GRADIENT ELUTION

Blending and Mixing Mobile Phase Components 

In many of the modes of modern liquid chromatography, it becomes readily apparent that the most practical system for the delivery of the mobile phase is that which can combine several liquids in different proportions at the command of the operator. This blending capability greatly speeds the process of selecting the optimum eluent mixture required for isocratic analysis and becomes absolutely necessary when programming the mobile phase composition ("gradient elution"). These techniques have been discussed earlier from the point of view of chromatography; now we shall treat them from the point of view of instrumentation.

The two primary methods of blending the mobile phase components are known as high-pressure mixing and low-pressure mixing.