The common detection principles are as follows:

The detection principle of the Total Organic Carbon (TOC) swabs for cleaning validation mainly lies in converting the carbon elements in the organic pollutants collected by the swabs into a detectable form, and then conducting quantitative analysis through specific technical means. The common detection principles are as follows:

Combustion Oxidation – Non-dispersive Infrared Absorption Method

• Principle: The organic carbon in the TOC swabs that have collected samples is burned at a high temperature, making it completely oxidized to generate carbon dioxide. Carbon dioxide has an absorption effect on infrared light of a specific wavelength, and the degree of its absorption is directly proportional to the concentration of carbon dioxide. The absorption amount of infrared light by carbon dioxide is measured through a non-dispersive infrared detector, and then the total organic carbon content in the sample is calculated.
• Advantages: It has a high oxidation efficiency, which can convert most of the organic carbon into carbon dioxide. It has high detection sensitivity and can detect low concentrations of organic carbon. It has a fast analysis speed and is suitable for various types of samples.
• Limitations: For some organic compounds that are difficult to oxidize, they may not be completely oxidized, resulting in a lower detection result. If there is inorganic carbon (such as carbonate) in the sample, pre-treatment or a special method is required for differentiation; otherwise, it will interfere with the determination result.

Persulfate Oxidation – Ultraviolet Spectrophotometry Method

• Principle: Utilize the strong oxidizing free radicals generated by persulfate under the irradiation of ultraviolet light. These free radicals can oxidize the organic carbon in the samples collected by the swabs into carbon dioxide. The generated carbon dioxide reacts with a specific reagent to form a substance that has absorption at a specific wavelength. The absorbance of this substance at the corresponding wavelength is measured by an ultraviolet spectrophotometer, and according to the relationship between the absorbance and the organic carbon content, the TOC content in the sample is calculated.
• Advantages: It does not require a high-temperature combustion device, and the equipment is relatively simple with convenient operation. For some samples containing organic substances that are easily oxidized, the oxidation effect is good, and it can accurately determine the organic carbon content in them.
• Limitations: The speed and degree of the oxidation reaction may be affected by other components in the sample. For example, certain metal ions may catalyze or inhibit the oxidation reaction. For complex samples, more pre-treatment steps may be required to eliminate interference.

Electrochemical Oxidation Method

• Principle: On the surface of the electrode, by applying a certain potential, the organic carbon in the sample undergoes an oxidation reaction on the electrode, generating an electrical current signal. This electrical current signal is directly proportional to the organic carbon content in the sample, and the TOC content in the sample is determined by measuring the magnitude of the electrical current.
• Advantages: The instrument is relatively small in size, making it convenient to carry and conduct on-site detection. It has a fast detection speed and can provide real-time detection results, which is suitable for occasions with high requirements for detection time.
• Limitations: The performance and stability of the electrode have a great influence on the detection results, and the electrode needs to be cleaned and calibrated regularly. For samples with a high concentration of organic carbon, phenomena such as contamination and poisoning of the electrode surface may occur, affecting the accuracy of the detection.

Wet Oxidation – Conductivity Detection Method

• Principle: A strong oxidant (such as sulfuric acid, hydrogen peroxide, etc.) is used to carry out wet oxidation on the samples collected by the swabs under heating conditions, converting the organic carbon into carbon dioxide. When carbon dioxide dissolves in water, it will change the conductivity of the water. By measuring the change in the conductivity of the solution before and after oxidation, the TOC content in the sample is calculated.
• Advantages: It does not require complex optical or combustion equipment, and the cost of the instrument is relatively low. For some samples containing a large amount of inorganic impurities, the conductivity detection method is relatively less affected by the impurities.
• Limitations: The oxidation reaction requires certain time and temperature conditions, and the analysis speed is relatively slow. The detection sensitivity is relatively low, and for samples with a low concentration of TOC, the detection error may be relatively large.