Total carbon (TC) determination can be routinely performed on a wide variety of organic materials such as coal, coke, and fuel oils, as well as some inorganic materials such as soil, cement, and limestone.
Analysis of a solid sample begins as the dried material is weighed into a combustion boat, then passed into a furnace at >1250° C while in a pure oxygen environment. The sample combusts through an oxidative-reduction process that frees the carbon which is then oxidized to form CO2. The sample gases are swept through a series of scrubber tubes to remove interferences such as water vapor and halogens anhydrone tube to remove moisture, then through a flow controller that sets the flow of sample gases through the NDIR (non-dispersive infrared detector) cells. The intensity of the CO2 signal as typically measured at 2350 cm-1 is directly proportional to the concentration of carbonaceous material in the sample. The weight per cent of total carbon in the original sample can then be calculated by comparison to known calibration standards.
The technique can be adapted to measure inorganic (TIC) or organic carbon (TOC). To measure total organic carbon, the samples are treated with dilute acid to remove any inorganic carbon in the form of bicarbonate or carbonate. The decarbonized samples are dried, then run through the analyzer to measure total organic carbon. The difference in the total carbon and total organic carbon results will provides a measure of the inorganic carbon content of the sample.
Liquid samples can be analyzed in much the same way. Liquid samples can also be purged of volatile organics prior to analysis by sparging in order to obtain a non-purgeable organic carbon result (NPOC).