What is VOCs?

According to the World Health Organization (WHO) definition, VOCs(volatile organic compounds) are various boiling points of 50 ℃ to 260 ℃ at normal temperature.organic compound. In our country,VOCs refers to the saturation vapor pressure greater than 70 Pa at normal temperature and under normal pressure.Boiling PointInOrganic compounds below 260 ℃, or all organic compounds with vapor pressure greater than or equal to 10 Pa and volatility at 20 ℃.

As peopleThe hazard awareness of VOCs gas is strengthened, and the detection methods and instruments of VOCs are constantly upgrading and improving.

VOCs detection method

The instrument methods of volatile organic compounds in the air in foreign countries, especially in the United States, are mainly gas chromatography and gas chromatography.-Mass spectrometry. The sampling methods are mainly container capture method and solid adsorbent sampling method. The adsorbent is divided into activated carbon, carrier (also known as carrier) and thermal desorption tube and so on.

Most of the early analytical methods in China are solid adsorbent adsorption.-Solvent desorption-gas chromatography, the adsorbent has an enrichment effect on air samples, the detection limit of the method is relatively low, the determination cost is low, but there are defects such as long sampling time, adsorbent leakage, desorption/resolution efficiency and secondary pollution.In the back, our country's mining.sample and analysis methodAlsoGradual convergence with the international frontier approach。

At present, it is widely used at home and abroad.gas chromatographyGC. shouldThe method has the advantages of high efficiency, fast speed, wide monitoring range and high sensitivity.One of the important means of VOCs.

VOCs detector

ForDetectorThe choice at home and abroadUsually usedThe detectors are:Hydrogen Flame Ionization Detector (FID), electron capture detector (ECD), photo ionization detector (PID) and mass spectrometry detector (MSD)

1. Hydrogen Flame Ionization Detector (FID) is a universal detector, which is commonly used in gas chromatography.。

它With the advantages of high sensitivity, wide linear range, good stability and rapid response, it is widely used in the detection of volatile hydrocarbons and many carbon-containing organic compounds;The outstanding advantage of FID is that it is responsive to almost all organic compounds, especially to hydrocarbons, and the response is proportional to the number of carbon atoms. It is not sensitive to inorganic substances such as H2O, CO2 and CS2, and is not sensitive to gas flow rate, pressure and temperature changes. It has a wide linear range, simple results and convenient operation. It has almost zero dead volume and can be directly connected to a capillary column. Therefore, FID has been widely used in the past packed column period and capillary column.The disadvantages of FID are:Gas path relative impurities, ignition or gain in operation.Zui.Good performance requires repeated adjustment of the airflow ratio, which is troublesome compared to other detectors.。

2. Electron capture detector (ECD）It is a gas chromatography detector with high sensitivity zui, and it is also a selective detector with early appearance of zui.

It is only for those compounds that can capture electrons, such as halogenated hydrocarbons, containingCompounds with heteroatoms such as N, O and S have a response. Because of its high sensitivity and good selectivity, it is also a widely used radioactive ionization detector. It is widely used in biology, medicine, pesticide, environmental protection, metal chelate and weather tracking and other fields.Although ECD has the characteristics of high sensitivity, its shortcomings are also obvious: the first isIn daily operation, there are many matters needing attention. If you don't pay attention to it, it will cause stability deterioration immediately,Sensitivitysubstantial decrease, linear narrowing, and therefore, is often mistaken for aBad operating detector；At the same time,It is difficult and time-consuming to establish a chromatographic analysis method for ECD, such as pre-treatment of samples, preparation and aging of chromatographic columns, cleanliness of the system, and solvent utensils used.

3. Mass SpectrometryDetector(MSD) is a mass, universal detector that responds to all ionizable compounds suitable for GC detection.

Because mass spectrometry has higher sensitivity, strong qualitative ability and can provide relative molecular mass and structure information and other advantages, improve the limitations of gas chromatography qualitative, now gas chromatography-mass spectrometry (GC/MS) is more and more widely used in the detection of VOCs in the environment.The advantage of MSD is that it can measure accurately and respond to compounds suitable for GC detection and capable of calligraphy and painting. Its disadvantage is that MSD data processing workload is very large, it must cooperate with computer system to work effectively, and the cost is high.

4. Photoionization detector (PID），PID(Photo Ionization Detector) photoionization detector is a sensor mainly used to monitor VOCs in the atmosphere.

itsThe principle is that the organic gas will produce the ionization of the gas under the excitation of the ultraviolet light source,PID uses a UV (ultraviolet) lamp, the organic matter is ionized under the excitation of the ultraviolet lamp, and the ionized "fragments" carry positive and negative charges, thus generating a current between the two electrodes. The detector amplifies the current and displays the concentration of VOCs gas through the instrumentation equipment.The advantage of the light ion detector is non-destructive, and the sensor is small, can be used in a wide range of environments, and with the improvement of sensor technology, its detection accuracy is not inferior to large-scale testing instruments.

Agent of the United KingdomAlphasense ofPID-AHSensor resolution is1ppb, the sensitivity of 20mv/ppb or more, to meet and achieve the accurate detection of atmospheric VOCs, monitoring needs.

CurrentlyPID-AH technology is very mature and has been used in a large number of industrial projects.

JustPID, its main applications are: mainly for the oil refining industry monitoring, emergency treatment of hazardous chemicals leakage, leakage of hazardous areas defined, oil tank station safety monitoring, organic emissions purification efficiency monitoring.

If you are interested inPID detection sensor is in demand, welcome to call Technology Co., Ltd!