Organic carbon samples are combusted at high temperature to produce CO2 in our Sample Prep Lab. But first, depending on the sample, these also can require special labor-intensive pretreatment steps.
Pretreatment of Organic Carbon Samples
Plant/wood and charcoal samples undergo a series of heated acid-base-acid leaches to remove inorganic carbon and mobile organic acid phases. This process necessarily removes some sample mass. We will repeat up to 20 base leaches; even if the solution is not clear after 20, we stop the base treatment and move on to a final acidification. Sediment samples undergo the acid pretreatment only. If neither pretreatment is required, the sample is considered "ready to burn" and the fee is less accordingly.
Inorganic carbon samples, or carbonate minerals, are directly hydrolyzed with strong acid, H3PO4, to convert the carbon in the sample to CO2.
Water Strip - DIC
Dissolved inorganic carbon is "stripped" in an automated system in our Sample Prep Lab using acidification and sparging with nitrogen to "strip" the evolving CO2 from the water.
UV Oxidation - DOC
Dissolved organic carbon is oxidized in an automated system in our Sample Prep Lab using ultraviolet light to oxidize the dissolved organic carbon and sparging to "strip" the evolving CO2 from the water.
Samples submitted as ampoules of CO2 are cracked, quantified, split (if required), and transferred to a reaction tube for reduction to pure carbon. The CO2 is reduced with use of a catalayst (Fe or Co) in the presence of excess hydrogen
CO2 + 2 H2 C (graphite) + 2 H2O
Samples submitted as solid carbon (graphite) require pressing into target cartridges for loading into the AMS.
AMS & Data Analysis
Samples submitted as solid carbon, pressed into targets, require only AMS and data analysis
Contamination check/swipe samples
Samples submitted on quartz or glass filters are combusted in sealed tubes at high temperature to produce CO2 then further reduced to graphite using a modified version of the sealed-tube graphite method developed by John Vogel (Radiocarbon Vol. 34, No.3, 1992, p344-350). Methods are aimed to prevent sample cross-contamination. All procedures are carried out in a dedicated separate laboratory.
Last updated: September 5, 2012