Introduction
Gradients are used in process chromatography separations by
continuously varying the liquid phase with respect to the solid phase.
This allows components to be selectively desorbed from the solid phase. It
is important that the variation in the gradient to be repeatable with
respect to time and scale, so that the product of interest elutes with a
consistent temporal separation from any impurities. If a gradient is not
reproductable, impurities may not be sufficiently separated and may
co-elute with the collection of the product.
There are three common ways of forming gradients in large-scale
chromatography systems (>1 L/min flow rate):
1) Two-Tank Method
2) Valve Switching Method (low-pressure mixing)
3) Two Pump Method (high pressure mixing)
Each method has advantages and disadvantages which are discussed here.
Theoretical output curves are provided for each method.
The two-tank method is the least expensive alternative, but very
limited in producing multi-step gradients.
The switching valve method is more expensive, but limited in range and
accuracy.
The dual pump method is more expensive, but is the most versatile
gradient making method. |
