Wavelength-resolved REMPI mass spectrometry in a hostile industrial environment, limitations and promises of the method

The complementary REMPI (resonance-enhanced multi-photon ionisation) techni ques using either a tuneable laser or a fixed-frequency laser are compared. Our Jet-REMPI apparatus, consisting of a tuneable laser unit (Nd:YAG pump laser and OPO) and a reflectron mass spectrometer, is briefly introduced. T his machine has been upgraded to cope with the difficult, conditions (such as vibrations, temperature fluctuations and dust) prevailing in an incinera tor. On-line measurements of the raw gas have been carried out at the munic ipal waste incinerator (MWI) in Stuttgart. Although this lest series could not be completed the results are encouraging. They show that wavelength res olution can provide valuable information beyond that which can be obtained by fixed-frequency REMPI. Examples discussed include identification of phen anthrene as major constituent of the isomeric pair phenanthrene/anthracene and the structural identification of xylene isomers in the incinerator raw gas. Both examples are also of more general interest, the former with regar d to investigation of soot precursors and the latter for quality assessment of refinery products. Spectra of some deuterated aromatics are reported fo r use of these compounds as standards. In addition, a mass spectrum contain ing DDT is shown and a chlorobenzene profile measured earlier in a pilot sc ale incinerator as demonstration of the sensitivity of the instrument. As i s to be discussed, significant further sensitivity gains through increase o f the beam density are limited because of ion collisions within the sample beam.