Unknown surfactant

The high water-solubility of surfactants and their, often more polar, metabolites prevents direct application of gas chromatographic separation (GC) with appropriate detection. The necessary volatilisation without thermal decomposition can be achieved by derivatisation of the analytes, but these manipulations are time- and manpower-consuming and can be susceptible to discrimination. Additionally, each derivatisation step in environmental analysis is normally target-directed to produce volatile derivatives of the compounds to be determined. Unknown surfactants that are simultaneously present, but differ in structure and therefore cannot react with the derivatisation reagent, are discriminated under these conditions. 

The MS analysis using ESI was applied for the determination of an unknown surfactant compound contained in an extract of a shampoo formulation [44]. MS leading to sequential product ions helped to identify the constituents. The MS4 experiments together with other spectral observations confirmed the hypothesis that the unknown compound was a N-( 2-aminoethyl) fatty acid amide with the general formula R-C(0)-NH(CH2-CH2-N)R/R,/. An authentic sample of the proposed laury ampho mono acetate (LAMA) (R = -CH2-CH2-OH and R" = -CH2-CH2-COOH) that was available led to the same [M + H]+ parent ion at m/z 345. The fragmentation that could be observed under ESI-FIA-MS-MS(+) conditions resulted in an intensive examination of amide surfactants. However, only two of them—lauryl diethanol amide ([M + H]+ m/z 288), a non-ionic surfactant and laurylamido-(3-propyl betaine ([M + H]+ m/z 343)—... 

Fig. 3.14 Anodic stripping square-wave voltammetry (ASSWV) of 1 X 10- M Dependence of peak currents on the accumulation time, itacc = —0.8 V, tacc = 5 s. (1) organic carbon-free water and (2) double-distilled water contaminated by unknown surfactant. Additions of Triton X-100 to (2) inmg/1 (3) 0.1, (4) 0.3, (5) 0.5, (6) 0.8 and (7) 1. Esv/ = 30 mV, / = 100 Hz and AE = 2.4 mV (reprinted from [247] with permission)...

This double scan technique allows to experimentally estimate the characteristic parameter of an unknown surfactant from the value of a known one, which should preferably be close enough to make the change not too large. The advantage of the technique is that the contributions of the other variables (oil, alcohol, and temperature) do not need to be known accurately, because they are canceled out. This technique is particularly handy if the formulator has a series of known surfactants on hand that possess a wide range of characteristic values, from very hydrophilic to very Upophilic. It is recommended that the selected base surfactant have a characterisitic parameter close to the one of the unknown surfactant, so that the variation of optimiun formulation does not go outside the feasible scanned variable range. 

Figure 3.7 Principle of the double-scan technique to determine the characteristic parameter of an unknown surfactant.

A part of the base surfactant mixture, for instance 0.5 wt.% of the total 2 wt.%, that is 25%, is substituted by the unknown surfactant, indicated by subscript 3 in what follows. A scan is carried out by mixing the two base surfactants, i.e. by changing only a part of the three surfactant mixture, since the unknown surfactant content is constant, i.e. in... 

A cloud chamber operates on the principle that a supersaturated vapor phase is caused to condense into visible droplets by the passage of high energy particles. In a hypothetical experiment, an unknown particle induces the formation of 200 water droplets 2000 nm in diameter in a cloud chamber at 1 atm pressure and 25°C. The density and surface tension of water under the conditions of the experiment are 0.9971 g cm and 72.49 mN m respectively. Calculate the free energy increase caused by the passage of the particle. The surface tensions of a series of solutions of an unknown surfactant where found to be the following Concentration Concentration (mM) [Pg.175]

To classify an unknown surfactant, either acid or alkaline hydrolysis or both are carried out, and the reaction products are examined. Procedures for this examination are discussed later quantitative analysis of hydrolysis products is usually necessary. Comparison against the previously mentioned lists will in most cases identify the class of surfactant. Mixtures may present difficulties. 

The principles established in the preceding two sections can now be applied to identifying an unknown surfactant. The example of Figure 11.4 will be used here as the unknown, simply because the information obtained from this exercise will be applied later (section 11.6) to gain quantitative information about alkyl chain length and ethoxylate number for this anionic surfactant. 

Bare and Read describe a system by which the unknown surfactant mixture is first separated by TLC into the classes of anionics, cationics, and nonionics (14). The spots are then transferred to the FAB probe of a mass spectrometer for identification. 

Information provided by UV sjrectroscopy is usually limited to showing the presence or absence of an aryl group in the structure, although an experienced spectroscopist can often also distinguish phenyl from naphthyl character. Once other tests have indicated that an unknown surfactant is anionic, the UV spectram will indicate if it is an alkylbenzene-sulfonate or alkylnaphthalene sulfonate. If the surfactant is cationic, the UV spectrum will indicate whether or not one of the substituents is benzyl or pyridyl. If the surfactant is nonionic, the UV absorbance spectram indicates if a phenol or a naphthol group is present. With experience, it is possible to identify certain other functionalities of pure surfactant compounds (26). 

