T01_07

An automated processing line for the extraction of dissolved inorganic carbon from water for radiocarbon dating

Yang B¹,  Williams A², Nguyen T¹, Freeman P¹, Jacobsen G¹, Smith A¹

¹Australian Nuclear Science & Technology Organization (ansto), Lucas Heights, Australia, ²Deceased. , ,

At ANSTO, radiocarbon analyses of dissolved inorganic carbon (DIC) in groundwaters are in high demand for water resource sustainability research. A grant from the NSW Research Attraction and Acceleration Program enabled the development of an automated DIC extraction line for unattended processing of 10 samples.  This line operates at ambient pressure with helium (He) gas as carrier. CO₂ gas is extracted from 50 mL of water in a 250 mL reaction vessel by adding 5 mL of phosphoric acid. The He gas is sparged through the water sample and then passed through two water traps at -100°C to remove water; and two CO₂ traps at -165°C to collect CO₂ gas. Complete recovery of CO₂ is determined by passing the He flow through a CO₂ analyser before releasing to waste to verify the absence of any residual CO₂. The CO₂ gas is then cryogenically transferred into one of 10 storage vessels until all queued samples on the system are processed. Between samples, the water traps and CO₂ traps are cleaned by evacuation to a pressure <5/10³ mbar. The water loop is flushed by He gas, followed by Milli-Q® water and a portion of the next sample, so eliminating sample memory. The line is controlled by a Python program running on a PC through serial connections, and several important parameters are logged to check that the system is working properly. After processing 10 samples, CO₂ sample is manually transferred to glass break seals for purification and conversion to graphite for AMS measurement.