I am trying to figure out how to determine the amount of organic, or un-burned, material there is in an ash sample, or any other complex sample for that matter. I will consider charcoal or activated carbon as organic in this case. The most common way is probably the use of loss of ignition (LOI) which can be performed at different temperatures, i.e. heat the sample and measure the mass loss. This will (or can) however be affected by many other factors as well, e.g. oxidation of not fully oxidized compounds (negative LOI), volatilization of chlorides and loss of hydroxides, sulfates, carbonates and crystalization water. I guess it should be possible to include carbon in the elemental analysis, but that will again be affected by e.g. carbonates. Any suggestions?
The solution is to burn (oxydise) your ashes with air or oxygen and measure the quantity of CO2. It is not affected by carbonates as they are rather difficult to reduce if temperature is not to high.
Carbonates are already oxidized species. They won't be oxidized by air/O2 but however, they will decompose to CO2 (endothermic) at some point during heating. Decomposition temperatures may vary a lot depending on the metal, the presence of bulk or surface carbonates species...Hence, if you use a TG-DTA apparatus (or TG + DSC) and air/O2 as atmosphere, you can possibly titrate the organic carbon if a mass loss occurs simultaneously with a heat release (exotherm due to oxidation reaction). As Paul said, it would be better to monitor online the CO2 evolution (with MS or FTIR) anyway to confirm this.
That sounds reasonable. Measuring the CO2 with MS or FTIR would probably do the trick, as long as the temperature is not too high. The next question for me though, is how I can figure out a way to determine the organic content without having access to the actual samples, i.e. when I can't do any MS or FTIR. I was hoping to find a cleaver way to calculate the organic content from the data I have available (e.g. LOI and elemental content etc).
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