With the emphasis and attention of human beings on environmental quality, in the actual environmental testing process, people often need to be able to carry both the convenience and the continuous dynamics of various objects to be tested. Analytical equipment and instruments for monitoring. With the new sensor technology, it can meet the above requirements.
Sensor technology generally consists of two parts: the part that can react with the object to be tested and the part of the signal converter. The latter function is to convert the changes after reaction with the analyte into electrical or optical signals that can be recognized by the instrument.
Depending on the detection method, the sensor can be divided into optical sensor, electrochemical sensor, etc.; depending on the reaction principle, the sensor can It is divided into enzyme biosensors, immunosensors, and chemical sensors. Depending on the object to be detected, sensors can be classified into liquid sensors and gas sensors.
Sensors in Atmospheric Monitoring Applications
1. Monitor NOx Sensors
Nitrogen oxides are common atmospheric pollutants. Excessive nitrogen oxides are also the culprit of photochemical smog, seriously affecting people's physical and mental health, and even Endanger the lives of the public. The main source of nitrogen oxides is the burning of fossil minerals, which form NO2, which is a serious environmental hazard under the conditions of light. The principle of NOx sensor is to use oxygen electrode to generate a specific nitrite-consuming bacteria.The content of nitrogen oxides was calculated by calculating the change in dissolved oxygen concentration.
Because the bacteria produced are based on nitrates and only use this nitrate as an energy source, they are unique in the actual application process. It will be affected by the interference of other substances. Some foreign scholars have conducted more in-depth research using the principle of membranes, which indirectly measured the concentration of NO2 in the air.
2, sulphate sensor application
in the atmosphere In addition to nitrides in the monitoring process, sulfides are also pollutants that seriously affect people's production and life. Among the nitrogen oxides, SO2 is the main cause of acid rain and acid mist formation, and the traditional method can measure the content of SO2, but the method is complicated and not accurate enough.
Researchers have recently discovered that certain sensors can oxidize sulfites, which consume a portion of the oxygen during oxidation, which causes the dissolved oxygen in the electrode to drop to produce a current effect. The sulfite content can be effectively obtained, which is fast and reliable.
3. Application of carbon dioxide sensor
Carbon dioxide is the main substance that forms the greenhouse effect. In the process of monitoring carbon dioxide, traditional methods will interfere with different ions and volatile acids. Seriously affecting the monitored carbon dioxide value. After several years of scientific development, Lu Zhongming et al. have developed an indicator using an indicator to monitor carbon dioxide. Such an indicator can accurately measure the concentration of carbon dioxide below 190 ppm. The measurement is small, and the sensor is small in size and low in energy consumption. The application of this sensor solves the problem of long-term automatic monitoring in engineering and greatly improves work efficiency.
4, Applications in other types of gases
In addition to the high content of pollution, some common gases: formaldehyde, methane, ammonia, etc. also affect people's lives. However, due to the low content of these gases, and the fact that these gases are concealed, they are often not taken seriously by people in actual life. Zhu Yantao and others have synthesized a series of research status through research on formaldehyde and other gases, analyzed a series of problems existing in existing formaldehyde sensors, and predicted the development trend of formaldehyde sensors according to their own actual research; other scholars use specific Bacteria act as a substrate to enable uninterrupted monitoring of atmospheric pollutants.
Electrochemical sensing application
1, feature analysis.
Electrochemical sensors are less affected by pressure changes, but the pressure difference inside the sensor may damage the sensor, so maintaining pressure equalization is a prerequisite for normal operation of the sensor; electrochemical sensor Sensitive to temperature, the reading is higher when the temperature is higher than 25 °C, and the reading is lower when the temperature is lower than 25 ° C. The electrochemical sensor is more selective for the sample to be tested, the sensor type, the concentration of the sample to be tested and the target gas will affect Sensors that select the degree of selectivity, high reliability and good detection of oxygen, other types are susceptible to interference.
2, measurement principle.
The electrochemical sensor uses the reaction with the gas to be tested, and then determines the gas content based on the ratio of the electrical signal to the gas concentration. Typical electrochemical sensor main components include gas permeable membranes, electrodes, electrolytes, and filters.
3, the application of electrochemical sensors.
