Ambient air VOCs commonly used monitoring methods? Atmospheric VOCs monitoring methods mainly include offline technology and online technology, these technologies usually include sampling, preconcentration, separation and detection of several processes. VOCs in the air sampling can be divided into direct sampling, dynamic sampling and passive sampling. Sample preparation methods include solvent analysis, solid phase microextraction, low temperature preconcentration and thermal analysis. Methods for the analysis of VOCs include gas chromatography, high performance liquid chromatography, gas chromatography-mass spectrometry and the latest development of proton transfer reaction mass spectrometry techniques. Off-line technology and online technology comparison: Off-line technology is more accurate qualitative and quantitative analysis and testing sensitivity is high, but the monitoring frequency and monitoring results of the timeliness is not enough to timely reflect changes in gas concentrations, and sampling, sample storage, The transportation process can easily lead to sample loss and cross-contamination, the testing process is cumbersome and time-consuming, the test sample quantity is limited and the testing cost is high. VOCs monitoring methods and their advantages and disadvantages? Sampling method: â‘ container trapping method: the inner wall of the silanized stainless steel tank vacuum evacuated, with decompression or pressure sampling. The method can collect the entire air sample, to avoid penetration and decomposition of adsorbent samples, and can analyze many of the components. However, the technical input is larger, and is currently less used in China. The method for low concentration (ppb level) is often due to the lack of the corresponding stable standard material can not be accurately set value, while the detection limit of the instrument also limits the promotion and application of the method. â‘¡ adsorption method: with solid adsorbent capture VOCs in the air. Common solid adsorbents are: Tenax tube, activated carbon tube, activated carbon fiber tube and mixed adsorbent. A single adsorbent is difficult to meet the broad boiling range of VOCs collection. â‘¢ solid phase microextraction (SPME): solid phase microextraction device consists of extraction head and handle two parts. Sampling using the handle to extract the first push, so that it is directly exposed to the indoor air sampling, no power. SPME is easy to operate and requires no organic solvents for sample collection, extraction, concentration and injection. Sample preparation method: Solvent desorption method: solvent desorption has the advantages of low cost and simple operation. However, desorption of sample due to volume of desorption solution much larger than the sample volume will result in lower sensitivity; impurities such as impurities or laboratory contamination will lead to larger errors. â‘¡ thermal desorption method: the adsorbent is heated while introducing carrier gas, desorption of adsorbed VOCs into the column. The advantage of thermal desorption is the higher sensitivity, which avoids the interference of the solvent on the analysis, but the sample recovery is lower. Common analysis methods: â‘ gas chromatography (GC): the collected samples in the GC by the use of substances in the two phase partition coefficient of minor differences. Based on the basic data, including the qualitative retention time, the peak area associated with the quantitation gives the sample contents. Chromatography with high performance, high selectivity, high sensitivity, fast analysis and wide range of applications, and multi-component organic mixture qualitative and quantitative analysis of good results. The use of hydrogen flame ionization detector (FID) in gas chromatography for the qualitative and quantitative determination of organic contaminants is a more established method. â‘¡ Gas Chromatography / Mass Spectrometry (GC-MS): The collected samples were separated by small differences in the partition coefficient between the two phases in the GC, and the separated substances were ionized in the MS and then used Different ions in the electric field or the magnetic field of different behavior, the ion mass-to-charge ratio to get the mass spectrum. Through the sample of the relevant information, you can get qualitative and quantitative sample results. Compared with the GC method, the GC-MS method not only has high separation ability and accurate qualitative identification ability, but also can analyze unknown samples, detect the peaks that have not been separated yet, have high sensitivity and reliable data.