Total Organic Carbon (TOC) Analysis

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Total Organic Carbon (TOC) serves as a crucial measurement guideline monitored by industries worldwide to ensure quality, regulatory compliance, and product and process safety. During a TOC analysis, the total carbon level present in aqueous solutions is measured, providing valuable insights into compound purity and potential contamination.

The role of TOC analysis in environmental monitoring cannot be overstated. Monitoring organic carbon levels in soil and water bodies aids in assessing the health of an ecosystem and predicting potential hazards such as algal blooms or eutrophication. TOC analysis is also important for discharging of water.

What is a TOC analyser?

Total Organic Carbon (TOC) analysers are highly sophisticated instruments designed to measure the concentration of organic, inorganic, or total carbon content in water or soil samples. Moreover, with TOC being an essential parameter in environmental and analytical chemistry, it is a key indicator in assessing water quality and the extent of pollution.

Additionally, this parameter is used to measure organic contamination in various matrices. Within the water sector, TOC is an indicator of disinfection byproducts in drinking water processes. Regulatory agencies have set rules for disinfection byproducts that underscore the need for TOC reading in drinking water since TOC removal is one of the parameters used to determine byproduct rules. Finally, since TOC correlates with the BOD and COD tests, it is used as an alternative tool for measuring these liquid parameters in several applications.

Methodologies for TOC analysis

There are two major methods for TOC quantification: direct measurement of Non-Purgeable Organic Carbon (NPOC), excluding inorganic carbon from calculation, or the subtraction method, which calculates the difference between the total carbon content in the sample and the inorganic carbon. The direct measurement of NPOC is generally preferred due to the potential inaccuracies associated with the subtraction method.

The core distinction of a total organic carbon analyser lies in the oxidation technique, in which carbon is transformed to carbon dioxide (CO2) for measuring. Most of the TOC analysers use a Non-Dispersive Infrared (NDIR) detector specifically for leveraging a carrier gas to transport CO2 through the detection system. This method is preferred over alternatives such as membrane conductivity, which measures CO2 diffusion through a membrane into an absorbing solution.

Alignment to Environmental Protection Agency (EPA) approved methods is crucial, with high-temperature combustion (e.g., SM 5310B, ASTM D7573) and wet chemical oxidation (e.g., SM 5310C, ASTM D4839) being the primary standards for a total organic compound oxidation TOC analyser.

Catalytic combustion vs. wet chemical oxidation

Catalytic combustion

This method involves the oxidation of organic compounds to CO2 and water (H2O) at high temperatures through a carrier gas enriched with oxygen passing over a heated catalyst.

Wet chemical oxidation

This technique consists of oxidising chemicals, such as persulfate, to react with organic compounds, converting them into CO2 and H2O. The efficacy of persulfate as an oxidizer improves with heat or UV light exposure, sample matrix constituents like chloride, which can inhibit oxidation efficiency, but can be counteracted by changing method parameters. Wet chemical oxidation will reduce the cost of operation, due to the lack of a degrading catalyst.

Choosing the right TOC Analyser

Total Organic Carbon instrument (TOC) is more than just a number on a data sheet; it’s an essential for ensuring the safety, quality, and regulatory compliance of numerous industries. With the risks associated with high TOC levels ranging from operational inefficiencies to environmental and health concerns, it’s clear that an accurate TOC analyser is more than just a regulatory requirement; it’s a cornerstone of sustainable and responsible operations.

There are several factors to take in consideration when selecting the right TOC analyser, including the sample matrix, desired detection limits, and the presence of interfering substances. Catalytic combustion can reduce matrix effect, analysis time and reagent time compared to persulfate analysers. Persulfate analysers are recommended due to their lower detection limits and the reduced consumable costs. Need help choosing the correct oxidation technique? Don’t hesitate to contact us!

In conclusion, the choice of a TOC analyser should be based on your specific analytical needs, considering both the operational aspects of the instrument and the analytical goals of the study. With advancements in TOC (total organic carbon) analysis technology, selecting an instrument that aligns with regulatory requirements and provides accurate, reliable results is essential for effective environmental monitoring and analysis.