The oxidation process in many TOC analyzers – that is total organic carbon analyzer, or meter – follows acidification in TOC analysis and is the step in which carbon present in the remaining sample is oxidized to form carbon dioxide and other gases. In a modern TOC analyzer, oxidation is performed by several methods, such as Photo-Oxidation (UV Light), The UV/Chemical (Persulfate) Oxidation, Thermo-Chemical Oxidation, High Temperature Combustion and High Temperature Catalytic Oxidation (HTCO).
TOC Analyzer Analytical Method #1 – Photo-Oxidation (UV Light)
In this process, only ultra-violet light is used to oxidize the carbon present in the sample to produce carbon dioxide by the TOC analyzer. Photo-oxidation is the most reliable, low maintenance method used for TOC analysis of ultra-pure waters.
TOC Analyzer Analytical Method #2 – UV/Chemical (Persulfate) Oxidation
In this method, UV light is used for oxidation but the oxidation power of the reaction is magnified by the use of a chemical oxidizer, which in most cases is a persulfate compound. It is difficult for a TOC analyzer that uses this method to analyzer levels of total organic carbon below 200 ppb.
TOC Analyzer Analytical Method #3 – Thermo-Chemical (Persulfate) Oxidation
Some TOC analyzer manufacturers may also call this process “heated persulfate”. The free radical formation method that is used in it is the same as UV persulfate oxidation but heat is used to magnify the oxidation power of persulfate. Unlike UV Persulfate, this method is not susceptible to lower recoveries resulting from turbidity in samples. A TOC analyzer in which persulfate is used as a chemical oxidizer is useful in wastewater, drinking water, and pharmaceutical water analysis. When used with sensitive NDIR detectors, heated persulfate TOC analyzers can readily measure TOC up to hundreds of ppm depending on volumes of samples.
TOC Analyzer Analytical Method #4 – High Temperature Combustion
Many TOC analyzers oxidize the prepared sample at a high temperature of 1,350 oC. In the process, the atmosphere is oxygen-rich and all the carbon converts to carbon dioxide. Many modern TOC analyzers use non-dispersive infrared (NDIR) to detect the carbon dioxide produced.
TOC Analyzer Analytical Method #5 – High Temperature Catalytic Oxidation (HTCO)
In HTCO, the sample is injected onto a platinum catalyst at 680 oC in an oxygen-rich environment. The carbon dioxide produced is measured with a non-dispersive infrared (NDIR) detector.
The main drawback of this process is its unstable baseline, which results from the gradual accumulation of non-volatile residues within the combustion tube. Continuous background correction is required as these residues continuously change TOC background levels.