Why does the European Pharmacopoeia suggest that TOC analyzers should completely oxidize the TOC present in the sample to CO2?

TOC analyzers calculate the amount of TOC present in the sample by oxidizing the TOC and then measuring the amount of CO2 generated. If the TOC in the sample is not completely oxidized, then the TOC analyzer will not report correctly the TOC present in the sample.

TOC analyzers work by oxidizing the TOC in the sample to turn the carbon present to CO2. If oxidation is not complete then not all of the organic carbon is turned into CO2. This could result in the TOC either over reporting, or under reporting. If the intermediate species formed as the TOC is oxidized are organic acids, then the TOC analyzer may over-report the TOC levels. The PAT700 uses dynamic end-point detection to detect during oxidation that the levels of CO2 have stopped changing indicating that all the TOC has been completely oxidized to CO2.

 Complete oxidation illustration