TOC Analyzer – How it Works

A total organic carbon (TOC) analyzer measures the total amount of organic carbon present in a liquid sample. Generally, the same technique is used by all analyzers, and virtually all of them measure the carbon dioxide formed as a result of the oxidation of carbon and/or the acidification of inorganic carbon. A modern high-performance TOC analyzer can detect carbon concentrations well below 1 ppb.

Working of a TOC Analyzer

The amount of total organic carbon present in a sample is determined by the analyzer by acidification of the liquid sample followed by a flushing action in which nitrogen or helium is used to get rid of the inorganic carbon (IC). Only organic carbon sources remain in the sample after these processes, which are then measured.

Types of TOC Analyzers

A TOC analyzer can either be one that uses combustion or one that makes use of oxidation. This works as a test for checking water purity test, as bacteria produces organic carbon.

TOC Analyzers Using Combustion Method

In this type of TOC analyzer, the sample divided into two equal parts and one part is injected into a chamber for acidification, normally with phosphoric acid, so that all of the inorganic carbon turns into carbon dioxide. The gas is then measured with the help of a detector.

The remaining sample is injected into a combustion chamber which has a temperature of 600–700°C; sometimes the temperature is raised even up to 1200°C. Here, the reaction of carbon with oxygen within the TOC analyzer produces carbon dioxide. It’s then flushed into a cooling chamber, and finally into the detector. Usually, a non-dispersive infrared (NDIR) spectrophotometer is used. The total IC is subtracted from the total carbon (TC) to calculate the amount of organic carbon.

TOC Analyzers Using Chemical Oxidation

A chemical oxidation TOC analyzer injects the sample into a chamber with phosphoric acid followed by persulfate. The analysis is a two step process. In the first step, IC is removed by acidification and purging. Then, persulfate is added to the sample which is either heated or bombarded with UV light from a mercury vapor lamp. Free radicals are formed from the persulfate. These radicals react with any carbon present to form carbon dioxide. The carbon formed in both steps is either passed through membranes which measure conductivity changes, or is detected by a sensitive NDIR detector. Total organic carbon calculation by the TOC analyzer is the same in both methods.