A rapid method for the preparation of O₂ from CO₂ for mass spectrometric measurement of ¹⁷O/¹⁶O ratios

Following the discovery of strong oxygen isotope enrichment in stratospheric O₃ and in particular the puzzling concomitant large excess enrichment in ¹⁷O, more atmospheric gases, importantly CO₂ and CO, have been found to suffer from this effect, known as mass independent fractionation. Understanding this new category of isotope effects, which for O₃ appears to be a rare, symmetry related kinetic isotope effect, is of fundamental importance. Moreover, the search for the presence of mass independent fractionation effects in atmospheric trace gases and understanding their causes is of interest to atmospheric chemistry. Conventional accurate oxygen isotope ratio analysis is based on mass spectrometry of CO₂. However, using CO₂ does not allow measurement of the ¹⁷O/¹⁶O ratio due to isobaric interference from ¹³C variations. Therefore, conversion to O₂ is necessary, for which a fast and safe method has been developed. The essence of the new method is that CO₂ is first converted to H₂O and CH₄ by reacting it with H₂. To increase reaction speed and to achieve quantitative conversion, a Ni powder catalyst is used at its Curie point. Subsequently, the formed H₂O readily reacts with F₂ to form the desired O₂ with HF as waste product. A safe reaction is assured by using a mixture of only 5% F₂ in He. The validity of the produced isotope ratios is verified independently.