Preparative columns optimum column length

Employing Equation (3) and the data given in table 1, the optimum column length was calculated for the preparative separation of a solute where the separation ratio of the critical pair ranged from 1.01 to 1.50, again at inlet pressures of 1,10,100,1,000 and 10,000 p.s.i. The results obtained are shown in figure 2... 

It is seen from figure 2 that the optimum column length ranges from over 500 meters to a fraction of a millimeter. It is also obvious that there must be further limitations placed on the design of the column to ensure its practical use. A preparative column less than 5 cm in length would be very difficult to pack as would a preparative column that had a length greater... 

Some common terms used in preparative-scale liquid chromatography are summarized in Table 11.4, The production rate, specific production, or the recovery yield provide suitable objective functions to judge the relative success of individual methods. For efficient use of the separation system, the production rate and the recovery yield should be maximized. Invariably, this results in operating the column in an overloaded condition. Unfortunately, column operation under nonlinear conditions is complex, and optimum conditions are not as easy to predict as the less demanding, although less powerful, scale-up approach. To scale up an analytical separation, the same column packing, column length, and mobile phase velocity are used, and the column diameter increased... 

In order to accumulate the data for a van Deemter plot (described above) it is necessary to carry out a series of separations on a preparative column of at least 50 mm diameter. This can be done isocratically or using the gradient and optimum load conditions selected above. However, if the study is done using gradient elution the gradient length should be reduced in proportion to increased flow rate. Suggested linear flow rates for this study are 60, 75, 90, 105, 120 and 135 cm/h. These flow rates correspond to approximately 20, 25, 30, 35, 40 and 45 cm3/min for a 50 mm diameter column. 

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