External electron ionization 7T Fourier transform ion cyclotron resonance mass spectrometer for resolution and identification of volatile organic mixtures

An external electron ionization (EI) source has been interfaced to a 7T Fourier transform ion cyclotron resonance mass spectrometer and tested for volatile complex mixture analysis. A new Sulfinert®-deactivated inlet system provides continuous stable sample flow to the EI source, leading to stable ion signal (±10% deviation) for 2h from a 200nL mixture of 15 n-alkylbenzenes. Ultrahigh-mass resolving power, m∕Δm50%≈735000, was obtained for 1-bromo-2-chlorobenzene with accurate isotopic ratio measurement. Base line resolution was observed for two of the closest commonly encountered mass doublets, C3∕SH4 (m2−m1=3.4mDa at m∕z=190) and SH3C13∕C4 (m2−m1=1.1mDa at m∕z=190). Although hydrocarbons dominate the positive-ion 18eV EI Fourier transform ion cyclotron resonance mass spectrum from diesel fuels, many sulfur-, nitrogen-, and oxygen-containing compounds were readily observed without prior fractionation. By comparing 18eV EI Fourier transform ion cyclotron resonance mass spectra of unprocessed and processed ...