Nitrous oxide

Nitrous oxide, colorless and sweet gas

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This entry is made by Institute of Chemistry, Chinese Academy of Sciences, College of Chemical Sciences, University of Chinese Academy of Sciences Participate in editing and review Science Popularization China · Science Encyclopedia authentication.

Nitrous oxide or Dinitrogen oxide, also known as "nitrous oxide", with the chemical formula of N two O。 At room temperature, nitrous oxide is a colorless and nonflammable gas with a slightly sweet smell, a slight anesthetic effect, and can make people laugh. At high temperatures, nitrous oxide is a strong oxidant similar to oxygen. Nitrous oxide has important medical uses. It has the effect of anesthesia and pain relief, and is widely used in surgery and dentistry as an anesthetic. The name "laughing gas" originated from Humphry Davy, who first discovered N two Anesthetic effect of O. Nitrous oxide has been included in the list of essential drugs of the World Health Organization. Nitrous oxide is also used as an oxidant for rocket propellants and to increase the power output of engines in racing cars.

Nitrous oxide is the main scavenger of stratospheric ozone, and its effect is equivalent to that of chlorofluorocarbons. Nitrous oxide is used as propellant for a wide range of purposes, from rocket launch to the production of fresh cream. Nitrous oxide can act on the central nervous system. Long term or large dose use will lead to hypoxia of the brain, damage to the nervous system, lethargy, depression or insanity, and even endanger life when the symptoms are serious.^[21]

Chinese name: Nitrous oxide
Foreign name: nitrous oxide
Alias: Laughing gas 、 Nitrous oxide
chemical formula: N two O
molecular weight: forty-four point zero one three
CAS login number: 10024-97-2
EINECS login number: 233-032-0
Melting point: -90.8 ℃
Boiling point: -88.48 ℃^[1]
Density: 1.9775 kg/m³^[2] (Gas)
Appearance: Colorless and sweet gas
Application: Motor racing propellant, performance, anesthetic
Security description: S38

Hazard symbol: O
Hazard description: R8
UN dangerous goods number: one thousand and seventy
Magnetic susceptibility: −18.9·10 −6 cm three /mol
Refractive index: 1.000516 (0 °C, 101.325 kPa)
Viscosity: 14.90 μPa·s^[3]
Solubility: Slightly soluble in water, soluble in alcohol, ether, concentrated sulfuric acid
molecular structure: Linear, symmetry C ∞v
dipole moment: 0.166 D
Standard molar entropy: 219.96 J/(K·mol)
Standard enthalpy of formation: 81.60 kJ/mol
appearance: Colorless and sweet gas
application: Motor racing propellant, performance, anesthetic

catalog

A brief history of research

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Joseph Priestley, a British natural philosopher and chemist, first synthesized nitrous oxide in 1772, and called it "combustible nitrogen air". Priestley published his discovery in his book Experiment and Observation of Different Types of Air (1775), and described how to prepare the gas by heating iron chips soaked with nitric acid^[4] 。

Early discovery and use

Thomas Beddoes and James Watt jointly published the book "Considerations about Medical Use and Making Fictional Air" (1794), which laid the foundation for the application of nitrous oxide. This book is important for two reasons. First, James Watt invented a new device for producing "imaginary air" (including nitrous oxide) and a new "respirator" for inhaling gas. Secondly, the book also introduces Thomas Beddoes' new medical theory that tuberculosis and other lung diseases can be treated by inhaling "imaginary air"^[5] 。

The machine is composed of three parts: a furnace for burning the required materials, a container with water, the generated gas passes through a spiral tube (used to remove impurities), and finally a cylinder with a barometer. The generated gas can be loaded into a portable air bag (made of impermeable oily silk). The respirator consists of a portable air bag and a tube connected to the blowing nozzle. In 1798, Thomas Beddoes established the "Medical Air Disease Alleviation Agency", paving the way for clinical trials. In 1800, Chemistry and Philosophical Research was published. In this book, David mentioned the analgesic effect of nitrous oxide and pointed out its potential for surgery^[6] 。

Although David found that inhaling nitrous oxide could reduce pain, it took many years for doctors to try to use it for anesthesia. Since 1799, nitrous oxide has been used as a recreational drug in the "laughing gas party" mainly arranged for the British upper class. Laughing gas usually makes users drowsy, dreamy and calm, but some people "giggle" when they are excited.

