Determination of Surfactants

Kawase et. al.[24] determined anionic surfactants using liquid-liquid extraction based on the methylene blue method at an early stage of development. Sahlestrom and Karl-berg [25] used the same reaction to determine anionic surfactants using a microconduit extraction system. The methods were not intended for very low concentration levels. 

Anionic surfactants were determined in river waters and treatment plant waters in the concentration range 0.04-3.5 pg ml based on an ion-pair extraction reaction with methylene blue in chloroform using a FI spectrophotometric system. Time-based continuous sampling was used to improve the sensitivity for meeting the requirements of environmental monitoring [26]. 

After an extensive comparison of different cationic dyes and extraction solvents for the FI liquid-liquid extraction spectrophotometric determination of anionic surfactants, Motomitzu et al.[27] recommended the use of Methylene Blue and 1,2-dichlorobenzene. A detection limit of 5 pg 1 was achieved with a sampling frequency of 20 h , and a precision of 0.9% r.s.d. in the analysis of river waters (for details cf. Sec. 8.8.2). 

Kawase [29] determined cationic surfactants by FI liquid-liquid extraction with chloroform after ion-pair formation with Orange II. The method features a high precision of 

Martinez-Jimenez et al.[30] determined cationic surfactants in natural, tap and waste waters indirectly by flame AAS. The method is based on the on-line extraction of the deteigent-tetrathiocyanatocobaltate(II) ion-pair into IBMK. The surfactants were determined by measurement of cobalt in the separated organic phase. A sampling frequency of 35 5 h was achieved with a precision of 1.2% r.s.d. 

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A reexamination of so-called renewabdity has shown that advantages for oleochemicals are not sufftcientiy clear (115), especially because manufacture of surfactants ia the United States accounts for only 0.03% of aimual cmde oil consumption (62). On these bases, the primary determinants of surfactant choice will continue to be cost effectiveness and availability. The 1993 U.S. market has been estimated to be worth 3.7 x 10 (110). Approximately one-half was anionic surfactant ( 1.8 x 10 ) and one-third nonionic surfactant ( 1.2 x 10 ). The balance was made up by cationics ( 1.2 X 10 ) and amphoterics ( 600 x 10 ). The U.S. International Trade Commission (116) provides a minutely detailed breakdown of surfactant production. 

ISO 7875-1 1984, Water quality. Determination of surfactants—Part 1 Determination of anionic surfactants by the methylene blue spectrometric method. 

The quantitative determination of surfactant concentration in solution is an essential part of any experimental work on surfactant adsorption or phase behaviour. In the field of experimental enhanced oil recovery the technique employed should be capable of determining surfactant concentrations in sea water, and in the presence of oil and alcohols, the latter being frequently added as a co-surfactant. 

Figure 1. CMC determination of surfactant mixtures. (Reproduced with permission from ref. 16. Copyright 1987 Deutsche Wissenschaftliche Gesellschaft.)...

Heinig, K., Vogt, C. (1999). Determination of surfactants by capillary electrophoresis. Electrophoresis 20(15-16), 3311-3328. 

Steinbrech, B., Neugebauer, D., Zulauf, G. (1986). Determination of surfactants by liquid chromatography (HPLC). Reversed phase ion-pair chromatography of alkyl sulfates and alkyl sulfosuccinates. Analytische Chemie 324(2), 154—157. 

Bruno F, Curini A, Di Corcia A, Fochi I, Nazzari M, Samperi R (2002) Determination of surfactants and some of their metabolites in untreated and anaerobically digested sewage sludge by subcritical water extraction followed by liquid chromatography-mass spectrometry. Environ Sci Technol 36 4156—4161... 

Direct determination of surfactants in complex matrices can also be carried out using ion-selective electrodes. Depending on the membranes and additives used, the detergent electrodes are optimized for the detection of anionic surfactants [81], cationic surfactants [82], and even nonionic surfactants [83]. The devices are sensitive to the respective group of surfactants but normally do not exhibit sufficient stability and reproducibility for their use in household appliances. With further optimization of membrane materials, plasticizers and measurement technology, surfactant-selective electrodes offer high potential for future applications. 

Many separation and detection methods applied in combination with liquid chromatography (LC) that are described in the literature for the determination of surfactants are not specific to the detection of these compounds at trace levels. Even ultraviolet (UV) spectra obtained from diode array detectors often give only limited information. Furthermore, non-reproducible retention behaviour as well as coelution interference effects are frequently observed during the separation of surfactant-containing extracts. This is recognised, however, only in those cases where specific detection methods such as mass spectrometry (MS) are applied. 

