Reference compounds anionic surfactants

The common gangue material quartz (silica) is naturally hydrophilic and can be easily separated in this way from hydrophobic materials such as talc, molybdenite, metal sulphides and some types of coal. Minerals which are hydrophilic can usually be made hydrophobic by adding surfactant (referred to as an activator ) to the solution which selectively adsorbs on the required grains. For example, cationic surfactants (e.g. CTAB) will adsorb onto most negatively charged surfaces whereas anionic surfactants (e.g. SDS) will not. Optimum flotation conditions are usually obtained by experiment using a model test cell called a Hallimond tube . In addition to activator compounds, frothers which are also surfactants are added to stabilize the foam produced at the top of the flotation chamber. Mixtures of non-ionic and ionic surfactant molecules make the best frothers. As examples of the remarkable efficiency of the process, only 45 g of collector and 35 g of frother are required to float 1 ton of quartz and only 30 g of collector will separate 3 tons of sulphide ore. 

As such, when considering this class of compounds as environmental contaminants, they are referred to as the perfluorocarboxylates. Some authors prefer to remove the A from the acronyms of individual PFCAs (i.e. PFO instead of PFOA) to indicate the anion, but in this discussion acronyms of individual PFCAs are used interchangeably to refer to both the anion and free acid forms. Like the PFSAs, PFCAs are also anionic surfactants. 

SDDBS and AOT denote the anionic surfactants sodium dodecyl-benzenesulfonate and sodium dioctyl-sulfosuccinate, respectively. Triton X-100 is the nonionic surfactant nonylphenol decafethylene-glycolether). Compound 1 is a mixture of sihcone oil and hydropho-bized silica Compound 2 is an emulsion of Compound 1, which contains also solid particles of Span 60. Data from References 684 and 687. 

After the deconvolution step, giving the contribution coefficients of reference spectra (see Chapter 2), the parameters calculation is possible by using the same coefficients and a corresponding calibration file (Fig. 11). This calibration file includes the corresponding concentrations for specific compounds (nitrate, nitrite, anionic surfactants, etc.) and the values related to the reference spectra of mixtures (Table 3). The latter are statistically calculated for the purpose, through a preliminary stepwise regression study, from a set of at least 30 samples (with 30 corresponding values of parameters and 30 sets of contribution coefficients). 

The anionic category represents the major part of surfactant consumption. Anionic surfactants include linear alkylbenzene sulphonates (LASs), alcohol sulphates or alcohol ethersulphates. The latter compounds have a poor absorption in the UV range, whereas the LASs show a significant absorption (see Chapter 11). Dodecylbenzene sulphonate (DBS) is used as a reference for LAS measurements (standard method) and shows an absorption band at 225 nm (Fig. 14). 

Higher order aUphatic quaternary compounds, where one of the alkyl groups contains - 10 carbon atoms, exhibit surface-active properties (167). These compounds compose a subclass of a more general class of compounds known as cationic surfactants (qv). These have physical properties such as substantivity and aggregation ia polar media (168) that give rise to many practical appHcations. In some cases the ammonium compounds are referred to as iaverse soaps because the charge on the organic portion of the molecule is cationic rather than anionic. 

Linear alkylbenzenesulfonates (LAS), alcohol ethoxylates (AEO), and nonylphenol ethoxylates (NPEO) are synthetic surfactants used in the formulation of detergents and other cleaning products and are widely applied in the dye and leather industry and other industrial processes. These compounds, considered as estrogenic, have aroused considerable interest due to the large quantities produced globally. Their low volatility and anionic form make LC-based methods the preferred approach [7]. Due to the presence of different positional isomers, to the biodegradation intermediates, and to the lack of reference standards, LC-MS, and in particular with ESI, is the only technique which enables their identification and quantification in environmental waters. 

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