Anesthetic use

In 1844, dentist Horace Wells, with the help of Gardner Quincy Colton and John Mankey Riggs, proved that nitrous oxide made patients insensitive to the pain caused by tooth extraction. In the following weeks, Wells treated more than a dozen patients with the gas. According to his records, only two patients failed. Although Wells reported these results to the Boston Medical Association in December 1844, this new method was not immediately adopted by other dentists. Until 1863, Gardner Quincy Colton successfully used this method in his clinic. In the following three years, Colton and his colleagues successfully administered nitrous oxide to more than 25000 patients^[7] 。

However, nitrous oxide is not a strong enough anesthetic to be used for major operations in hospitals. In 1876, Joseph Thomas Clover invented "Gas Ether Inhalator ". Subsequently, the general practice of hospitals is to use mild nitrous oxide for initial anesthesia treatment, and then use stronger ether or chloroform to gradually increase the anesthetic effect. Until the 1930s, many hospitals were still using this equipment. Although modern hospitals use more advanced anesthesia machines, they still use the same principle as Clover's inhaler. Before using stronger anesthetics, use nitrous oxide to start anesthesia^[6] 。 Nowadays, nitrous oxide is used as an anti anxiety agent in dentistry, and is an auxiliary drug of local anesthetics.

Physical and chemical properties

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Density: 1.977 kg/m ³ (gas)

Melting point: - 91 ℃

Boiling point: - 88 ℃

Refractive index: 1.469

Critical temperature: 36.5 ℃

Lewis structure

The nitrous oxide molecule has a linear structure. One nitrogen atom is connected to the other, and the second nitrogen atom is connected to the oxygen atom. The Lewis structural formula of nitrous oxide is shown in the figure, which can be regarded as a resonant hybrid of two structures. In the structure shown in the left figure, the central nitrogen forms four bonds (forms three bonds with another nitrogen, and forms a single bond with oxygen). Nitrogen contributes its lone pair electrons to the bond formed with oxygen, so nitrogen has a positive charge and oxygen has a negative charge.

N two Hybridization of O

In the calculation of hybridization, the most common form of nitrous oxide should be considered. In this form, there is a triple bond between two N atoms and a single bond between N and O. This involves mixing atomic orbitals with similar energies to form a number of mixed orbitals or hybrid orbitals whose orientation in space allows them to overlap with subsequent appropriate orbitals. If the orbits have the same energy, it is called equal hybridization; If the energies of mixed orbits are different, it is called unequal hybridization. Where, the end N and the center N are both sp hybrids, and the end O is sp three Hybridization.

N two O bond angle

Through hybridization, we know that the central N atom of nitrous oxide is sp hybridization, so the bond angle of N-N-O is 180 o 。

Because the terminal O atom is sp three Hybrid, so the molecular shape around the terminal O atom is slightly tilted.

Note that N two O is linear, while NO two It is curved. Therefore, NO two The dipole moment of is higher than N two O， So NO two Is more polar.

Preparation method

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industrial production

The industrial preparation method of nitrous oxide is to convert ammonium nitrate into o It is heated carefully at the temperature of C, and then decomposed into nitrous oxide and water vapor. The addition of various phosphates is conducive to the formation of more pure gas at a slightly lower temperature. However, as ammonium nitrate is very sensitive to heat, a slight carelessness will lead to an explosion accident.

Laboratory production

Method 1: The decomposition of ammonium nitrate is also a common method for preparing this gas in the laboratory. Similarly, it can also be heated Sodium nitrate and ammonium sulphate To obtain this gas.

Method 2: reaction of urea, nitric acid and sulfuric acid.

Method 3: Ammonia is directly oxidized with manganese dioxide bismuth oxide catalyst.

Method 4: Hydroxy ammonium chloride reacts with sodium nitrite to produce nitrous oxide. If nitrite is added to the hydroxylamine solution, the only by-product left is brine. However, if the hydroxylamine If the solution is added to the nitrite solution (excessive nitrite), other toxic high valence nitrogen oxides may also be formed.

Method 5: Nitric acid reacts with tin chloride and hydrochloric acid.

