RESUMO
A tandem time-of-flight (TOF) mass spectrometer has been designed to obtain complete MS/MS spectra from compounds eluting from a gas chromatograph. This application requires high spectral generation rate, unit mass resolution for both precursor selection and product spectra, and efficient ion utilization. These objectives are achieved by reflectron TOF mass separation in both stages and laser photoinduced dissociation as the ion fragmentation method. Careful timing of the laser pulse relative to ion extraction allows ions of a single m/z value up to m/z 1000 to be photodissociated while ions with adjacent m/z values are essentially unaffected. The convergent foci of the ion packet and laser pulse results in ion fragmentation efficiencies as high as 79%. An ion gate prevents the nonselected precursor ions from convoluting the product spectra. Product spectra can be generated at the maximum laser repetition rate (currently 200 Hz). To achieve unit mass resolution for all product m/z values simultaneously, a novel reflectron was designed for the second TOF stage.
Assuntos
Espectrometria de Massas , Fotoquímica , Cromatografia Gasosa/normas , LasersRESUMO
High efficiency photo-induced dissociation (PID) has been demonstrated in a tandem time-of-flight mass spectrometer. This instrument focuses isomass ion packets to temporal and spatial dimensions similar to those of the focused laser pulses from a high power excimer laser. This high density overlap of photons and ions yields highly efficient fragmentation and also provides high resolution selection of specific precursor ion mass-to-charge ratio values. Using 193 nm photon excitation of the molecular ion of bromobenzene (m/z = 1561, fragmentation, collection, and PID efficiencies af 79%, 132%, and 104%, respectively, were obtained. Characteristic fragmentations of toluene, nitrobenzene, acetophenone, triethylamine, N,N-diethylformamide, N-methylacetamide, and cyclohexene have also been demonstrated.
