Optimization of sample application conditions for solid-phase extraction columns

Abstract When extraction recoveries during solid-phase extraction are affected by the volume or type of matrix applied to the column, the assay is not very robust. Using as examples the extraction of four basic drugs from biologica matrices using cyano and octadecyl solid-phase extraction columns, it is shown that the recovery from 1 ml of plasma can be good while the recovery from water or diluted plasma is poor. Control of sample pH was found to increase recoveries from the cyano column by improving adsorption during sample application. Addition of detergent was found to enhance recoveries from the octadecyl column by moderating retention and allowing the drugs to be eluted more easily.