Challenges and opportunities for a greener and sustainable GC-MS with hydrogen as carrier gas

Summary: This work aimed at evaluating hydrogen as carrier gas in GC-MS for selected case-study applications. Analytical performance was assessed in terms of key features such as speed, sensitivity and spectral quality. Results were compared to helium as benchmark to weigh the feasibility of this approach for various real-life application. Keywords: GC-MS, carrier gas, hydrogen Helium is historically used as carrier gas for gas chromatography coupled to Mass Spectrometry (GC-MS). It is commonly preferred due to its favorable chromatographic characteristics and for its inertness, which minimize the occurring of unwanted reactions for active/labile compounds in the chromatographic process and during MS detection. In the last years, helium shortage has been making its use increasingly more challenging to sustain. Availability can be limited, with detrimental effect on timely delivery, and prices are soaring making this resource less accessible. As a consequence, more effort is being invested in reducing its use and finding viable alternatives. From a chromatographic perspective, hydrogen is an effective replacement as carrier in GC: it offers excellent resolution at reducing analysis time, thanks to its capacity to deliver efficiency at high speed. In addition, hydrogen can be produced by generators, removing altogether the need for bottles. This allows to reduce long-term operational costs and use of resources, making it a greener and more sustainable solution. However, hydrogen is not an inert gas. This is the main factor limiting widespread use in GC-MS, as reactivity raises concerns regarding compatibility with MS detection. Behaviour during ionization is in fact a key feature for a reliable mass spectrometric process. Unwanted reactions in the electron ionization source can potentially lead to irregular fragmentation and formation of by-products, resulting in unconventional MS patterns. Poor mass fidelity would undermine matched against commercial libraries built on helium, making confident identification less successful. Moreover, carrier gas ionization can suppress signal and decrease sensitivity. In this study we investigated the use of hydrogen as carrier in GC-MS including - next to established configurations - a novel EI source (HydroInert, Agilent Technologies) recently developed specifically to ensure compatibility with hydrogen. We ranged across different fields of application to achieve a better understanding of the impact analytes’ chemistry plays on performance. Namely, test mixtures involved volatile organic compounds (VOC), pesticides, allergens and key aroma compounds. Analytical performance was evaluated using selected key indicators such as speed, sensitivity and spectral quality. The HydroInert source often showed a significant, beneficial impact on performance with hydrogen. It was observed that, as expected, performance strongly depends on compounds. In some cases, the use of hydrogen does somewhat impact analysis whereas, in others, results are fully consistent with the gold standard, helium.