Method 6: Continuous secondary nitric acid at 25 ℃ o C. Decomposition into nitrous oxide and water at pH 1-3^{[8 ]} 。

application area

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rocket engine

Nitrous oxide can be used as an oxidant for rocket engines. Compared with other oxidants, it has the advantage of much less toxicity, and because it is stable at room temperature, it is also easier to store, and it is relatively safe to carry in flight. Secondly, it is also easy to decompose to form nitrogen and oxygen. The density of nitrous oxide is high and the storage pressure is low (at low temperature), so it has strong competitiveness compared with other high-pressure gas storage systems.

In a patent issued in 1914, Robert Goddard, the American rocket pioneer, proposed to use nitrous oxide and gasoline as liquid fuel propellants for rockets. In some rocket designs (using solid fuel+liquid or gaseous oxidants), nitrous oxide is often the preferred oxidant. SpaceShipOne and some other rockets use a combination fuel of nitrous oxide and hydroxyl terminated polybutadiene^[10] 。

Nitrous oxide can also be used in single propellant rockets. Under the action of heated catalyst, nitrous oxide will o It is exothermically decomposed into nitrogen and oxygen at the temperature of C. In vacuum thrusters, although the role of nitrous oxide is lower than that of hydrazine thrusters (single propellant or dual propellant containing nitrous oxide), its low toxicity makes it a choice worthy of further study.

internal-combustion engine

In racing, nitrous oxide can provide more oxygen during combustion, so that the engine can burn more fuel. The increase of oxygen can increase the injection amount of fuel and make the engine produce more power. This gas is not flammable at low pressure/temperature, but it decomposes at high temperature (about 300 ℃), providing more oxygen than air. Therefore, it is usually mixed with another fuel that is more prone to deflagration. Nitrous oxide is a kind of strong oxidant, its oxidizability is roughly equivalent to hydrogen peroxide, much stronger than oxygen.

Nitrous oxide is stored as a compressed liquid. The evaporation and expansion of liquid nitrous oxide in the intake manifold will cause a sharp drop in the intake air temperature, allowing more air/fuel mixture to enter the cylinder. Sometimes, nitrous oxide will be injected into the intake manifold (or before the intake manifold), while other systems will be injected directly in front of the cylinder (direct nozzle injection) to increase power.

One of the main problems of using nitrous oxide in reciprocating engines is that it can produce enough power to damage or destroy the engine. If the mechanical structure of the engine is not properly reinforced, the engine may be seriously damaged or destroyed during this operation.

medicine

As an anesthetic and analgesic, nitrous oxide has been used in dentistry and surgery since 1844^[11] 。 Nowadays, in hospitals, people use this gas through anesthetic evaporators and medical respirators, which can accurately deliver nitrous oxide mixed with oxygen.

Nitrous oxide is a weak anesthetic, so it is generally not used alone for general anesthesia, but as the carrier gas (mixed with oxygen) of other powerful general anesthetics, often used together with halothane, methoxyflurane, ether or intravenous general anesthetics. It is now used less. N two O It is used for anesthesia and has no irritation to respiratory tract and no damage to heart, lung, liver, kidney and other important organs. Without any biotransformation or degradation in the body, most of them are still discharged from the body with the breath of the original drug, only a small amount is evaporated from the skin, without accumulation. It only takes 30-40 seconds for inhalation to produce analgesic effect. The analgesic effect is strong but the anesthetic effect is weak. The patient is in a conscious state (not an anesthetic state), which avoids the complications of general anesthesia and recovers quickly after surgery. The use of nitrous oxide during anesthesia will increase the risk of postoperative nausea and vomiting.

matters needing attention

1. For major surgery, thiopental sodium and muscle relaxants should be used; The oxygen concentration in the inhaled gas shall not be less than 20%; After termination of anesthesia, pure oxygen should be inhaled for 10 minutes to prevent hypoxia.

2. When the patient has low blood volume, shock or obvious heart disease, it can cause severe hypotension. Nitrous oxide may also be harmful to patients with pulmonary thromboembolism.

contraindication

(1) Pneumocyst; (2) Intestinal obstruction and flatulence; (3) Pneumothorax; (4) Qi brain; (5) High head position craniotomy

Function and use

Inhalation of high-purity nitrous oxide will quickly cause anesthesia and asphyxia, so it must be mixed with oxygen. The induction time of anesthesia is short, and if the maintenance dose is not supplemented, the patient can recover quickly. This product can be used for maintaining anesthesia of horses, ruminants, dogs and cats.

