Mobile Phase Composition

Even high densities of CO2 may be insufficient to permit migration of certain solutes, and the addition of polar modifiers may be necessary. Chromatographic retention may then be empirically expressed by:

where a, b and c are constants and x is the mole fraction of organic modifier. The constant a is often small, so that retention decreases linearly as the mole fraction of organic modifier is increased.

A second approach models SFC retention in terms of solute solubility in the mobile phase via the Hildebrand solubility parameter: ¿s for the stationary phase, ¿m for the mobile phase and ¿i for the solute. The retention variation is represented here by:

ln k = Vt (<5m # <5s " 2<5i)(<5m - <5S) # In ) [8]

where Vi is the molar volume of the solute, ns the total number of moles of the stationary phase and nm the total number of moles of mobile phase. This approach predicts a decrease in retention with increasing modifier content if ¿m < ¿i, a retention minimum when ¿m = ¿i, and a retention increase when ¿m > ¿i. Such correlations are not always observed, and the dielectric constant has also been invoked as a predictor of retention.

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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