Column Channeling—Center-Voids

The present method recommended by this major industrial account is to disconnect the center-voided column, grasp it in one hand, and rap the counter with it twice, reverse the column, and do the same with the other end. Obviously, not hard enough to bend the column Hook it up backwards and run it at high flow rate for a minute or two. Then run the four-standard mixture. The column is run reversed from then on. It is possible that an end void may be formed yielding rabbit-eared split peaks, and must be repacked, but the column bed should be restored. 

A center void probably occurs because small wall and bed voids link up under pressure changes and shock to form a channel. The channel is a path of least resistance and diverts the flow from the bed. This effectively removes this part of the column from the separation and gives a shorter column and shorter retention times. Eventually, the whole column is channeled and you have a center void the length of the column. If you have ever run a gravity-fed, packed glass column, you have probably seen this channeling phenomena if you accidentally let the column run dry. 

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Voids—Spaces or openings in the column bed leading to poor chromatography. End voids are directly under the inlet frit. Center voids are channels through the center of the packing bed. 

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