Accurate Stable Carbon Isotope Ratio Measurements in Rapidly Varying CO2 Concentrations

Stable isotope analysis relies on the simultaneous or near-simultaneous measurement of two individual species. In the case of the Picarro G1101-i and G2101-i gas analyzers, these two species are ¹²C¹⁶O₂ and ¹³C¹⁶O₂, which we denote ¹²C and ¹³C for simplicity. In the G1101-i, alternate measurements of ¹²C and ¹³C are made with a period of about eight seconds; the fact that the two gas measurements are not made simultaneously leads to systematic errors in the reported delta in certain conditions when the gas concentration is varying significantly. In this white paper, we report on improvements that we have made in the G2101-i to reduce these systematic errors by more than a factor of eight.