Mark Klemp

Instrumentation and strategies for high-speed gas chromatography

Short lengths of capillary column operated at unusually high carrier-gas velocities are used to separate relatively simple mixtures on a timescale of 20 s or less. Two inlet systems are described which can generate the narrow injection bands needed for these elution times. A cryofocusing inlet using a vacuum-pump-operated gas flow direction control is used for compounds generally less volatile than n-pentane. A low-friction gas valve inlet combined with porous-layer open-tubular columns is used for volatile compounds of low molecular mass. Strategies for high-speed separations including high-speed backflush, backflush with recycle, vacuum-outlet operation and selective detection are described. These techniques are used to increase the operational flexibility and the amount of information that can be obtained using high-speed gas chromatography.

High-speed capillary column GC for rapid screening of gasoline to diesel range organic compounds

A high-speed gas chromatography (GC) instrument has been developed for near real-time screening of soil gas samples continuously generated from a cone penetrometer (CPT) equipped with a heated probe tip. The GC instrument uses a cryofocusing inlet system which can preconcentrate gasoline and diesel vapor and introduce a very narrow vapor plug into the capillary separation column. The GC instrument can be operated either in a high-speed screening mode or in a higher resolution advanced field analysis mode. In the high speed mode, a short capillary separation column is used with a photolonization detector to selectively detect aromatic (BTEX) compounds in petroleum fuel spills in a time frame of 10–20 s and with detection limits in the ppb range. In the advanced field mode, a longer column and flame ionization detector are used to obtain a finger-print chromatogram which is useful in determination of fuel type. In this mode, analysis times are typically about 200 s. The high-speed GC instrument is designed to be located in the CPT truck and connected directly to a heated gas transport line. In the high-speed screening mode, continuous sampling and near real-time analysis provide very high spatial resolution as well as high speed for site characterization.