Determination of niflumic acid in human urine by gas chromatography negative chemical ionization mass spectrometry

A sensitive method has been developed for the detection and determination of niflumic acid (NA) in human urine. Samples were extracted with diethylether. Flunixin (FN) was added to the sample prior to extraction as an internal standard. Niflumic acid was converted to its methyl derivative and analyzed by capillary gas chromatography/negative chemical ionization mass spectrometry. Using selected ion monitoring (SIM), the levels of NA down to 5 pg/ml could be detected in 5 mi spiked urine sample. Calibration curve was linear over the range of 0.5 ppm-50 ppm. The recovery of niflumic acid from urine at 40 pg/ml was to be 91.7+/-3.8(n=3) and the coefficient of variation was 4.1%.