Quantitative determination of niflumic acid and its beta-morpholinoethyl ester in human plasma by gas-liquid chromatography.

Niflumic acid and its beta-morpholinoethyl ester are extracted from plasma with diethyl ether. After methylation with diazomethane the solution is evaporated to dryness and the residue dissolved in methanol before injection in the chromatographic column. Using a nitrogen-sensitive detector the method permits the determination of 100 ng of each compound in 1 ml of plasma. The coefficient of variation is 5.3% and 4.8% for the acid and the ester, respectively, at the 2-microgram level.