Promoting the transition away from fossil fuels in gas chromatography: Nitrogen as alternative carrier gas for GC analysis of essential oils

In European Raw Materials Act, the EU listed the helium among the thirty-four critical raw materials to ensure a sustainable and diversified supply for modern technologies. In gas chromatography (GC), helium is the most used carrier gas for the separation of volatile compounds due to its inertness, relatively wide optimum linear velocity range, and safety. However, hydrogen and nitrogen represent valid and more-sustainable alternative carrier gases for GC separations. The purpose of this research is to explore the effectiveness of nitrogen carrier gas for the GC analysis of aromatic volatiles in Citrus essential oils (EOs) (Citrus bergamia, Citrus limon, Citrus deliciosa Ten., Citrus sinensis L.). For an exhaustive evaluation, the performance of hydrogen gas was also investigated. Golay curves demonstrated optimal chromatographic resolution in the widest range of linear velocities for hydrogen (25–60 cm s-1) compared to helium (20–45 cm s-1). On the other hand, nitrogen carrier gas showed comparable or better separative efficiency at lower linear velocity (optimal linear velocity range 10–20 cm s-1) without compromising significantly the analysis times for conventional GC applications (about 50 min for nitrogen, 43 min for hydrogen, and 44 min for helium). The effectiveness of the nitrogen was also exploited in dual-detection enantioselective gas chromatography (enantio-GC) consisting of two parallel and different chiral stationary phases to obtain improved separation of enantiomers. The perspective to replacing helium with nitrogen gas produced on-site represents a viable scenario in terms of energy-environment-economic benefits.