Experimental Evaluation and Optimisation of Sealed‐Tube Combustion Methods for Silicate Nitrogen Extraction

Rationale Nitrogen (N) abundance and isotopic compositions in silicate rocks are commonly measured by sealed‐tube continuous‐flow isotope ratio mass spectrometry (CF‐IRMS), but combustion protocols vary widely. It remains uncertain how the quality of data obtained from different published methods compares for differing sample types. Methods To address this uncertainty, nitrogen abundance ([N]) and isotopic composition (δ 15 N) were measured in granite, plagioclase, alkali feldspar and biotite using tube‐cracker CF‐IRMS with seven different combustion protocols: One followed a combined tube‐ and box‐furnace method, whereas the other six used a simplified box‐furnace‐only approach, generally involving longer heating durations at lower temperatures. Results For granite, plagioclase, alkali feldspar and biotite, we successfully identified a method that does not require a 1200°C heating step in the tube furnace without negatively impacting N yield. For granitic rocks, in cases where the highest yield methods are unsuitable (i.e., due to low [N], high sample mass requirements or lower sample melting point), we propose a suitable alternative that requires corrections on the final measured value to account for incomplete N extraction. Conclusions For sealed tube combustion paired with continuous‐flow isotope ratio mass spectrometry, lower combustion temperatures typically reduce N extraction from silicate materials. However, increasing the combustion duration at temperatures equal to or below 1000°C can reduce, and in some cases eliminate, this yield difference.