Total-transfer comprehensive three-dimensional gas chromatography with time-of-flight mass spectrometry

Abstract

Although comprehensive two-dimensional (2D) gas chromatography (GC × GC) is a powerful technique for complex samples, component overlap remains likely. An intriguing route to address this challenge is to utilize the additional peak capacity and chemical selectivity provided by comprehensive three-dimensional (3D) gas chromatography (GC3), especially with time-of-flight mass spectrometry detection (GC3-TOFMS). However, the GC3-TOFMS instrumentation reported to date has employed one or both modulators with a duty cycle < 100%, making the potential gain in detection sensitivity over GC × GC modest, or perhaps even worse. Herein, we describe instrumentation for GC3-TOFMS in which both modulators provide total-transfer (100% duty cycle). Specifically, the instrument is based on the facile modification of a commercial thermally modulated comprehensive GC × GC-TOFMS platform for modulation from the 1D column to the 2D column, with recently described dynamic pressure gradient modulation (DPGM) as the second modulator from the 2D column to the 3D column, which is a total-transfer flow modulation technique. Area measurements of 1D peaks are compared to the sum of 3D peak areas to validate the assumption that total-transfer from 1D to 3D is accomplished. Additionally, peak heights were amplified by as high as a factor of 177 (x̅ = 130, s = 47) via comparison of 1D peak heights to the maximum 3D peak heights. Column selection is explored, with emphasis on the resulting peak width-at-base on each dimension and usage of 3D space as evaluation metrics. Using a nonpolar × polar × ionic liquid column combination, an effective peak capacity which considers modulation-induced broadening as high as 32,300 for select analytes was achieved (x̅ = 19,900, s = 10,700). The analytical benefits of employing three selective phases, mass spectrometry detection, and total-transfer modulation are explored with separations of a metabolomics-type sample, i.e., derivatized porcine serum, and a jet fuel spiked with various sulfur-containing compounds.