Comprehensive two-dimensional gas chromatography using partial modulation via a pulsed flow valve with a short modulation period

Abstract

Partial modulation via a pulsed flow valve for comprehensive two-dimensional (2D) gas chromatography (GC × GC) is demonstrated, producing narrow peak widths, ²W_b, on the secondary separation dimension, ²D, coupled with short modulation periods, P_M, thus producing a high peak capacity on the ²D dimension, ²n_c. The GC × GC modulator is a pulse flow valve that injects a pulse of carrier gas at the specified P_M, at the connection between the primary, ¹D, column and the ²D column. Using a commercially available pulse flow valve, this injection technique performs a combination of vacancy chromatography and frontal analysis, whereby each pulse disturbance in the analyte concentration profile as it exits the ¹D column results in data that is readily converted into a ²D separation. A three-step process converts the raw data into a format analogous to a GC × GC separation, incorporating signal differentiation, baseline correction and conversion to a GC × GC chromatogram representation. A 115-component test mixture with a wide range of boiling points (36-372°C) of nine compound classes is demonstrated using modulation periods of P_M = 50, 100, 250, and 500ms, respectively. For the test mixture with a P_M of 250ms, peak shapes on ²D are symmetric with apparent ²W_b ranging from 12 to 45ms producing a ²n_c of ~ 10. Based on the average peak width of 0.93s on the ¹D separation for a time window of 400s, the ¹D peak capacity is ¹n_c ∼ 430. Thus, the ideal 2D peak capacity n_c,2D is 4300 or a peak capacity production of 650 peaks/min using the P_M of 250ms. Additionally, for a P_M of 50, 100 and 500ms, the ²n_c are 4, 7, and 12, respectively. Retention times on ²D, ²t_R, are reproducible having standard deviations less than 1ms. Finally, the processed data is shown to be quantitative, with an average RSD of 4.7% for test analytes.

Keywords: Comprehensive two-dimensional; Gas chromatography; High speed separations; Vacancy chromatography.