FAST SAMPLING AND ANALYSIS OF OFFGAS DIOXINS/FURANS USING A THERMAL DESORPTION-GAS CHROMATOGRAPHY-HIGH RESOLUTION MASS SPECTROMETRY METHOD

摘要

The United States Department of Energy is using or evaluating several Alternatives-to-rnIncineration (ATI) technologies for treating hazardous wastes and low-level mixed wastes. ATIrntreatment technologies may have the potential for generating gaseous or other emissions ofrnpolychlorinated dioxins/furans, a class of highly toxic compounds which are regulated to veryrnlow levels. At present, the emission limit for dioxins/furans from hazardous waste incinerators isrn0.2 ng TEQ/dscm (0.4 ng TEQ/dscm w/TC). Emissions from ATI technologies are expected tornbe subject to similar restrictions.rnThe regulatory method for sampling and analyzing offgas dioxins/furans is EPA Method 23. ForrnMethod 23, the offgas sample is passed through a filter to retain any particulate-boundrndioxins/furans, and a resin cartridge to adsorb any vapor phase dioxins/furans. For all samplernmedia, offgas, liquid, or solid, the overall procedure for extraction and analysis is complex andrnlabor intensive, and requires specialized laboratory facilities as well as specialized sampling andrnanalysis equipment. Sampling and analysis turnaround time is normally several weeks. The costrnand complexity, and turnaround time, make Method 23 impractical as a tool for processrnoptimization or routine process monitoring. A faster and simpler method for dioxin/furanrnsampling and analysis is needed. Simplifying or eliminating sample preparation steps providesrnthe most significant opportunity for reducing overall turnaround time. Thermal desorption-basedrnsampling and sample preconcentration offers an attractive means to simplify and speed up thernsample preparation process. In this approach, vapor phase and particulate-bound dioxins/furansrnare trapped in a conventional sampling tube packed with a suitable filter/adsorbent material. Inrnprinciple, the compounds of interest can then be thermally vaporized and presented to a GC/MSrnor other analyzer system in a single, rapid step.rnA potential shortcoming of thermal desorption-based sampling and analysis, which may be veryrnsignificant for “dirty” samples, is that compared to Method 23 it offers little ability to removerninterfering compounds prior to introducing the sample into a GC/MS. One approach to removingrninterferences is to thermally desorb the sample in stages, so that dioxins/furans and interferingrncompounds are presented to the GC/MS at different times. In previous work we found that gasrnchromatography/low resolution mass spectrometry (GC/LRMS) provided adequate compoundrnresolution for thermal desorption of pure dioxins/furans spiked onto adsorbent media, but did not