LC-MS/MS Detection of Tryptophan, Kynurenine, Kynurenic Acid, and Quinolinic Acid in Urine Samples from Drug-Positive and Illicit Drug-Negative Patients with a Known History of Substance Use Disorder. - Contella L; Farrell CL; Boccuto L; Litwin AH; Flanagan H; Melanson SEF; Tolan NV; Snyder ML; Greene DN (Metabolites, 2025)