Selectivity in secondary ion mass spectrometry. A study of pyrimidine derivatives

Abstract

The influence of the molecular structure and surface environment on the secondary ion emission induced by keV ions was investigated for a series of compounds derived from 4(2′-hydroxyphenyl)-2,5-dimethylpyrimidine; the 2-methyl of the pyrimidine ring was substituted by different functional groups. The secondary ion mass spectra recorded under various experimental conditions are presented. A strong enhancement of the protonated molecular ion yield was correlated with an increase of the basicity of the functional group for samples prepared under strong acidic conditions; such a correlation has not been observed with aprotic solvents. The fixation of metal cations (Ag +, Li + and Na +) exhibits a complex behaviour. Ag + fixation is likely to occur on the phenolic moiety and therefore, is not selective. In contrast, Li + and Na + fixation strongly depends on the nature of the substituting group. The observed behaviour cannot be explained from simple chemical considerations such as the intrinsic base properties of the molecules; steric hindrance and matrix effects must be taken into consideration.