HYPHENATION OF GAS-CHROMATOGRAPHY AND RESONANCE-ENHANCED LASER MASS-SPECTROMETRY (REMPI-TOFMS) - A MULTIDIMENSIONAL ANALYTICAL TECHNIQUE

Analysis of environmental samples usually requires time consuming samp le preparation and clean-up procedures prior to instrumental detection . Faster analysis requires an enhanced instrumental selectivity in ord er 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 u se UV-laser induced, resonance-enhanced multi-photon ionization (REMPI ) as a compound specific ion source for time-of-flight mass spectromet ry (TOFMS). The REMPI ionization involves the UV absorption spectrosco py 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 sho rt supersonic jet gas pulses (approximate to 150 mu s duration) into t he vacuum of the mass spectrometer, The sample molecules are cooled do wn to temperatures of 10-40 K within the jet expansion. Under these co nditions, UV absorption spectroscopy (i.e. REMPI spectroscopy) becomes highly compound selective, even able to distinguish isomeric compound s, The ions formed by REMPI ionization are mass-analyzed in the TOFMS. Thus the GC-REMPI-TOFMS coupling presented here is actually a three-d imensional analytical instrument, providing gas chromatographic (reten tion time) as well as mass spectrometric (molecular mass) and UV-spect roscopic (excitation laser wavelength) selectivity. In combination wit h gas phase sampling and concentration techniques for semi-volatile or ganic air pollutants based, e.g., on silicone rubber traps, the GC-LAM S technique can be a powerful tool for fast environmental target analy sis, e.g. for industrial emission control purposes.