What is the principle of the Total Organic Carbon Clean Verification Swab test?

The detection principle of total organic carbon cleaning verification swabs mainly relies on oxidizing the carbon elements in organic matter to carbon dioxide, and then indirectly determining the content of total organic carbon by detecting the amount of carbon dioxide. The following are several common detection principles:

Combustion oxidation – nondispersive infrared absorption method

• Oxidation process: The swab that has collected the sample is placed in a high-temperature combustion tube, and under high temperature (usually 900°C-950°C) and the action of catalysts (such as platinum and cobalt trioxide or chromium trioxide), the organic matter on the swab is burned and cracked, and the carbon elements in it are completely oxidized and converted to carbon dioxide.
• Detection process: The generated carbon dioxide enters the nondispersive infrared detector along with the carrier gas. Because carbon dioxide has a strong absorption effect on infrared rays of a specific wavelength, and within a certain concentration range, the intensity of carbon dioxide’s absorption of infrared rays is proportional to the concentration of carbon dioxide. By detecting the intensity of infrared absorption, the concentration of carbon dioxide can be determined, and then the content of total organic carbon can be calculated. The organic matter of various types can be detected by this method, which is one of the widely used methods for detecting total organic carbon.
• Advantages: This method has high accuracy and sensitivity, and can detect extremely low concentrations of organic carbon, and is suitable for detecting various types of organic matter.

Conductivity method

• Oxidation process: First, the organic matter on the swab is converted into carbon dioxide, water and other products through chemical oxidation or other methods.
• Detection process: The generated carbon dioxide dissolves in water to form carbonate ions, etc., thereby changing the conductivity of the solution. By measuring the change in the conductivity of the solution, based on the quantitative relationship between the conductivity and the concentration of carbon dioxide, the content of total organic carbon is calculated. Different amounts of carbon dioxide are produced after the oxidation of different organic substances, thereby causing different changes in conductivity, thereby indirectly determining the total organic carbon.
• Advantages: The instrument and equipment of the conductivity method are relatively simple, the operation is convenient, and the detection speed is fast, which can be used for on-line monitoring and real-time analysis.

Gas chromatography method

• Oxidation process: Under specific conditions, the organic matter on the swab reacts with oxygen or other oxidants to convert the organic carbon into gaseous products such as carbon dioxide.
• Detection process: Using a gas chromatograph to separate the generated carbon dioxide from other gases, and quantitatively analyze the carbon dioxide through a detector. By comparing the peak area or peak height of the carbon dioxide with a known concentration of a standard substance, the content of total organic carbon in the sample is determined.
• Advantages: Gas chromatography has the characteristics of high separation efficiency and high sensitivity, and can accurately determine the total organic carbon in complex samples, and can simultaneously detect multiple organic compounds.

Wet oxidation – nondispersive infrared absorption method

• Oxidation process: Under acidic conditions, using strong oxidants (such as potassium persulfate, etc.) to oxidize and decompose the organic matter on the swab into carbon dioxide and water, etc.
• Detection process: Similar to the combustion oxidation – nondispersive infrared absorption method, the generated carbon dioxide is introduced into the nondispersive infrared detector for detection, and then the content of total organic carbon is obtained.
• Advantages: For some organic substances that are difficult to be completely oxidized and converted by combustion oxidation, wet oxidation has a better oxidation effect and can improve the detection accuracy.