2004 Volume 53 Issue 12 Pages 1441-1448
The emissions of organic hazards from environmental protection equipments and other facilities have become a major social issue, and the evaluation of toxicity concentration requires methods having both high precision and high chemical selectivity. LI-IT-TOFMS (laser ionization/ion trap storage/time of flight mass spectrometry) is expected to be a powerful tool for environmental monitoring. This report, discusses real-time LI-IT-TOFMS measurements gaseous 2∼4 chlorinated PCBs in order to evaluate the applicability of the environmental monitoring method. With respect to the effect of ion trap storage for PCBs, we found that it was due to the driving RF voltage on the ring electrode in the ion trap. For the ions of PCBs produced by laser irradiation, we observed that it was more efficient to reach the center of the ion trap by using a gated RF voltage rather than by using a continuous RF voltage. We simulated the ion trajectories in the ion trap by using SIMION 7.0. We found that the voltage of the exit end cap electrode affected both the number of ions trapped and the orbit of ions inside of the trap cell. Optimization of this parameter was performed using both simulated and experimental results. The achievable PCB sensitivity for real-time (1 minute) measurements using the LI-IT-TOFMS technique was found to be in the pptV range (<0.01 mg/Nm3) by a comparison with the conventional gas sampling GC/MS method. A satisfactory proportional relationship was confirmed between laser-based and conventional results. In the future we will pursue the method for environmental monitoring.
