Automatic Thermal Desorption Unit (TDU) is a method used to desorb volatile organic compounds (VOCs) from solid or liquid samples. It heats the sample to desorb organic substances from the sample and enter the gas phase, which is then analyzed by a gas analyzer (such as gas chromatograph, GC). Automatic thermal desorption desorption instrument is widely used in environmental monitoring, food quality control, materials science and other fields. The following is its typical parsing process:
1. Sample preparation and loading
Sample pretreatment: Samples usually need to undergo certain pretreatment to remove moisture or other irrelevant impurities, in order to improve the accuracy of analysis.
Load sample: Place the processed sample into a thermal desorption tube (usually a metal or glass tube). The desorption tube is equipped with appropriate adsorbents (such as activated carbon, molecular sieves, or polymer materials) for capturing volatile organic compounds (VOCs).
2. Sample heating and desorption
Heating process: Place the desorption tube carrying the sample into the heating chamber of the thermal desorption instrument, and desorb the VOCs adsorbed on the adsorbent through heating. The thermal desorption process usually requires a high temperature (usually between 150 ° C and 350 ° C), and the heating rate and temperature are key factors affecting the desorption effect.
The flow of desorbed gas: After heating, the desorbed volatile compounds will be discharged through the desorption tube together with the carrier gas (usually nitrogen or helium). The flow rate of the carrier gas is usually controlled between 10-50mL/min to ensure smooth gas flow.
3. Gas inflow analysis system
Entering the gas chromatograph: The desorbed gas (including VOCs) enters the gas chromatograph (GC) through the gas flow path for separation and analysis. The chromatographic column in a gas chromatograph separates the various components in the gas.
Other analytical instruments: In some cases, the desorbed gas can also enter other types of analytical instruments, such as mass spectrometers (MS) or spectrometers, to further analyze the molecular structure and concentration of compounds.
4. Chromatographic separation
Chromatographic column: In a gas chromatograph, the desorbed gas passes through the chromatographic column, which separates the various components of the gas based on the interaction forces between different compounds and the stationary phase.
Analyzing temperature and pressure: The efficiency of chromatographic separation is affected by conditions such as the temperature, pressure, and flow rate of the chromatographic column, and it is usually necessary to optimize these parameters to achieve the best separation effect.
5. Detection and quantitative analysis
Detector: The separated gas components are sent to the detector for qualitative and quantitative analysis. Common detectors include flame ionization detector (FID), electron capture detector (ECD), mass spectrometry detector (MS), etc.
Qualitative analysis: Based on the retention time of each component in the gas, its chemical composition can be determined.
Quantitative analysis: By comparing standard samples with known concentrations, the concentration of various organic compounds in the sample can be quantitatively analyzed.
6. Data processing and result output
Data collection: All data collected during the analysis process will be automatically recorded and can be displayed in real-time. The chromatogram shows the compound corresponding to each peak.
Data processing: Using data analysis software to process data, perform peak recognition, integration, quantitative analysis, and other operations on chromatograms.
Result report: The final results include the concentration, types, and related mass spectrometry information of various organic compounds in the sample.
7. Cleaning and Reuse
Cleaning the desorption tube: After each test, the desorption tube needs to be cleaned to remove residual substances to ensure the accuracy of the next test. The cleaning process may include blowing with inert gas or cleaning with solvent.
System calibration: Regularly calibrate the thermal desorption desorption instrument and gas chromatograph to ensure the accuracy and reliability of the instrument.
Summary:
The analytical process of an automatic thermal desorption instrument usually includes several steps, such as sample preparation, thermal desorption, gas analysis, chromatographic separation, quantitative detection, and data processing. Through this process, volatile organic compounds (VOCs) in solid or liquid samples can be efficiently and accurately analyzed. This process has a wide range of applications in fields such as environmental monitoring and materials science.