Hyphenation of Gas Chromatography and Resonance-Enhanced Laser Mass Spectrometry (REMPI-TOFMS): A Multidimensional Analytical Technique

Analysis of environmental samples usually requires time consuming sample preparation and clean-up procedures prior to instrumental detection. Faster analysis requires an enhanced instrumental selectivity in order to reduce the necessary clean-up effort. In this context we present a novel concept for coupling gas chromatography/mass spectrometry (GC-MS) with high resolution UV spectroscopy to increase selectivity. We use UV-laser induced, resonance-enhanced multi-photon ionization (REMPI) as a compound specific ion source for time-of-flight mass spectrometry (TOFMS). The REMPI ionization involves the UV absorption spectroscopy into the ionization process as an additional analytical dimension. The heart of the GC-REMPI-TOFMS coupling is a specially designed valve, which repetitively (20 Hz) expands the chromatographic eluent as short supersonic jet gas pulses (≈150 μs duration) into the vacuum of the mass spectrometer. The sample molecules are cooled down to temperatures of 10-40 K within the jet expansion. Under these conditions, UV absorption spectroscopy (i.e. REMPI spectroscopy) becomes highly compound selective, even able to distinguish isomeric compounds. The ions formed by REMPI ionization are mass-analyzed in the TOFMS. Thus the GC-REMPI-TOFMS coupling presented here is actually a three-dimensional analytical instrument, providing gas chromatographic (retention time) as well as mass spectrometric (molecular mass) and UV-spectroscopic (excitation laser wavelength) selectivity. In combination with gas phase sampling and concentration techniques for semi-volatile organic air pollutants based, e.g., on silicone rubber traps, the GC-LAMS technique can be a powerful tool for fast environmental target analysis, e.g. for industrial emission control purposes.