GLC Determination of Probenecid in Biological Fluids

A highly specific and quantitative GLC method for the determination of probenecid in biological fluids is described. The method is adaptable to automation with an automatic sample injector and a peak area integrator. The procedure involves the addition of an internal standard (N-dibutyl analog of probenecid) to plasma or urine samples followed by extraction at pH 1 into benzene. The extracted acids are converted to methyl esters for GLC analysis by reaction with ethereal diazomethane. The sensitivity of the method is such that 250ng. of material can be detected in 1ml. of plasma. GLC-mass spectrometry techniques confirmed that the developed method measures the parent drug probenecid.