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

Eur. J. Mass Spectrom. 5, 157–163 (1999)
DOI: 10.1255/ejms.263

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, Germany.

ABSTRACT:

The ionization behavior of stable radicals (1–8) 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 (1–8) were efficiently oxidized to give M⁺ as the base peak. Under ESI conditions using methanol + water with 1% acetic acid, stable radicals (5–7) gave [M + 1]^+· , (2–4) 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 (2–8) were efficiently oxidized to give M⁺ ions. Radical (1) was detected as the [M + 2]⁺ ion. Detection
limits for the radicals (1–8) were between 3 × 10^–9 mol L^–1 and 5 × 10^–7 mol L^–1
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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