What are the test methods for common gases and the air tightness of the device?

1. Catalytic combustion.

Catalytic combustion gas sensor uses the thermal effect principle of catalytic combustion, under certain temperature conditions, the combustible gas undergoes flameless combustion under the action of the carrier surface of the detection element and the catalyst, and outputs an electrical signal proportional to the concentration of the combustible gas. By measuring the magnitude of the change in the resistance of the platinum wire, the concentration of flammable gases is known. It is mainly used for the detection of flammable gases, with good output signal linearity, reliable index, cheap, and no cross-infection with other non-flammable gases.

2. Semiconductor.

Semiconductor gas sensor is a gas sensor that uses a semiconductor gas sensor as a sensitive element, and is the most common gas sensor, which is widely used in combustible gas leakage detection devices in homes and factories, and is suitable for the detection of methane, natural gas, liquefied gas, hydrogen, etc.

Naoyoshi Taguchi, the founder of Figaro Engineering Co., Ltd., was the first to invent semiconductor gas sensors in May 1968.

3. Electrochemical formula.

The electrochemical gas sensor uses the electrochemical activity of the measured gas to electrochemically oxidize or reduce it, so as to distinguish the gas composition and detect the gas concentration.

It can accurately measure the content of trace gases (ppm level) in the air or for environmental monitoring, such as O2, CO, H2S, CO2, SO2, NH3, HCN, HF and other corrosive or toxic gases.

There must be oxygen involved in the redox reaction.

4. Infrared.

It is made by the absorption of a gas into the infrared spectrum at a specific frequency. Infrared light is emitted from the transmitter to the receiver, and when there is gas, the infrared light is absorbed, and the received infrared light is reduced, so that the gas content is detected.

Good selectivity, only detects specific wavelength of gas, adopts optical detection method, and is not easy to be affected by harmful gases and poisoning and aging; Fast response speed and good stability; It has no chemical reaction and good explosion-proof; High signal-to-noise ratio and strong anti-interference ability; Long service life; High measurement accuracy.

Each gas is detected by infrared light.

5. PID photoion.

Photoionized gas sensors, often referred to as PIDs. It is an extremely sensitive, versatile detector that can detect volatile organic compounds and other toxic gases from 10 ppb to higher concentrations of 10,000 ppm. Many hazardous substances contain volatile organic compounds, and PID is highly sensitive to volatile organic compounds.

PID detects aromatic hydrocarbons, ketones, aldehydes, chlorinated hydrocarbons, amines and amine compounds, and unsaturated hydrocarbons.

1. Microthermal method.

This is one of the most commonly used methods for chemical testing equipment in secondary schools, and it is also the most basic method for testing the air tightness of equipment. The principle of this test method is to use the gas to expand after being heated and then escaping from the device and seeing the bubbles emerge. Here's how it works:

Insert the end of the trachea B into the sink and hold the test tube A with your hand or heat it slightly with an alcohol lamp, so that the gas in the tube A is heated and expanded, and bubbles will be generated at the end of the trachea. When the hand is released or the alcohol lamp is withdrawn, a section of water rises at the end of the air duct, which proves that the device is airtight and does not leak. See the diagram below for details.

2. Liquid difference method.

The liquid difference method uses the "supporting force" generated by the pressure difference between the inside and outside of the device to lift a section of water column and no longer fall. For different experimental setups, the experimental operation methods adopted are different when using the liquid difference method to test the air tightness. The following describes two common methods of liquid difference method to test the air tightness of the device.

1) Air tightness test of Qipu generator: close the piston of the air guide pipe, add water to the spherical funnel, so that the liquid level in the funnel is higher than the liquid level of the container, and when the liquid level does not change after standing for a while, it can prove that the air tightness of Qipu generator is good. See the diagram below for details.

2) Another method of air tightness testing, as shown in the figure below. The specific operation is as follows: connect the instrument and inject an appropriate amount of water into tube B to make the liquid level of tube B higher than the liquid level of tube A. After a few moments, if the liquid level remains the same, it is a sign that the device is airtight.

3. Liquid sealing method.

As shown in the figure below, the method of testing the air tightness of the device is as follows: close the piston K, add water to it to the lower end of the submerged long neck funnel, and if a stable water column appears in the funnel neck, it proves that the air tightness of the device is good.

It should be noted that if you want to check the airtightness of the whole device, in order to form a certain air pressure difference and produce an obvious phenomenon, you can use an alcohol lamp to slightly heat a container that can be heated in the device, and then observe whether there are bubbles coming out of the air duct mouth of the liquid inserted, so as to judge whether the airtightness of the whole device is good.

The method is to immerse the lower end of the catheter orifice in water and hold the tube tightly with both hands. If air bubbles are observed coming out of the airway orifice, the device is not leaking.

Note: If the external temperature is high and the experimental phenomenon is not obvious, we can use the alcohol lamp to heat the bottom of the test tube slightly, but the phenomenon must be noted that after the alcohol lamp is removed, a water column can be formed in the catheter and does not drop for a period of time, which can indicate that the air tightness is good.

2 As shown in Figure 2, the funnel of this device communicates with the atmosphere and cannot be inspected as in the example above. To carry out its air tightness check, the first question to consider is how to make the Erlenmeyer flask not communicate directly with the atmosphere through the funnel. To solve this problem, it is obvious to use water (or liquid) as a liquid seal, thus achieving this purpose.

