B

In liquid column chromatography A characterizes the quality of the packing and is usually between 1 and 5; A = 1 corresponds to a very good packing. Much work has been done to prepare excellent columns and even now manufacturers each have their own procedure. To our knowledge nothing has been seriously done to improve the packing in TLC, probably because it is easier to achieve a good two-dimensional bed than a three-dimensional one. No precise data on packing in TLC are available but we may suppose a small value of A. The C term characterizes the mass transfer inside the particle. It comes from diffusion in the stagnant mobile phase, kinetics of adsorption-desorption, etc. C varies with RF (or k) for a given chromatographic system. An average value of 0.01 will be used in most calculations. The B term is mainly a diffusion term. In GC the diffusion in the stationary phase is considered as negligible since the diffusion in the gas phase is several orders of magnitude higher (105). In liquid chromatography, the situation is different and the contribution to axial diffusion resulting from molecular diffusion in the stationary phase may become of the same order of magnitude as the contribution of molecular diffusion in the mobile phase. A rigorous treatment has been published by Giddings and we thus write:

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.

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