Surfactants, determination separation

Surfactants are separated according to adsorption or partitioning differences with a polar stationary phase in NPLC. This retention of the polar surfactant moiety allows for the separation of the ethylene oxide distribution. Of all the NPLC packings that have been utilized to separate nonionic surfactants, the aminopropyl-bonded stationary phases have been shown to give the best resolution (Jandera et al., 1990). The separation of the octylphenol ethoxylate oligomers on an amino silica column is shown in Fig. 18.4. Similar to the capabilities of CE for ionic surfactants, the ethylene oxide distribution can be quantitatively determined by NPLC if identity and response factors for each oligomer are known. 

CPE is a technique in which an aqueous solution, upon addition of a surfactant and raising the temperature to its cloud point, becomes turbid and amenable to splitting into two phases a surfactant phase and a dilute aqueous phase (Hinze and Pramauro, 1993). A consolute curve (i.e., cloud point versus concentration curve) may be determined, separating the one-phase and two-phase regions of... 

Another characteristic is the surface activity how much surfactant is needed, or more precisely, how large should the surfactant activity be, to reach a certain value of r (or of y) The differences between a soap and a polymer are illustrated in Figure 2.8. It is seen that the polymer is far more surface active the value of me needed to obtain the same F is smaller by about 2 orders of magnitude for the polymer the difference expressed in mass concentration is even more, by about 4 orders of magnitude. Soaps and pol3miers also differ in the applicability of eqn. (2.35). For a soap, it nearly always appears to hold, also in an emulsion. For a polymer, equilibrium is often not obtained, at least in the timescales considered see e.g. ref 1 for explanations. This is borne out by the two curves for /3-casein in Figure 2.8 the one obtained by emulsification does not agree at all with the adsorption isotherm obtained by unhindered adsorption on a macroscopic interface. For a soap, the value of F can be calculated from the adsorption isotherm when an emulsion is made from known quantities of materials and the specific surface area is known. This is not so for a polymeric surfactant, where F has to be determined separately. 

According to Kunkel [67], the cationic surfactants are, by blowing out, concentrated in ethyl acetate and largely separated from interfering non-surfactant substances. Additions of an anionic surfactant and a neutral salt to the water sample ensure a complete transfer into the organic phase. After separation of the layers and evaporation of the solvent, the anionic surfactants are separated off by means of ion exchangers and the cationics are determined photometrically by a modified disulfine blue method. To avoid troublesome turbidity in this method, the dye complex formed is removed from the CHCI3 solution and redissolved in methanol. 

Because of the lack of specificity, polarographic techniques are only useful for analysis of real world samples if they are coupled with separation procedures. For example, one team has demonstrated that the BIAS procedure for trace analysis of nonionics can be improved by using an electrochemical procedure for surfactant determination after first precipitating and isolating the potassium iodobismuthate-nonionic complex from the sample (18,26). They prevent interference of hydrocarbons by washing the precipitate with isooctane (27). 

Discussion If the nonionic surfactant is contaminated by the presence of polyethylene glycols, these should be separated by extraction (Chapter 6) and determined separately. This same method serves for determination of PEG. The pH of the system is critical. If the final solution is diluted, as, for example, by use of a larger sample size than specified, the white precipitate of hydrated bismuth hydroxide will form. The procedure has been tested for ethoxylation products of fatty acids, fatty alcohols, amines, alkylphe-nols, and amides, as well as the polyethyene and polypropylene glycols. In the case of surfactants with low degree of ethoxylation, it may be necessary to dissolve the sample in isopropanol, rather than water, and dilute to a final concentration of 60 40 2-P1OH/H2O. 

Tajima and co-workers [108] determined the surface excess of sodium dode-cyl sulfate by means of the radioactivity method, using tritiated surfactant of specific activity 9.16 Ci/mol. The area of solution exposed to the detector was 37.50 cm. In a particular experiment, it was found that with 1.0 x 10" Af surfactant the surface count rate was 17.0 x 10 counts per minute. Separate calibration showed that of this count was 14.5 X 10 came from underlying solution, the rest being surface excess. It was also determined that the counting efficiency for surface material was 1.1%. Calculate F for this solution. 

An unknown commercial detergent may contain some combination of anionic, nonionic, cationic, and possibly amphoteric surfactants, inorganic builders and fillers as weU as some minor additives. In general, the analytical scheme iacludes separation of nonsurfactant and inorganic components from the total mixture, classification of the surfactants, separation of iadividual surfactants, and quantitative determination (131). 

For fluorescence PAH determination in tap water acid-induced cloud point extraction was used. This kind of extraction based on the phase separation into two isotropic liquid phases a concentrated phase containing most of the surfactant (surfactant-rich phase), where the solubilised solutes are exttacted, and an aqueous phase containing a surfactant concenttation closes to the critical micellar concentration. 

The first two aspects entail relatively high concentrations of surfactants. In the last case, trace amounts are to be determined. When performing surfactant analysis, preconcentration and/or separation of the different surfactant classes are prerequisites for identifying and quantifying the compound in question. Furthermore, the trend is to analyze the individual components of any surfactant mixture. 

