A systematic analysis of a flow-switching modulator for comprehensive two-dimensional gas chromatography

A simple flow-switching device has been designed for use as a comprehensive two-dimensional gas chromatography modulator. The device is constructed from fused silica tubing, t-unions, and a solenoid valve. A series of experiments were conducted to determine the influence of primary flow, secondary flow, modulation time, and device dimensions on the performance of the modulator. The flow-switching device was found to produce pulses with widths near the theoretical minimum. High-performance was maintained over a wide range of modulation times. The flow-switching device did not introduce extra broadening along the primary retention axis. However, the modulator performance was optimal only over a narrow range of primary to secondary flow ratios. The ideal flow ratio is determined by the dimensions of the tubes that connect the t-unions. A simple flow resistance model has been developed that can predict the dimensions that will produce optimal results for a specified primary to secondary flow ratio. Thus, it is possible to construct a device that operates near the theoretical limit without numerous alterations. Under optimal conditions, the flow switching modulator generates peaks that are narrower than those produced by a diaphragm valve.