Normal phases, surfactants

An application of an LC-SFC system has been demonstrated by the separation of non-ionic surfactants consisting of mono- and di-laurates of poly (ethyleneglycol) (23). Without fractionation in the precolumn by normal phase HPLC (Figure 12.18 (a)) and transfer of the whole sample into the SFC system, the different homologues coeluted with each other. (Figure 12.18(b)). In contrast with prior fractionation by HPLC into two fractions and consequent analysis by SFC, the homologues in the two fractions were well resolved (Figures 12.18(c) and 12.18(d)). 

Figure 12.18 LC-SFC analysis of mono- and di-laurates of poly (ethylene glycol) ( = 10) in a surfactant sample (a) normal phase HPLC trace (b) chromatogram obtained without prior fractionation (c) chromatogram of fraction 1 (FI) (d) chromatogram of fraction 2 (F2). LC conditions column (20 cm X 0.25 cm i.d.) packed with Shimpak diol mobile phase, w-hexane/methylene chloride/ethanol (75/25/1) flow rate, 4 p.L/min UV detection at 220 nm. SFC conditions fused-silica capillary column (15 m X 0.1 mm i.d.) with OV-17 (0.25 p.m film thickness) Pressure-programmed at a rate of 10 atm/min from 80 atm to 150 atm, and then at arate of 5 atm/min FID detection. Reprinted with permission from Ref. (23).

Normal-phase chromatography is still widely used for the determination of nonpolar additives in a variety of commercial products and pharmaceutical formulations, e.g. the separation of nonpolar components in the nonionic surfactant Triton X-100. Most of the NPLC analyses of polymer additives have been performed in isocratic mode [576]. However, isocratic HPLC methods are incapable of separating a substantial number of industrially used additives [605,608,612-616], Normal-phase chromatography of Irgafos 168, Irganox 1010/1076/3114 was shown [240]. NPLC-UV has been used for quantitative analysis of additives in PP/(Irganox 1010/1076, Irgafos 168) after Soxhlet extraction (88%... 

There have been some examples of the use of LDMS applied to the analysis of compounds separated via TLC, although not specifically dealing with polymer additives [852]. Dewey and Finney [838] have described direct TLC-spectroscopy and TLC-LMMS as applied to the analysis of lubricating oil additives (phenolic and amine antioxidants, detergents, dispersants, viscosity index improvers, corrosion inhibitors and metal deactivators). Also a series of general organics and ionic surfactants were analysed by means of direct normal-phase HPTLC-LMMS [837]. Novak and Hercules [858] have... 

The sulfonate content was determined either by the well-known technique of two-phase titration with hyamine or by liquid chromatography (HPCL). Nonionic surfactants were analyzed by HPLC (16) in the reverse or normal phase mode depending on whether the aim was to determine their content in effluents or to compare their ethylene oxide distribution. 

Jandera, P., Holcapek, M., Theodoridis, G. (1998). Investigation of chromatographic behavior of alcohol ethoxylate surfactants in normal-phase and reversed-phase systems using high-performance liquid chromatography-mass spectrometry. J. Chromatogr. A 813(2), 299-311. 

Aliphatic AEOs, considered as environmentally safe surfactants, are the most extensively used non-ionic surfactants. The commercial mixtures consist of homologues with an even number of carbon atoms ranging typically from 12 to 18 or of a mixture of even-odd linear and a-substituted alkyl chains with 11—15 carbons. Furthermore, each homologue shows an ethoxymer distribution accounting typically for 1—30 ethoxy units with an average ethoxylation number in the range 5—15. The separation of the AEO complex mixtures was achieved by reversed-phase and normal-phase chromatographic systems [74—76]. 

Quaternary ammonium cationic surfactants, such as DTDMAC, were determined in digested sludge by using supercritical fluid extraction (SFE) and FIA-ESI-MS(+) after separation by normal phase LC. Standard compounds—commercially available DTDMAC— were used to check the results. The DTDMAC mixture examined showed ions at m/z 467, 495, 523, 551, and 579 all equally spaced by A m/z 28 (-CH2-CH2-) resulting from the ionisation of compounds like RR N (CH3)2 X (R = / RO as shown in Fig. 2.12.11(a) and (b) [22],... 

