Overpressured layer chromatography mobile phase

Several mobile-phase optimization strategies in TLC are based on the use of isoeluotropic solvents (i.e., solvent mixmres of identical strengths but different selectivities). Selecting mobile phase will be achieved based on the eluotropic series (Figs. 1 and 2). These considerations are very general. The selection and optimization of one system of eluent is a more complex problem and must be discussed for each particular system. For example, the separation of 13 phenylurea and s-triazine herbicides was performed by overpressured layer chromatography (OPLC) with a binary... 

Nurok, D., Kleyle, R. M., McCain, C. L., Risley, D. S., and Ruterbories, K. J. (1997). Statistical method for quantifying mobile phase selectivity in one- and two-dimensional overpressured layer chromatography. Anal. Chem. 69 1398-1405. 

Vuorela, P., Rahko, E.-L., Hiltunen, R., and Vuorela, H. (1994). Overpressured layer chromatography in comparison with thin layer and high performance liquid chromatography for the determination of coumarins with reference to the composition of the mobile phase. J. Chromatogr., A 670 191-198. 

Pothier et al. (1991) described the separation of numerous alkaloids in plant extracts by overpressured layer chromatography on alumina plates with only a single solvent, ethyl acetate, as the mobile phase. The method was applied with success to plant extracts and to the determination of hRf values of 81 authentic samples of natural alkaloids or their derivatives. 

Pothier, J., Galand, N., and Viel, C. (1991). Separation of alkaloids in plant extracts by overpressured layer chromatography with ethyl acetate as mobile phase. J. Planar Chromatogr.—Mod. TLC 4 392-396. 

OPLC. Overpressured or overpressure layer chromatography, in which mobile phase is forced by a pump through a sealed analytical or preparative layer. 

The second example relates to the separation and determination of steroid isomers. The separation of R- and S-budesonide, syn- and antinorgestimate, -norgestreloxime, and 6-hydroxy-norgesti-mate have been done on silica, and amino-bonded silica stationary phases by conventional and overpressurized layer chromatography (OPLC) (35). Application of amino-bonded silica as stationary phase, and chloroform-diethyl ether-methyl ethyl-ketone (4 3 3, v/v) as mobile phase results in a satisfactory separation of the isomer pairs, especially, if OPLC technique is used. 

Mazaruk, M. Witkiewicz, Z. The analysis of organophos-phorus warfare agents in the presence of pesticides hy overpressured thin layer chromatography. J. Planar Chromatogr.-Mod. TLC 1991, 4 (5), 379-384. (Paper includes optimization of the mobile phase using the PRISMA model.)... 

Because TLC is open-bed development chromatography, the mobile phase velocity is determined by capillary forces and is not controlled. (An exception is overpressured TLC Chapter 7.) The mobile phase velocity in closed HPLC is controlled and easily adjusted. In TLC, the mobile phase usually encounters a dry layer at the start of the separation, while the column is in equilibrium with the mobile phase when the sample is applied in HPLC. 

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