Differentiated correction on the signal intensity dependence of GasBench II-IRMS from blank effect and instrument nonlinear effect

Abstract

Continuous-Flow Isotope Ratio Mass Spectrometry (CF-IRMS) coupled with a GasBench II was designed to rapidly analyze δ13C in carbonate or CO2 in air. The dependence of measured δ13C (δ13Cm) on signal intensity (peak area or peak height) was the main error source resulting from blank effect of samples and/or instrument itself effect. To determine the reasons and origins of signal intensity dependence, eight signal intensity gradients for two carbonate (δ13C values were −49.64 and 1.61‰, respectively) and a gas mixture of 0.3% CO2 in He (δ13C=−19.32‰) standards were made respectively. The results showed that there was obvious signal intensity dependence, in particular when sample amount (peak area) was smaller. Given that the dependence was caused by blank effect and/or instrument nonlinear effect, without considering the blank effect, the signal intensity dependence could not be eliminated directly by the instrument nonlinear correction (empirical equation) methods However, it could be eliminated by blank correction (indirect subtraction method). In practice, blank effect should be corrected first, and then the instrument nonlinear effect.