Quantitative thin-layer chromatography of pyrimethamine and related diaminopyrimidines in body fluids and tissues

Several 2,4-diaminopyrimidines which inhibit the enzyme dihydrofolate reductase are quantitated following extraction and separation on silica gel thin-layer chromatographic plates. These compounds are candidates for the treatment of brain tumors and meningeal leukemia, because they have the ability to cross the blood-brain barrier. The ultraviolet absorption of the pyrimidine ring at 275 nm is utilized to quantitate these compounds on thin-layer chromatographic plates with a scanning instrument. This method offers the advantages of speed, specificity, versatility and sensitivity, and has proven to be satisfactory for the measurement of as little as 10 ng/ml of these compounds in biological fluids.