The more common ones are humidity sensors, nitrogen oxide sensors, sulfide gas sensors, etc. Traditional instruments for measuring air humidity are wet bulb thermometers, hand-operated thermometers, and ventilated thermometers. Electrochemical sensors are more sensitive to humidity. The sensor for coating a piezoelectric quartz crystal is a commonly used humidity measuring instrument. The instrument is made into a small quartz crystal oscillator by photochemical technique, and then four substances with higher humidity sensitivity are coated on the quartz crystal; the crystal is oscillated. Resonator in circuit,The frequency of the vibration varies with the quality, and the relative humidity of different gases can be determined by selecting different coatings.
Sulphur dioxide is the main cause of acid rain and one of the main causes of air pollution. Therefore, the use of sensors to detect sulfur dioxide can reduce the detection time and improve the detection accuracy. At the time of detection, the ion exchange membrane is a solid polymer, and one side of the membrane contains an internal electrolyte of the counter electrode and the reference electrode, and the other side is inserted into a platinum electrode to constitute a sulfur dioxide sensor.
1 Characteristic analysis.
With the continuous development of biotechnology and electronic technology, biosensing technology has gradually emerged and is widely used. Biosensors are integrated, miniaturized and highly automated.It can be quickly and effectively tested for samples, so it has been widely used in biopharmaceutical, environmental testing, food industry and other fields.
2, detection principle.
The biosensor consists of two parts: a molecular recognition unit and a transducer. The biomolecule is used to identify the sample to be tested, and then the biological system The physical or chemical changes that occur in the molecule are converted into corresponding electrical signals, and the analysis results are analyzed and displayed.
3, biosensor application.
According to foreign reports, biosensors have certain advantages over traditional electrochemical sensors, with organophosphorus and carbamate pesticides. As an example, the minimum detection amount of the traditional detection method is 400 ng/kg.The enzyme sensor that has cured the aldehyde dehydrogenase can greatly improve the detection accuracy, and the minimum detection amount is 9 ng/kg.
The cell sequence that recombines fluorescent cells with the eggs of Chinese big cheeks can be used to detect toxic substances in the environment. In addition, the continuous development of technology has also promoted Improvement of biosensors, biosensor chips based on PCR technology and chip technology, various biochemical analysis instruments are constantly being developed, convenient to carry, accurate and fast analysis has become a reality, the application of biosensing technology in environmental detection will increase widely.
Optical Sensing Application
1, feature analysis.
Fiber sensing is a sensing technology developed based on fiber optic box technology.It can be used for detection in the atmosphere, water quality and ecological protection. The technology has the advantages of small volume, high sensitivity, strong anti-interference ability and corrosion resistance, so it can be applied in toxic, harmful, flammable and explosive environments. Fiber optic sensors have the advantages of real-time online and distributed telemetry, which can meet the needs of the current environmental protection market for rapid and efficient detection of environmental indicators.
2, detection principle.
Fiber optic sensors use the pollutants to be tested to interact with light to cause changes in the optical signal in the fiber (or contaminants and other substances, Indirectly changing the characteristics of the fiber signal), and then detecting it by the optical signal detection system, thereby obtaining the relevant information value of the pollutant. Fiber optic sensors generally consist of light sources, fiber optic leads, sensitive components, and signal detection and analysis equipment.
3, fiber optic sensor applications.
The fiber optic pH sensor can detect the pH value of the water body. The detection principle is based on the principle of fixing the colorimetric indicator according to the pH value of the specific dyeing material. The material is made into a light transmissive or reflective film, and the pH value in the water can be determined by spectroscopic analysis. The fiber ion sensor combines flow injection analysis, laser excitation fluorescence spectrometry, fiber optic conduction technology, and CCD photography to detect copper ions, zinc ions, cadmium ions, and nickel ions. The optical turbidity sensor measures the decrease in the transparency of the water sample by using the laser to change the intensity of the reflected light and the intensity of the incident light in the water sample to be tested. China's research on optical fiber sensing is relatively late, but decades of development have achieved remarkable results in this field. For example, the fiber-optic gas sensor and its on-line detection system developed by the Shandong Branch of the Chinese Academy of Sciences can accurately detect flammable and explosive gases such as methane by using infrared absorption spectroscopy and light technology.
With the continuous development of the economy and the continuous improvement of people's living standards, environmental issues have aroused widespread concern in the whole society. Environmental issues are not only related to the healthy survival of human beings, but also have an impact on economic development. Environmental testing is not only Help us understand the current state of the environment, and provide reliable technical guidance for us to manage environmental problems and improve living conditions. Under the continuous development of science and technology, environmental testing technology and testing equipment will be continuously optimized to achieve fast and efficient. , environmental protection, accurate environmental indicators testing.