Total Organic Carbon (TOC)

The Total Organic Carbon (TOC) is one of the most important composite parameters in the assessment of the organic pollution of water. Since it includes all carbon compounds as one mass, it is exactly defined and an absolute quantity. Therefore, it may be determined directly. In relation to the TOC also parameters like TC, TIC, DOC, (POC, VOC) are mentioned. The connections between these sum parameters and their meanings are shown in the following figure:

Definition of TC, TIC and TOC

Chart of total organic carbon components
This chart is showing the individual components of TOC.

Extracts of DIN EN 1484:1997-08

TC „The organic and inorganic carbon in water, including the elemental carbon“

TIC „The carbon contained in water; elemental carbon, total carbon dioxide“

TOC „The organic carbon in water, bound on dissolved or suspended substances. Elemental carbon will be also determined“

„The total organic carbon (TOC) is a measurement method for the content of carbon of dissolved and undissolved organic substances in water“

Online TOC Measurement Methods

In general, the TOC is determined by oxidizing a water sample. The produced CO2 is detected and defined quantitatively. However, not all methods succeed in the complete oxidation of a sample. Often enough this may result only in SOC (Some Organic Carbon) instead of the TOC.

Chart of the difference between Total Organic Carbon and Some Organic Carbon
The difference between TOC and Some Organic Carbon.
Chart of dissolved and particulate organic carbon
TOC contains dissolved and particulate organic carbon.

Thermal Oxidation

With this oxidation method the sample will be combusted in a reactor. Usually, a maximum temperature of about 1,000°C will be reached, which however does not allow the complete oxidation of all carbon compounds. Therefore, a catalyst, such as copper oxide or platinum, must be used at this temperatures. Normally, the catalytic combustion method can handle a TOC concentration of up to 4,000 mg/l. To reach higher ranges the sample usually needs to be diluted with demin water.

LAR Process Analysers AG offers a unique and patented high temperature (HT) method at 1,200°C. This temperature enables the complete oxidation of all carbon compounds without any catalysts. It measures TOC concentrations up to 50,000 mg/l without dilution. In a special heat resistant ceramic reactor the water sample is evaporated and all carbons are completely oxidized to CO2 gas. Afterwards, the CO2 concentration will be analysed with a Non-Dispersive Infrared (NDIR) detector. Thus, the TC, TOC and TIC can be determined within only 3 minutes.

This ultra high temperature method is used for both, the most challenging and highly contaminated waters (QuickTOCultra, QuickTOCairport) and waters relativily free of solid maters (QuickTOCeffluent). LAR Process Analysers AG uses the batch injection method with the advantage that the analysers can easily handle sticky, oily and hard to oxidise dissolved and suspended organics resulting in a fast, reliable and accurate analysis. Even with rapidly fluctuating TOC levels the correct TOC concentration will be measured, whereby peaks throughout the course of the day are determined without any memory or adsorption effects.

For applications with purified water, this LAR method allows the patented simplified, ready-at-any-time calibration and validation method  (QuickTOCcondensate, QuickTOCpurity, QuickTOCpharma).

Photochemical Oxidation (UV-Persulphate Method)

Here the TOC is oxidized by means of UV light and a digesting reagent, sodium persulphate, and the produced CO2 is measured with a NDIR detector. This method suits the determination of TOC in clean water (drinking water, condensate, boiler feed water), since particles are hard to oxidize completely. The QuickTOCuv combines this technique with the direct TOC method or Non-Purgable Organic Carbon (NPOC) method, whereby the continuously provided water samples will be treated in a multi stage process.

Wet Chemical Oxidation

With this method the water sample is oxidized by means of strong chemicals as oxidants such as ozone, which are slightly dangerous to health and environment. The ozone oxidation acids and bases are used to adjust the pH value of the sample along the pH scale.However, the oxidation potential of such methods is relative, since particles and more complex carbon compounds can only be partially digested or not at all. With regards to the latest standards of occupational safety and environmental protection these methods are not recommended.

Our TOC analyzers

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The total organic carbon (TOC) is one of the most important sum parameters in the assessment of the organic pollution of water. Since it includes all carbon compounds as one mass, it is exactly defined and an absolute quantity. Therefore, it may be determined directly.

Read more about TOC measurement methods.

Total organic carbon analyzers of LAR Process Analysers AG

The chemical oxygen demand (COD) indicates the amount of oxygen which is needed for the oxidation of all organic substances in water and is thus an important indicator for water analysis. It is considered in the planning and controlling of treatment, as well as assessing its efficiency, thus forming the basis for the calculation of waste water charges.

The COD can be determined in laboratory or online, whereby these methods significantly differ in duration and consumables used.

Read more about COD measurement methods.

COD analyzers of LAR Process Analysers AG

The biochemical oxygen demand (BOD) indicates the amount of oxygen which is needed for the biological degradation of organic substances in water.

Since the generally used BOD5 excludes the nitrification part of the process, this parameter is poorly suited for the control of waste water treatment plants. Alternatively, the total BOD is well-suited, due to the determination of the nitrogen as well as the carbonaceous part of biological degradation.

Read more about the online measurement of BOD.

Toxicity is described as the direct harmful effect of a substance on organisms. These effects can already occur at low concentraions of toxic substances and are dependent on the incubation period and the dosage.

Some test methods that are available on the market can detect toxicity by using fish, daphnia, molluscs, algae or luminous bacteria and testing whether a water sample has a toxic effect on the organisms. They do not, however, identify exactly which toxins are present.

Read more about online toxicity measurements.

BOD / toxicity analyzers of LAR Process Analysers AG

The total nitrogen bound (TNb) shows the pollution of water caused by nitrogen compounds. Nitrogen may be present as ammonia, ammonium salts, nitrites, nitrates and organic nitrogen compounds.

In contrast to single measurements of the above-mentioned components, the TNb determination contains all these substances in a single analysis process.

Read more about online TNb measurements.

The total phosphorus (TP) is a sum parameter that shows the organic and inorganic phosphorus compounds in water. Phosphorus is an essential nutrient for humans as well as flora and fauna. However, the substance – depending on its concentration– may cause serious damage.

Read more about online TP measurements.

TN TP analyzer of LAR Process Analysers AG