| dc.description.abstract | Hazardous Air Pollutants (HAPs), also called air toxics, have become a subject of attention in recent years due to their effect on public health. Of these air toxics, the volatile organic compounds (VOCs) are the targets of interest in this study, called toxic VOCs. The current most common analytical method for toxic VOCs is to use surface treated stainless canisters with gas chromatography mass spectrometry (GC/MS) to form a offline method, because the monitoring results are not obtained immediately. The data cannot effectively reflect the instantaneous characteristics of an emission source. As a result, this research continued
to improve the online method of Thermal Desorption Gas Chromatography / Mass Spectrometry (TD-GC/MS) with a water removal solution to achieve hourly measurements of 86 toxic VOCs.
From the past experience, the ion source of the mass spectrometer is easily contaminated by moisture in the sample, resulting in weekly cleaning of the ion source. This study used a commercial Jetclean technology by Agilent by directly introducing a small flow of high-purity hydrogen into the ion source. The complex sample matrix, which is oxidized at high temperature and prone to adhering to the surface of the ion source can be greatly alleviated by the addition of hydrogen, thereby extending the lifetime of the ion source and improving the continuity of the online technique.
The research results show that the optimal combination of parameters for extending the ion source’s lifetime is the use of the Inert ion source, the 6 mm drawout plate, the high hydrogen flow rate at 0.53 mL/min, and the online Jetclean mode. By doing so, the lifetime can be effectively
prolonged the monitoring time length to 21 days. Under the optimized condition, the quality assurance/control (QA/QC) results are as follows: the relative standard deviations (RSD) of the calibration curves ranging from 0.43% to 11.09%, linearity (R2) ranging from 0.992 ~ 1.000, MDL between 0.04 and 0.77 ppb, the recoveries between 94.3% and 124.3%, and the precision (RSD) results between 1.3% and 7.4%. All the QA/QC aspects complied with the specifications set by the NIEA A715.16B method.
This research used Jetclean technology developed by Agilent to successfully prolong the continuity of the online measurements to more than two weeks and thus broaden the prospect of of online monitoring of toxic VOCs. As a result, for future applications of the online TD-GC/MS technique, not only can one obtain the reliable instantaneous concentrations of toxic VOCs, but also allow back-tracking pollution sources from the spikes of the hourly data. | en_US |