Total Organic Carbon (TOC) | Civil Engineering Optional Notes for UPSC PDF Download

What is Total Organic Carbon?

Definition and Importance: Total Organic Carbon (TOC) is a measure of the concentration of organic carbon in a substance. It serves as an important indicator of contamination or purity in water and other substances. TOC can help determine the quality of water used in various industrial processes, ensuring it is clean enough for specific applications and will not cause environmental harm when released.

Measuring Other Carbon Types In addition to TOC, it is possible to measure:

• Total Inorganic Carbon (TIC)
• Total Carbon (TC)
• Purgeable Organic Carbon (POC)
• Non-Purgeable Organic Carbon (NPOC)

Importance of Measuring TOC

1. Industrial Applications: TOC measurement is crucial across many industries to ensure that water used in processes is free from harmful contaminants. This is particularly important in:

   • Pharmaceutical manufacturing
   • Semiconductor production
   • Power generation
   • Drinking water supplies
   • Electronics manufacturing

2. Water Purity: High purity water is essential in industries to prevent contamination that can lead to product quality issues, equipment damage, and health risks.

Methodology of TOC Analysis :
TOC analysis involves three main stages:

1. Sampling: Samples can be introduced into the analyser manually or using an autosampler. Techniques include flow-injection, where a syringe pump introduces the sample into a reservoir, and direct-injection, where the sample is directly injected onto the catalyst inside the furnace.

2. Oxidation: Various oxidation methods can be used to break down the organic compounds in the sample:

   • Photocatalytic oxidation using UV light
   • Chemical oxidation using sodium persulfate and UV light
   • High temperature combustion with an oxidation catalyst

3. Detection: Two main detection systems are used in TOC analysers:

   • Non-Dispersive Infrared (NDIR): Measures CO2 levels by analysing the absorption spectrum in the infra-red region.
   • Conductivity Detectors: Measure dissolved CO2 as it forms a weak acid, indicating different levels of CO2 in the sample.

Types of Carbon Measured by TOC Analysers

• Total Organic Carbon (TOC)
• Total Carbon (TC)
• Total Inorganic Carbon (TIC)
• Purgeable Organic Carbon (POC)
• Non-Purgeable Organic Carbon (NPOC)
• Dissolved Organic Carbon (DOC)

Calculating TOC
Two common methods are used to determine TOC values:

1. Differential Method: This method requires two measurements:

   • Total Carbon (TC)
   • Total Inorganic Carbon (TIC) after acidifying the sample and converting inorganic carbon to CO2

2. The TOC value is then calculated using the formula: TOC = TC - TIC.

3. NPOC Method: This method involves acidifying the sample and purging it to remove purged carbon. The remaining non-purgeable organic carbon (NPOC) is measured and considered equivalent to TOC.

Conclusion

TOC analysis is a critical tool for ensuring water quality across various industries. By measuring TOC and other forms of carbon, industries can safeguard their processes, products, and consumers from contamination and maintain compliance with regulatory standards.