Characterization of CMPO and its radiolysis products by direct infusion ESI-MS

Abstract

Direct infusion electrospray ionization mass spectrometry (ESI-MS) approaches were developed for rapid identification of impurity compounds formed from octylphenyl-(N,N-(diisobutyl)carbamoylmethyl) phosphine oxide (CMPO) during alpha and gamma irradiation experiments of this compound in dodecane. CMPO is an aggressive Lewis base, and produces extremely abundant metal complex ions in the ESI-MS analysis that make identification of low abundance compounds that are less nucleophilic challenging. Radiolysis products were identified using several approaches including restricting ion trapping so as to exclude the abundant natiated CMPO ions, extraction of acidic products using aqueous NaOH, and extraction of basic products using HNO3. These approaches generated protonated, natiated and deprotonated species derived from CMPO degradation products formed via radiolytic cleavages of several different bonds. Cleavages of the amide and methylene–phosphoryl bonds appear to be favored by both alpha and gamma irradiation, while alpha irradiation also appears to induce cleavage of the methylene–carbonyl bond. The degradation products observed are formed from recombination of the initially formed radicals with hydrogen, methyl, isopropyl and hydroxyl radicals that are derived either from CMPO, contacted aqueous nitric acid, or the dodecane solvent.