Potassium halide adducts as reagent ions in infrared laser desorption/ionization fourier transform ion cyclotron resonance mass spectrometry

Abstract

Potassium halide adducts of the form K 2X + (X = F, Cl, Br, and I) desorbed from neutral salts by high power, pulsed, infrared laser radiation are detected in abundance by Fourier transform-ion cyclotron resonance (FT-ICR) mass spectrometry. FT-ICR detection of the K 2X + adduct is favored at increased laser power densities (> 10 8 W/cm 2) and at trapping potentials below 3 V, independent of X. In contrast, detection of K + is promoted at laser power densities below 10 8 W/cm 2 or at higher trapping potentials, with a threshold for trapping that is strongly dependent on X. When laser desorption/ionization (LDI)/FT-ICR is performed on 1:1 mixtures of KX and organic molecules, ejection pulses applied continuously at the cyclotron resonance frequency of K 2X + inhibit formation of the cation-attached product, [M + K] +. Conversely, resonance ejection of K + enhances [M + K] +, apparently by reducing the matrix ion population trapped in the cell. In evaluating higher molecular weight adducts, only K 3F 2 + formed in abundance by laser desorption of KF is found through double resonance experiments to contribute significantly to formation of [M + K] +. Finally, among the potassium halides, KI generates the highest ratio of detected K 2X + to K + at low trapping potentials and is therefore best suited for cationtransfer reactions in infrared LDI/FT-ICR experiments performed at power densities in the 10 8 W/cm 2 range.