The dentist uses a simpler machine that only provides N two O/O two Mix the gas and let the patient inhale it in a conscious state. The patient can stay awake throughout the process and have enough mental ability to answer the dentist's questions and instructions.

Inhalation of nitrous oxide is often used to relieve pain caused by childbirth, trauma, oral surgery and acute coronary syndrome (including heart attack). Facts have proved that the use of nitrous oxide during childbirth can safely and effectively help women who give birth.

food processing aids

It is used as foaming agent and sealant in the food industry.

Calculate chemical data

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Reference value for drainage parameter calculation (XlogP): 0.5

Number of hydrogen bond donors: 0

Number of hydrogen bond receptors: 2

Number of rotatable chemical bonds: 0

Number of tautomers: 0

Topological molecular polar surface area: 19.1 Å ²

Number of heavy atoms: 3

Surface charge: 0

Complexity: 25.8

Number of isotope atoms: 0

Determine the number of atomic structure centers: 0

Number of uncertain atomic structure centers: 0

Determine the number of chemical bond structure centers: 0

Number of uncertain chemical bond structure centers: 0

Number of covalent bond units: 1^[2]

Molecular structure data

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Molar refractive index: 8.35

Molar volume (cm three /mol）：29.9

Isotonic specific volume (90.2K): 86.9

Surface tension (dyne/cm): 70.7

Polarization (10 -24 cm three ）：3.31^[9]

security information

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Safety terminology

S38：In case of insufficient ventilation, wear suitable respiratory equipment.

Wear proper respirator in case of poor ventilation.

Risk terminology

R8：Contact with combustible material may cause fire.

Contact with combustible materials may cause fire

Nitrous oxide is a serious occupational hazard for surgeons, dentists and nurses. As the metabolic rate of nitrous oxide in the human body is extremely low (only 0.004%), it can still maintain its effectiveness when the patient breathes it into the room. If the room is poorly ventilated, it will cause the risk of poisoning and long-term exposure to clinic staff. When applying nitrous oxide, a continuous flow fresh air ventilation system or N two O Scavenger system to prevent the accumulation of exhaust gases.

Mental and physical injuries

Exposure to nitrous oxide will lead to a short-term decline in mental status, audio-visual ability and hand flexibility. These impacts, together with the induced space and time loss, may lead to environmental hazards and cause bodily harm to users^[13] 。

Neurotoxicity and neuroprotection

Nitrous oxide has neurotoxicity. There is evidence that long-term habitual intake of large amounts of nitrous oxide will cause damage to the nervous system. If not treated in time, it may cause permanent damage^[14] 。

Like other NMDA receptor antagonists, some people believe that nitrous oxide will produce neurotoxicity after long-term (several hours) exposure in rodents, which is manifested as Orney's disease^[15] 。 Some people think that because N two O will be rapidly discharged from the body under normal conditions, so it is less likely to produce neurotoxicity than other NMDAR antagonists^[16] 。 In fact, in rodents, short-term exposure to nitrous oxide can only cause slight damage, and this damage can be quickly reversed. Only after continuous exposure to nitrous oxide can neurons die [15] 。 Prolonged exposure to nitrous oxide may also cause neurotoxicity due to hypoxia.

In the case of a large amount of drug (≥ 400g or ≥ 200L N) reported to the US Poison Control Center two O gas) or frequent (frequent use, that is, daily or weekly use) users have found signs of peripheral neuropathy: dyskinesia (abnormal gait) or paralysis (sensory abnormalities, such as tingling, numbness, tingling, mainly in the limbs). These symptoms are considered to be early signs of nervous system damage and indicate chronic poisoning^[17] 。

75% volume of nitrous oxide can reduce neuron death caused by ischemia due to occlusion of middle cerebral artery in rodents, and can reduce NMDA induced Ca in neuron cell cultures 2+ Inflow, which is a key factor of excitatory poisoning.

