Emission of M_2X~+ cluster ions in thermal ionization mass spectrometry in the presence of graphite

摘要

The emission of M_2X~+ cluster ions in thermal ionization mass spectrometry when graphite is loaded on the heating filaments was studied. The emission model of non-reductive thermal ionization of graphite was preliminarily discussed and factors influencing the thermal emission of M_2X~+ ions were investigated. The results show that the intensities of M_2X~+ cluster ions are related to ionic radius and crystal lattice energy, and possible also to the solvation energies of ions. The intensities of M_2Cl~+ ( M stands for K, Rb, and Cs) cluster ions, the M_2Cl~+/M~+ rations, and the ~(37)Cl/~(35)Cl ratios determined from M_2Cl~+ion measurement usually increase with measurement time. The variation of the ~(37)Cl/~(35)Cl ratios determined from Cs_2Cl~+ ion measurement is lower than those based on K_2Cl~+and Rb_2Cl~+ ion measurement, indicating the lowest isotopic fractionation.