Abstract

European Journal of Mass Spectrometry
Volume 13 Issue 3, Pages 227–232 (2007)
doi: 10.1255/ejms.871

Letter: In situ chemical ionization in ion trap mass spectrometry—the beneficial influence of isobutane as a reagent gas

Stéphane Bouchonnet,^a,* Saïd Kinani^a, Michel Sablier^a and Stéphane Pirnay^b
aDépartement de Chimie des Mécanismes Réactionnels, Ecole Polytechnique, route de Saclay, 91128 Palaiseau Cedex, France. E-mail: stephane.bouchonnet@dcmr.polytechnique.fr
^bUniversité Paris Descartes, Faculté de Pharmacie, Neuropsychopharmacologie des addictions, CNRS, UMR7157 et Université Paris 7, Paris F-75010, France

We report a comparison of the ionization yields provided by the most common reagents (methane, ammonia, methanol, acetonitrile, isobutane) performing in situ chemical ionization with an ion trap mass spectrometer. Four molecules were chosen in the medical field to illustrate experimental results: alprazolam, diazepam, flunitrazepam and acetaminophen. Under usual operational conditions, relative abundances of protonated ions appreciably depend on the reagents. The greatest abundance of MH⁺ ions was obtained with isobutane while observed intensities for MH⁺ ions varied from 73% for methanol and ammonia to about 23% for acetonitrile and methane. Results were temptatively rationalized comparing energies of formation of the reagent ions and storage efficiency in the trapping field.

Keywords: ion trap mass spectrometry, chemical ionization reagents, isobutane, benzodiazepines

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