A two-dimensional, heart-cutting preparative gas chromatograph facilitates highly resolved single-compound isolations with utility towards compound-specific natural abundance radiocarbon (14C) analyses

Abstract

Motivated by the need to develop clean, high purity preparative enrichments of individual compounds for micro-scale compound-specific natural abundance isotope and radiocarbon ((14)C) analyses, we describe a new, two-dimensional, heart-cutting, low-bleed, three-oven, single GC preparative system, demonstrate its resolving capabilities as applied to a typically complex environmental sample matrix, and investigate the robustness with which it preserves the authigenic (13)C/(12)C and (14)C/(12)C ratios of individual compounds it targets for preparative enrichment. The system is comprised of a programmable temperature vaporizing (PTV) inlet, a single GC oven, two modular, door-mounted, resistively heated low thermal mass (LTM) columns, a preparative fraction collector (PFC), and a Deans pneumatic switching device which facilitates heart-cutting between the system's 1° and 2° chromatographic dimensions. Further, the system's inlet and trapping parameters are optimized for the efficient preparative enrichment of the methyl ether and ester derivatives of the lignin phenol compound class. The lignin phenols include such compounds as the vanillyl and syringyl aldehydes, ethanones, and acids and are unrivaled biomarkers of terrestrial organic matter, some of which are also important components of fragrances and flavors. Using this suite of compounds, the suitability of this augmented preparative capillary GC (PCGC) system was investigated for micro-scale compound-specific (CS) stable isotope and natural abundance radiocarbon analyses (RA). Analysis of a >300 injection enrichment scheme reveals the instrument to fractionate (13)C in predictable ways and to preserve the authigenic Δ(14)C of compounds it targets for preparative enrichment to within 6.7±5.0‰, demonstrating the promising new utility of such systems towards micro-scale CSRA investigations for which clean and high resolution separation techniques are prerequisite.