Analysis of CO₂ by GasBench-IRMS

The SIF provides ¹³C and/or ¹⁸O analysis of CO₂ in headspace vials using a Thermo Scientific GasBench interfaced to a Delta V Plus IRMS.

Analysis of ¹³C in Carbon Dioxide

Stable isotope ratios of carbon (δ¹³C) and/or oxygen (δ¹⁸O) in carbon dioxide are measured using a ThermoScientific GasBench system interfaced to a ThermoScientific Delta V Plus isotope ratio mass spectrometer (ThermoScientific, Bremen, Germany).  CO₂ is sampled by a six-port rotary valve (Valco, Houston TX) with either a 100 µL, 50 µL, or 10 µL loop programmed to switch at the maximum CO₂ concentration in the helium carrier gas.  The CO₂ is then separated from N₂O and other residual gases by a Poraplot Q GC column (25 m x 0.32 mm ID, 45 °C, 2.5 mL/min). A pure reference gas (CO₂) is used to calculate provisional delta values of the sample peak.  Final ¹³C delta values are obtained after adjusting the provisional values for changes in linearity and instrumental drift such that correct ¹³C delta values for laboratory reference materials are obtained.  At least two laboratory reference materials are analyzed with every 10 samples.  Laboratory reference materials are calibrated directly against NIST 8545. Final ¹³C delta values, delivered to the customer, are expressed relative to the international standard V-PDB (Vienna PeeDee Belemnite)

Limit of Quantitation and Long-term standard deviation for CO₂ Analysis by GasBench-IRMS

CO₂ : Limit of Quantitation: approx. 150 nanomoles

           Long-term standard deviation: 0.1 ‰

Maximum measurable CO₂ concentrations (without sample dilution or subsampling) is 50,000 ppm.  Actual sample measurement limits are dependent upon both gas concentration and isotopic enrichment.  Please contact us if you intend to submit ¹³C-enriched samples at gas concentrations more than ten times that of ambient CO₂ concentration.