Characterization of additives in plastics: from MS to MS 10 multistep mass analysis and theoretical calculations of tris(2,4-di- tert -butylphenyl)phosphate

Abstract: In the analysis by electrospray (+) of an extract of hemp sprouts put in a polypropyl-ene vial, we found a large contamination of a plastic additive. It was characterized bymultiple-stage MSnexperiments (MSMS10) and identified as tris(2,4-di-tert-butylphenyl)phosphate, also known with the synonyms F32IRS6B46, oxidizedNaugard 524, and others. The MS2MS7spectra are characterized by consecutiveeliminations of six isobutene molecules from thetert-butyl moieties, some of themalso occurring in the ion source. The first three are calculated to occur preferentiallyfrom theorthopositions, whereas eliminations from theparapositions are estimatedto be less favored at about 5-6 kcal/mol in each step. Once the first three isobutenemolecules are eliminated, the remaining three are lost from thetert-butyl moieties inparapositions (MS5MS7), yielding protonated triphenylphosphate, whose struc-ture has been confirmed by the MS2spectrum of triphenylphosphate standard: thelatter spectrum is almost superimposable with the MS8spectrum of the analyteunder investigation. MS8and MS9spectra show main losses of water and C6H4mole-cules. The MS10spectrum of precursor ions atm/z215 shows the gas-phase additionof water and methanol and ions atm/z168, attributable to the loss of a phosphorusoxide radical. Density functional theory (DFT) calculations (Becke 3LYP [B3LYP]6-311+G(2d,2p)) have been used to evaluate structure and stability of different ionicand neutral species involved in the decomposition pathways and to calculate thermo-chemical data of the decomposition reactions. This multistep mass analysis combinedwith theoretical calculations resulted to be particularly useful and effective, yieldingchemical, thermochemical, and mechanistic data of significant utility in the structuralcharacterization and identification of the unknown analyte as well as to define itsgas-phase reactivity under a multistep low-energy collision-induced dissociationregime.