Effect of Sample Signal Intensity on δ15N and δ34S Measurement by EA-IRMS System

Carbon-nitrogen ratio (C/N) and carbon-sulphur ratio (C/S) of unknown samples can vary greatly in the natural environment. There are also distinct differences in the ionization efficiencies of N and S elements. These factors will introduce the fluctuation of signal intensity to the element analysis-isotope ratio mass spectrometry (EA-IRMS), which can has a further impact on the measurements of sample δ15N and δ34S. However, the analysis of unknown sample δ15N and δ34S is always restricted by the low content or the scarcity of the target elements. In this study, we focused on the effect of sample amount and signal intensity on the δ15N and δ34S measurement by EA-IRMS. Our results indicated that the EA-IRMS measurement of δ15N and δ34S was significantly affected by the “blank effect” when the sample amount and signal intensity were limited during the mass spectrometry analysis. Under the injection conditions of 1.71-561.93 μg N and 3.74-100.62 μg S, the variation ranges of the measurement errors of the isotopic