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.

Keywords: Comprehensive three-dimensional gas chromatography; Dynamic pressure gradient modulation; Time-of-flight mass spectrometry; Total-transfer modulation.