A Method for Combining a Stable Isotope Mass Spectrometer with an Isotopic Spectroscope to Analyze the ¹⁷O/¹⁶O

Since the discovery of mass-independent isotope effects, the study of triple oxygen isotope abundance has become a focus and frontier. In traditional oxygen isotopic ratio analysis methods, multiform oxygen is converted to CO₂ and the oxygen isotopic ratios of CO₂ are measured by Stable Isotope Mass Spectrometer. However, this method cannot be used to measure ¹⁷O isotopic abundance because ¹⁷O and ¹³C in carbon dioxide have the same m/z. The key for the triple oxygen isotope abundance analysis is to analyze the ¹⁷O isotopic abundance. To measure the ¹⁷O isotopic abundance multiform oxygen to O₂ is usually converted and then analyzed by Stable Isotope Mass Spectrometer, although the conversion process is complicated and/or dangerous. In this paper a new way to measure ¹⁷O/¹⁶O by Stable Isotope Mass Spectrometer and Isotopic Spectroscope is presented. The traditional method to convert multiform oxygen to CO₂ is adopted. The CO₂ was then analyzed by Stable Isotope Mass Spectrometer to obtain m/z45/44 (defined as R₄₅), and by isotopic spectroscope such as cavity ring down spectroscope (CRDS) to obtain ¹³C/¹²C (defined as R₁₃). The ¹⁷O/¹⁶O was calculated by ¹⁷O/¹⁶O=(R₄₅-R₁₃)/2. This method has an analytical precision which is better than ±0.08‰ (1σ). The new method is based on the traditional method with the addition of an analysis step of the carbon isotopic spectroscope for CO₂. With simple data processing, the ¹⁷O isotope composition was obtained without conversion of the multiform oxygen to O₂. Moreover, there is no risk in sample preparation for ¹⁸O isotopic analysis, and the precision is better than, or equal to, other methods.