Analysis of nonionics

This chapter deals with the analysis of individual nonionic surfactants. Analysis of raw materials includes not only the determination of the active content, but also of impurities and by-products, and determination of oxyalkylene chain length. Any nonionic can be determined in formulated products by deionisation, which was described in section 4.6.2 and is not further discussed here. Nonionic fractions isolated in this way may have more than one principal active, and some of the methods given here are applicable to the analysis of such mixtures. There are also a few procedures for the determination of nonionics in formulated products. 

Ethoxylated carboxylic acids may be regarded as monoesters of polyethylene glycol. If made by ethoxylation of the acid, all the carboxylate groups become ethoxylated before further addition of ethylene oxide occurs, so that there is no unreacted acid in the product. However, transesterification can occur between two molecules of the ethoxylate, with production of a molecule of diester and a molecule of polyethylene glycol  

Such materials therefore usually contain free polyethylene glycol and diester in equimolar proportions. The spread of EO chain lengths is similar to that in alkylphenol ethoxylates. If they are made by esterification of polyethylene glycol, the spread of EO chain lengths obviously depends on the composition of the starting material, and the product always contains unreacted free fatty acid as well as diester and polyethylene glycol [2]. 

Hydrocarbon and ethylene oxide chain-length distributions are determined by gas or liquid chromatography. 

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Deionized water can be used as an eluent for the analysis of nonionic polymers such as pullulan and polyethylene glycol. However, in most cases, salt solutions or buffer solutions are used to decrease ionic or other interactions between samples and the stationary phase or to prevent sample association (Eigs. 6.22 and 6.23, pages 196 and 197). 

Rivera, J., Carxach, S., Ventura, F. et al. FAB-CAD-MIKES. Analysis of nonionic surfactant in raw sewage sludges, (ed J.F.F.Todd), Proceedings of the 10th International Mass Spectrometry Conference, Swansea September 9-13 1985, J.Wiley, Basingstoke, UK (1985). 

We have previously reported on the coupling of an SEC to a mass spectrometer operated in the electrospray mode of ionization and its application to the molecular weight characterization of octylphenoxy-poly(ethoxy)ethanol oligomers (20). The analysis of nonionic surfactants... 

High-performance liquid chromatography is performed using a Hewlett-Packard 1090 chromatograph equipped with a ternary-solvent delivery system, an autoinjector with a 0 -20- u.L injection loop, an oven compartment, and a diode-array UV detector. An ELS detector (Alltech Associates, Deerfield, IL) is connected in series to the UV detector. Hexane, 2-propanol, and water were used for the analysis of nonionic surfactants. Water and tetrahydrofuran (THF) are used for the analysis of anionic surfactants. No preliminary sample preparation is used other than dilution. The nonionic surfactants are diluted 1 40 (v/v) with hexane. The anionic surfactants (alkyl ether sulfates and synthetic and petroleum sulfonates) are diluted 1 20 (v/v) with water-THF (50 50). The calcium sulfonate surfactants were diluted 1 20 (v/v) with a THF-38% hydrochloric acid solution of pH 1. Hydrochloric add is required to prevent salt precipitation by converting any excess water-insoluble caldum carbonate into water-soluble calcium chloride. All diluted samples are... 

Garti, N., Kaufman, V. R., Avraham, A. 1987. Analysis of nonionic surfactants by high-performance liquid chromatography. In Cross. J, ed. Nonionic Surfactant Ghemical Analysis. New York Marcel Dekker, Vol. 19, pp. 225-283. 

Another interesting sorbent type is the Amberlite XAD range of resins. These are cross-linked polystyrene resins, like many ion-exchange resins, but without the ionic functional groups. XAD-1 to XAD-4 differ in specific surface and pore size. XAD-7 has carboxylic ester groups. They have been used for the analysis of nonionics [12-14] and cationics... 

Applications, Analysis of aikylbenzene sulphonates and alkyl sulphonates on a fused silica open tubular column (10 m x 0.53 or 0.25 mm i.d.) coated with 0.1 or 0.2 micron SE54 with carbon dioxide as mobile phase and FID is described in [8]. The anionics were derivatised before analysis. Among the many examples of analysis of nonionic surfactants are the following ... 

Particle beam (PB) El MS is less sensitive than capillary GC-MS. This can be partly compensated for by the fact that much larger volumes of sample can be introduced in the LC-MS method [8]. The method can therefore be applied to the trace analysis of nonionic surfactants. Certain species, which due to their low volatility, high polarity or thermal instability cannot be detected by GC-MS, can be analysed by LC-PB-MS. Similarly, some highly volatile species are difficult to analyse by PB-MS, and the two techniques are therefore complementary. 

Suggest how ion chromatography can be used for the analysis of nonionic gases. 

