Generation of Improved Gas Linear Velocities in a Comprehensive Two-Dimensional Gas Chromatography System

A comprehensive two-dimensional gas chromatography (GC × GC) system (for convenience defined as “split flow” GC × GC), which may be operated at improved gas linear velocities in both dimensions, has been developed. The setup is formed of an apolar 30 m × 0.25 mm i.d. column connected, by means of a Y press fit, to a detector-linked 1 m × 0.1 mm i.d. polar analytical column, which passes through the (cryogenic) modulator, and to a 0.3 m × 0.1 mm i.d. retention gap, which is connected to a manually operated split valve. The latter enables the regulation of gas flows through the second analytical column [e.g., 60:40 (FID) ratio, 50:50 ratio, 40:60 (FID) ratio, etc.], in order to generate the most appropriate gas linear velocity, which is related to each specific analysis. In the pre-sent investigation, two sets of traditional and split flow GC × GC analyses were carried out on a cod liver oil fatty acid methyl ester sample by using the same temperature programs [180−250 °C at (a) 3 °C/min and at (b) 1.3 °C/min] and at an average first-dimension linear velocity of 35.0 cm/s; thus, primary column retention times (and therefore elution temperatures) were essentially maintained. The second-dimension linear velocity was calculated to be 333 cm/s in the traditional applications, while it was split valve-regulated until the most appropriate values [(a) 213 cm/s; (b) 264 cm/s] were attained in the alternative applications. Substantial improvements were observed and measured in the chromatography along the y-axis, while the contour plot chemical class structure was maintained.