NMR spectroscopy is very useful for identifying organic compounds, provided that they can be obtained in a reasonably pure state. Kdnig has published a table of chemical shifts of functional groups found in common surfactants (39). This allows use of proton magnetic resonance to identify components of commercial products, where the range of possible structures is limited. Carminati and coworkers recommend the use of C NMR for the identification of unknown surfactants, both alone and in formulated products. With experience, not only the surfactants, but other components of products can be identified (40). 

The determination of nonionic surfactants has been demonstrated using mixed micelle formation. This relies on the principle that, to a great extent, micelle formation is additive, i.e., if two surfactants are present, each will be present in the micelles, and the critical micelle concentration (CMC) is the sum of the concentrations of the two surfactants. A dye is chosen which has an absorbance which changes if surfactant micelles are present in solution. A blank solution is titrated with a surfactant, usually an anionic, to determine the CMC. A solution of the unknown surfactant is then titrated, giving an apparent CMC lower than the blank. The difference in the two values represents the contribution of the unknown surfactant, a contribution which is additive over a useful concentration range (85). 

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). 

Penetration enhancers are low molecular weight compounds that can increase the absorption of poorly absorbed hydrophilic drugs such as peptides and proteins from the nasal, buccal, oral, rectal, and vaginal routes of administration [186], Chelators, bile salts, surfactants, and fatty acids are some examples of penetration enhancers that have been widely tested [186], The precise mechanisms by which these enhancers increase drug penetration are largely unknown. Bile salts, for instance, have been shown to increase the transport of lipophilic cholesterol [187] as well as the pore size of the epithelium [188], indicating enhancement in both transcellular and paracellular transport. Bile salts are known to break down mucus [189], form micelles [190], extract membrane proteins [191], and chelate ions [192], While breakdown of mucus, formation of micelles, and lipid extraction may have contributed predominantly to the bile salt-induced enhancement of transcellular transport, chelation of ions possibly accounts for their effect on the paracellular pathway. In addition to their lack of specificity in enhancing mem-... 

By asserting that the film thickness remains proportional to the 2/3 power of the capillary number, they establish that the dynamic pressure drop for surfactant-laden bubbles also varies with the capillary number to the 2/3 power but with an unknown constant of proportionality. New pressure-drop data for a 1 wt% commercial surfactant, sodium dodecyl benzene sulfonate (Siponate DS-10), in water, after correction for the liquid indices between the bubbles, confirmed the 2/3 power dependence on Ca and revealed significant increases over the Bretherton theory due to the soluble surfactant. 

Additionally, the test materials used in the validation process should be as closely related as possible to the characteristics of the unknowns to be tested. It is clear from the literature, for instance, that many cytotoxicity assays give good correlations with the in vivo ocular irritancy data for surfactants, but the correlations fail when compounds from other chemical classes are tested. Since any particular assay may be used differently by individual safety assessment programs, users must evaluate potential methods under conditions likely to be encountered in their own situations. 

Fig. 2.9.13. APCI-FIA-MS-MS(+) (CID) product ion mass spectrum of unknown parent ion with rn/z 598, identified as non-ionic surfactant of AP type (CnH2n+i-0-(CH(CH3)-CH2-0) ,-H) (inset) fragmentation scheme under CID conditions [24]. 

The situation is, however, different in the alveolar region of the lung where the respiratory gas exchange takes place. Its thin squamous epithelium is covered by the so-called alveolar surface liquid (ASL). Its outermost surface is covered by a mixture of phospholipids and proteins with a low surface tension, also often referred to as lung surfactant. For this surfactant layer only, Scarpelli et al. [74] reported a thickness between 7 and 70 nm in the human lung. For the thickness of an additional water layer in between the apical surface of alveolar epithelial cells and the surfactant film no conclusive data are available. Hence, the total thickness of the complete ASL layer is actually unknown, but is certainly thinner than 1 gm. 

Because the inverse Debye length is calculated from the ionic surfactant concentration of the continuous phase, the only unknown parameter is the surface potential i/io this can be obtained from a fit of these expressions to the experimental data. The theoretical values of FeQx) are shown by the continuous curves in Eig. 2.5, for the three surfactant concentrations. The agreement between theory and experiment is spectacular, and as expected, the surface potential increases with the bulk surfactant concentration as a result of the adsorption equilibrium. Consequently, a higher surfactant concentration induces a larger repulsion, but is also characterized by a shorter range due to the decrease of the Debye screening length. 

The area between phases A is the surface area of the drops. It will clearly be a strong function of the stirring characteristics (we assume that stirring is always fast enough to mix both phases). The presence of surfactants, drop size distributions, stirrer design, and circulation patterns. Interfacial area is frequently an unknown in emulsion reactors, but the above formulation should be applicable. Another complication in emulsion reactors is the fact that mass transfer coefficients depend strongly on drop size and stirring rate. The relevant parameter in an emulsion reactor is A km wilh neither factor known very well. 

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