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.
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
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: July 10, 2012