In order to assess the precision of the IRMS system for nitrogen isotope signatures under measurement conditions, ten consecutive reference gas peaks were injected with constant (stability) and increasing (linearity) signal intensities. Table presents the average (Avg 6 for linearity and peak no. 4 for stability measurements, marked with * in Table ) throughout the complete series of ten reference gas injections. The cause for these outliers were small shifts in the m/z 29/28 ratios (see Supporting Information Figure ) occasionally appearing throughout chromatograms. The shifts tend to be one-minute-long and, due to the nature of the interface to produce wide peaks, they might originate from the liquid phase of the system, possibly due to piston movement of the HPLC pumps. We took great care to manually check and avoid measurements where one of these shifts occurred under peaks of interest. Despite these interferences, the system performs sufficiently robust and is able to measure nitrogen isotope signatures of elemental nitrogen with a precision better than 0.5 ‰ over a peak area range of 4.6 to 21.3 Vs and possibly more precise if background shifts are avoided.