Thermal energy distribution observed in electrospray ionization

A new method was developed which fits a thermal internal energy distributio n to ions formed by electrospray ionization, The molecular ion survival yie ld was measured and determined by RRKM calculations as a function of temper ature. The ('characteristic') temperature was determined when the calculate d and measured molecular ion survival yields were equal. The 'characteristi c' temperatures were very similar (average RSD errors were 8%) for a set of analogous compounds (benzylpyridine salts), and the resulting thermal inte rnal energy distributions were close to those determined by De Pauw's metho d, The validity of the method was also checked performing blackbody infrare d radiation and on-resonance excitation experiments on a Fourier transform ion cyclotron resonance instrument with benzylpyridine salts and leucine en kephalin, The results strongly suggest that internal energy distributions i n electrospray ionization are very close to thermal distributions. It was f ound that the characteristic temperature increases linearly with the cone v oltage. It is suggested that the characteristic temperature can be used as a quantitative measure to control and standardize conditions in electrospra y ionization, Copyright (C) 1999 John Wiley & Sons, Ltd.