Analysis of Semivolatile Organic Compounds in Diesel Exhaust Using a Novel Sorption and Extraction Method

As interest has grown in diesel emissions and diesel engine aftertreatment, so has the importance of analyzing all components of the exhaust. One of the more costly and difficult measurements to make is the collection and analysis of semivolatile organic compounds (SOCs) in the exhaust. These compounds include alkane and alkenes from C₁₂-C₂₄, and the 2-5 ring polycyclic aromatic hydrocarbons (PAH). These compounds can be present in both the particulate (i.e. on the filter) and gaseous phase, and cannot be collected with bag samples. Typically, a sorbent is used downstream of the particulate collection filters to collect these compounds. Sorbent phases include polyurethane foam (PUF), Tenax™, XAD-type resins, and activated carbon. The SOCs are removed from the sorbent either by solvent extraction (PUF and XAD) or thermal desorption (Tenax™ and activated carbon). Each of these methods have advantages and disadvantages. We report here on the use of special solid phase extraction (SPE) disks as a new sorbent phase. While commonly used for pre-concentration of trace compounds in aqueous samples, the SPE disks have never been applied to exhaust sampling. These disks offer the high throughput advantages of PUF without the large solvent volumes needed for preparation and extraction. Bench experiments with trace gases as well as exhaust studies are presented. Hydrocarbon compounds as volatile as decane demonstrated minimal breakthrough. Solvent volumes are typically 1/100 of the amount required to use PUFs. In addition, no special equipment is required to adopt the method.