Surfactant procedure

A recent design of the maximum bubble pressure instrument for measurement of dynamic surface tension allows resolution in the millisecond time frame [119, 120]. This was accomplished by increasing the system volume relative to that of the bubble and by using electric and acoustic sensors to track the bubble formation frequency. Miller and co-workers also assessed the hydrodynamic effects arising at short bubble formation times with experiments on very viscous liquids [121]. They proposed a correction procedure to improve reliability at short times. This technique is applicable to the study of surfactant and polymer adsorption from solution [101, 120]. 

Prior to about 1920, flotation procedures were rather crude and rested primarily on the observation that copper and lead-zinc ore pulps (crushed ore mixed with water) could be benefacted (improved in mineral content) by treatment with large amounts of fatty and oily materials. The mineral particles collected in the oily layer and thus could be separated from the gangue and the water. Since then, oil flotation has been largely replaced by froth or foam flotation. Here, only minor amounts of oil or surfactant are used and a froth is formed by agitating or bubbling air through the suspension. The oily froth or foam is concentrated in mineral particles and can be skimmed off as shown schematically in Fig. XIII-4. 

There are many laboratory methods for testing the relative merits of one defoamer against another. It is a simple matter to measure foam height as a function of time to compare the performance of various foam surfactants and defoamers. Unfortunately, this simplicity has led to a wide variety of methods and conditions used with no standard procedure that would make the measurement of foaminess as characteristic of a solution as its surface tension or viscosity. It has been suggested that the time an average bubble remains entrapped ia the foam is such a quantity (49), but very few workers ia the defoamer iadustry have adopted this proposal. Ia practice, a wide variety of methods are used that geaerally fall iato oae of five maia categories ... 

Recent publications indicate the cloud-point extraction by phases of nonionic surfactant as an effective procedure for preconcentrating and separation of metal ions, organic pollutants and biologically active compounds. The effectiveness of the cloud-point extraction is due to its high selectivity and the possibility to obtain high coefficients of absolute preconcentrating while analyzing small volumes of the sample. Besides, the cloud-point extraction with non-ionic surfactants insures the low-cost, simple and accurate analytic procedures. 

The system of anionic surfactants is another example of organic compounds mixtures. The procedure of their determination is proposed using coordinate pH in two-dimensional spectra of ionic associates anionic surfactants with rhodamine 6G. This procedure was tested on the analysis of surfactant waters and domestic detergents. 

The method of the analysis of the CS described in the international standai d ASTM (D 820 - 93) is a long time, multi-stage procedure. Accuracy of AIST determination is low, since surfactants determined by an indirect method of subtraction. Thus, the objective of our research was to develop an exact and express method of AIST determination in CS. 

The aqueous micellai solutions of some surfactants exhibit the cloud point, or turbidity, phenomenon when the solution is heated or cooled above or below a certain temperature. Then the phase sepai ation into two isotropic liquid phases occurs a concentrated phase containing most of the surfactant and an aqueous phase containing a surfactant concentration close to the critical micellar concentration. The anionic surfactant solutions show this phenomenon in acid media without any temperature modifications. The aim of the present work is to explore the analytical possibilities of acid-induced cloud point extraction in the extraction and preconcentration of polycyclic ai omatic hydrocai bons (PAHs) from water solutions. The combination of extraction, preconcentration and luminescence detection of PAHs in one step under their trace determination in objects mentioned allows to exclude the use of lai ge volumes of expensive, high-purity and toxic organic solvents and replace the known time and solvent consuming procedures by more simple and convenient methods. 

An obvious modification of the above procedure will permit the determination of long-chain amines or quaternary ammonium salts (cationic surfactants) ... 

The higher molecular weight unbranched C10-C18 n-olefins—not only a-olefins but also n-olefins with internal double bonds, so-called n-vj/-olefins—are important initial products for the manufacture of anionic surfactants, e.g., linear alkylbenzenes or olefinsulfonates. These linear C10-C18 olefins are manufactured technically by the following procedures ... 

Higher molecular primary unbranched or low-branched alcohols are used not only for the synthesis of nonionic but also of anionic surfactants, like fatty alcohol sulfates or ether sulfates. These alcohols are produced by catalytic high-pressure hydrogenation of the methyl esters of fatty acids, obtained by a transesterification reaction of fats or fatty oils with methanol or by different procedures, like hydroformylation or the Alfol process, starting from petroleum chemical raw materials. 

