POSITIVE AND NEGATIVE-ION MASS-SPECTROMETRY OF 10 XANTHINE DERIVATIVES AND THEIR RAPID CLEANUP WITH SEP-PAK C-18 CARTRIDGES FROM BIOLOGICALSAMPLES

Positive ion electron impact (PIEI), positive ion chemical ionization (PICI) and negative ion chemical ionization (NICI) mass spectra are pr esented for ten xanthine derivatives; and each fragmentation pathway h as been analyzed. In the PIEI mode, molecular ions were generally inte nse and constituted base peaks in five compounds. Peaks at m/z 42 (NCO ) appeared in all compounds; fragment cations at m/z 55, 68 (or 67) an d 82 were observed in many compounds. In the PICI mode, all drugs show ed intense [M+H](+) quasi-molecular peaks together with small peaks at m/z M+C2H5 and M+C3H5; fragment peaks at m/z 44, 58, 72 and/or 84 (or 86) were also observed. In the NICI mode, [M-H](-) quasi-molecular pe aks appeared in nine compounds and constituted base peaks in five comp ounds; adduct anions at m/z M+32 and/or M+C3H7, and fragment anions at m/z 42, 165 and/or 179 were also observed in many compounds. Detectio n limits for total ion monitoring of the drugs in the PIEI, PICI and N ICI modes were 2.2-10 ng, 11-28 ng and 7.8-14 ng on column, respective ly. Xanthine derivatives present in human plasma or urine could be rap idly extracted by use of Sep-Pak C-18 cartridges with chloroform/metha nol as elution solvent; recovery of the drugs from the plasma and urin e was >75%. They were also detected by capillary gas chromatography (G C) with both flame ionization detection (FID); their limits were 1.6-8 .3 ng on column.