Urine pH, container composition, and exposure time influence adsorptive loss of 11-nor-Δ9-tetrahydrocannabinol-9-carboxylic acid

11-nor-Δ9-Tetrahydrocannabinol-9-carboxylic acid (11-nor-Δ9-THC-COOH) is the primary cannabinoid present in the urine of individuals who have used marijuana and is the target analyte identified at forensic urinalysis drug testing laboratories. The preparation, storage, transport, and processing of control materials for gas chromatography-mass spectrometric (GC-MS) analysis of human urine specimens is critical to accurate compound identification and quantification. Previous studies have suggested that adsorptive loss of 11-nor-Δ9-THC- COOH is influenced by container composition and storage temperature. In this study, urine solutions of 11-nor-Δ9-THC-COOH (7.5, 15, 60, and 500 ng/mL) at three physiologically-relevant pHs (4.6, 6.5, and 8.4) were prepared and subjected to storage and processing in containers of different compositions (polypropylene and borosilicate glass). Analyte identification and quantification were achieved using tetramethylammonium hydroxide/iodomethane- based derivatization followed by GC separation and electron-impact MS. These analyses demonstrate that adsorptive loss of 11-nor-Δ9-THC-COOH is a phenomenon found in acidic urine solutions and is relatively absent in urine solutions that are near-neutral or basic. Furthermore, the data indicate that the adsorptive loss of 11-nor-Δ9-THC-COOH is dependent on solution-container exposure time and is similar between containers of two distinct compositions. These results suggest that for optimal analytical control performance, solution pH and control processing times are critical elements.