Analysis of Dissolved Inorganic Carbon (DIC) in Water by GasBench-IRMS

Analysis of Dissolved Inorganic Carbon (DIC) in Water by GasBench-IRMS

The SIF provides δ13C analysis of Dissolved Inorganic Carbon (DIC) in water samples using a GasBench II system interfaced to a Delta V Plus IRMS (Thermo Scientific, Bremen, Germany).

Analysis of 13C-DIC

Water samples (1-4 mL) are injected into helium-filled 12 mL septum capped vials (Exetainers, Labco, High Wycombe, UK) containing 1 mL 85% phosphoric acid, which forces the equilibrium between CO2 and H2CO3 to gaseous CO2. The evolved CO2 is purged from vials through a double-needle sampler into a helium carrier stream (20 mL/min). The gas is sampled using 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. The CO2 is passed to the IRMS through a Poroplot Q GC column (25m x 0.32mm ID, 45°C, 2.5 mL/min). A reference CO2 peak is used to calculate provisional delta values of the sample CO2 peak. Final δ13C values are obtained after adjusting the provisional values for changes in linearity and instrumental drift such that correct δ13C values for laboratory reference materials are obtained. At least two laboratory reference materials are analyzed with every 10 samples. Laboratory reference materials are lithium carbonate dissolved in degassed deionized water and a deep seawater (both calibrated against NIST 8545). Final δ13C 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 13C-DIC by GasBench-IRMS

13C-DIC as CO2 : Limit of Quantitation: approx. 150 nanomoles

                                 Long-term standard deviation: 0.1 ‰