Total Organic Carbon (TOC) analysis is a well-established technique for the determination of water cleanliness and purity. However applications can range from the analysis of ultra pure water used in the biotechnology and pharmaceutical industries for Clean-In-Place (CIP) procedures through to drinking water and then to more contaminated samples such as wastewater and soils. With such a wide variation in the organic content of different waters, it is not surprising that different analytical approaches are needed for different applications. In a recent blog, basic operating principles of the TOC Analyser, we discussed the two main analytical methods used in the TOC analyser. These are the high temperature catalytic combustion oxidation and UV-persulphate oxidation methods. In both methods the carbon in the sample is converted into CO2, which is then measured using a CO2-specific Non-Dispersive, Infrared (NDIR) detector. Here we look at the differences between the two methods and the types of application to which they are best suited.
Catalytic combustion oxidation TOC analyser
In catalytic combustion systems, the carbon is converted into CO2 by injecting the sample with an oxygen-rich carrier gas into a catalyst-packed tube, typically heated to 680°C -1000 ˚C. The CO2 is then swept into the NDIR detector for measurement. The catalyst enhances the oxidation process and generally allows it to take place at lower temperatures than non-catalytic combustion. This system offers good versatility with 50 parts per billion (ppb) detection limit as well as measuring much higher concentrations up to 20,000 parts per million (ppm) range. This method is particularly good for samples containing particulates, hard to oxidise matrices or salt. Typical use is for wastewater and surface water applications, as well as drinking water applications.
UV-Persulphate oxidation TOC analyser
UV-Persulphate oxidation is a wet chemical method. A sparged sample is transferred to a UV reactor where it is oxidised in solution by sodium persulphate in combination with UV light before passing to the NDIR detector. The UV-Persulphate method offers detection limits typically at 5 (ppb) levels and is therefore ideally suited for low level TOC analysis. It is typically used for water used in the pharmaceutical, biotechnology and electronic industries, where low levels of contamination need to be measured as well as monitoring drinking water. It is not suitable for seawater or other samples with high chloride content since the chloride reacts with the persulphate, significantly reducing oxidation efficiency. It is also not suitable for samples with high levels of particulates.
Find out more
More detailed information to help users choose the best technique for their analysis can be found in the following publication: Total Organic Carbon (TOC) Analysis Technique Comparison.
TOC analysers from Lambda
Lambda is a leading supplier of analytical instruments and preparation equipment for a wide range of applications, including a choice of TOC analysers. If you would like more information, simply contact a member of the team today.