Planar Chromatography

For a single development under capillary-controlled flow conditions the TLC analogue of the general resolution equation for column chromatography can be expressed in approximate form as:

Rs = [(N1Rf2)1/2/4] x [(k1/k2) - 1)] x (1 - Rf2) [6]

where N1 is the maximum number of theoretical plates available corresponding to the solvent front position. The use of N1RF2 is only a rough

Figure 17 Variation of the resolution of two closely migrating zones as a function of the RF value for the faster moving zone. (Reproduced with permission from Poole CF and Poole SK (1991) Chromatography Today, p. 669, copyright © Elsevier Science B.V.)

Figure 17 Variation of the resolution of two closely migrating zones as a function of the RF value for the faster moving zone. (Reproduced with permission from Poole CF and Poole SK (1991) Chromatography Today, p. 669, copyright © Elsevier Science B.V.)

approximation for the number of theoretical plates that a particular zone has migrated across. Relatively small changes in selectivity have enormous impact on the ease of obtaining a given separation in TLC, since the total number of theoretical plates available for a separation is never very large. Separations in TLC are fairly easy when RF2 — RF1 >0.1 and very difficult or impossible for RF2 — RF1 < 0.05 in the region of the optimum RF value for the separation. Maximum resolution is obtained at an RF value of about 0.3 and does not change much in the RF range of 0.2 to 0.5, as can be seen in Figure 17. Resolution is zero for compounds that are retained at the origin or migrate with the solvent front.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

Get My Free Ebook


Post a comment