Coplen, T. B., Brand, W. A., Gehre, M., Gröning, M., Meijer, H. A. J., Toman, B., & Verkouteren, R. M. (2006). New Guidelines for δ13C Measurements. Analytical Chemistry, 78(7), 2439–2441. https://doi.org/10.1021/ac052027c