Flowing FS-MMLLE with on-line hyphenation to FtPLC has also been investigated. Sandahl et al. were the first to interface FS-MMLLE with reversed-phase HPLC for the on-line extraction of methyl-thiophanate in natural water, obtaining an LOD of 0.5 pg L-1.89 Also, a parallel FS-SLM and FS-MMLLE design was coupled on-line to reverse-phase HPLC for the extraction of methyl-thiophanate (by MMLLE) and its metabolites (by SLM) in natural water.90 In addition, on-line coupling of FS-MMLLE and normal-phase HPLC has been successfully applied in the determination of vinclozolin (Ee =118 and LOD = 1 pg I. ) in surface water91 and of in-sample ion-paired cationic surfactants (Ee > 250 and LOD = 0.7-5 ug L-1) in river water and wastewater samples.92... 

Norberg, J., E. Thordarson, L. Mathiasson, and J.A. Jonsson. 2000. Microporous membrane liquid-liquid extraction coupled on-line with normal-phase liquid chromatography for the determination of cationic surfactants in river and waste water. J. Chromatogr. A 869 523-529. 

The basic mode of mesophase formation is as described above for CTAB. However, as one might expect, things are not quite so straightforward and there are various types of mesophase which can be formed from various types of surfactant. The surfactant structure can be varied so that fluorocarbon chains can be employed in place of the hydrocarbon variety, while anionic (e. g. -SOa") and the neutral (e.g. -(0CH2CH2) -0H) polar headgroups are often used. These surfactants can then form a variety of different mesophases as a function of (mainly) concentration in the solvent of choice (normally water). These phases are the lamellar (L ) phase, a simple bilayer phase, and variations on the cubic (li, I2, Vi, V2) and hexagonal (H, H2) phases. For these last phases, the subscript 1 implied a normal phase as found in a water-rich system, while the subscript 2 implied a reversed phase as found in an oil-rich system. For the cubic phases, the letter F implied a micellar phase (e. g. 

However, while using microemulsion as an eluent, it should be remembered that several factors such as concentration of surfactants, co-surfactants and organic phase, pH of the aqueous phase, column temperature can influence the resolution and retention of the compounds. The microemulsions described so far are based on sodium dodecyl sulphate, short-chain alcohols such as butanol and octanol and aqueous phase of different pH values [78, 159-161]. The utility of w/o microemulsions in the normal phase HPLC analysis has also been described [162]. The microemulsion liquid chromatography (MELC) has been used for resolution of several API such as paracetamol, loratidine, simvastatin, niacinamide, fosinoprilat from their impurities or degradants or metabolic products [159-162]. 

Shang, D. Y., Ikonomou, M. G., and Macdonald, R. W., Quantitative determination of nonylphenol polyethoxylate surfactants in marine sediment using normal-phase liquid chromatography-electrospray mass spectrometry, J. Chromatogr. A, 849, 467-482, 1999. 

Four mesoporous silicas, formed of isometric particles with 2.8 nm and 5.6 nm pores, were prepared by varying the synthesis conditions (silica source, surfactant, pH and temperature). A part of each sample was silylated with C8 chains. The silanol and silyl groups contents were estimated by Si NMR. Good separations have been obtained on mixtures of aromatic molecules by normal-phase HPLC with the four materials. In reversed-phase HPLC the results exhibit differences in function of the pore filling by the silyl groups. 

The sequence in which reversed phases occur is much more complicated than that for the normal phases and is not yet understood in terms of surfactant molecular structures. The main reason is (probably) that there is no limitation on the radius of the inverse micelles such as that imposed by the length of the paraffin chain on normal micelles. Water could swell the micelles indefinitely (this does not happen because the size and shape of inverse micelles is controlled by limits on surfactant packing on a curved surface). Figure 21.12 (or something similar) is often employed to describe the general pattern of mesophase behaviour as a function of surfactant (water) concentration. In the description... 

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