Open tubular columns optimum design

Equation (13) is the first important equation for open tubular column design. It is seen that the optimum radius, with which the column will operate at the optimum velocity for the given inlet pressure, increases rapidly as an inverse function of the separation ratio (cc-1) and inversely as the square root of the inlet pressure. Again it must be remembered that, when calculating (ropt)5 the dimensions of the applied pressure (P) must be appropriate for the dimensions in which the viscosity (r)) is measured. 

In a packed column the HETP depends on the particle diameter and is not related to the column radius. As a result, an expression for the optimum particle diameter is independently derived, and then the column radius determined from the extracolumn dispersion. This is not true for the open tubular column, as the HETP is determined by the column radius. It follows that a converse procedure must be employed. Firstly the optimum column radius is determined and then the maximum extra-column dispersion that the column can tolerate calculated. Thus, with open tubular columns, the chromatographic system, in particular the detector dispersion and the maximum sample volume, is dictated by the column design which, in turn, is governed by the nature of the separation. 

Several Interface designs are available for GC/MS and selection depends on the circumstances of the experiment [3-6,8,25,26]. Column flow rates of 1-2 ml/min (adjusted to STP) into the ion source are compatible with modem mass spectrometer vacuxim systems. This is also the optimum floi te range for open tubular capillary columns of conventional lensions. Coupling such columns to a modern mass spectromet er, therefore, presents... 

GC capillary coliunns have a uniform geometry and in the absence of a stationary phase H in is directly proportional to the column internal diameter dc and retention characteristics, k, of the stationary phase film including polar character and film thickness [9-11]. Column design may be evaluated for efficiency and optimum mobile phase velocity using the following equation for proposed by Golay when he developed the theory for open tubular (WCOT) columns [9] ... 

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