The application of UV spectroscopy to the analysis of nonionic hydrocarbon-type surfactants is limited to nonionics, which contain functional groups which absorb in the UV region, such as aromatic nuclei [65]. The main functional group of nonionics, the oxyethylene ether linkage, does not absorb in the UV region. In spite of this limitation, UV spectroscopy can be useful for determining impurities in nonionic fluorinated surfactants. 

Either HPLC or TLC analysis is suitable for determining noncarboxylated ethoxylate impurities, as described in Chapters 7 and 9. These impurities can also be determined on a preparative scale by passing an ethanolic solution through an anion exchange column the nonionics pass through unretained (142). A simple hydroxyl number determination, as described for the analysis of nonionics in Chapter 2, is used for quality control determination of residual nonionic surfactant and PEG (145). 

Noguchi, K., Y. Yanagihara, M. Kasai, B. Katayama, Chromatographic properties of a vinyl alcohol copolymer gel column for the analysis of nonionic surfactants, / Chromatogr., 1989, 461, 365-375. 

Rockwood, A. L., T. Higuchi, LC/MS analysis of nonionic surfactants using the frit-FAB method, Tenside, Surfactants, Deterg., 1992,29,6-12. 

The low volatility of nonionic surfactants makes them challenging subjects for GC analysis. Even with the best of derivatization and high-temperature techniques, oligomers containing more than about 20 EO units will not elute from the GC column. Quantitative GC analysis of nonionics of higher degree of ethoxylation requires chemical reaction to put the sample into a more volatile form. 

Kusz, R, J. Szymanowski, E. Dziwinski, Analysis of nonionic surfactants after their predegradation with acetyl chloride, Proc. Second World Surfactants Congress, Paris, 1988, 239-248. Szymanowski, J., P. Kusz, E. Dziwinski, H. Szewczyk, K. Pyzalski, Degradation and analysis of polyoxyethylene monoalkyl ethers in the presence of acetyl chloride and ferric chloride, J. Chromatogr., 1989,469, 197-208. 

TABLE 5 Capillary Electrophoresis Analysis of Nonionic Surfactants... 

The commercial nonionic surfactants do not absorb radiation in the visible spectrum. The simplest form of spectrophotometric analysis of nonionics is the direct measurement of the UV absorbance of the sample. The ethoxylated alkylphenols are the only compounds which can be readily determined by this method, with a maximal absorbance at about 223 nm and another peak at 276 nm (69). Ethoxylated amides may be determined in model systems by their absorption of light at 202 nm (70), but many other compounds found in typical samples also have absorbance in this region. Because of the sensitivity of direct UV analysis to interference, it can only be used in well-defined situations. Interferences often encountered in nonionic surfactants are oxidation inhibitors like butylated hydroxytoluene. 

NMR is quite suitable for the characterization of nonionic surfactants and even of mixtures of surfactants. NMR is used to determine the concentration ratios of various functionalities in a sample which is concentrated and reasonably pure. If a mixture of materials is present, such as a blend of polyethylene glycol and ethoxylated surfactant, this must be known in advance or false qualitative and quantitative information will be developed. A review of NMR analysis of nonionic surfactants appears in a companion volume of the Surfactant Science Series (17). 

MS has found most use in qualitative rather than quantitative analysis of nonionic surfactants. This is partly due to their lack of volatility, but also because the ionization efficiency varies for different homologs and oligomers, so that the average degree of ethoxylation found by MS usually differs from that found by other methods. Nonionics are usually analyzed in the positive ion mode. Few negative ions are formed hydroxyl groups are not deprotonated in the mass spectrometer. Rauscher has compiled a table of fragments found in the MS analysis of common nonionic surfactants (40). 

Because of the lack of specificity, polarographic techniques are only useful for analysis of real world samples if they are coupled with separation procedures. For example, one team has demonstrated that the BIAS procedure for trace analysis of nonionics can be improved by using an electrochemical procedure for surfactant determination after first precipitating and isolating the potassium iodobismuthate-nonionic complex from the sample (18,26). They prevent interference of hydrocarbons by washing the precipitate with isooctane (27). 

X-ray fluorescence can be used for trace analysis of nonionic surfactants. In this case, the analysis is performed according to the titrimetric method using tetraiodobismuth-ate reagent, but the final measurement of bismuth concentration in the precipitate is made not by potentiometric titration, but by XRF (109). 

Alumina can be used for cleanup of extracts during analysis of nonionic surfactants. A great many ionic and polar nonionic impurities are removed by this treatment (107). Typically, impurities are eluted from the alumina with 50 50 hexane/methylene chloride, followed by elution of the surfactants with 100 1 methylene chloiide/methanol. 

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