New liquid nitrogen cryogenic modulator for comprehensive two-dimensional gas chromatography

A new liquid nitrogen (LN2) jet-based thermal modulator for performing comprehensive two-dimensional (2D) gas chromatographic (GC×GC) separations has been designed and constructed. Temperature measurements of the trapping zone, a segment of uncoated fused silica capillary, show that it can be cooled to −196 °C in about 300 ms. A film of liquid nitrogen develops on the outside of the trapping capillary even when the oven temperature is in excess of 200 °C. Compounds as volatile as propane can be trapped by the modulator and held for periods of at least 1 min without breakthrough. The peak widths for n-alkanes are on the order of 80 ms at half height after passing through an 80 cm second dimension column. Repeated analysis of gasoline demonstrated excellent run-to-run reproducibility of the system.