Copyright IM Publications 2010 Cite as L. Zoia and D. Argyropoulos, Eur. J. Mass Spectrom. (2010) doi: 10.1255/ejms.1062 1 Characterization of free radical spin adducts of the DIPPMPO using Mass Spectrometry and 31 P NMR Luca Zoia b , Dimitris Argyropoulos a* a Organic Chemistry of Wood Components Laboratory Department of Forest Biomaterials, North Carolina State University, NC 123321, USA. e-mail: dsargyro@ncsu.edu b Dipartimento di Scienze dell’Ambiente e del Territorio, Università degli Studi di Milano-Bicocca, Piazza della Scienza 1, 20125, Milano, Italy. e-mail: luca.zoia@unimib.it ABSTRACT 5-Diisopropyloxy-phosphoryl-5-methyl-1-pyrroline-N-oxide (DIPPMPO) was used to trap a variety of free radicals and the stable compounds generated by the natural decomposition of the initially formed spin adducts were characterized by 31 P NMR and mass spectrometry. Initially, the starting spin trap DIPPMPO was completely characterized using GC-MS and its fragmentation pathway was studied in detail. Then, DIPPMPO was used to trap an oxygen-centered free radical (the hydroxyl radical ·OH) and two carbon-centered free radicals (methyl ·CH 3 and 1-phenyl-ethanol-1-yl ·CCH 3 (OH)Ph radicals). The 31 P NMR signals were thus assigned and the structures of adducts were studied and confirmed by mass spectrometry. Overall, the fragmentation pathways of the radical adducts proceed mainly via the loss of the diisopropyloxy(oxido)phosphoranyl radical. For the specific case of trapping ·OH radicals, it is possible to visualize the rearrangement of the nitroxide radical adduct to its nitrone form as invoked in the literature. This spin trapping technique, coupled with 31 P NMR and MS, provides a tool for the identification of short-lived and low molecular weight free radicals present in a variety of processes. Keywords: Free radicals; Spin trapping; DIPPMPO; Mass Spectrometry; GC-MS; 31 P NMR. * Corresponding author. Tel.: +1 919 515 7708; fax +1 919 515 6302; e-mail: dsargyro@nscu.edu