Cationic surfactants isolation

The bioluminescence spectrum of P. stipticus and the fluorescence and chemiluminescence spectra of PM are shown in Fig. 9.7. The fluorescence emission maximum of PM-2 (525 nm) is very close to the bioluminescence emission maximum (530 nm), but the chemiluminescence emission maximum in the presence of a cationic surfactant CTAB (480 nm) differs significantly. However, upon replacing the CTAB with the zwitter-ionic surfactant SB3-12 (3-dodecyldimethylammonio-propanesulfonate), the chemiluminescence spectrum splits into two peaks, 493 nm and 530 nm, of which the latter peak coincides with the emission maximum of the bioluminescence. When PM-1 is heated at 90°C for 3 hr in water containing 10% methanol, about 50% of PM-1 is converted to a new compound that can be isolated by HPLC the chemiluminescence spectrum of this compound in the presence of SB3-12 (curve 5, Fig. 9.7) is practically identical with the bioluminescence spectrum. 

Liquid-liquid extraction is used extensively and successfully (6). If the analytes are acidic or basic, as is often the case when HPLC is the analytical method selected, appropriate ionization suppression can be employed to affect the desired extraction. Back extraction of the analytes into an appropriately buffered aqueous volume can then serve to isolate and concentrate. Anionic and cationic surfactants, or so-called ion-pairing reagents, can be added prior to extraction to increase the partition coefficients of the trace organic ionic compounds. 

Kupfer" ° applied the same sublation procedure for isolation of cationic surfactants. Eor separation of anionic and nonionic surfactants, the sublation extract is passed through a cation exchanger. Afterwards, the adsorbed cationic surfactants are eluted with methanolic HCl. 

IR spectroscopy is used for the qualitative identihcation of surfactants and for differentiating between them and nonsurfactant compounds. Prior to IR spectroscopy, however, separation of the organic compound complex into different fractions, performed by, e.g., the use of thin-layer chromatography, is required to obtain meaningful spectra. °" ° By comparing the IR spectra of the isolated fractions with IR spectra of standard compounds with regard to characteristic bands, the qualitative determination of surfactants in environmental samples is possible. The method is equally applicable to anionic, ° nonionic, °" and cationic surfactants.The prerequisite for a clear identification of surfactants, however, is the availability of suitable standards. Moreover, considerable experience and knowledge are needed to interpret IR spectra of environmental samples. 

The presence of a cationic surfactant is also necessary to achieve a selective condensation between indene and benzaldehyde in water. A catalytic amount of CTACl favors the bis-condensation, while a large excess of surfactant allows the mono-adduct to be isolated quantitatively [6a]. 

Isolated as the hexachloantimonate (V) complex after benzene extraction Sensitive color reaction with antimony (III) by use of cationic surfactants Antimony (Ill)-iodide complex formation in the presence of ascorbic acid Ion pair or ion association extraction by use of toluene or benzene as solvents... 

Equivalent weight of sulfated and sulfonated anionics can be determined directly by titration with base or by titration with a cationic surfactant. This requires that the active agent be isolated in relatively pure condition. A more general procedure is the para-toluidine hydrochloride method, which includes pimification of the anionic by extraction to eliminate interferences commonly found in detergents. These procedures are described in Chapter 16. 

I, Cationic surfactants from nonionic surfactants Dowex 50-X4, acid form 4—5 g of mixture dispersed in 100 mL water is stirred 4—5 hr with 20 g resin, keeping the mixture acid to Congo red by addition of HCl. The resin is wa.shed with 95% EtOH, the filtrate and washings neutralized and evaporated to dryness, then washed with acetone to isolate the nonionic. 42... 

Infrared spectra of the most common cationic surfactant, distearyldimethylammo-nium chloride are very simple, little different from hydrocarbon spectra. The two methyl groups and the N-C group cannot be distinguished from the overpowering -CH2- bands, at least not by ordinary dispersive IR (23). Cross published information on the infrared spectra of the tetraphenylborate salts of common cationics (24). He finds IR spectroscopy suitable for the classification (he reserved the term identification for a technique which would give the exact length of the alkyl chain) of surfactants isolated by precipitation from complex samples. 

In another version of this procedure the nonionic surfactant was first extracted batch-wise with sodium tetraphenylborate into 1,2-dichloroethane. The tetraphenylborate in the isolated organic phase was then titrated with a cationic surfactant, using Victoria Blue B as indicator (70). This titration can also be performed to an electrochemically detected end point. In this version, an excess of anionic surfactant is added to the cationic complex formed by the ethoxylated nonionic surfactant and potassium ion. The ion pair is extracted into dichloroethane, separated from the initial aqueous phase, then titrated with cationic surfactant in the presence of additional water. The ion pair of the anionic surfactant and Fe(II)(l,10-phenanthroline)3 is added as indicator. The end point of the titration is indicated when the last of the anionic surfactant is complexed by the cationic titrant, causing the iron-phenanthroline cation to migrate to the aqueous phase, where it is detected as a change in potential at a platinum electrode (71). 

A more efficient method of isolating anionic surfactants is extraction as part of an ion pair (33). An inorganic salt is added to decrease the solubility of the ion pair in the aqueous phase. Sometimes, the methylene blue spectrophotometric method described in Chapter 12 is used as the cleanup step. This permits the analyst to estimate the amount of surfactant isolated before proceeding with more definitive analytical techniques. Methylene blue may be removed from the surfactant extract by passage through a cation exchange column (56). If concentration is performed by liquid-liquid extraction of the ion pair with an alkyl quaternary compound, the UV spectrum of the ion pair is identical to that of LAS alone (55). 

Figure C2.3.14. Isolated surfactant modes of adsorjDtion at liquid-solid interfaces for a surfactant having a distinct headgroup and hydrophobic portion (dodecyltrimetlrylammonium cation) (a), (b) headgroup specific interaction (c), (d) hydrophobic tail interaction, (e),(f) headgroup and tail interactions.

A synthetic alternative to this is the chemical reduction of metal salts in the presence of extremely hydrophilic surfactants have yielded isolable nanometal colloids having at least 100 mg of metal per litre of water [105], The wide range of surfactants conveniently used to prepare hydrosols with very good redispersibility properties include amphiphilic betaines A1-A4, cationic, anionic, nonionic and even environmentally benign sugar soaps. Table 3.1 presents the list of hydrophilic stabilizers used for the preparation of nanostructured colloidal metal particles, and Table 3.2 shows the wide variety of transition metal mono- and bi-metallic hydrosols formed by this method [105,120],... 

The solvent sublation procedure of Wickbold [18] is another method that has been used for the analysis of LAS present in seawater [19,20], The solvent sublation technique (gaseous stripping into organic solvent, often ethyl acetate) has also been used to isolate and concentrate nonionic surfactants, e.g. AEs and APEO in aqueous samples [21,22], The co-extracted interferences can be eliminated by cation/anion ion-exchange and alumina chromatography [23,24]. 

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