Chip-Based Nanospray Ionisation Mass Spectrometry for the Routine Analysis of Intact Reactive Phosphine Ligands and Phosphino Organometallic Complexes

The analysis of intact phosphine ligands and phosphino organometallic complexes by mass spectrometry is problematic due to the reactivity of phosphorous(III) leading to rapid oxidation and decomposition of the ligands and complexes. Traditionally, the preferred ionisation method for this problematic class of analytes is electrospray ionisation. However, electrospray is often performed in protic solvents which can promote oxidation of the analyte, especially for those that are already prone to oxidation. This study presents the application of chip-based nanospray ionisation for the analysis of these classes of analyte. Nanospray operates at significantly reduced voltages compared to electrospray and at room temperature and, most importantly, is compatible with a wider range of solvents—included non-protic solvents like toluene and THF. The success of this methodology is initially demonstrated by analysis of the commercial ligand DPPE and then by analysis of a wide range of synthetic phosphine ligands and phosphino organometallic complexes produced in-house at the School of Chemistry, University of Bristol. In all cases, the resulting mass spectra are dominated by intact molecular species with only a small number of oxidised products being observed. In some cases, cationated ions are also observed along with some minor fragmentation or decomposition of the complexes.