With the continuous deepening of air pollution control in our country, VOCs has become a new concern in air pollution control in China following particulate matter, sulfur dioxide and nitrogen oxides. The author analyzed the detection methods of volatile organic compounds (VOC) in the air, and compared the difference of detection methods such as gas chromatography, high performance liquid chromatography, membrane technology, chemical method and online test chamber. The rapid development of VOCs detection technology has greatly promoted the detection, monitoring and emission reduction of VOCs. This time to introduce you to commonly used VOCs detection technology.

Laboratory VOCs testing

VOCs laboratory analysis developed earlier, more mature. The analytical method is to collect the VOCs back to the laboratory using a sampling bag, a canister, an adsorbent or an absorption liquid, and then subjected to a pretreatment process such as thermal analysis and solvent analysis, followed by GC or HPLC analysis.

The main challenge of laboratory VOCs testing is to select the appropriate sampling method to ensure that all VOCs can be collected, to develop a standardized transport program to prevent the loss of VOCs during transport, and to select the appropriate pretreatment process to ensure that all volatile organic compounds enter the analysis instrument.

The main advantage of the laboratory analysis method is accurate results, the main drawback is the poor timeliness, sample and transport process can easily lead to sample loss, affecting the accuracy and reliability of the determination.

Online VOCs detector

VOCs on-line analyzers are mainly online gas chromatograph, online mass spectrometer, on-line mass spectrometer, online PID and FID detector, online infrared spectrometer, online laser detector and on-line differential optical absorption spectrometer.

VOCs do not have standard detection methods, and online systems are used for on-site testing. Volatile organic compounds in different sites vary greatly in size and are relatively stable. Therefore, testing needs are different. Therefore, according to their own needs and the characteristics of a variety of testing equipment to choose the appropriate detection methods.

On-line gas chromatographs detect concentrations of known volatile organic compounds; online mass spectrometry allows the simultaneous qualitative and quantitative detection of volatile organic compounds but does not distinguish between isomers; on-line PID and FID detectors yield VOCs The total volume, and the smaller instrument; a variety of online spectrometer detection range, can be adapted to a variety of industrial applications.

Online VOCs detector mainly concentrates the domestic manufacturers, Guangzhou Wo letter, Baoyin technology, photoelectric, Fu Zhan environmental protection, Wuhan Tianhong, foreign manufacturers have the British Markes, Japan's Yanagami, Austria IONICON, South Korea KNR, Germany AMA, France Chromatotec, USA CerexMS and so on.

Portable VOCs instrument

Portable VOCs analyzers are mainly portable FID / PID detector, portable infrared analyzer, portable laser spectrometer, portable GC / MS and so on.

Recently released MEP standard portable instruments mentioned FID detector, PID detector and infrared absorption detector three.

Portable VOCs detector main domestic manufacturers have something analysis, Lao Ying, Fu Zhan environmental protection, foreign manufacturers are the United States Inficon, the United Kingdom SIGNAL, the United States Regowayewo, the United States Huarui, Japan's Yanas, the United States Keer Kang and so on.

Gas Chromatography GC and GC-MS

Gas chromatography is the most commonly used instrument, it has the advantages of high efficiency, high selectivity, high sensitivity, fast analysis and wide range of applications, especially for qualitative and quantitative analysis of isomers and multi-component mixtures Advantage. Detectors commonly used for VOCs in conjunction with GC are: Flame Ionization Detector (FID), a universal detector that is also one of the most commonly used detectors in gas chromatography, an electron capture detector (ECD) (Detection of halogenated hydrocarbons and alkyl nitrates), mass spectrometry (MS) and photoionization detector (PID).

Reference to EPA TO-14A and TO-15 standard analytical methods of atmospheric VOCs in the atmosphere, the preconcentrator and GC were used to detect and analyze C2-C4 alkanes, alkenes and alkynes by using FID detector for ambient air C2-C4 volatile components of non-methane hydrocarbons. GC-MS is the common method used to detect VOCs. Can carry out qualitative and quantitative analysis of unknown compounds. However, note that component loss and cross-contamination between the components during sample flow can cause bias in test results. EI ionization sometimes form a variety of ion fragments, mass spectrometry complex, difficult to analyze.

As the main VOCs detection technology or chromatography technology. However, this technique requires complex sampling and pretreatment processes. GC-MS and automatic headspace sampler, purge and trap system, thermal analysis system is now commonly used technology. Dramatically reduce the requirements for sample preparation technology, faster and more efficient. Currently, there are many assays for the analysis of VOCs using GC × GC-qMS (GC-MS) and GC × GC-TOF-MS (Total 2D GC-TOF-MS).

Online monitoring of proton transfer reaction mass spectrometry PTR-MS

PTR-MS is a trace-level volatile organic compounds online detection technology, high sensitivity, fast analysis time and other advantages, and online sampling, without concentration. It will sample the atmosphere directly into the sample, which measures fast. Proton transfer soft ionization of a variety of VOCs as a single ion, no fragment ions, easy mass spectrometry recognition, the sensitivity can reach tens of ng. The main limitation is the more difficult to distinguish isomers.

Time of flight mass spectrometry TOF-MS

TOF-MS is an analysis method that uses the same kinetic energy but different mass-to-charge ratio to move in a constant electric field and determine the composition or structure of matter by the principle of different time required by a constant distance. Wide range of quality, fast response, high resolution, high sensitivity and so on. The instrument is easy to process and miniaturize, with the potential to monitor organic pollutants online. Others include selective ion tube mass spectrometry (SIFT-MS) for the immediate identification and quantification of volatile organic compounds (VOCs).

Atmospheric VOCs are not only the main precursor of photochemical smog pollutants, but also an important source of toxic and harmful organic components in atmospheric fine particles. They contribute greatly to the formation of haze, and some VOCs are themselves toxic and carcinogenic. With the continuous deepening of air pollution control in our country, VOCs has become a new concern in air pollution control in China following particulate matter, sulfur dioxide and nitrogen oxides.

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