Determination of five abused drugs in nitrite-adulterated urine by immunoassays and gas chromatography-mass spectrometry.

Tsai SC, ElSohly MA, Dubrovsky T, Twarowska B, Towt J, Salamone SJ

International Drug Monitoring Business Unit, Roche Diagnostic Systems, Inc., Somerville, New Jersey 08876, USA.

The adulteration of urine specimens with nitrite ion hasseen shown to mask the gas chromatography-mass spectrometry (GC-MS) confirmation testing of marijuana use. This study was designed to further investigate the effect of nitrite adulteration on the detection of five commonly abused drugs by immunoassay screening and GC-MS analysis. The drugs tested are cocaine metabolite (benzoylecgonine), morphine, 11-nor-delta-tetrahydrocannabinol-9-carboxylic acid (THCCOOH), amphetamine, and phencyclidine. The immunoassays evaluated included the instrument-based Abuscreen ONLINE assays, the on-site Abuscreen ONTRAK assays, and the one-step ONTRAK TESTCUP-5 assay. Multianalyte standards containing various levels of drugs were used to test the influence of both potassium and sodium nitrite. In the ONLINE immunoassays, the presence of up to 1.0M nitrite in the multianalyte standards had no significant effect for benzoylecgonine, morphine, and phencyclidine assays. With a high concentration of nitrite, ONLINE became more sensitive for amphetamine (detected more drug than what was expected) and less sensitive for THCCOOH (detected less drug than what was expected). No effects of nitrite were observed on the results of the Abuscreen ONTRAK assays. Similarly, no effects were observed on the absolute qualitative results of the TESTCUP-5 when testing the nitrite-adulterated standards. However, the produced intensities of the signals that indicate the negative test results were slightly lowered in the THC and phencyclidine assays. The presence of 1.0M of nitrite did not show dramatic interference with the GC-MS analysis of benzoylecgonine, morphine, amphetamine, and phencyclidine. In contrast, nitrite ion significantly interfered with the detection of THCCOOH by GC-MS. The presence of 0.03M of nitrite ion resulted in significant loss in the recovery of THCCOOH and its internal standard by GC-MS. The problem of nitrite adulteration could be alleviated by sodium bisulfite treatment even when the specimens were spiked with 1.0M of nitrite ion. Although bisulfite treatment decomposed all nitrite ions in the sample to recover the remaining THCCOOH by GC-MS, the net recovery of THCCOOH depended on urinary pH and time and conditions of sample storage. The presence of nitrite concentrations that might arise from all possible natural sources, including microorganisms, pathological conditions, and medications, did not interfere with the GC-MS analysis of THCCOOH.

PMID: 9788522, UI: 99002571