Stationary phases permanently coated

When strongly hydrophobic cationic surfactants are present in the mobile phase the hydrophobic surface of the stationary phase becomes dynamically conditioned with respect to the adsorption of the surfactant. This confers an ion-exchange capability on the stationary phase. Cassidy and Elchuk (32, 33) reported use of cetylpyridinium chloride to coat the stationary phase "permanently", but used tetrabutyl and tetramethylammonium salts in the mobile phase. Their equilibration procedure also employed the use of acetonitrile in the initial conditioning step, thus increasing the overall cost of the analysis. Knox and Hartwick (36)... 

In gas-solid chromatography (GSC) the stationary phase is a solid adsorbent, such as silica or alumina. The associated virtues associated therewith, namely, cheapness and longevity, are insufficiently appreciated. The disadvantages, surface heterogeneity and irreproducibility, may be overcome by surface modification or coating with small amounts of liquid to reduce heterogeneity and improve reproducibility 4,15). Porous polymers, for example polystyrene and divinyl benzene, are also available. Molecular sieves, discussed in Chapter 17, are used mainly to separate permanent gases. 

Phases made by covalently bonding a molecule onto a solid stationary phase are intended to prepare liquid coatings which will be permanent. Silica is a reactive substrate to which various functionalities can be attached or bonded. The functionalities most widely bonded to silica are the alkyl (C 8 and C8), aromatic phenyl, and cyano and amino groups. The most popular bonded phase is the octadecylsiloxy support commonly referred to simply as a Ci8 phase or an ODS phase. Bonding the silica with a nonpolar functional group alters the surface chemistry of the silica particle to an essentially nonpolar one. However, since the starting surface is silica, a totally nonpolar surface will never be attained. This, in itself, is not a problem but it does mean that bonded phases are unique entities and not easily classified as liquid-solid or liquid-liquid surfaces. 

Permanently coated stationary phases were also used in the presence of an IPR in the eluent different from that used for the coverage. Incorporation of a non-ionic surfactant in the coating solution proved very useful for improving peak shape the underlying material in coated columns still participates in analyte retention [10]. 

As mentioned in the introduction, the explosive growth of HPLC would not have taken place without the recognition that instead of coating the stationary phase to the silica surface, a permanent bonded phase would do away with some... 

Traditional gaseous fuel analysis is based on packed columns. Multidimensional chromatography, i.e. the use of columns with different retention characteristics coupled in series in one GC system, improves resolution of complex samples. But packed-column systems are not normally able to separate all compounds. To obtain more precise information about the composition of a gas sample, capillary columns were introduced in fuel analysis. The first were wall-coated open tubular (WCOT) columns with a nonpolar methylsilicone as stationary phase for hydrocarbon separation. However, the permanent gases were still separated in packed columns containing cross-linked polystyrene carbosieve, and molecular sieve as separation phases. 

The use of bilayer coatings was reported from Kapnissi et al. [31], where a permanently adsorbed coating of a cationic polymer salt [poly(diaIlymethylammo-nium chloride)] was covered with a dynamically adsorbed polymeric surfactant [poly (sodium undecylenic sulfate)]. In contrast to the stable coatings, the adsorbed layers can be easily prepared. Traditionally, polymeric surfactants have been used in MEKC [38] and the separation principle can therefore be transferred to o-CEC. However, several other types of dynamically attached pseudo-stationary phases (PSPs) exist, such as cyclodextrins [39], dendrimers [40], proteins [41], liposomes [42], ionenes [43], siloxanes [44] micelles [3, 38] and microemulsions [45]. Comparisons between MEEKC and MEKC are often made, as their separation basis is similar [46-48]. In MEKC, surfactant molecules form micelles and solutes dissolve in them, which facilitates separation. Solutes can penetrate a microemulsion droplet more easily than a more rigid micelle and the loadability of a droplet compared with a micelle is much higher. 

Fig. 7-16 shows the separation of a mixture of permanent gases separated on a porous polymer coated ALOT column. Here a 100% styrene-divinylbenzene porous polymer was used as the stationary phase. In Fig. 7-16A the split injection was used and in... 

In 1993, Hu, Takeuchi and Haraguchi [5] described a technique in which anions and cations were separated simultaneously on a zwitterion stationary phase with pure water as the eluent. An octadecyl silica column acquired a semi-permanent coating when a solution of a zwitterionic surfactant was passed through the column. It was demonstrated that analyte cations and anions were eluted together. The ability to separate ions by ion chromatography with a mobile phase containing no chemicals whatsoever is an ideal situation for detection of the ionic analytes. 

With this method the moving phase is a permanent gas and columns contain either an inert support (e.g. Celite) on whose surface is the stationary liquid phase or else are themselves narrow tubes on whose wall is a thin layer of the stationary phase. The latter are known as wall-coated-open-tubular (WCOT) or capillary columns. Because no inert support is present, the flow of gas is relatively unimpeded and very long thin columns (say 100 m long and only 0.25 mm internal diameter) capable of quite remarkable separations are possible. Columns containing inert support may be either... 

Chiral-coated stationary phases (CCSPs) consist of specific chiral selectors permanently adsorbed onto the surface of achiral thin layer chromatography (TLC) materials without covalently modifying their chemical characteristics. 

Gas chromatography columns for interplanetary exploration should be very efficient, due to the stringent demands imposed on payload. Porous-layer open tubular (PLOT) columns loaded with a styrene-divinyl benzene copolymer showed better performance than Cromosorb 103 or Porapak Q columns in the analysis of low molecular weight hydrocarbons and nitriles. Potassium chloride-deactivated alumina PLOT columns, on the other hand, were not good for the intended purpose, because low molecular weight nitriles were difficult to elute. Wall coated open tubular (WCOT) columns with a stationary chemically bonded phase of dimethyl siloxane have the mechanical resilience to endure the conditions of extraterrestrial exploration and separated efficiently C1-C4 nitriles. Permanent gases were analysed in the presence of hydrocarbons and nitriles with a PLOT capillary column. The equilibrium constant for the interaction of nitrile groups with various solutes was determined by GLC. ... 

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