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.