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Eur. J. Mass Spectrom. 5, 157 - 163 (1999)

Electrospray ionization and atmospheric pressure ionization mass spectrometry of stable organic radicals

Jürgen O. Metzger and Jens Griep-Raming
Department of Chemistry, Carl von Ossietzky University Oldenburg, Carl-von-Ossietzky-Straée 9-11, D-26129 Oldenburg, .

ABSTRACT:
The ionization behavior of stable radicals (18) was studied under electrospray ionization (ESI) and atmospheric pressure ionization (APCI) conditions. With APCI, using methanol + water as the solvent, most radicals were protonated to give the radical cation [M + 1], whereas TEMPO (5) was detected as the M+ ion and galvinoxyl (1) gave the [M + 2]+ ion. Using benzene as the solvent, all radicals (18) were efficiently oxidized to give M+ as the base peak. Under ESI conditions using methanol + water with 1% acetic acid, stable radicals (57) gave [M + 1] , (24) M+ , whereas (1) and (8) showed the [M + 2]+ ion as the base peak. Using the ESI source as a controlled-current electrolytic cell, radicals (28) were efficiently oxidized to give M+ ions. Radical (1) was detected as the [M + 2]+ ion. Detection limits for the radicals (18) were between 3 x 109 mol L1 and 5 x 107 mol L1 using APCI or ESI in the full-scan mode. In most cases detection limits were lower using the tandem mass spectrometry (MS/MS) full-scan mode.

Keywords: electrospray ionization, atmospheric pressure chemical ionization, stable radicals.

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