Anionic surfactants environmental analysis

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]. 

The qualitative determination of anionic surfactants in environmental samples such as water extracts by flow injection analysis coupled with MS (FIA-MS) applying a screening approach in the negative ionisation mode sometimes may be very effective. Using atmospheric pressure chemical ionisation (APCI) and electrospray ionisation (ESI), coupled with FIA or LC in combination with MS, anionic surfactants are either predominantly or sometimes exclusively ionised in the negative mode. Therefore, overview spectra obtained by FIA—MS(—) often are very clear and free from disturbing matrix components that are ionisable only in the positive mode. However, the advantage of clear... 

Two independent analytical methods—LC-MS-MS and 19F-NMR— for the determination of perfluorinated anionic surfactants in environmental water samples were presented. Perfluorinated alkanesulfonates and perfluorocarboxylates were determined qualitatively and quantitatively because of an accidental release of perfluorosurfactant contaminated fire-fighting foam [55]. Ci8-SPE was applied for concentration of the compounds from water samples. Methanol was used for elution prior to ESI-LC-MS(—) analysis. The negatively recorded LC-MS-MS TIC for the determination of PFOS, PFHxS, PFOA, perfluor-oheptanoic acid (PFHpA), perfluorododecanoic acid (PFDoA internal standard) in water samples was presented [55]. 

In polymer applications derivatives of oils and fats, such as epoxides, polyols and dimerizations products based on unsaturated fatty acids, are used as plastic additives or components for composites or polymers like polyamides and polyurethanes. In the lubricant sector oleochemically-based fatty acid esters have proved to be powerful alternatives to conventional mineral oil products. For home and personal care applications a wide range of products, such as surfactants, emulsifiers, emollients and waxes, based on vegetable oil derivatives has provided extraordinary performance benefits to the end-customer. Selected products, such as the anionic surfactant fatty alcohol sulfate have been investigated thoroughly with regard to their environmental impact compared with petrochemical based products by life-cycle analysis. Other product examples include carbohydrate-based surfactants as well as oleochemical based emulsifiers, waxes and emollients. 

Depending on the nature of the hydrophilic groups of surfactants, they can be divided into anionic, nonionic, cationic, and amphoteric surfactants. The last-mentioned class only plays a minor role with respect to domestic and industrial applications and practically no methods for the environmental analysis of amphoteric surfactants have been published so far. 

GC analysis of LAS is only possible after derivatization into volatile derivatives. Desulfonation of LAS in the presence of strong acids like phosphoric acid leads to linear alkylbenzenes (LAB). The identification of every single LAB isomer by GC-FID is achieved with detection limits lower than 1 /rg/1. In an alternative derivatization method, LAS are converted into their alkylbenzene sulfonyl chlorides by PCI5, which can be directly analyzed by GC-FID. Derivatization reactions for aliphatic anionic surfactants have mainly been described for product analysis. Among the very few methods for environmental analysis, the derivatization of alkyl sulfates to their corresponding trimethylsilylesters followed by determination with GC-FID is mentioned here. ... 

Some reviews were published dealing with this type of interface and its application in environmental analysis [24, 42, 123). Qualitative and quantitative analysis of polar pollutants by FAB or CF-FAB was performed with extracts of aqueous matrices, such as wastewater, surface water, seawater, raw and drinking water [124-129], for all types of surfactants (non-ionics, anionics, cationics and amphoterics) in urban wastewaters, receiving waters (rivers and costal receiving areas), and groundwater [124-148], for metabolites of surfactants [130, 149-153], and bromi-nated surfactants [137, 154). 

The anionic surfactant sodium dodecylsulfate (SDS) is by far the most commonly used surfactant in micellar separations. Examples of the use of simple buffered/SDS systems in environmental applications include the simultaneous analysis of 10 A-methylcarbamate pesticides and their hydrolytic phenolic metabolites in river, well, and pond water (pH 8 phosphate/borate buffer/SDS), and the analysis of insecticides (imidacloprid and its metabolite 6-chloronicotinic acid) in air samples collected from a greenhouse cropped with tomatoes (pH 8.5 ammonium chloride/ammonia buffer/SDS). ... 

FAB or LSIMS using a probe inlet does not readily lend itself to quantitative work. Firstly, it is not possible to know how much of the sample has been consumed in the analysis. Secondly, discrimination effects (see section 12.3.3) prevent the comparison of intensities between species of differing surface activity. Semiquantitative results may be readily obtained if discrimination effects are assumed to be constant for the species of interest, for example the determination of homologue distributions in a mixture. For accurate quantitation an internal standard of an isotopically enriched analogue of the analyte should be used. For example, in the determination of cationic surfactants in environmental samples [10], quantitation was achieved by using an internal standard of a trideuterated form of the analyte. In this way the standard will be subject to the same level of discrimination as the analyte. Discrimination effects between different cationic species may also be reduced by adding to the sample an excess of a highly surface-active anionic surfactant. The anionic species will dominate the matrix surface and attract cations into the surface monolayer [10]. 

