Experimental Conditions A JEOL AccuTOF-DART mass spectrometer was used as the detector. The GC/MS interface consisted of short piece of 1/8 inch OD copper tubing wrapped with heat tape. A thermocouple was used to check the interface temperature. The GC column extended about 1 cm from the tubing into the heated gas stream of the DART ion source and positioned directly in front of the sampling orifice for the mass spectrometer atmospheric pressure interface. The DART source was operated with helium gas with the gas heater set to 300 degrees C. The GC was operated with the standard GC column (30 m ID x 0.32 mm film thickness DB-5 column) used for GC/MS measurements in our laboratory. GC conditions for the Grob mix were: split injection, oven temperature ramped from 40 to 200 degrees at 6 degrees per minute.