DNA damage

Nitrous oxide is related to DNA damage, which is caused by the interruption of DNA synthesis^[18] 。 This correlation is dose related. However, further research is needed to confirm the exposure time and amount required to cause damage.

hypoxia

If pure nitrous oxide is inhaled without oxygen, hypoxia will occur, leading to hypotension, fainting and even heart attack. This will happen if the user continuously inhales a large amount of nitrous oxide, such as using a belt mask connected to the gas tank. This can also happen if the user holds his or her breath excessively or uses any other suction system that cuts off the fresh air supply.

Vitamin B12 deficiency

Long term exposure to nitrous oxide may cause vitamin B twelve Deficiency. It will oxidize vitamin B twelve Cobalamin in is inactivated. Subclinical vitamin B twelve Deficiency patients may develop vitamin B within days or weeks after exposure to nitrous oxide anesthesia twelve Symptoms of deficiency include sensory neuropathy, myelopathy, and encephalopathy. These symptoms can be treated with large doses of vitamin B twelve But the recovery may be slow and incomplete.

Nitrous oxide on vitamin B twelve People with normal levels have little effect unless they are exposed to nitrous oxide repeatedly for a long time. With vitamin B twelve People lacking risk factors should check vitamin B before using nitrous oxide anesthesia twelve Horizontal.

Prenatal development

Experimental studies on rats show that long-term exposure of pregnant women to nitrous oxide may have adverse effects on developing fetuses^[19] 。

Chemical/Physical Risk

The pressure curve of nitrous oxide is sensitive to temperature. In addition, like many strong oxidizers, rocket launch accidents are also related to fuel contaminated components. In these accidents, a small amount of nitrous oxide/fuel mixture will explode because the heat generated by adiabatic compression of gas reaches the decomposition temperature. The decomposition of nitrous oxide in pipelines leads to the explosion of large storage tanks from time to time.

Protective measures and leakage emergency treatment

Protective treatment

Respiratory system protection: no special protection is generally required. In case of high concentration contact, wear a self-priming filter type gas mask (half mask).

Eye protection: no special protection is generally required.

Body protection: wear general work clothes.

Hand protection: wear chemical resistant gloves.

Other protection: Avoid high concentration inhalation. When entering tanks, confined spaces or other high concentration areas for operation, someone must supervise.

Leakage emergency treatment

Evacuate the personnel in the leakage contaminated area to the windward place quickly, isolate them, and strictly restrict access. It is recommended that emergency personnel wear self-contained positive pressure respirators and general work clothes. Cut off the leakage source as much as possible. Reasonable ventilation to accelerate diffusion. Leaking containers shall be properly treated, repaired and inspected before reuse.

Pharmacopoeia information

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source^[12]

This product contains N two O shall not be less than 95.0% (mL/mL).

character

This product is colorless gas, no significant odor, slightly sweet, heavier than air.

The product is easily soluble in water or ethanol and dissolved in ether at 20 ℃ and 101.3 kPa (760 mmHg) air pressure.

identify

1. This product can make the red wood stick burn.

2. Take this product and mix it with equal volume nitric oxide [take 5g of sodium nitrite and 2.5g of potassium iodide, put them in a test tube, add 15mL of water to dissolve them, and then drop sulfuric acid solution to produce nitric oxide], without red smoke (different from oxygen).

inspect

1. pH

Take 0.3 mL of methyl red indicator solution and 0.3 mL of bromothymol blue indicator solution, add 400 mL of water to boil for 5 minutes, cool down, take 100 mL of each, put them into three colorimetric tubes A, B, and C, add 0.2 mL of hydrochloric acid titrant (0.01 mol/L) to tube B, add 0.4 mL of hydrochloric acid titrant (0.01 mol/L) to tube C, and then pass 2000 mL of the product into tube B (at a rate of 4000 mL per hour), The color of tube B shall not be darker than the orange red of tube C or the yellow green of tube A.

