title: Determination of 11-nor-delta9-tetrahydrocannabinol-9-carboxylic acid in a urine-based standard reference material by isotope-dilution liquid chromatography-mass spectrometry with electrospray ionization.
abstract: A new method is presented for the determination of 11-nor-delta9-tetrahydrocannabinol-9-carboxylic acid (THC-9-COOH) in urine-based standard reference materials (SRMs) for marijuana metabolite. This method is based on isotope-dilution liquid chromatography-mass spectrometry (LC-MS) using electrospray for ionization (ESI). An isotopically labeled compound, 5',11-nor-delta9-THC-9-carboxylic acid-d3, was used as an internal standard. Solid-phase extraction (SPE) was used to prepare samples for LC-MS analyses. LC was performed on a C18 column with an isocratic mobile phase consisting of 0.05 M of ammonium acetate in methanol/water (75:25). Electrospray ionization in the negative ion mode was used to monitor the [M-H]- ions at m/z 343 and 346 for THC-9-COOH and its labeled internal standard, respectively. Samples of SRM 1507b (THC-9-COOH in freeze-dried urine) were prepared and measured on three separate sets. The within-set coefficients of variation ranged from 0.32% to 2.77%. The correlation coefficients of the regression lines were 0.999 to 1.000. The detection limit for THC-9-COOH with this method is estimated to be 5 pg/mL. This method compared well with the gas chromatography-mass spectrometry method used for certification, and results were within the certified values of THC-9-COOH for SRM 1507b.
authors.affiliation: College of American Pathologists, Northfield, Illinois 60093, USA.
authors.forename: S S
authors.initials: SS
authors.lastname: Tai
authors.forename: M J
authors.initials: MJ
authors.lastname: Welch
mesh_terms: D002853:Chromatography, Liquid / Q000379:methods*; D013759:Dronabinol / Q000031:analogs & derivatives* / Q000652:urine*; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods; D006801:Humans; D007553:Isotope Labeling; D013058:Mass Spectrometry / Q000379:methods*; D012015:Reference Standards; D015203:Reproducibility of Results; D015813:Substance Abuse Detection / Q000379:methods*
chemical_list: D013759:Dronabinol; C025351:delta(9)-tetrahydrocannabinolic acid