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]. 

Alcohol sulfates commonly have free alcohol and electrolytes as impurities. Other hydrophobic impurities can also be present. A method suitable for the purification of surfactants has been proposed by Rosen [120]. Consequently, commercial products have CMCs that deviate from the accepted reference values. This was demonstrated by Vijayendran [121] who studied several commercial sodium lauryl sulfates of high purity. The CMC was determined both by the conductimetric method and by the surface tension method. The values found were similar for both methods but while three samples gave CMC values of 7.9, 7.8, and 7.4 mM, close to the standard range of 8.0-8.2 mM, three other samples gave values of 4.1, 3.1, and 1.7 mM. The sample with a CMC of 7.9 mM was found to have a CMC of 8.0 mM with no detectable surface tension minima after purification and recrystallization. This procedure failed in all other cases. 

Solutions with low content of alcohol and alcohol ether sulfates cannot be analyzed by the two-phase method and specialized procedures have been developed. ISO method 7875/1 [267] is the standard method for analyzing sulfates and other anionic surfactants at very low concentrations, such as in waste-waters. The absorbance of the chloroform layer containing the surfactant-dye complex is spectrometrically measured at 650 nm and quantified using a calibration curve. Different improvements of this method have been developed [268,269]. 

Similarly, the presence of sulfonate esters also indicates incomplete hydrolysis. Residual saponifiable material in a final AOS product is then a measure of the quality of the surfactant. In practice, such material can be extracted, subjected to drastic conditions of saponification, and the quantity of residual saponifiable material calculated. Methods have been developed which can be used for the determination of 10 or more ppm of saponifiable material in the neutral oil of AOS. Unfortunately, the procedures outlined below are now of historic interest only, since they give unrealistically high values for residual saponifiable material content. Methods listed in the sultones section are now the analyses of choice. 

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. 

Although the chlorosultones can be isolated by the same procedure, the isolation is tedious at concentrations below 5 ppm. The chlorosultones are best determined by performing two analyses, one on the intact surfactant and one in which the sultone-containing concentrates are treated with collidine to de-hydrohalogenate the chlorosultones before measurement of the total quantity of unsaturated sultones. 

Brain et al. [137] reported a tandem mass spectrometry (MS-MS) procedure by which a direct measurement from an n-pentane extract of a surfactant is possible. This procedure is excellent from the standpoint of sensitivity and simplicity of sample preparation but is not commonly applied because of the need of an MS-MS instrument. 

In a broad evaluation also the sulfosuccinate disodium laureth sulfosuccinate (DLSS) was a part of a variety of surfactants tested for their dermatological mildness, and some different test methods were applied [16]. Products were compared applying in vitro methods (Zein test, hemolysis) and in vivo methods (Duhring-Chamber test, skin mildness by intracutaneous test on mice and topical application on hairless mice, mucous membrane irritation according to the Draize procedure on rabbit eyes). In the Duhring-Chamber test the DLSS elicited no reactions in the animal tests it ranged in the least irritant third of the 15 products tested. 

In Fig. 11 results are given for sulfosuccinate surfactants of different molecular structure tested according to the Draize skin irritation procedure. The test method defines test scores verbally as described in Table 21. The data in Fig. 11 prove the nonirritant character of sulfosuccinates tested at 10% concentration. Similar results were found for another group of sulfosuccinates [103]... 

In the production of anionic surfactants, the analytical procedures to be adopted for quality control and/or assessment are of particular importance. Their reliability as well as their time and chemical demand is a fundamental topic for the economy and success of the surfactant production cycle. To this end the most important analyses to be done on the various types of anionic surfactants are outlined in Tables 15-19. Mention must be made of potentiometric titration of the sulfonic acid (whatever the processed feedstock), which allows one to obtain reliable results over a very short time. 

From surfactant molecules it is known that the repeated vertical dipping of a substrate through a floating monolayer of these molecules leads to the formation of an LB multilayer on the substrate. In principle, the same procedure should also allow the preparation of multilayers of latex particles. In Figure 8b, the preparation of a particle bilayer is schematically indicated multiple repetition should result in the formation of an LB multilayer of particles. However, if one tries to realize this concept, one immediately gets into difficulties, because the contact of the particles with the underlying substrate is very poor, and the already deposited particle layer tends to detach from the surface when the substrate is dipped into... 

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