TOC analyzers are used to measure organic carbon contamination in water.TOC is a common water quality test used in a wide range of industries. Carbon in water can be organic (e.g. plants, decaying material, plastics, etc.) or inorganic (e.g. carbonates, carbon dioxide, cyanide, etc.). Measuring TOC (Total Organic Carbon) in water helps to assess the quality of water, especially organic pollutants in the water. Join us to learn what Toc is, types of Total Organic Carbon Analyzer, steps to use it, and more.
What is TOC?
Total Organic Carbon (TOC) is a measure of the total amount of carbon in organic compounds in pure water and water systems. TOC is a valuable analytical technique used by organizations and laboratories to determine the suitability of solutions for their processes. Organic contamination reduces ion exchange capacity and causes undesirable biological growth, making treated water unsafe. Unless the water is ultrapure, it will naturally contain some organic compounds. TOC becomes an important indicator of the total amount of organic matter in the water. Although there is no direct correlation between TOC and the concentration of specific organic compounds, it is still a good indicator of the level of organic contamination in the water, and is therefore an effective tool that is simple to measure.
Types of TOC Analyzers
TOC analyzers work by converting the organic carbon in a water sample to carbon dioxide through an oxidation reaction, which is then accurately measured using a non-dispersive infrared (NDIR) detector. Depending on the oxidation method, TOC analyzers can be divided into two main types:
High Temperature Catalytic Combustion Oxidation: This method completely oxidizes the organic carbon in the water to carbon dioxide by heating the water sample to a high temperature, typically between 680°C and 950°C, in the presence of a catalyst such as platinum or palladium. The resulting carbon dioxide is then measured by an NDIR detector. This method is suitable for most water samples, especially those that are complex or contain difficult-to-oxidize organic matter.
UV-Persulfate Oxidation: In this method, the water sample is reacted with persulfate and oxidized under UV light, and the resulting carbon dioxide is captured by an NDIR detector. This method is particularly suitable for low concentration TOC measurements, especially in water samples that do not contain too many interfering substances.
Total Organic Carbon Analyzer Principle
The principle of a Total Organic Carbon (TOC) analyzer is based on the oxidation of organic carbon in a sample to carbon dioxide (CO₂), followed by the detection of CO₂ to quantify the amount of organic carbon present. Here’s a step-by-step breakdown of the principle:
Oxidation of Organic Carbon:
Organic carbon in the water sample is oxidized to carbon dioxide (CO₂).
The oxidation can be achieved by two primary methods:
High-Temperature Catalytic Combustion: The sample is heated to very high temperatures (usually 680°C to 950°C) in the presence of a catalyst (like platinum or palladium). This causes the organic carbon to break down into CO₂.
UV/Persulfate Oxidation: The sample is treated with persulfate and exposed to ultraviolet (UV) light, which oxidizes organic carbon into CO₂.
Measurement of CO₂:
After oxidation, the generated CO₂ is measured using a Non-Dispersive Infrared (NDIR) Detector.
The NDIR detector measures the infrared absorption of CO₂ in the sample. Since CO₂ absorbs infrared light at a specific wavelength, the amount of light absorbed correlates directly to the concentration of CO₂, and thus to the concentration of organic carbon.
Calculation of TOC:
The amount of CO₂ detected is used to calculate the total organic carbon in the sample. Since the amount of CO₂ generated is directly proportional to the amount of organic carbon in the sample, the TOC value is determined based on the CO₂ concentration.
Key Points:
The TOC analyzer does not directly measure organic carbon, but instead measures the CO₂ produced by the oxidation process.
The result is typically expressed as the amount of organic carbon in milligrams per liter (mg/L) or parts per million (ppm).
This principle allows TOC analyzers to provide a fast, efficient, and accurate measurement of organic carbon in water, helping to monitor water quality, detect pollution, and ensure environmental compliance.
Major Steps in Total Organic Carbon Analyzer
TOC analysis can be divided into four main steps: sample introduction, oxidation, detection and display. Each step can be accomplished in a variety of ways; this ultimately depends on the TOC analyzer used.
Sample Introduction
Samples can be introduced for analysis in a single pass through a simple pipette system, or batch loaded with multiple samples for analysis using an autosampler. In the case of on-line TOC analyzers, they are connected directly to a pumping system that automatically collects samples for real-time analysis.
Oxidation
There are several standard methods for TOC measurement, including wet chemical persulfate oxidation and high temperature catalytic combustion. Wet chemical methods convert organic carbon to carbon dioxide (CO₂) through reagents and heat or UV light. Combustion methods, on the other hand, heat the sample with an oxidizing catalyst to convert to CO₂. Commonly used methods include heated persulfate, UV persulfate, and high temperature catalyzed combustion.
Detection
TOC analysis typically detects CO₂ by means of a solid-state non-dispersive infrared detector (NDIR), which determines the organic carbon content of a sample by measuring the amount of infrared light absorbed by the sample at a specific wavelength (e.g., CO₂ absorbs infrared light at 4.26 µm).
Display
Results are usually presented through a display or computer interface, and modern TOC analyzers are equipped with a touch screen or are controlled by an external PC for easy operation and data viewing.
Considerations for Selecting an Oxidation Technique
Selection of the appropriate oxidation technique depends on the characteristics of the sample and the needs of the TOC analysis. The combustion technique is suitable for samples with suspended material (e.g., humic acids, bacteria, plant residues, or high molecular weight substances) or organic carbon concentrations greater than 1 ppm. It performs better in high concentration samples but is less efficient in samples below 1 ppm C and produces a higher system background due to high temperature operation which can lead to catalyst carbon memory effects.
For low concentration samples, wet chemical oxidation techniques such as heated persulfate and UV persulfate are generally more effective. These techniques are performed at lower temperatures (95-100°C), so more samples can be processed with greater accuracy and reliability. The heated persulfate technique is considered the most reliable because it transfers heat to the reagent through convection. The UV persulfate technique, on the other hand, uses UV light to activate the reagent, and turbid samples may reduce the intensity of the UV light, which can affect the oxidation.
Conclusion
Total Organic Carbon (TOC) is an important indicator for water quality monitoring related to regulatory compliance, drinking water treatment, wastewater management, and other water treatment applications. Accurately measuring TOC is critical to ensuring safe water quality and improving operational efficiency. With a variety of TOC analyzers and technologies available on the market, it is important to choose the solution that best fits your needs.
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