How Do TOC Analyzers Measure Total Organic Carbon (TOC)?

Most TOC analyzers works by measuring the CO2 released during the oxidization of organic carbon to determine the total organic carbon level. However, it is not uncommon to find TOC analyzers which works by measuring the CO2 formed during the acidifying of inorganic carbon, or which uses a combination of both measuring methods.

Common organic carbon oxidation methods employed by TOC analyzers include:

1. Pt-catalyzed combustion
2. Heated persulfate
3. UV/Persulfate reactor

Common CO2 detection method employed by TOC analyzers include:

1. Conductivity cell – if the CO2 is aqueous, the raised acidity level of the water sample will increased its conductivity.
2. Non-dispersive infrared cell (after the aqueous carbon dioxide is purged into gaseous state), TOC analysers using the NDIR detection method tends to excel in most TOC ranges.
3. Membrane Conductivity Detection can allow for measurement of TOC across a wide analytical range in both deionized and non-deionized water samples.

TOC analyzers can determine the TOC level by measuring the leftover organic carbon after removing the inorganic carbon, or by measuring the difference between the total carbon and the total inorganic carbon to determine the actual TOC level.

An example of measuring leftover organic carbon is where a TOC analyzer works by measuring the amount of total organic carbon by measuring the leftover organic carbon in the water sample after removing the inorganic carbon by acidifying the sample or flushing the water sample with nitrogen or helium.

An example of measuring the difference between the total carbon and total inorganic carbon is where the TOC analyzer works by measuring the difference between the background conductivity level and the peak conductivity level after the oxidization of organic compound.

Other common types of TOC analyzers include those which use combustion and those which use chemical oxidation.