Gas chromatography-mass spectrometry-single ion monitoring measurement of 11-nor-delta 9-tetrahydrocannabinol-carboxylic acid in urine.

Gas chromatography combined with mass spectrometry is used to determine the urinary elimination of 11-nor-Delta(9)-tetrahydrocannabinol-carboxylic acid. Single ion monitoring of both 11-nor-Delta(9)-tetrahydrocannabinol-carboxylic acid and the internal standard (11-nor-Delta(9)-tetrahydrocannabinol-carboxylic-D9) offers selective and sensitive measurement. In order to check the method and the results, we employ 11-nor-Delta(9)-tetrahydrocannabinol-carboxylic acid-glucuronide as an external standard. Our study also demonstrates that the wall of the glass liner (glass tube) in the injector retards the active compound, which makes it imperative to replace the glass insert after each run. Otherwise, the value of the drug measured in subsequent runs will decrease because more of this compound will adhere to the glass walls.