A systematic study has been made of the effect of precolumn size and shape in relationship to the size of analytical column for column switching systems in HPLC. It is found that, even for miniature precolumns (volumes 30–500 μl) the volume does not affect the efficiency achieved nor the recovery of a set of six steroids from aqueous solution when 4.6 and 2 mm diameter analytical columns are used. Coupling of these precolumns with 1 mm diameter analytical columns results in decreased efficiency although in the systems tested sensitivity increased as analytical column diameter decreased. Such coupled systems could be applied to analysis of selected steroids in matrices of urine and saliva with little difficulty. Deterioration in both efficiency and recovery were found when extracting from a plasma matrix although linear calibrations were obtained.
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