Thermospray surfactants

Examples of such compounds include anionic surfactants whose analysis had previously been limited to desorption techniques such as FAB and thermospray but which yielded interpretable El spectra when using a parUcle-beam interface... 

Applications Various surfactant types (ABS, AES, secondary alkane sulfonates, and alkylphenol ethoxy-sulfates) have been analysed by means of a QQQ using a thermospray source [89]. Other applications of hyphenated thermospray ionisation mass-spectrometric techniques (LC-TSP-MS) are described elsewhere (Section 73.3.2). 

Evans et al. [4] carried out a quantitative determination of linear primary alcohol ethyoxylate surfactants in environmental waters by thermospray liquid chromatography-mass spectrometry. 

With the advent of new, more versatile and more robust LC-MS interfaces based on atmospheric-pressure ionization, the use of thermospray will rapidly diminish. However, the above-mentioned applications in sugar analysis as well as a large number of other applications in organic ion analysis such as phenoxy-acetic acids [128], quaternary ammonium pesticides [129, 130], anionic surfactants [131, 132], sulfated azo dyes [133, 134], sulfonamides [135], and ff-lactam antibiotics [136, 137] have proved the potential of this coupling technique in qualitative and quantitative analysis. 

Schroder [88,89] analyzed fluorinated surfactants in water and wastewater using HPLC coupled by a thermospray interface to a tandem mass spectrometer (MS/MS). Alternatively, the chromatographic column was bypassed and the analyte was injected into the mass spectrometer (FIA, flow injection analysis). 

Schroder [20b] used high-performance liquid chromatography (HPLC)/ mass spectrometric (MS)/MS with a thermospray interface [20c] to detect, identify, and quantify metabolites of Fluowet OTN, a nonionic fluorinated surfactant with the structure R F2,i+iCH2CH2(OCH2CH2)wOH. The biodegradation was limited to the poly(oxyethylene) hydrophile [20b]. The absence of fluoride ions indicated that the perfluorocarbon chain was not degraded. 

Mass spectrometric detection allows analysis of most nonionic surfactants without deriva-tization. Thermospray, electrospray, or atmospheric pressure chemical ionization interfaces permit direct introduction of the effluent of the LC into the MS and make the MS a very selective detector for nonionics. Quasimolecular ions are produced for each discrete compound, so that the HPLC system is not required to separate both by degree of ethoxylation and by alkyl character. A relatively simple HPLC separation, coupled with MS anal-... 

Ott, K. H., W. Wagner-Redeker, W. Winkle, On-line thermospray-LC-MS of nonionic surfactants (in German), Fett VW.m. TechnoL, 1987, 89, 208-213. 

It is a challenge to analyze surfactants by the most common configuration of MS GC-MS. As discussed in Chapter 8, most surfactants are not sufficiently volatile to pass through the GC unless they are first derivatized or degraded to form volatile products. Liquid chromatography-MS presents problems of its own, since there is no one LC-MS interface suitable for all compounds. The use of LC-MS in characterizing surfactants in the environment has been reviewed (1). Electrospray ionization gives better results for surfactants than thermospray, with not much published on particle beam or atmospheric pressure ionization of surfactants. 

Continuous flow FAB has been demonstrated for HPLC detection of the components of ditallowdimethylammonium chloride fabric softener. In this technique, the matrix substance is added to the HPLC colunrn effluent prior to introduction to the MS. MS-MS was demonstrated for confirmation of identity. While continuous flow FAB is typically performed with aqueous HPLC systems, the solubility of dialkyl quats is such that normal phase HPLC with nonpolar solvents is preferred. Lawrence was able to adapt a FAB system to this analysis, using a matrix solution of 75 25 glycerol/methanol (118). The use of FAB for analysis of surfactants has dropped off sharply with the availability of electrospray and thermospray interfaces for HPLC-MS. 

As is the case with other fluoro compounds, negative ion MS of fluorinated surfactants is more informative and less subject to interference than is positive ion MS. Negative ion spectra generated by thermospray analysis of perfluorinated alkyl compounds are dominated by peaks at intervals of Am/z 50 or 100, corresponding to loss of the CF2 and C2F4 groups (38). 

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