Electrospray Ionization Mass Spectrometry of Intrinsically Cationized Nanoparticles, [Au144/146(SC11H22N(CH2CH3)3+)x(S(CH2)5CH3)y]x+

Electrospray ionization triple-quadrupole mass spectrometry of ca. 1.6 nm diameter thiolate-protected gold nanoparticles has been achieved at higher resolution than in previous reports. The results reveal the presence of nanoparticles with formulas Au144L60 and Au146L59, present in the sample as a mixture. The improved resolution is based on lowering m/z by exchanging multiple [-SC11H22N(CH2CH3)(3)(+)] ligands into the original [-S(CH2)(5)CH3] ligand shell. The nanoparticles are thus intrinsically cationized and appear as a series of 10+ to 15+ mass spectral peaks. The assigned state of charge was confirmed by a collision-induced dissociation measurement.