A sensitive determination of alkanesulfonates combines RP-HPLC with an on-line derivatization procedure using fluorescent ion pairs followed by an online sandwich-type phase separation with chloroform as the solvent. The ion pairs are detected by fluorescence. With l-cyano-[2-(2-trimethylammonio)-ethyl]benz(/)isoindole as a fluorescent cationic dye a quantification limit for anionic surfactants including alkanesulfonates of less than 1 pg/L per compound for a 2.5-L water sample is established [30,31]. 

Baviere et al. [41] determined the adsorption of C18 AOS onto kaolinite by agitating tubes containing 2 g of kaolinite per 10 g of surfactant solution for 4 h in a thermostat. Solids were separated from the liquid phase by centrifugation and the supernatant liquid titrated for sulfonate. The amount of AOS adsorbed is the difference between initial solution concentration and supernatant solution concentration at equilibrium. 

The amount of residual sulfonate ester remaining after hydrolysis can be determined by a procedure proposed by Martinsson and Nilsson [129], similar to that used to determine total residual saponifiables in neutral oils. Neutrals, including alkanes, alkenes, secondary alcohols, and sultones, as well as the sulfonate esters in the AOS, are isolated by extraction from an aqueous alcoholic solution with petroleum ether. The sulfonate esters are separated from the sultones by chromatography on a silica gel column. Each eluent fraction is subjected to saponification and measured as active matter by MBAS determination measuring the extinction of the trichloromethane solution at 642 nra. (a) Sultones. Connor et al. [130] first reported, in 1975, a very small amount of skin sensitizer, l-unsaturated-l,3-sultone, and 2-chloroalkane-l,3-sultone in the anionic surfactant produced by the sulfation of ethoxylated fatty alcohol. These compounds can also be found in some AOS products consequently, methods of detection are essential. 

The analytical methods for a-sulfo fatty acid esters reported in the literature deal with the determination of the surfactants in different matrices like detergents or product mixtures from the fabrication. The methyl esters of a-sulfo fatty acids can be separated from a mixture of different surfactants together with sulfonated surfactants by adsorption on an anionic exchanger resin such as Dowex 1X2 or 1X8. Desorption from the exchanger resin is successful with sodium hydroxide (2%) in a 1 1 mixture of isopropanol and water [105]. 

Collagen, the major component of most connective tissues, constimtes approximately 25% of the protein of mammals. It provides an extracellular framework for all metazoan animals and exists in virmally every animal tissue. At least 19 distinct types of collagen made up of 30 distinct polypeptide chains (each encoded by a separate gene) have been identified in human tissues. Although several of these are present only in small proportions, they may play important roles in determining the physical properties of specific tissues. In addition, a number of proteins (eg, the Clq component of the complement system, pulmonary surfactant proteins SP-A and SP-D) that are not classified as collagens have... 

SFC-FID is widely used for the analysis of (nonvolatile) textile finish components. An application of SFC in fuel product analysis is the determination of lubricating oil additives, which consist of complex mixtures of compounds such as zinc dialkylthiophosphates, organic sulfur compounds (e.g. nonylphenyl sulfides), hindered phenols (e.g. 2,6-di-f-butyl-4-methylphenol), hindered amines (e.g. dioctyldiphenylamines) and surfactants (sulfonic acid salts). Classical TLC, SEC and LC analysis are not satisfactory here because of the complexity of such mixtures of compounds, while their lability precludes GC determination. Both cSFC and pSFC enable analysis of most of these chemical classes [305]. Rather few examples have been reported of thermally unstable compounds analysed by SFC an example of thermally labile polymer additives are fire retardants [360]. pSFC has been used for the separation of a mixture of methylvinylsilicones and peroxides (thermally labile analytes) [361]. 

Major applications of modern TLC comprise various sample types biomedical, pharmaceutical, forensic, clinical, biological, environmental and industrial (product uniformity, impurity determination, surfactants, synthetic dyes) the technique is also frequently used in food science (some 10% of published papers) [446], Although polymer/additive analysis takes up a small share, it is apparent from deformulation schemes presented in Chapter 2 that (HP)TLC plays an appreciable role in industrial problem solving even though this is not reflected in a flood of scientific papers. TLC is not only useful for polymer additive extracts but in particular for direct separations based on dissolutions. 

Normal-phase chromatography is still widely used for the determination of nonpolar additives in a variety of commercial products and pharmaceutical formulations, e.g. the separation of nonpolar components in the nonionic surfactant Triton X-100. Most of the NPLC analyses of polymer additives have been performed in isocratic mode [576]. However, isocratic HPLC methods are incapable of separating a substantial number of industrially used additives [605,608,612-616], Normal-phase chromatography of Irgafos 168, Irganox 1010/1076/3114 was shown [240]. NPLC-UV has been used for quantitative analysis of additives in PP/(Irganox 1010/1076, Irgafos 168) after Soxhlet extraction (88%... 

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