High pressure liquid chromatographic method for probenecid in flavored oral suspensions containing ampicillin: collaborative studies

A high pressure liquid chromatographic method for determining probenecid in oral suspensions of amoxicillin was applied to the determination of probenecid in oral suspensions of ampicillin. Three preparations containing various known amounts of probenecid in synthetic mixtures of ampicillin oral suspensions were analyzed by 5 chemists in an intralaboratory study, with satisfactory results. Blind duplicates of 3 prepared oral suspensions were sent to 12 collaborators, who were instructed to analyze the samples in a fixed random order. The standards showed a satisfactory linear response. Average recoveries of probenecid in the interlaboratory study for the 6 mixtures ranged from 95.2 to 99.1%, and the coefficients of variation ranged from 1.63 to 4.9%.