Ion-selective electrodes (ISEs) constitute an example of potentiometric sensors that offer several advantages over other analytical techniques for the analysis of environmentally important ions. Specifically, the sensing platform of a membrane-based ISE consists of an ion carrier (ionophore) entrapped within a liquid polymeric membrane. The membrane does offer some interaction with numerous species, but the main interaction governing the selectivity of the sensor is between the analyte/interferences and the ionophore. Once an ionophore that offers the preferred selectivity has been developed and the polymer components that are ionophore-compatible have been optimized, the production of a functional ISE is rather facile and rapid. Presently, ISEs have been reported for several species including metal ions, anions, surfactants, and gases (5). 

Hons, G., Alkylarylsulfonates history, manufacture, analysis, and environmental properties, in H. W. Stache, ed.. Anionic Surfactants Organic Chemistry, Marcel Dekker, New York, 1996. 

Like the two-phase titration methods (Chapter 16), almost all of the colorimetric methods rely on the formation of an ion pair by the anionic surfactant and a cation, in this case a dye. The ion pair is extractible into an organic solvent, while the dye alone is not, so the color of the organic phase is directly proportional to the surfactant concentration. This approach is suitable for determination of low concentrations and has been used most often for environmental analysis. 

Because of its simplicity, the methylene blue ion pair method has been a standard for environmental analysis for a half-century. The absorbance of the ion pair is maximum at about 658 nm, depending on the specific anionic surfactant. Maximal color extraction is reached after a minute of agitation, and the color is stable in the organic phase for a half-hour (13). The methylene blue method is susceptible to positive and negative interference, and this... 

While infrared spectrophotometry is most useful for the qualitative analysis of surfactants, various quantitative methods have been developed for well-characterized systems. For example, an attenuated total reflectance cell with a ZnSe crystal is useful for direct analysis of aqueous anionic surfactant solutions by FTIR, while avoiding the deleterious effects of water on the usual transmission cells. In this case, the sulfonate absorbance at 1175 cm" , or the sulfate absorbance at 1206-1215 cm , is used for quantification (10,26). In another application, the weak absorption bands in the 1429-1333 cm" region are used to measure the relative amounts of linear and branched chain alkylbenzene sulfonates extracted from environmental waters (27). This is the one advantage of the infrared technique over those that have supplanted it for wastewater analysis its ability to differentiate the straight and branched chain compounds (28). No procedure will be given here, since the cleanup prior to IR analysis can be handled adequately by the method for LAS analysis by desulfona-tion/gas chromatography, described in Chapter 8. 

Nowadays, it is rare for infrared techniques to be used for qualitative or quantitative analysis of environmental materials. In either case, exhaustive separation of the surfactant from other materials must first be made. It is possible for inexperienced practitioners to go far wrong when identifying materials by IR, a technique best applied to pure compounds. Most environmental extracts, even after substantial cleanup, are mixtures which give complex spectra. It requires an experienced analyst to obtain useful information from the spectrum of a mixture containing unknown materials. As a general rule, a compound cannot be said to be present unless all of its characteristic absorbance bands are exhibited by the mixture. A once-common use of IR spectroscopy was confirmation of the identity of anionic surfactants isolated by the methylene blue spectrophotometric method. By proper choice of workup procedures and bands, this approach permitted exact determination of individual types of surfactants (78). 

Mass spectrometric analysis of cationic surfactants is difficult, so MS has not been applied as much to environmental analysis of cationics as it has to anionics and nonionics. 

Ion-selective electrodes (ISEs) are used in clinical, pharmaceutical or environmental analysis for the detection not only of inorganic ions but also of some organic species such as anionic or cationic surfactants. However, the need for an internal filHng solution causes many problems, such as fragihty, and it is obstructive for miniaturization. The need for microstructures or even nanostructures leads to the concept of an all-solid-state ISE. 

The analyses of environmental samples confirmed the ubiquitious presence of surfactants in surface and sea water as a result of the surfactants discharged with STP effluents. Analysis of River Elbe (Germany) water samples by GC-MS and APCl-LC-MS and MS/MS confirmed qualitatively the presence of nonpolar and polar organic pollutants of AEO, NPEO, CDEA and aromatic sulfonic acid type, respectively [226], After Cjg and/or SAX SPE anionic and non-ionic surfactants were qualitatively and quantitatively analysed in surface water samples by APCI-LC-MS in the negative or positive mode, respectively. Alkylphenol ethoxylates (APEOs) could be confirmed in river water at levels of 5.6 pg L [331]. 

Inaba reports that AE-type nonionics may be isolated from environmental waters by toluene extraction (113). The presence of salts, as in sea water, will cause the co-extraction of anionic siufactants and other materials, so that a preliminary ion exchange step may be required prior to extraction. Liquid-liquid extraction with methylene chloride is generally applicable to isolation of ethoxylated surfactants from water (114). Liquid-liquid extraction with chloroform or methylene chloride was found to be equivalent to sublation in concentrating the NPE metabolite nonylphenoxyacetic acids from water. A pH of 2 is suitable for the extraction (35). Sublation was superior for analysis of sewage, since emulsion formation was minimized (115). 

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