Procainamide interference with liquid chromatography of theophylline in serum

We described potential interference of procainamide with our high pressure liquid chromatography procedure for assaying theophylline (similar to that given by Orcutt et al.). In participating in the AACC-TDM quality-control program, we discovered procainamide interference on a column dedicated to theophylline and acetaminophen serum analyses. Following attempts at rejuvenation, this 7-month-old column was replaced with a new one, which gave base-line separation of theophylline and procainamide with no difficulty. We recommend close attention to the aging characteristics of columns and participation in a quality-control program.