TOC Cleaning Verification Swab

The detection principle of the TOC Cleaning Verification Swab is mainly based on oxidising organic matter to carbon dioxide and then indirectly determining the amount of total organic carbon in the sample by detecting the amount of carbon dioxide, as described below:
Oxidation process
Combustion oxidation: This is one of the most common oxidation methods. A TOC cleaning verification swab is placed into the high temperature oven of the TOC analyser. Under high temperature (usually 680°C to 950°C) and sufficient oxygen, the organic matter adsorbed on the swab is completely burned and oxidised into products such as carbon dioxide and water. For example, in the pharmaceutical equipment cleaning verification, equipment surface residual drug ingredients, cleaning agents and other organic substances in the high temperature combustion will be decomposed into carbon dioxide.
Chemical oxidation: the use of strong oxidants such as sodium persulfate, hydrogen peroxide, etc. and organic matter chemical reaction, the organic matter will be oxidised to carbon dioxide. This method is relatively mild and is suitable for some temperature-sensitive or difficult-to-burn organics. In practice, the swab will be put into the solution containing the oxidising agent, and after a certain reaction time and conditions, the organic matter will be oxidised.
Photocatalytic oxidation: Using the strong oxidising free radicals generated by photocatalysts (e.g. titanium dioxide, etc.) under light conditions to oxidise the organic matter to carbon dioxide. This method has the advantages of mild reaction conditions, no need for high temperature and high pressure, etc., but the requirements for the activity of the photocatalyst and the intensity of the light source are high.

Carbon Dioxide Detection
Non-Dispersive Infrared Detection (NDIR): This is one of the most commonly used carbon dioxide detection methods in TOC analysers. Carbon dioxide molecules have absorption properties at specific wavelengths of infrared light. When oxidised carbon dioxide passes through the NDIR cell, it absorbs infrared light at specific wavelengths, resulting in a decrease in light intensity. By detecting the change in light intensity, the concentration of carbon dioxide can be calculated, and thus the amount of total organic carbon in the sample.
Thermal Conductivity Detection (TCD): Based on the principle that different gases have different thermal conductivity. When a gas containing carbon dioxide passes through a thermal conductivity detector, it causes a temperature change in the thermal element in the detector, which results in a change in its resistance. By measuring the change in resistance, the amount of carbon dioxide can be detected.
Flame Ionisation Detection (FID): Gases such as carbon dioxide produced by oxidation are introduced into a hydrogen flame. Under the high temperature of the flame, gases such as carbon dioxide are ionised into ions, generating a weak electric current. By detecting the size of the current, the concentration of carbon dioxide can be determined, and thus the total organic carbon content can be calculated.