Determination of Total Organic Carbon (TOC) in Laboratory Ultrapure Water

Pollutants in water are usually expressed as carbon content, but depending on the application and analytical method, carbon content has different definitions as follows:

① Total Carbon (TC): The total amount of elemental carbon in a substance or solution;

② Total Inorganic Carbon (TIC): The total amount of carbon in bicarbonates, carbonates, and dissolved carbon dioxide in an aqueous solution;

③ Total Organic Carbon (TOC): The total amount of carbon in organic molecules bound by covalent bonds;

④ Particulate Organic Carbon (POC): Total organic carbon (TOC) that can be retained by a 0.45 μm filter membrane;

⑤ Dissolved Organic Carbon (DOC): Total organic carbon (TOC) that can pass through a 0.45 μm filter membrane;

⑥ Volatile Organic Carbon (VOC): Total organic carbon (TOC) that can be removed from an aqueous solution under specific conditions using vapor transfer or displacement methods via aeration;

In ultrapure water, TOC measurements primarily detect DOC, along with some VOCs. While VOC detection is affected by sampling conditions (e.g., temperature, pressure) and the volatility (vapor pressure) of organic matter, TOC measurements do not include TIC, and high concentrations of ions (conductivity) can interfere with certain testing methods. However, overall, TOC measurement remains an effective method, not only because it is simple to measure, but also because it can represent the types of organic matter in water.

The Influence of Organic Matter in Water

With the continuous improvement in the sensitivity of analytical instruments and experimental methods, organic pollutants in ultrapure water have become a primary concern in laboratories. High levels of organic pollutants in water can cause the following problems:

① Reduced detection sensitivity and increased detection limit

② Poor reproducibility

③ Elevated blank background

④ Coating of reactive surfaces

⑤ Chemical interference with products

⑥ Diffuse or non-diffuse effects

⑦ Fouling of purification media

⑧ Promotion of microbial growth

⑨ Toxicity

Appropriate combinations of water purification technologies (such as activated carbon adsorption, ultraviolet (UV) oxidation, and ion exchange) can effectively reduce organic matter in water. Whether for laboratory analysis or industrial production, choosing a pure water system that produces water meeting TOC requirements is crucial.

Similarly, accurate monitoring of organic matter purity in water is extremely important. The ionic strength of the produced water is usually measured directly using a built-in online detector, continuously displaying its resistivity (MΩcm) or conductivity (μs/cm). However, since many organic compounds are non-ionized or only partially ionized in water, resistivity values cannot accurately represent the organic compound content. Furthermore, many offline organic analysis methods suffer from low sensitivity, long processing times, and susceptibility to sample contamination. Therefore, online organic compound detection can accurately, rapidly, and with high sensitivity measure dissolved organic compounds in water. Installing an online TOC monitor in an ultrapure water system is an ideal method for monitoring and ensuring the organic compound content in ultrapure water.

Applications and Advantages of Online TOC Measurement

Online TOC measurement directly in a pure water system provides unique assurance and quality control for experimental analysis. Generally, organic contaminants are less likely to be "adsorbed" by purification media than ionic contaminants, and are more prone to leakage. Therefore, resistivity (conductivity) values alone cannot determine whether the organic compound content in water has increased, changed, or is excessively high.

TOC measurement can provide early warning of organic contamination, thus avoiding the use of pure water with excessively high organic compound content. Other advantages include:

① Compliance with standards and specifications (USP, BP, GLP)

② Quality control of reagents and liquid products

③ Identifying the most appropriate analytical method (limits of determination, retention time, shelf life of purification columns)

④ Solving analytical method problems

⑤ Online TOC measurement provides necessary monitoring and maintenance for ultrapure water systems. Utilizing TOC measurement technology allows laboratories to have better control methods when performing analyses with high sensitivity to organic matter.

Compiled by: Sichuan Youpu Ultrapure Technology Co., Ltd.

National Service Hotline: 400-884-6567