GC AND GC-MS DETERMINATION OF SURFACTANTS Francesc Ventura and Pint de Voogt... 

The trend of discovering the analytical field of environmental analysis of surfactants by LC-MS is described in detail in Chapters 2.6-2.13 and also reflected by the method collection in Chapter 3.1 (Table 3.1.1), which gives an overview on analytical determinations of surfactants in aqueous matrices. Most methods have focused on high volume surfactants and their metabolites, such as the alkylphenol ethoxylates (APEO, Chapter 2.6), linear alkylbenzene sulfonates (LAS, Chapter 2.10) and alcohol ethoxylates (AE, Chapter 2.9). Surfactants with lower consumption rates such as the cationics (Chapter 2.12) and esterquats (Chapter 2.13) or the fluorinated surfactants perfluoro alkane sulfonates (PFAS) and perfluoro alkane carboxylates (PFAC) used in fire fighting foams (Chapter 2.11) are also covered in this book, but have received less attention. 

Many chapters in this book, especially those dealing exclusively with LC-MS determination of surfactants and their metabolites, illustrate the power of MS state-of-the-art techniques for accurate determinations of polar organic pollutants in environmental samples. LC-ESI-MS(MS) is of unparalleled value in identifying and characterising degradative products and is a highly valuable tool in elucidating... 

The determination of surfactants in blends, formulations and environmental samples using FIA-API combined with MS and MS-MS... 

The prediction that LC-MS will become a powerful tool in the detection, identification and quantification of polar compounds such as surfactants in environmental analysis as well as in industrial blends and household formulations has proven to be true. This technique is increasingly applied in substance-specific determination of surfactants performed as routine methods. From this it becomes obvious that no other analytical approach at that time was able to provide as much information about surfactants in blends and environmental samples as that obtainable with MS and MS-MS coupled with liquid insertion interfaces. 

The development of an easy-to-handle method for the qualitative and quantitative determination of surfactants in consumer products was the goal for applying ESI in the FIA-MS(+/—) mode by direct infusion into the mass spectrometer. In this way Ci2, Ci4, Ci6 and Ci8 ASs could be determined besides other anionics (LASs, alkylcarboxylates), nonionics (alkyl polyglucosides (APGs)) and cationics (quats and ester-quats). The methods applied for concentration and determination (MS-MS) helped to identify the compounds and in addition deuterated internal standards were applied for confirmation [57]. 

Prior to the quantitative determination of surfactants from aqueous environmental samples, a preconcentration step is needed to enrich low amounts of target analytes and to remove interfering matrix components. 

Modern methods of sample handling for determination of surfactants in aqueous samples are practically all based on SPE and modifications thereof. Substantial reductions in analysis time, solvent consumption, sample volume required, and number of off-line steps have thus been achieved. This has not only increased the analysts capacity and analysis price per sample, but also decreased the risk of both analyte loss and contamination during sample handling. Whether or not this has indeed resulted in an increased quality of analytical results still needs to be validated through, e.g. intercalibration exercises. This aspect is discussed in more detail in Chapter 4. 

Analytical methods for the determination of surfactant in sludge-amended soils... 

Analytical methods used for the determination of surfactants and biodegradation products in subsurface and groundwaters... 

Zhang, X., J. K. Jackson, and H. M. Burt. 1996b. Determination of surfactant micelle concentration by a novel uorescence depolarization techniqlifiiochem. Biophys. MethoiM 145-150. 

Blake-Haskins, J., Scala, D., Rhein, L., et al. Determination of surfactant irritancy from the swelling behavior of a collagen membrane. J. Soc. Cosmet. Chem. 36 379, 1985. 

Lastly, the use of micellar mobile phases allows a convenient means of studying micelle - solute interactions (i.e. determination of binding constants) (1,10 4,105) as well as determination of surfactant CMC values (from breaks in the log k gQ vs. log C, plots)... 

Thus it is possible to estimate the time for surfactant adsorption required for the formation of black spots. Table 11.2 presents the clinical and threshold concentrations for total phospholipids (PL) and for disaturated phosphatidylcholine (DSPC) in each preparation. The most abundant PL of the lung surfactant system is DSPC, principally the DPPC species, which is believed the essential determinant of surfactant function in vivo [2], While DPPC is the only PL in EX, both IN and SU contain other PLs and small quantities of hydrophobic surfactant-associated proteins that may add to the desired functional properties of the material in situ. 

The laboratory determination of surfactants involves using methylene blue. This is done by measuring the color change in a standard solution of the dye. The surfactant can be measured using methylene blue, so its other name is methylene blue active substance (MBAS). 

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