Total organic carbon (TOC) is a measure of the quantity of carbon in organic compounds.
In various places of interest, diverse sources of organic carbon exist. In water and soil samples, this could be natural organic matter like humic and fulvic acids, or organic pollutants like pesticides, hydrocarbons and other volatile organic compounds. It can be found as organic components in pharmaceuticals, food and beverages, or as biological organic matter like microbial colonies.
Preparing samples for TOC analysis is vital for accurate results. First, a clean, representative sample must be collected. If there is particulate in the sample, this must be filtered out and, in necessary, acidified. If there is to be a delay before analysis, the sample must be preserved. Following this, the TOC analyser must be calibrated using a known standard, and the samples volume measured and injected into the analyser. During analysis, the sample undergoes oxidation, and the resulting CO2 measured to calculate the TOC concentration. Proper sample preparation is essential to ensure reliable TOC data.
TOC is measured using a TOC analyser, or an instrument with TOC capabilities such as varieties of absorbable organic halogen (AOX) and total organic halogen (TOX) analysers. While different types of analysers may differ slightly in methodology, most follow the same underlying principles of combustion or chemical oxidation.
In the combustion method, the sample is introduced into a combustion chamber in the instrument alongside a catalyst like palladium or platinum. In the chamber, the sample is subjected to extreme temperatures of 800 to 1400 degrees Celsius. In doing so, the sample is oxidised into CO2 before measurement.
Chemical oxidation works by mixing the sample with a strong oxidising agent, often a combination of persulfate and acids. Subsequently, the sample is heated to promote the oxidation reaction of the compounds into CO2.
The detection of the CO2 varies by instrumentation, although most use non-dispersive infrared (NDIR) or conductivity detection.
NDIR directs infrared light at the sample CO2, measuring the absorption of light by the molecules. This amount of absorption is directly proportional to the concentration of CO2, which in turn corresponds to the TOC in the sample.
Conductivity detection instead uses the formation of carbonic acid via a reaction between water and CO. Carbonic acid in a solution increases the conductivity of the solution. This change in conductivity is then measured to determine the TOC concentration.
Using either of these principles, the instrument will calculate the TOC based on sample volume and detected CO2 levels. The result is typically displayed as milligrams of carbon per litre (mg C/L) or parts per million (ppm).
The analyser can detect an array of different carbon types. Some of these instruments are capable of detecting not only the TOC, but several other parameters. This includes the complete total carbon (TC), total inorganic carbon (TIC), both purgeable and non-purgeable organic carbon (POC and NPOC), and total dissolved organic carbon (DOC), to name a few.
As the name suggests, TC includes measurements of both organic and inorganic carbon components. Organic carbon, as previously discussed, are compounds composed primarily of carbon and hydrogen. Inorganic carbon, conversely, refers to carbon present in the form of carbonates and bicarbonates, using acidification to generate and measure the CO2 produced.
The capability to differentiate between these three measurements, TC, TOC and TIC, proves valuable in applications where differentiation is critical. The applications of this measurement spans a broad spectrum, including water quality studies, wastewater treatment, and food and pharmaceutical quality control.
In recent years, advancements of the analyser has led to the development of versatile instruments like AOX-TOX detectors. These devices have the capability to measure all of the previous carbon parameters, as well as various halogen and halide testing, all within a single piece of instrumentation.
TOC analysis finds multiple applications dependant on the industry it is being employed.
Environmental monitoring
TOC analysis is used to assess the organic carbon content in water, soils and sediments. An increase in TOC value can indicate the presence of pollutants in the sample, enabling environmental agencies to make informed decisions and develop effective pollution control measures.
Waste treatment
TOC ensures the quality of clean potable water. High TOC values can indicate a greater likelihood of disinfection byproduct formation during chlorination and the presence of microbial biomass. This data helps waste management industries optimise treatment procedures while minimising potential health risks.
Pharmaceutical and life sciences
Elevated TOC levels indicate organic contamination in sectors where purified water is vital. Regular TOC monitoring ensures the integrity of the manufacturing processes, prevents cross-contamination, and serves as a measurable indicator of drug safety standards.
Food and beverages
TOC analysis is crucial for maintaining product quality and safety standards in the food and beverage industry
Oil and gas mining
TOC assessment is used to determine the organic content of water used in processing and cooling, or that which is released as wastewater. High TOC levels can interfere with industrial processes and have environmental implications. Additionally, TOC analysis offers insights into potential hydrocarbon reserves, aiding in future exploration and drilling activities.
Wastewater Treatment
TOC analysis is fundamental for monitoring and understanding the organic load in incoming and outgoing wastewater. It enables the tracking of TOC removal efficiency and allows for adjustments in treatment processes to ensure the effective removal of organic pollutants.
SciMed offers two different TOC analysers, the Multi X2500 AOX-TOX Analyser and the Multi N/C Total Organic Carbon and Nitrogen Analyser.
For versatile environmental analysis and compliance with AOX/TOX regulations, the Multi X2500 offers a comprehensive solution. It excels in assessing organic carbon content in water and soil samples, meeting regulatory requirements like DIN ISO 9652 and more, and determining organic halogens in wastewater. With flexibility in analysis and an innovative double furnace technology, it provides precise results and regulatory adherence.
For robust TOC analysis with minimal maintenance, the Multi N/C analyser is the ideal choice. It suits various TOC applications, including monitoring drinking water, waste water, pharmaceutical water and more. Offering sensitivity, versatility, and compliance with 21 CFR 11 regulations, this model finds usage in many pharmaceutical, industrial and environmental contexts.
Interpreting TOC results involves evaluating the concentration of organic carbon in a sample, typically measured in mg/L or ppm. First, compare the results to regulatory limits, and then consider the samples context. TOC levels can vary dependent on whether the sample is drinking water, wastewater, or elsewhere. Additionally, the quality of the TOC analysis method can be assessed by checking the precision, accuracy and variability using a collection of standardised calibration samples.
Finally, the TOC results must be correlated with other relevant parameters such as pH or other specific compounds in order to gain a holistic understanding. With this knowledge, environmental implications, water quality and microbial growth can be investigated. If results are outside the expected range or raise concerns, further documentation and instrumentation are crucial. Accurate interpretation of TOC results is key to making informed decisions about sample quality and environmental management.
To find out more about the TOC analysers on offer, visit SciMed’s web pages for the Multi X2500 AOX-TOX Analyser, and Multi N/C Total Organic Carbon and Nitrogen Analyser.
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