The cleaning validation TOC swab is mainly based on the principle of total organic carbon (TOC) detection, as follows:

. Sample Collection

TOC swabs are used to wipe the surface of medical devices to collect potentially residual organic substances. These organic substances include, but are not limited to, proteins, carbohydrates, oils, residual drugs, or biological tissues. The material of the swab is usually specially designed to effectively adsorb and capture organic residues, ensuring that as much organic matter on the surface as possible is transferred to the swab during the wiping process.

2. Oxidation Reaction

• High – temperature Catalytic Oxidation Method
  After sample collection, the swab is placed in a specialized TOC analyzer. During the high – temperature catalytic oxidation process, the organic carbon compounds in the sample react with oxygen under high temperature (usually 680 – 950 °C) and the action of a catalyst (such as platinum, cerium dioxide, etc.). The organic carbon is oxidized to carbon dioxide (CO₂). For example, for organic matter residues containing hydrocarbons, the reaction formula is roughly:

• This process can completely decompose complex organic molecules into carbon dioxide and water, facilitating the accurate measurement of carbon content subsequently.
• UV – Persulfate Oxidation Method
  Another common oxidation method is UV – persulfate oxidation. In this method, the sample is mixed with persulfate (such as potassium persulfate) and, under the irradiation of ultraviolet light (UV), the persulfate generates highly oxidizing free radicals (such as sulfate radical ). These free radicals attack the carbon – carbon and carbon – hydrogen bonds in organic compounds, oxidizing the organic carbon to carbon dioxide. For example, in the case of methanol (), a series of oxidation reactions occur under the action of persulfate and ultraviolet light, ultimately generating carbon dioxide.

3. Carbon Dioxide Detection

• Non – Dispersive Infrared Detection (NDIR)
  The carbon dioxide generated by the oxidation reaction is detected. One of the commonly used detection methods is non – dispersive infrared detection. The carbon dioxide molecule has an absorption peak at a specific wavelength of infrared light. The NDIR detector determines the concentration of carbon dioxide by measuring the absorption degree of infrared light after passing through the sample gas. When the gas containing carbon dioxide passes through the detection chamber, it absorbs infrared light of a specific wavelength, and the degree of absorption is proportional to the concentration of carbon dioxide. Through a pre – calibrated standard curve, the absorption signal can be converted into the content of carbon dioxide, and then the content of organic carbon can be calculated.
• Other Detection Methods
  In addition to NDIR, there are some other detection methods, such as conductivity detection. In this method, carbon dioxide is absorbed into a solution containing a specific electrolyte, forming carbonic acid (), which changes the conductivity of the solution. By measuring the change in conductivity, the concentration of carbon dioxide can be indirectly calculated, thereby determining the content of organic carbon.

4. Result Analysis and Judgment

The organic carbon content data obtained through detection are compared with the pre – set cleaning limit standards. These standards are usually determined according to the type, use of medical devices, as well as relevant regulations and quality requirements. If the detected TOC content is lower than the limit standard, it indicates that the cleaning degree of the medical device meets the requirements; otherwise, re – cleaning or other measures may be required to ensure the cleanliness of the device. For example, for implantable medical devices, the cleaning limit standards are usually very strict, requiring extremely low TOC content to ensure patient safety and the reliability of the device.