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What Is The Total Organic Carbon (TOC)?

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Total Organic Carbon (TOC) is a measure of the total amount of carbon in organic compounds in pure water and aqueous systems. TOC is a valued analytical technique used by organizations and laboratories to determine how appropriate a solution is for their processes. Unless it is ultrapure, water naturally contains some organic compounds, and it is important to understand how much.

TOC has become an important parameter to monitor the total concentrations of organic compounds present. This happened despite the lack of a direct quantitative correlation between total organic carbon and the total concentration of organic compounds present and reflects the importance of an easily measurable general indicator of the approximate level of organic contamination.

It also reflects the appeal of a parameter whose name sounds more fundamental than it is! In many cases, the table of contents is used as continuous tracking of changes or lack of changes in organic content.

What is measured when calculating total organic carbon?

Upon completion of the TOC analysis, the following will be measured:

 • TC – Total Carbon

 • TIC – Total Inorganic Carbon

 • POC – Disposable Organic Carbon

 • NPOC – Non-Disposable Organic Carbon

 • DOC – Dissolved Organic Carbon

 • NDOC – Undissolved Organic Carbon

 To calculate TOC, you can subtract the total amount of inorganic carbon from the total carbon found. Alternatively, you can add disposable and non-disposable organic charcoal, or dissolved and undissolved organic charcoal. A Summer sehen sie sound birds:




How is total organic carbon measured?

 TOC is measured at very different concentrations in a wide variety of systems. The following table gives an indication of the total organic carbon content in different types of water. Levels vary widely within each type, but generally range from levels below ppb in ultrapure water for laboratory and microelectronic applications to hundreds of ppm in wastewater and process streams.

 For many of these systems, the index alone does not provide enough information. Carbon-containing compounds can be in various forms and the proportions involved can be critical. A breakdown of some of these divisions is shown in the figure above.

 Dissolved organic carbon (DOC) is generally believed to be that which passes through a 0.45 µm filter. Large TOC is classified as particulate or undissolved (NDOC). Approximately 50 to 75% of DOC in natural waters is in the form of fulvic polymeric organic acids and humic acids.

Approximately 10% of TOC is contained in colloids, mainly humic acids and various minerals. Another 10 to 20% are small molecules from the decomposition of organic substances. Table Showing Total Organic Carbon (TOC) Levels in Various Types of Water. PURELAB ultrapure water purification systems with integrated total organic carbon monitoring are available through our approved partners. Click here to obtain more information.

Total Organic Carbon Analysis

TOC is universally measured by oxidizing the organic compounds present in quantifiable forms. Depending on the type and concentration of TOC measured and analytical requirements (eg speed, sensitivity), different oxidation and detection methods are used.

  • High-temperature combustion at 1200 ° C in an oxygen-rich atmosphere. The generated CO2 is passed through scrubber tubes to eliminate interference and is measured by non-dispersive infrared absorption (NDIR).
  • High-temperature catalytic oxidation at 680 ° C in an oxygen-rich environment in tubes filled with a platinum catalyst, followed by NDIR. Thermochemical oxidation by heat and a chemical oxidizing agent, usually persulfate.
  • Photochemical oxidation with UV and a chemical oxidizing agent, usually persulfate.Photooxidation by ultraviolet (UV) light alone or with a catalyst. The UV oxidation method offers the most reliable and low maintenance method for the determination of TOC in ultrapure water.
  • Combustion methods (1 and 2) are primarily used at higher TOC concentrations (ppm or more) or at high particulate concentrations. Heat or UV enhanced persulfate oxidation is widely used for laboratory TOC determination in many types of water, from potable water to pharmaceutical and electronic grades. The CO2 produced is generally measured by NDIR, or the change in conductivity it creates when it dissolves in a separate stream of pure water.

To exclude the effects of other oxidation products, the gas can pass through a membrane. Good oxidation can be achieved, but a compensation method is required to account for the reagent blank value. TOC can be detected in the ppb range.

All TOC analyzers that measure CO2 contain CO2 from bicarbonates and carbonates unless this inorganic carbon (IC) is taken into account. The IC can be removed by acidifying the sample to pH 2 or less to release the IC as CO2, which can be measured or discarded. The remaining non-disposable TOC (NPOC) in the liquid is oxidized and CO2 is released, which is sent to the detector for measurement.

The situation is somewhat different with ultrapure water with low conductivity. Water with sufficiently low conductivity (resistance value is close to 18.2 Mohm. cm) cannot contain significant concentrations of bicarbonates or carbonates (or other soluble salts) and no correction is required for IC. As mentioned above, all these trace measurements must be done online.

A range of TOC monitors has been developed to meet the need for rapid monitoring of low TOC (ppb) levels in high purity laboratory water systems. A quick response is required to ensure that the results are available and relevant to the relatively small amounts of water dispensed. These monitors generally measure the conductivity of the water before and after oxidation; the change is calibrated against the TOC content. Due to time constraints, oxidation is not always complete but is sufficient for monitoring purposes.

TOC testing online or in the lab?

The vast majority of TOC samples are collected and analyzed in a laboratory. Where TOC subdivisions are needed, such as B. DOC, samples are prepared prior to analysis.

Online analyzes are used for higher-level TOC analysis when the required frequency or speed of analysis is favorable. Online measurements are also essential to measure TOC levels below 50 ppb to avoid contamination. This contamination can come from foreign TOC in the environment or in containers but is more severe from carbon dioxide in the air, which dissolves quickly in pure water. Carbon dioxide interferes with many of the techniques used to monitor traces of TOC.

Water for TOC Monitors and Analyzers

 Of course, the purity of the water, which is required for the preparation of standards and blanks, for rinsing systems and cleaning components, is highly dependent on the measured concentrations. For many high-end applications performed in the laboratory or online, Type II water is more than adequate.

Consistent quality is more important than very high purity. For the TOC trace determination to be carried out online (<50 ppb), the purity requirements of the water are extremely high. Since TOC contains carbon from all kinds of compounds, virtually none of them need to be present. Ultra-high purity water with built-in TOC monitoring is highly recommended. To contact us visit us at .

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