What is the detection principle of the Clean Verify TOC swab?

The detection principles of cleaning validation TOC swabs mainly involve oxidizing and decomposing the organic substances collected by the swabs, and then detecting the generated carbon dioxide to indirectly determine the total organic carbon (TOC) content. The common methods include combustion oxidation and chemical oxidation, which are introduced in detail as follows:

Combustion Oxidation Method

• Dry Oxidation
  • Principle: The organic substances on the TOC swab collected with the sample are fully reacted with oxygen at a high temperature, causing the organic carbon to completely burn and generate carbon dioxide. Usually, in a high – temperature furnace, the temperature is controlled at around 600 – 1000 °C. In an atmosphere of pure oxygen, the carbon element in the organic substances is oxidized to carbon dioxide.
  • Detection: A specific detector is used to detect the amount of generated carbon dioxide. A commonly used detector is the non – dispersive infrared detector (NDIR). Carbon dioxide absorbs infrared light of specific wavelengths. NDIR determines the content of carbon dioxide by measuring the degree of infrared light absorption, and then calculates the TOC content in the sample.
• Wet Oxidation
  • Principle: First, the sample on the swab is dissolved in a specific acidic solution. Then, a strong oxidant, such as potassium persulfate, is added. Under the conditions of heating or ultraviolet irradiation, the carbon in the organic substances is oxidized to carbon dioxide. For example, in some methods, at a temperature of 90 – 100 °C, the strong oxidizing property of potassium persulfate in an acidic environment is used to oxidize the organic carbon.
  • Detection: The generated carbon dioxide can also be detected by NDIR to obtain the TOC content. In some methods, the generated carbon dioxide reacts with a specific reagent to form a substance with a specific color, and then the colorimetric method is used to determine the content of carbon dioxide, and then the TOC content is calculated.

Chemical Oxidation Method

• Principle: Some strong oxidants are used to react with organic substances at room temperature or a specific temperature, converting the organic carbon into carbon dioxide. Besides potassium persulfate mentioned above, potassium permanganate is also a commonly used oxidant. In a specific reaction system, potassium permanganate reacts with organic substances under acidic or alkaline conditions to oxidize the carbon in them.
• Detection: For the carbon dioxide generated after the reaction, detection methods similar to those of wet oxidation can be used, such as colorimetric determination after reaction with a specific reagent, or acid – base titration. For example, the generated carbon dioxide is introduced into an alkaline solution containing a specific indicator. After the carbon dioxide reacts with the base, the acidity and alkalinity of the solution change, and the amount of carbon dioxide is determined by acid – base titration, so as to calculate the TOC content.

In addition, there are some other detection principles, such as the conductivity method. It is based on the fact that the conductivity of the solution changes before and after the oxidation reaction, and the TOC content is indirectly calculated by measuring the change in conductivity.