Computer-generated density gradient

Figure 7. Computer-generated density gradient distributions.

Pressure or density programming is the most popular of the gradient techniques in SFC. Density is the important parameter with respect to retention but pressure is the physical property which is directly monitored by SFC instruments. If enough experimental density-volume-temperature data are available for the mobile phase then a computer-based algorithm can be used to generate specific density programs. Such data are available for only a few mobile phases, such as carbon dioxide and the n-... 

Further development then avoided this direct evaluation and advanced a general strategy for the computation of both MBPT and CC gradients [132,133] by relying on the so-called relaxed densities, a procedure that also enables the computation of other first-order properties, such as various multipole moments. In fact, the relevant codes based on this idea were first generated and exploited by Schaefer s group [134] (for numerous applications, see Refs. [18-26] in Ref. [135]). 

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