On-line emission analysis of polycyclic aromatic hydrocarbons down to pptvconcentration levels in the flue gas of an incineration pilot plant with amobile resonance enhanced multiphoton ionization time-of-flight mass spectrometer

A newly developed, mobile laser mass spectrometer (resonance-enhanced multi photon ionization - time-of-flight mass spectrometer, REMPI-TOFMS) was appl ied to on-line measurements at a waste incineration pilot plant. REMPI-TOFM S combines the optical selectivity of resonance-enhanced multiphoton ioniza tion with a time-of-flight mass analysis to give a two-dimensional analytic al method. Special care was taken to build up a sampling and inlet system s uitable for on-line measurements of large, semivolatile polycyclic aromatic hydrocarbons (PAHs). An effusive molecular beam, inlet in combination with a fixed frequency UV laser (Nd:YAG at 266 mn or KrF excimer at 248 mn) was used. Under these conditions, many different PAHs can be ionized selective ly from the complex flue gas matrix. For example, the achieved detection li mit for naphthalene is in the 10 parts-pertrillion by volume (pptv) concent ration range. Calibration was performed by using external concentration sta ndards supplied in low ppbv concentrations. The instrumentation is sufficie ntly robust to be operated under industrial conditions at incineration plan ts, for instance. The REMPI mass spectra can be acquired at 5-50 Hz, Time p rofiles of the concentrations of different PAHs in the flue gas were monito red with a time resolution of 200 ms. Significant variations in the concent ration profile of several PAHs up to mass 276 amu (e.g., benzo[ghi]perylene ) and methylated PAHs have been observed while combustion parameters were c hanging. In summary, it was demonstrated that laser mass spectrometry (REMP I-TOFMS) enables a real-time on-line trace analysis of combustion flue gase s or indus trial process gases.