Detection of pharmaceutical compounds in tissue by matrix-assisted laser desorption/ionization and laser desorption/chemical ionization tandem mass spectrometry with a quadrupole ion trap

A novel quadrupole ion trap mass spectrometer laser microprobe instrument with an external ionization source was constructed and used to investigate the matrix-assisted laser desorption/ionization (MALDI) detection of pharmaceutical compounds in intact tissue. In addition to MALDI, laser desorption coupled with chemical ionization (LD/CI) was investigated. MALDI, using 2,5-dihydroxybenezoic acid (DHB) as a matrix, was employed to detect the anticancer drug paclitaxel from a thin section of rat liver tissue which had been incubated in a solution of paclitaxel. The results of that experiment showed that the ability to perform tandem mass spectrometry (MS/MS) with the quadrupole ion trap was crucial in the identification of drug compounds at trace levels in the complex tissue matrix. MALDI MS/MS was then used to detect the presence of paclitaxel in a human ovarian tumor at a concentration of approximately 50 mg/kg. Finally, the drug spiperone was detected in incubated rat liver tissue at an approximate level of 25 mg/kg using LD/CI (no MALDI matrix). Again, the MS/MS capability of the quadrupole ion trap was crucial in the identification of the drug at trace levels in the complex tissue matrix. (C) 1999 American Society for Mass Spectrometry.