Mobile resonance enhanced multiphoton ionisation–time-of-flight mass spectrometer with a novel hybrid laser desorption/molecular beam ion source for rapid detection of aromatic trace compounds from gas phase and solid samples

Abstract

A mobile, field applicable resonance enhanced multiphoton ionisation–time-of-flight mass spectrometer (REMPI–TOFMS) for direct-inlet gas-phase analysis as well as for characterisation of solid samples, has been developed. For solid-sample analysis, laser desorption (LD) with IR-laser pulses is used for volatilisation of the neutral analytes from a target in the ion source prior to REMPI–TOFMS analysis. For direct inlet gas-phase analysis, a needle gas inlet is used and the formed molecular beam is REMPI-ionised directly in the ion source. A special ion source was developed, which can be rapidly interchanged between the REMPI–TOFMS and the LD–REMPI–TOFMS modes. The system is equipped with a tuneable optical parametrical oscillator (OPO)-laser system. The analytical properties are characterised for both modes of operations. In both cases, analytical performance is similar to that achieved with instruments specifically designed for either gas-phase or solid-phase characterisation. Results from field measurements of a wood combustion flue gas of a 174 kW bio mass furnace are given. Gas-phase analysis was applied for time-resolved on-line REMPI–TOFMS of the semi-volatile aromatic flue gas constituents. The low-volatile aromatic compounds, which were precipitated with the particulate matter in the filtering unit of the sampling train, were characterised by direct LD–REMPI–TOFMS of the glass fibre filter material. By combining the gas-phase and particulate results a rather comprehensive characterisation of the aromatic species present in the flue gas (i.e. aerosol – gas phase plus particulate matter) was achieved.