Total Organic Carbon
Total Organic Carbon (TOC) is one of the most important environmental screening parameters for organic matter in all kind of water samples, including drinking water, ground water, surface water and waste water. Organic carbon deriving from substances like PCB’s, Acetic Acid, Xylene or Propanol could form compounds which are harmful to the environment and may deplete the amount of oxygen in water. The amount of TOC present in a water sample can be determined in two ways:
TC – IC = TOC
Total Carbon (TC) stands for the sum of all carbon present in a sample. A TC measurement is executed by introducing a sample into a heated furnace (680 °C) where all carbon is converted towards CO2. The detected amount of CO2 represents the amount TC in a sample.
There are four types of inorganic carbon (IC):
The different types are related to each other by the following pH-driven chemical equilibria:
CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3– ⇌ 2H+ + CO32-
For an IC analysis, a sample is transferred into the IC vessel. A fixed amount of acid is added to the sample in the IC vessel. The acid will drive the above mentioned equilibria towards CO2. The detected CO2 represents the amount of IC in the sample.
The amount of TOC present in a sample can be detected by subtracting the detected amount of IC from the detected amount of TC.
TOC = NPOC (when POC is neglectable small)
When the Purgeable Organic Carbon (POC) content of a water sample is neglectable small, the amount of TOC can be measured directly. First, the sample is acidified and purged with oxygen for a set amount of time. All Inorganic Carbon (IC) converts into CO2 and evacuates to the ambient air. The Organic Carbon (TOC) content remains in the sample and is introduced into a heated furnace (680 °C), where all carbon is converted towards CO2. In this context, the amount of non-purgeable organic carbon (NPOC) stands for the amount of TOC present in the sample. The purgeable organic carbon (POC) components are purged out during the ‘sparging step’.
International test methods to measure the amount of Total Organic Carbon (TOC) according to Non Dispersive Infrared (NDIR) technique: ASTM D7573, EN 1484, EPA 415.1, EPA 9060, ISO 8245, USP 643, SM 5310B.