Evaluation of capillary columns by separation number or plate number

Abstract The separation number (Trennzahl: TZ) as a measure of separation efficiency has been criticized because of its dependence on temperature, and its replacement by a measure based on the temperature-independent HETP concept has been suggested. We discuss the temperature dependence of TZ, then we show that this dependence, rather than being a weak point of the TZ concept, is directly related to an essential part (selectivity) of the column quality. The fact that this part is missing from all separation efficiency expressions based on HETP makes such expressions have poor suitability, and possibly be misleading, for direct pratical extrapolation. Another consequence, which is against the interests of most users, is that most commercial columns, at least in the past, have been manufactured with relatively thick films. Obviously, in order to obtain comparable TZ values more specifications regarding the method of determination are required than for plate numbers. This drawback is overcome by using a standardized test procedure, an esential part of which may be the use of temperature programming.