The specific method is as follows: add a certain amount of water from the funnel, make the lower end nozzle of the funnel immersed below the liquid level, clamp the spring clamp, add a small amount of water again, stop adding water, the liquid level difference between the funnel and the Erlenmeyer flask (i.e., the height of the water column) remains unchanged, indicating that the device does not leak.

There are three ways to do this.

One. After assembling the experimental instrument, put one end of the catheter into the water and heat the test tube, if after a while, there are continuous bubbles coming out of the catheter mouth, indicating that the device is airtight. If there is no above phenomenon, the air tightness is not good, and it is necessary to carefully use the above method to test it piece by piece.

Two. Put one end of the catheter in the water and cover the tube with your hand for a while, if there are continuous bubbles coming out of the catheter orifice, the air tightness is good.

Three. Put one end of the catheter into the water, if the other end of the catheter is inserted into the assembly instrument, when the front of the connected instrument is an empty reaction bottle with a jack, first use the separating funnel to add half a bottle of water to the bottle, insert the lower end of the separating funnel below the liquid level, and then add water dropwise. If the liquid level in the bottle rises, the air tightness is not good.

Summary: The first two methods use the characteristics of thermal expansion and cold contraction, and the third method uses the pressure, and the air tightness of the general inspection device is considered from these two factors.

How exactly should I check the airtightness of the device?

If it is a test tube, attach a single-hole rubber plug and a trachea, hold the tube in your hand, and go deep into the water tank, if there are air bubbles, the air tightness is good.

Verification content of the test method: 1. Accuracy refers to the degree to which the results measured by the method are close to the true value or reference value, which is generally expressed by the ** rate (%). 2. Precision refers to the proximity between the results obtained by multiple sampling and measurement of the same uniform test sample under the specified test conditions, which is generally expressed as deviation, standard deviation or relative standard deviation.

3. Specificity refers to the fact that the method used can correctly determine the characteristics of the analyte in the presence of other components (such as heterovertical pre-resistance, degradation products, excipients, etc.). The chromatography method should be accompanied by a representative map, and the position of each component in the figure should be indicated, and the separation of the regret type should meet the requirements. 4. The detection limit refers to the minimum amount of the analyte in the sample that can be detected.

Chromatography generally uses the signal-to-noise ratio method. Generally, the signal-to-noise ratio is 3:1 or 2:

1. The detection limit is determined by the corresponding concentration or the amount injected into the instrument. 5. The limit of quantification refers to the minimum amount of the analyte in the sample that can be quantitatively determined. The measurement results should have a certain degree of accuracy and precision.

The signal-to-noise ratio method is commonly used to determine the limit of quantification. Generally, the limit of quantification is determined by the corresponding concentration or the amount injected into the instrument when the signal-to-noise ratio is 10:1.

6. Linearity refers to the degree to which the measurement result is directly proportional to the concentration of the analyte in the sample within the designed range. Regression equations, correlation coefficients, and linear plots are required. 7. The range refers to the range of high and low limit concentrations or quantities that can achieve a certain precision, accuracy and linearity, and the test method is applicable.

8. Durability refers to the degree of tolerance that the measurement results are not affected when there is a small change in the measurement conditions. The variable factors of gas chromatography are: the same type of column of different brands or different lot numbers, stationary phase, different types of supports, column temperature, inlet detector temperature, etc.

Different gas detection methods are different, and grasping the gas detection method can not only correctly identify different gases, but also correctly grasp the relevant knowledge to avoid unnecessary damage.

Common Gas Test Methods:

Hydrogen Pure hydrogen burns in the air with a pale blue flame, and the mixed air ignites with a popping sound, and the product is only water. Hydrogen isn't the only gas that produces the popping sound; The igniteable gas does not have to be hydrogen.

The detection methods generally include catalytic combustion, electrochemistry, PID photoion, infrared, thermal conductivity, etc.

Electrochemical principle: The gas detection method is mainly a method of using an electrochemical reaction to detect gases.

Catalytic combustion is to detect the concentration value of the gas by principle to make the gas to be measured undergo flameless oxidative combustion, which is generally mainly used for the detection of flammable and explosive gases.

The principle of PID photoionization detection technology is mainly aimed at the detection of organic gases such as benzene, toluene, VOC and so on.

The principle technology of infrared gas detection mainly uses the characteristics of the gas absorption spectrum of the gas infrared absorption spectrum to detect the concentration.

The principle of thermal conductivity gas detection technology is mainly aimed at the detection of relatively high concentration or high purity concentration gas.

1. Add a little black cuo powder to the test tube, heat it with a gas lamp, if the black powder turns purple-red, the gas is hydrogen. 2. If it is carefully burned in oxygen, if the product can discolor anhydrous copper sulfate, the gas is hydrogen.

Hydrogen testing1. You can use a burning match to put slag in a place where there is hydrogen, if it is burned, it is hydrogen.

2. Add a little black cuo powder to the test tube, heat it with a gas lamp, and introduce hydrogen, and the black copper oxide will turn into purple-red metallic copper.

3. Let it burn in oxygen to see if the product can discolor anhydrous copper sulfate.