Efficiency losses caused by gradients in solute velocity in packed column supercritical fluid chromatography

Summary Under a few sets of extreme conditions, retention gradients caused losses in apparent efficiency in packed column SFC. Under most practical chromatographic conditions no such losses occurred. The efficiency of five columns were measured both individually and connected in series. Under most conditions, no loss occurred. Under a few sets of conditions, the apparent efficiency of the five columns connected in series was as much as 66 % lower than the sum of the efficiencies of the individual columns measured under the same conditions. To observe a loss, the local retention near the column outlet must be unrealistically high and a steep non-linear change in retention is required. Under some sets of conditions, an approximate form of a recently proposed theory predicted losses similar to those observed.