TOC, Total organic carbon — The amount of carbon bound in organic compounds. Often used as an indicator of water quality or cleanliness of pharmaceutical manufacturing equipment.

A typical analyis for TOC measures both the total carbon (TC) present as well as the inorganic carbon (IC, or carbonate). Subtracting the inorganic carbon from the total carbon yields TOC. Another common variant of TOC analysis involves removing the IC portion first and then measuring the leftover carbon. This method involves purging the acidified sample with carbon-free air prior to measurement, and so is more accurately called non-purgeable organic carbon (NPOC).

Virtually all TOC analyzers measure the CO₂ formed when organic carbon is oxidized and/or when inorganic carbon is acidified. Oxidation is performed either through Pt-catalyzed combustion or with a UV/persulfate reactor. Once the CO₂ is formed, it is measured by a detector: either a conductivity cell (if the CO₂ is aqueous) or a non-dispersive infrared cell (if the CO₂ is gaseous). Conductivity is only desirable in the lower ranges, whereas NDIR detection excels in the higher ranges. Modern TOC instruments are cabable of detecting carbon concentrations as low as 50 µg/L.

TOC is the first chemical analysis to be carried out on potential petroleum source rock. It is very important in detecting contaminants in drinking water, cooling water, and water for pharmaceutical use (ultra-pure).

The reason organic carbon detection is more desired is because of the environmental effects it poses. Chemical plants can only release so much organic carbon per year. Organic carbon readily binds with other elements in the water and air to form harmful compounds. TOC is also of interest in the field of water treatment due to disenfection byproducts formed in chlorination and ozonation reactions. Inorganic carbon poses little to no threat.

Chemical oceanography | Analytical chemistry

Gesamter organischer Kohlenstoff