Stationary phases development

Gas chromatography (gc) is inferior to hplc in separating abiUty. With gc, it is better to use capillary columns and the appHcation is then limited to analysis (67). Resolution by thin layer chromatography or dc is similar to Ic, and chiral stationary phases developed for Ic can be used. However, tic has not been studied as extensively as Ic and gc. Chiral plates for analysis and preparation of micro quantities have been developed (68). 

A theoretical model whereby maximum peak capacity could be achieved by the use of 3-D planar chromatographic separation was proposed by Guiochon and coworkers (23-27). Unfortunately, until now, because of technical problems, this idea could not be realized in practice. Very recently, however, a special stationary phase, namely Empore silica TLC sheets, has now become available for realization of 3-D PC. This stationary phase, developed as a new separation medium for planar chromatography, contains silica entrapped in an inert matrix of polytetrafluoroethy-lene (PTFE) microfibrils. It has been established that the separating power is only ca. 60% of that of conventional TLC (28) this has been attributed to the very slow solvent migration velocity resulting from capillary action. 

A third type of synthetic polymer-based chiral stationary phase, developed hy Blaschke. is produced when a chiral selecior is either incorporated within the polymer network or attached as pendant groups onto the polymer matrix. Both arc analogous to methods used lo produce polymeric chiral stationary phases for gc. 

Juza, M, Biressi, G., Di Giovanni, O., Mazzotti, M., Schurig, V., and Morbidelli, M. (1998b) Resolution of the inhalation anesthetic enfiurane on a cyclodextrin-based chiral stationary phase development of the GC-SMB separation, in F. Mennier (ed.), Fundamentals of Adsorption, Elsevier, Amsterdam, pp. 455-460. 

Stationary Phase Developing Phase Detection Reference ... 

Even the great separation power of these columns cannot always solve the problem of coelution of some components of a mixture. Therefore, coupling 2 capillary columns of different polarity am characteristics may be a good solution to such problems. Manufacturing of capillary columns with binary liquid phases is one of the new and interesting areas in stationary phase development. 

Column technology is one of the most rapidly developing areas of CE. The capillary is the key to separation, so it is likely that numerous column formats will be established to meet specific separation needs similar to stationary-phase development in HPLC. 

Jackson, P.E. Pohlandt, C. Advances in stationary phase development in suppressed ion chromatography. Trend. Anal. Chem. 1997,16, 393 00. 

The hydrophilic modified stationary phases developed so far for thin-layer chromatography possess as functional groups amino, cyano, and diol residues. In each case polar functional groups are bonded via short-chain nonpolar spacers to the silica matrix. Therefore, a straight- or normal-phase and a reversed-phase retention mechanism can be applied by using such stationary phases. 

The stationary phases requirements of selectivity and higher thermal stability then became more clearly defined the process of stationary-phase selection and classification became logical after the studies of McReynolds (28) and Rohrschneider (29,30) were pubUshed, both of which were based on the retention index (31). The Kovats retention index procedure and McReynolds constants are discussed in detail in the following section. Kovats retention indices today remain a widely used technique for reporting retention data, while every stationary phase developed for packed and capillary GC has been characterized by generation of its McReynolds constants. 

Most of the reported applications of this technique involve the direct resolution of derivatised enantiomers on chiral stationary phases. The earliest successful resolution of yV-trifluoroacetyl amino acid esters on glass capillary columns coated with N-trifluoroacetyl-5-isoleucine lauryl ester (2) was effected in 1966. Superior stationary phases developed quickly, such as (3), in which the additional amide bond may interact via hydrogen bonding. These chiral supports work well for the separation of A -perfluoracylated derivatives of a given amino acid. However, their low thermal stability (190 C maximum) and appreciable volatility have inhibited their use for the simultaneous... 

Kovats retention index procedure and the McReynolds and Rohrschneider constants are discussed in detail in the following sections. The Kovats index remains a widely used technique for reporting retention data, and every stationary phase developed for packed and capillary gas chromatography has been characterized by its McReynolds constants. 

Individual solutes migrating through a stationary phase develop an approximately S5munetiical band or peak profile which becomes broader as a function of time and distance travelled. 

Surfactants separated Stationary phase Developing system Visualizer Ref. 

Compounds studied Stationary phase Developing reagent Visualization Ref. 

---