Methanogenic pathways and δ13C values from swine manure with a cavity ring‐down spectrometer: Ammonia cross‐interference and carbon isotope labeling. (19th February 2020)

• Record Type: Journal Article
• Authors: Dalby, Frederik R.; Fuchs, Andrea; Feilberg, Anders
• Is Part Of: Rapid communications in mass spectrometry. Volume 34:Number 7(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-02-19
• Subjects: Mass spectrometry -- Periodicals; 543.65
• DOI: 10.1002/rcm.8628
• Languages: English
• ISSNs: 0951-4198

Abstract

Abstract : Rationale: Carbon isotope ratio analysis using cavity ring‐down spectroscopy (CRDS) offers insight into methanogenic activity. In livestock buildings, measuring 13 CH4 / 12 CH4 by CRDS is challenging and prone to errors, due to cross‐interference from NH3 . Therefore, an interference‐corrected and improved approach to monitor methanogenic pathways with CRDS was developed and described in this study. Methods: Cross‐interference from NH3 and other livestock gases on 13 CH4 / 12 CH4 was measured using CRDS. The removal efficiency of livestock gases was quantified using proton transfer reaction mass spectrometry. The linearity of the cavity ring‐down spectrometer was tested by dilution of a 13 CH4 standard up to 15.6 atom % in CH4 . 13 C isotope‐labeled acetate was utilized to elucidate the methanogenic pathway contribution in swine manure using a stoichiometric model. Results: Significant NH3 cross‐interference on 13 CH4 / 12 CH4 was observed, and correction factors were calculated. Cross‐interfering gases were effectively removed using a copper scrubber and a Nafion tube. The instrument responded linearly with 13/12 C ratios up to 7.6 atom % in CH4 . Isotope‐labeled experiments suggested that hydrogenotrophic methanogenesis was dominant and acetate‐derived CH4 was limited in the studied swine manure. The observations were cross‐validated and consistent with measurements of the natural isotope signatures. Conclusion: NH3 cross‐interference leads to major errors in isotope ratios and therefore in evaluating the relative methanogenic pathway activity. We present methodological approaches, which are crucial to apply in livestock‐related uses where NH3 is abundant. This methodology provides a considerable benefit to advance the understanding and reduction of methane emissions in the livestock sector.