Stationary phase coatings

Gyclodextrins. As indicated previously, the native cyclodextrins, which are thermally stable, have been used extensively in Hquid chromatographic chiral separations, but their utihty in gc appHcations was hampered because their highly crystallinity and insolubiUty in most organic solvents made them difficult to formulate into a gc stationary phase. However, some functionali2ed cyclodextrins form viscous oils suitable for gc stationary-phase coatings and have been used either neat or diluted in a polysiloxane polymer as chiral stationary phases for gc (119). Some of the derivati2ed cyclodextrins which have been adapted to gc phases are 3-0-acetyl-2,6-di-0-pentyl, 3-0-butyryl-2,6-di-0-pentyl,... 

SPME has been utilized for deterrnination of pollutants in aqueous solution by the adsorption of analyte onto stationary-phase coated fused-siUca fibers, followed by thermal desorption in the injection system of a capillary gas chromatograph (34). EuU automation can be achieved using an autosampler. Eiber coated with 7- and 100-p.m film thickness and a nitrogen—phosphoms flame thermionic detector were used to evaluate the adsorption and desorption of four j -triazines. The gc peaks resulting from desorption of fibers were shown to be comparable to those obtained using manual injection. 

Although solid-phase microextraction (SPME) has only been introduced comparatively recently (134), it has already generated much interest and popularity. SPME is based on the equilibrium between an aqueous sample and a stationary phase coated on a fibre that is mounted in a syringe-like protective holder. Eor extraction, the fibre... 

In lc there are other sorption mechanisms that can cause separation, depending on whether we choose to use a liquid or a solid as the stationary phase, or what kind of solid we use. Liquid-liquid chromatography (11c) uses a liquid stationary phase coated onto a finely divided inert solid support. Separation here is due to differences in the partition coefficients of solutes between the stationary liquid and the liquid mobile phase. In normal phase 11c the stationary phase is relatively polar and the mobile phase relatively non-polar, whilst... 

Small stationary phase coated fiber exposed to sample, then transferred to inlet Inert gas bubbles through sample vaporized analytes collected on trap and desorbed into GC Supercritical carbon dioxide extracts analytes from liquid and solid samples... 

Zhu et al. coupled OT-CEC to ESI/MS for the analysis of /i-blockers and benzodiazepines. The authors described the use of a polymeric surfactant as a stationary-phase coating that enabled minimal surfactant introduction in the MS compared to MEKC—ESI/MS, thus avoiding interferences from non-voIatile micelles in ESI/MS. ... 

Zhu, X., Kamande, M. W, Thiam, S., Kapnissi, C. P., Mwongela, S. M., and Warner, I. M. (2004). Open-tubular capillary electrochromatography/electrospray ionization-mass spectrometry using polymeric surfactant as a stationary phase coating. Electrophoresis 25, 562-568. 

C, is the resistance to mass transfer of a molecule in the stationary phase and is dependent on its diffusion coefficient in the stationary phase and upon the thickness of the stationary phase coated onto silica gel ... 

A gaseous mobile phase flows under pressure through a heated tube either coated with a liquid stationary phase or packed with liquid stationary phase coated onto a solid support. The analyte is loaded onto the head of the column via a heated injection port where it evaporates. It then condenses at the head of the column, which is at a lower temperature. The oven temperature is then either held constant or programmed to rise gradually. Once on the column separation of a mixture occurs according to the relative lengths of time spent by its components in the stationary phase. Monitoring of the column effluent can be carried out with a variety of detectors. 

The various properties exhibited by ILs make them ideal stahonary phases in GLC. ILs exhibit a unique dual-nature selechvity that allows them to separate polar molecules like a polar stationary phase and nonpolar molecules like a nonpolar stationary phase. In addition, the combination of cations and anions can be tuned to add further selectivity for more complex separations. Viscosity, thermal stability, and surface tension are vital properties that dictate the quality and integrity of the stationary phase coating and are additional characteristics that can be controlled when custom designing and synthesizing ILs. Furthermore, thermal stability and the integrity of stationary phase film can be improved by immobilizing the IL by free radical polymerization to form stationary phases suitable for low- moderate-, and high-temperature separations. Chiral ILs have been shown to enantioresolve chiral analytes with reasonable efficiency. 

The stationary phases coated on the inert supports are similar in the two classes of columns. Liquids of different polarities are chosen for the separation of non-polar or polar compounds a relatively small number of solvents, chemically inert and heat resistant, are sufficient for most residue analyses. The most commonly used for organophosphorus compounds vary from low-polarity hydrocarbons, methylsilicones, phenylsilicones, phenylmethylsilicones or carboranesiloxanes 165 168 175 178 180 182 184 192,195,197,198,... 

Columns are either packed or open tubular. A packed column is filled with particles of stationary phase, as in Figure 23-5. An open tubular column is a narrow, hollow capillary with stationary phase coated on the inside walls. 

Support-coated open tubular column (SCOT) liquid stationary phase coated on solid support attached to inside wall of column... 

The stationary phase coating should have a thickness of 0.25 to 3 pan. 

GiUespie, E. et al. Evaluation of capillary ion exchange stationary phase coating dis-tiihution and stability using radial capillary column contactless conductivity detection. Analyst 2006, 131, 886-888. 

Braun and Guillet 13) recently studied the variation in surface area of polystyrene stationary phases coated on a diatomaceous support (Chromosorb G) as a function of coating thickness. It was found that the retention volume per pam of inert support remained unaffected over three orders of magnitude of film thickness. By comparison with a system of known surface area it was shown that only a fraction of the total area of the support accessible to nitrogen molecules ( 1 m g ) was accessible to the larger polystyrene molecules (0.1 m g ). As a result of the smaller surface area, it was indicated that film thickness of packed columns would be considerably larger than generally believed. 

GLC is a separation process used for analysis of volatile substances and some non-volatile substances that can be made volatile by chemical derivatization. Historically, it was the first chromatographic method applied to trace analysis in biologic matrices. The sample to be analyzed is volatilized by flash evaporation and moved, in a relatively inert carrier gas, along a column that contains a liquid stationary phase coated... 

Fig. 29 Ligand-exchange liquid chromatographic separation of norephedrine (A) and norpseudoephedrine (B), using a Cis stationary phase coated with Y-n-dodecyl-r-hydroxy-proline and a mobile phase containing 5mM copper(II). (From Ref. l)...

X Chen, H Zou, L Yang, H Wang, O Zhang. Optical resolution of alpha-alkyl phenyl acetonitriles by HPLC on cellulose triacetate chiral stationary phases coated on underivatized silica gel. Chirality 12 599-605, 2000. 

The relationship between capillary column inside diameter, column efficiency, expressed as the number of theoretical plates per meter (N/L), and film thickness is illustrated in Figure 7. These curves represent the theoretical limits of column efficiency for a given column inside diameter and stationary phase coating. The very thin-film, narrow-bore columns will be the most efficient and their efficiency changes markedly as the film thickness increases. The efficiency of a 0.25-mm i.d. column with a stationary phase film thickness of less than 1 pm is shown to be limited by mass transfer in the mobile phase (designated by Cg from the van Deemter equation), whereas mass transfer in the stationary phase (CL) becomes predominate in thick-film columns. The point at which Cg = CL is shown for narrow- and wide-bore capillary columns in Figure 7. 

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