The concept of 'plates' in chromatographic theory (the plate theory) is by analogy with the distillation process and represents the notional length of the column in which the solute molecules reach a distribution equilibrium. Thus a large number of theoretical plates corresponds to an efficient column.

Consideration of the chromatographic process as controlled by equilibrium gives a satisfactory explanation of chromatographic retention in term of the distribution coefficients. However when considering band broadening a different approach is required, known as the rate theory of chromatography. This was first applied by van Deemter, Klinkenberg and Zuiderweg to packed columns, but has been extended and modified to include open-tubular columns.

As the solute band passes through the column the bandwidth increases and the solute is diluted by the mobile phase. Although the process of fluid flow is complex, three main contributions to band broadening (i.e. to the variance (a2) of the Gaussian peak) may be recognized in GC: the multipath effect, A (formerly called eddy diffusion); molecular diffusion, B; and mass transfer, C. These contributions have been combined by van Deemter and co-workers in the van Deemter equation, which expresses the broadening of a band in terms of the plate height, H, and the average linear velocity (U) of the mobile phase:

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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