2. Carbon monoxide

Take 5000-10000 mL of this product, and make it pass through (1) saturated sulfuric acid solution of chromium trioxide, (2) solid potassium hydroxide, (3) phosphorus pentoxide and other washing devices in turn, and then pass through the tube storing iodine pentoxide that has been dried at 200 ℃, keep the temperature at 120 ℃, and the iodine vapor released is introduced into the conical flask storing potassium iodide test solution. After passing through this product, Then introduce 5000mL of air without carbon monoxide (the air can be passed through the cuprous chloride solution to remove carbon monoxide) to remove the carbon monoxide remaining in the instrument. After passing through the tube containing iodine pentoxide, titrate with sodium thiosulfate titrant (0.002 mol/L), and use 5000mL of air without carbon monoxide for blank test correction. At 25 ℃ and 101.3 kPa (760 mmHg) air pressure, every 1mL of sodium thiosulfate titrant (0.002 mol/L) is equivalent to 0.112 mL of CO, and the carbon monoxide content of this product should not exceed 0.005% (mL/mL).

3. Carbon dioxide

Take 50 mL of clarified barium hydroxide test solution and put it into the colorimetric tube. Pour 1000 mL of this product into the colorimetric tube. In case of turbidity, it shall not be thicker than the control solution (take 0.10 g of sodium bicarbonate, add 100 mL of newly boiled cold water to dissolve it, take out 1.0 mL, and add 50 mL of clarified barium hydroxide test solution).

4. Halogen

Take two colorimetric tubes A and B, add 1mL of silver nitrate test solution and 50mL of water respectively, shake well, and then pour 2000mL of this product into tube A, which should be clarified as tube B.

5. Easily returned objects

Take two colorimetric tubes A and B, add 15mL of newly prepared potassium iodide starch indicator solution respectively, add one drop of glacial acetic acid to make it acidic, and put 2000mL of this product into tube A, and the color of tube A should be the same as that of tube B.

6. Easy oxides

Take two colorimetric tubes A and B, add 50 mL of water and 0.20 mL of potassium permanganate titrant (0.02 mol/L) respectively, fill 2000 mL of this product into tube A, and the color of tube A should be the same as that of tube B.

7. Hydrogen arsenide and phosphine

Take the device under the Arsenic Salt Inspection Method (General Rule 0822, Method 1), remove the conical flask A, put a piece of mercuric chloride test paper on the top plane of the cock D, slowly fill 2000 mL of the product, and no spots shall be generated on the mercuric chloride test paper.

8. Moisture

Take the absorption tube with phosphorus pentoxide stored in it, put it into the product, drive out the air, weigh it, and then pass a certain amount of the product, weigh it, the water content of the product per 1000 mL shall not exceed 2 mg.

Assay

1. Apparatus

As shown in the figure, A is a round glass tube with a volume of about 15ml. The lower part is thick and the upper part is thin and long, with 10 graduation lines. The volume of each small cell is 1% of the whole tube. The glass tube is connected to the upper double hole piston B at 100%, the first graduation line is 99%, and the lower graduation line is 98% to 90%. B and C are double hole pistons, D and F are curved tubes, and E and G are straight tubes.

Drainage parameter calculation reference value (XlogP)	zero point five
Number of hydrogen bond donors	zero
Number of hydrogen bond receptors	two
Number of rotatable chemical bonds	zero
Number of tautomers	zero
Topological molecular polar surface area	fifty-four point five
Number of heavy atoms	three
surface charge	zero
Complexity	twenty-nine point three
Number of isotope atoms	zero
Determine the number of atomic geometric centers	zero
Number of atomic geometric centers in uncertainty	zero
Determine the number of chemical bond stereocenters	zero
Number of uncertain chemical bond stereocenters	zero
Number of covalent bond units	one

1. Determination method

Take the dry instrument, turn it upside down, open the piston C, close the piston B, and take another thin rubber tube to siphon water from the water storage bottle. The rubber tube is connected with the conduit E. The instrument is lifted up to make the piston B above the liquid level of the water storage bottle. Open the piston B, and the instrument slowly drops to make the water fill the piston B hole. Immediately close the piston B, position the instrument, make the piston B on the top, and rotate the piston B, Connect conduit D with glass tube A. The product is introduced from the guide tube F or G, after several minutes, quickly close the piston C, then close the piston B, keep the instrument position below the liquid level of the water storage bottle, slightly open the piston B, put in a few drops of water, close the piston B, shake, then open the piston B, put in a little water, close the piston B, shake. Open the piston C, drain most of the water from the glass tube A, close the piston C, do not drain all of the water to prevent air from entering, then open the piston B, put a little water, shake, drain the water, repeatedly operate for many times, until the product is completely dissolved, and the volume of gas in the glass tube A will no longer decrease. At this time, both pistons B and C are closed. Connect the rubber tube of the water storage bottle with the guide tube F or G. Use water to exhaust the air in the piston C duct. Lift up the instrument, open the piston C. When the liquid level in the glass tube is equal to the liquid level in the water storage bottle, make the pressure in the tube equal to the atmospheric pressure, close the piston C, read the scale number, and calculate the volume of nitrous oxide according to the volume of unabsorbed gas.

