low volume of stationary phase, a component present in large volumes of mobile phase. It was shown that a 60-mL CCC instrument was able to extract 285 mg of a nonionic surfactant contained in 20 L of water (at 16.5 ppm or mg/L) and to concentrate it into 30 mL of ethyl acetate (at 9500 ppm or 9.5 g/L) [4]. 

When C02 foam is to be used for mobility control, it would be advantageous to inject (after the surfactant pad) a mixture of about 80% C02 and 20% surfactant-containing brine. The operational problem is the same as that faced when the use of WAG was first considered. If the two phases were to be simply pumped simultaneously into the injection well, there would be difficulties of two types. First, because the required injection pressures for the two specified rates would probably be far different from each other, the existing types of pumps would not work well together. Second, because of the appreciable difference in density between C02 and brine, the two fluids would probably not enter both upper and lower parts of the formation at the same relative rates. Worse, the extent of such gravity segregation in the wellbore would be unknown. 

As ultrafast MAS does not completely averages out the effects of multispin dipolar coupHngs in dense H networks, H NOESY-like spectra can be recorded to obtain structural information, using spin diffusion to mediate the magnetization transfer (Fig. 3.10 for an example with the P-L-Asp-L-Ala dipeptide). This is especially useful when the sample contains mobile molecules (e.g., hosted in mesoporous compounds) as spin diffiision and/or NOE transfers are stiU active and provide information about atomic proximities in the absence of recoupling. This has been illustrated at 40 kHz MAS for zeolites and surfactants for enhanced resolution [126]. Moreover, combining deuteration and ultrafast MAS suppresses the spin diffusion between protons and open a new route to observe chemical exchange between H in proteins [127]. 

This book provides an introduction to the nature, occurrence, physical properties, propagation, and uses of surfactants in the petroleum industry. The primary focus is on applications of the principles of colloid and interface science to surfactant applications in the petroleum industry, and includes attention to practical processes and problems. Books available up to now are either principally theoretical (such as the colloid chemistry texts), much more general (like Rosen s Surfactants and Interfacial Phenomena, Myers Surfactant Science and Technology, or Mittal s Solution Chemistry of Surfactants), or else much narrower in scope (like Smith s Surfactant Based Mobility Control). The applications of surfactants in the petroleum industry area are quite diverse and have a great practical importance. The area contains a number of problems of more fundamental interest as well. Surfactants may be applied to advantage in many parts of the petroleum production process in reservoirs, in oilwells, in surface processing operations, and in environmental, health, and safety applications. In each case appropriate knowledge and practices determine both the economic and technical successes of the industrial process concerned. 

Surfactants (surface active agents) are very important constituents of many industrial formulations. In these formulations, it is often not just one compound that is of interest. Rather, the overall identity, as determined by the presence and distribution of the individual components, is critical. Kondoh et al. [224] developed a method for determining non-ionic surfactants containing ester groups, such as sorbitan and sucrose fatty acid esters and polyoxyethylene fatty acid esters, as their o-nitro-phenylhydrazine derivatives. To remove the residual free fatty acid fraction, 6 mM triethylamine (TEA) was added to the 85/15 methanol/water starting mobile phase. The free fatty acids then eluted in the void volume and the separation of the analytes of interest was conducted on a C]g column (A = 550 nm). Elution and identification up to the penta-ester resulted when a 50-min 0/85/1575/25/0 ethanol/ methanol/water (6 mM TEA) gradient was used. 

Fluorescence probe and fluorescent label are two approaches that are generally applied to the study of surfactant-containing systems, yielding information on the properties of the micro-domain, such as the mean aggregation number and the mobility or fluidity of the aggregates. Pyrene is one of the popular... 

Mass-action model of surfactant micelle formation was used for development of the conceptual retention model in micellar liquid chromatography. The retention model is based upon the analysis of changing of the sorbat microenvironment in going from mobile phase (micellar surfactant solution, containing organic solvent-modifier) to stationary phase (the surfactant covered surface of the alkyl bonded silica gel) according to equation ... 

The pur pose of work is to develop the technique of separ ation of purine bases (caffeine, theophylline, theobromine) and the technique of detection of purine bases in biological fluid by TLC using micellar mobile phases containing of different surfactants. 

ANALYSIS OF MEDICINES BY TEC IN MOBILE PHASES CONTAINING SURFACTANTS AND CYCLODEXTRINES... 

The recent use of HPLC for the analysis of sulfophenyl carboxylates (SPCs) has been one of the most interesting applications of this technique for the study of the environmental behaviour of anionic surfactants. SPCs are separated by reversed-phase ion-paired chromatography, in which a hydrophobic stationary phase is used and the mobile phase is eluted with aqueous buffers containing a low concentration of the counter-ion [19]. 

One of the main problems to be solved in the analysis of cationic surfactants is the strong adsorption of the surfactant to glassware, tubing and apparatus. To avoid losses, the solvent system used should contain a substantial percentage of organic solvent. Additionally, mobile phases containing more than 20-25% methanol will help to inhibit micelle formation [46]. 

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