A STUDY OF PRECOLUMN AND ANALYTICAL COLUMN DIMENSIONS FOR ONLINE SAMPLE PRETREATMENT IN HPLC

A systematic study has been made of the effect of precolumn size and s hape in relationship to the size of analytical column for column switc hing systems in HPLC. It is found that, even for miniature precolumns (volumes 30 - 500 mu l) the volume does not affect the efficiency achi eved nor the recovery of a set of six steroids from aqueous solution w hen 4.6 and 2 mm diameter analytical columns are used. Coupling of the se precolumns with 1 mm diameter analytical columns results in decreas ed efficiency although in the systems tested sensitivity increased as analytical column diameter decreased. Such coupled systems could be ap plied to analysis of selected steroids in matrices of urine and saliva with little difficulty. Deterioration in both efficiency; and recover y were found when extracting from a plasma matrix although linear cali brations were obtained.