Studies in negative ion mass spectrometry. IX—electron capture by a series of tris- and bis-(dipivaloylmethanato) metal chelates

Electron capture data and negative ion mass spectra are reported for a series of tris- and bis-chelates of the types Metal·L₃, Metal·L₂, where L (or dpm) refers to the ligand or enolate ion of the β-diketone 2,2,6,6-tetramethyl-3,5-heptanedione (dipivaloylmethane) and the metals are: Sc(III), Cr(III), Mn(III), Fe(III), Co(III), Al(III), Ga(III), In(III), Co(II), Ni(II), Cu(II), Zn(II). The spectra were all very simple and the principal ions observed in all cases were the molecular anions and ligand ions. Reaction schemes have been established to account for the formation of ligand and other fragment ions, many of which carried less than 0.1% of the total ion currents. Variations in the negative ion mass spectra are attributed to the influence of the metal atom and its 3d electron configuration on the electron capture process. The simplicity of the negative ion mass spectra, together with the fact that many of these metal chelates gave relatively high total ion currents of c. 10^?9–10^?10 A, indicates the potential value of negative ion mass spectrometry in the area of ultra-trace metal analysis, and some estimates of detection limits for some of the metals considered in this study have been made.