NMR spectroscopy is an established tool for exploring the mechanisms of CO 2 capture in a large variety of materials. Most NMR studies focus on C NMR measurements, with N NMR also utilised in amine-based systems. In hydroxide systems, however, such C NMR data can be ambiguous due to the similar chemical shifts of certain products (e.g. bicarbonate and carbonate) or require further NMR measurements which can introduce their own ambiguity. Recently, Berge and Pugh et al. demonstrated O NMR spectroscopy as a novel and effective tool for deconvoluting CO 2 capture mechanisms in amine-functionalised metal-organic frameworks. At a cost of enrichment of about £50-75 per sample (20% atom 17-oxygen CO 2 ), these methods offer great potential for resolving mechanistic ambiguity, giving new insights alongside C NMR. Particularly, with the quadrupolar nature of O (I = 5/2), additional site-specific information is accessible from the quadrupolar parameters (C Q and η Q ) derived from the observed NMR quadrupolar lineshapes: