High speed Deans switch for low duty cycle comprehensive two-dimensional gas chromatography

A new high-speed valve-based modulator has been designed and tested for use in comprehensive two-dimensional gas chromatography (GC × GC). The modulator is a Deans switch constructed from two micro-volume fittings and a solenoid valve. Modulator performance was characterized over a wide range of device settings including the magnitude of the switching flow, the gap between the tips of the primary and secondary column, the primary column flow rate, and the carrier gas identity. Under optimized conditions, the modulator was found to be capable of generating narrow pulses (<50 ms) of primary effluent with a 2 mL/min secondary column flow. This capability will ultimately allow the modulator to be used with GC × GC separations employing a wide range of detectors and secondary column geometries. The main disadvantage of this modulator is that it employs a low sampling duty cycle, and thus it produces separations with sensitivities that are lower than those produced with thermal modulators or differential flow modulators. The efficacy of the new high-speed Deans switch modulator was demonstrated through the GC × GC separation of a hydrocarbon standard and gasoline. Precise quantitation of individual components was possible provided the modulation ratio was kept greater than 2.0.