Tandem mass spectrometry of thiolate-protected Au nanoparticles [Na.sub.x[[Au.sub.25][(S[C.sub.2][H.sub.4]Ph).sub.18-y][(S[([C.sub.2][H.sub.4]O).sub.5]C[H.sub.3]).sub.y]

The first collision-induced dissociation tandem mass spectrometry (CID MS/MS) of a thiolate-protected Au nanoparticle is described that has a crystallographically determined structure. CID spectra has shown that dissociation pathways for the mixed monolayer [Na.sub.x][Au.sub.25][(S[C.sub.2][H.sub.4]Ph).sub.18-y][(S[([C.sub.2][H.sub.4]O).sub.5]C[H.sub.3]).sub.y] has centrally involved the semi-ring [Au.sub.2][L.sub.3] coordination that constitutes the nanoparticle's protecting structure.