Isotopic analysis of CO2 in gases with variable CO2 concentrations (δ13C)

Isotopic analysis of CO₂ in gases with variable CO₂ concentrations (δ¹³C)

*“Petra” is a Delta V advantage IRMS coupled to a modified Gasbench II via a home-made ConFlow II - like open split system.*

*“Petra” is a Delta V advantage IRMS coupled to a modified Gasbench II via a home-made ConFlow II - like open split system.*

Numerous incubation and respiration experiments take place at the MPI-BGC. Such experiments require the analysis of δ¹³C from variable CO₂ concentrations, from 400 ppm to 5 % CO2 in air(like) matrices. To facilitate these types of analyses the BGC-IsoLab operates a Delta⁺XL for Bulk Isotope Analysis of Carbon “Bianca”.

GC-IRMS flow schematics. The gas sample traverses the GC column which is bracketed by two nafion water traps. After the second nafion water trap an additional Ethanol/dry ice (-70 °C) water trap is installed to make sure that the sample gas is dry upon reaching the open split, which finally feeds sample air, standard air and reference CO2 into the IRMS. — GC-IRMS flow schematics. The gas sample traverses the GC column which is bracketed by two nafion water traps. After the second nafion water trap an additional Ethanol/dry ice (-70 °C) water trap is installed to make sure that the sample gas is dry upon reaching the open split, which finally feeds sample air, standard air and reference CO₂ into the IRMS.

GC-IRMS flow schematics. The gas sample traverses the GC column which is bracketed by two nafion water traps. After the second nafion water trap an additional Ethanol/dry ice (-70 °C) water trap is installed to make sure that the sample gas is dry upon reaching the open split, which finally feeds sample air, standard air and reference CO₂ into the IRMS.

The system is made up of four functional units, a PAL-Autosampler (CTC-Analytics), a GC-System that separates CO₂ from its air-matrix, the open split, and the IRMS. The autosampler can be loaded with 5 or 10 ml sample vials. An air standard gas is made available in a septum-capped, sample vial-like copper vessel that is flushed continuously with standard air. Sample or standard air is injected using a 250 or 100 μl gas tight syringe. This allows aliquots of 150 to 12 μl of gas to be injected, facilitating the analyses of CO₂ in air at variable concentrations. Helium is used as a carrier gas transporting the analyte through a GC column that reliably separates N₂O from the preceding CO₂ peak.

*Measurement precision depending on the injection volume of the 250 μl gas tight syringe.*

*Measurement precision depending on the injection volume of the 250 μl gas tight syringe.*

The three water traps installed in the system make sure that the sample gases are completely dry. This is important as water can act as a protonation agent, thus affecting δ¹³C analyses in an unpredictable manner. Up to 90 samples are analysed in a sequence, allowing for multiple injections. Every sequence contains standard air and Q/C measurements that are placed after 5 or 15 sample injections, depending on the sample type. The precision of samples in one sequence is usually better than 0.1 ‰ (1 σ SD).

Isotopic analysis of CO2 in gases with variable CO2 concentrations (δ13C)

Further reading:

Isotopic analysis of CO₂ in gases with variable CO₂ concentrations (δ¹³C)