The specific introduction is as follows:

The detection principle of the TOC (Total Organic Carbon) cleaning verification swab mainly involves converting the organic carbon collected by the swab into detectable carbon dioxide, and then quantitatively analyzing the carbon dioxide through corresponding technical means to determine the content of total organic carbon. The specific introduction is as follows:

Sampling

The detection of the TOC cleaning verification swab first requires sampling. That is, the swab is used to wipe the target surface to collect the organic pollutants on the surface. The material of the swab usually has good adsorbability and chemical stability, which can effectively collect various organic substances and will not chemically react with the collected organic matter or interfere with subsequent detection.

Oxidation

• High-temperature Catalytic Oxidation: After the collection, the swab is placed in a TOC analyzer. Under the action of high temperature and a catalyst, the organic carbon in the sample will be completely oxidized to carbon dioxide. Generally, the sample is heated to a temperature range of 600°C – 1000°C, and catalysts such as platinum and cerium dioxide are added to accelerate the oxidation reaction and ensure that all organic carbon can be converted into carbon dioxide.
• Chemical Oxidation: Strong oxidants are used to chemically react with the organic carbon in the sample to oxidize it into carbon dioxide. Common oxidants include potassium persulfate, potassium permanganate, etc. Under certain temperature and pH conditions, the oxidant fully reacts with the organic carbon to achieve the conversion of organic carbon into carbon dioxide. For example, under acidic conditions, potassium persulfate can oxidize organic carbon into carbon dioxide. During the reaction process, a series of redox reactions will occur, and the carbon element in the organic carbon is finally converted into the form of carbon dioxide.

Detection

• Non-dispersive Infrared Absorption Method (NDIR): The carbon dioxide generated by oxidation is carried by a carrier gas (such as nitrogen) into a non-dispersive infrared absorption detector. Carbon dioxide has a characteristic absorption peak at a specific wavelength of infrared light. When infrared light passes through a gas containing carbon dioxide, part of the infrared light will be absorbed by the carbon dioxide, resulting in a decrease in the light intensity. By detecting the change in the infrared light intensity, according to the Lambert-Beer law, the content of carbon dioxide can be calculated, and then the content of total organic carbon in the sample can be obtained.
• Conductivity Method: The carbon dioxide generated by oxidation is introduced into deionized water. The carbon dioxide will react with water to form carbonic acid, causing a change in the electrical conductivity of the water. By measuring the change in the electrical conductivity of the deionized water before and after the reaction, the content of carbon dioxide can be indirectly calculated, thereby obtaining the content of total organic carbon in the sample. Since there is a certain quantitative relationship between the change in electrical conductivity and the concentration of carbon dioxide, accurate measurement of total organic carbon can be achieved through methods such as establishing a standard curve.
• Gas Chromatography (GC): The gas sample after oxidation is injected into a gas chromatograph. The gas chromatographic column is used to separate gases such as carbon dioxide. Different gases have different retention times in the chromatographic column, thus achieving separation. Then, the separated carbon dioxide is detected by a flame ionization detector (FID) or a thermal conductivity detector (TCD), etc. According to the peak area or peak height of carbon dioxide and by comparing with the standard curve, the content of carbon dioxide is calculated, and finally, the content of total organic carbon in the sample is obtained.

In practical applications, different TOC cleaning verification swab detection devices may adopt different combinations of oxidation and detection methods to meet different detection requirements and sample characteristics. However, the overall detection principle is based on converting organic carbon into carbon dioxide and conducting quantitative analysis.