During inspection or measurement, the gas accumulator shall be placed at 23~27 ℃ for more than 6 hours.

Pharmacological mechanism

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The pharmacological mechanism of nitrous oxide is not completely clear. However, it has been proved that it can directly regulate a variety of ligand gated ion channels, which may be the main source of its many roles.

Its main mechanism of action is to inhibit the central excitatory NMDA receptor, GABA receptor, spinal post synaptic opioid receptor and some downstream pathway proteins to show sedative and analgesic effects. The partial analgesic effect of nitrous oxide may be mediated by the dopamine D2 receptor in the nucleus accumbens shell region^[20] 。 It can also activate the double hole domain K + Channel. Although N two O can affect many ion channels, but its anesthetic, hallucinogenic and excitatory effects may be mainly or completely generated by inhibiting NMDA receptor mediated current. In addition to the effect on ion channels, nitrous oxide may also play a role in mimicking nitric oxide (NO) in the central nervous system, which may be related to its analgesic and anti anxiety properties. Nitrous oxide is 30 to 40 times more soluble than nitrogen.

environmental effect

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In environmental science research, especially in the field of global climate change, N two O is usually called nitrous oxide, which is a greenhouse gas with greenhouse effect and global warming. It is one of the six greenhouse gases specified in the Kyoto Protocol. N two O exists in the atmosphere for a long time and can be transported to the stratosphere, leading to the destruction of the ozone layer, causing ozone holes, exposing humans and other organisms to the radiation of solar ultraviolet rays, causing damage to human skin, eyes and immune system.

Compared with carbon dioxide, although N two The content of O in the atmosphere is very low, belonging to trace gas, but its single molecule warming potential is 298 times that of carbon dioxide (IPCC, 2007); The warming effect on global climate will become more and more significant in the future two The increase of O concentration has aroused great concern of scientists. The research on this issue is in depth.

Atmospheric N two One of the important sources of O is farmland ecosystem. In the soil, N two O is produced by nitrification and denitrification microorganisms. People apply excessive nitrogen fertilizer to farmland to promote microbial activities, and transform nitrogen into N through nitrification and denitrification two O。 The biological denitrification, nitrification and denitrification process of sewage will also cause the discharge of nitrous oxide. The limitation of dissolved oxygen, the accumulation of nitrite and the oxidation of hydroxylamine are all reasons for the generation of nitrous oxide.

management information

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Operation management : Closed operation, providing good natural ventilation conditions. Operators must be specially trained and strictly abide by the operating procedures. Keep away from kindling and heat sources, and smoking is strictly prohibited in the workplace. Keep away from flammable and combustible materials. Prevent gas leakage into the air of the workplace. Avoid contact with reducing agent. The cylinder and accessories shall be handled with care to prevent damage. Fire fighting equipment and leakage emergency treatment equipment of corresponding types and quantities shall be provided.

Storage management : Store in a cool and ventilated warehouse. Keep away from kindling and heat sources. The warehouse temperature should not exceed 30 ℃. It shall be stored separately from combustible (combustible) materials and reducing agents, and mixed storage is strictly prohibited. The storage area shall be equipped with leakage emergency treatment equipment.

Transportation management : The safety helmet on the cylinder must be worn when the cylinder is used for transportation. Cylinders are generally placed horizontally, and the mouth of the cylinder should be in the same direction, not crossed; The height shall not exceed the protective fence of the vehicle, and shall be firmly clamped with triangular wood pad to prevent rolling. It is strictly prohibited to mix with combustibles or combustibles, reducing agents, etc. Transport in the morning and evening in summer to prevent sunlight exposure. It is forbidden to slip during railway transportation.

Abandonment management : Please refer to relevant national and local regulations before disposal. Exhaust gas is discharged directly into the atmosphere.

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