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Optimization in Prep HPLC

The recent years has seen a tremendous increase in the use of Industrial Scale HPLC, especially in emerging countries like India and China. Many large DAC columns have been installed, and are run using short bed lengths, together with small, spherical, silica-based particles, and relatively high flow rates. This is what we call the High Performance Concept in preparative HPLC.

The influence of separation factor on the total cost

plot of cost vs separation factor

The figure shows the effect of the separation factor on the separation cost, for a certain separation

An industrial scale HPLC process is a relatively expensive process to operate, and it is very important to optimize the process so that the cost per kg of the product is minimized. In order to do so, the optimization of the separation factor, α, might be the single most important factor!

To maximize the space in the chromatogram between the product and the most critical impurity, i.e. maximize separation factor, really pays off: if this space can be doubled, the increase in loading amount is roughly 4 times! This means that also the productivity is 4 times higher, and the cost per produced kg of product is only 25% of the cost before the optimization.

How to maximize the separation factor

The factors to consider for these experiments are typically:

  • Type and brand of stationary phase
  • Mobile phase composition, including:
    • Organic modifier
    • Buffer type
    • pH

Method development for large scale

In the screening experiments suggested above we strongly recommend to use small, analytical columns, packed with preparative packing material. This will save sample, solvent, time, etc. The efficiency that can be obtained even in very large DAC columns are similar to what can be achieved in an analytical column, so the results seen in the experiments can quite easily be scaled up in a linear fashion.

Other factors to optimize

After having optimized the separation factor, there are of course many other parameters to optimize! The flow rate, bed length, and loading amount are some of the most important ones.

Also, it should be investigated if for example stacked injections can be used to increase productivity, or if some multi-column technology could be applied. More about these other parameters in coming KromaNews!