Scientific nouns define Chinese names:
Dissolved oxygen English name:
Dissolved oxygen; DO
Definition 1:
The amount of oxygen dissolved in the molecular state of water under certain conditions.
Subject:
Electricity (a subject); thermal automation, power plant chemistry and metals (secondary discipline)
Definition 2:
Oxygen dissolved in the solution.
Subject:
Mechanical Engineering (first-level discipline); corrosion and protection (secondary discipline); general term for corrosion and protection (third-level discipline)
Definition 3:
Molecular oxygen dissolved in water. Its content is related to water temperature, partial pressure of oxygen, salinity, activity of aquatic organisms, and concentration of oxygen-consuming organic matter.
Subject:
Ecology (a subject); water ecology (two subjects)
Definition 4:
The amount of dissolved oxygen in a unit of water.
Subject:
Aquaculture (a subject); fishery environmental protection (two subjects)
Definition 5:
Oxygen dissolved in water in a molecular state.
Subject:
Water conservancy science and technology (a subject); hydrology, water resources (two subjects); applied hydrology (water conservancy) (three subjects)

The molecular oxygen in the air is dissolved in water and is called dissolved oxygen. The dissolved oxygen content in the water is closely related to the partial pressure of oxygen in the air and the temperature of the water. Under natural conditions, the oxygen content in the air does not change much, so the water temperature is the main factor. The lower the water temperature, the higher the dissolved oxygen content in the water. The molecular oxygen dissolved in water is called dissolved oxygen and is usually referred to as DO, expressed in milligrams of oxygen per liter of water. The amount of dissolved oxygen in water is an indicator of the self-purification ability of water bodies.
Dissolved oxygen is closely related to the partial pressure of oxygen in the air, atmospheric pressure, water temperature and water quality. At 20 ° C, 100 kPa, about 9 mg / L of dissolved oxygen in pure water. Some organic compounds biodegrade under the action of aerobic bacteria, consuming dissolved oxygen in water. If the organic matter is calculated in terms of carbon, it is known from C+O2=CO2 that 32 g of oxygen is consumed per 12 g of carbon. When the dissolved oxygen value in the water drops to 5 mg/L, some fish have difficulty breathing. Dissolved oxygen in the water is constantly replenished by the incorporation of oxygen from the air and the photosynthesis of green aquatic plants. However, when the water body is contaminated by organic matter, the oxygen consumption is severe, and the dissolved oxygen is not replenished in time, the anaerobic bacteria in the water body will quickly multiply, and the organic matter will become black and smelly due to spoilage.
Dissolved oxygen value is a basis for studying the self-purification ability of water. The dissolved oxygen in the water is consumed, and the time required to return to the initial state is short, indicating that the water body has a strong self-cleaning ability, or that the water body is not seriously polluted. Otherwise, it indicates that the water body is seriously polluted, the self-purification ability is weak, and even the self-purification ability is lost.

Determination of dissolved oxygen in water by iodometric method. The principle water sample is added with manganese sulfate and basic potassium iodide. The dissolved oxygen in the water oxidizes the low-priced manganese into high-priced manganese to form a hydroxide brown precipitate of the tetravalent dissolved oxygen electrolyte manganese. After acid addition, the hydroxide precipitate dissolves and reacts with iodide ions to release free iodine. Using starch as an indicator, the iodine released was titrated with a sodium thiosulfate standard solution, and the dissolved oxygen content was calculated based on the titration solution consumption.
2. Reagent 1, manganese sulfate solution: Weigh 480 g of manganese sulfate (MnSO4•4H2O) dissolved in water and dilute to 1000 mL with water. This solution is added to the acidified potassium iodide solution and does not produce blue color when the starch is present.
2, alkaline potassium iodide solution: weigh 500g sodium hydroxide dissolved in 300-400mL water; another 150g potassium iodide dissolved in 200mL water, after the sodium hydroxide solution is cooled, the two solutions are combined, mixed, diluted with water to 1000mL . If there is a precipitate, place it overnight, pour out the supernatant, store in a brown bottle, stopper with a rubber stopper, and store in the dark. After the solution is acidified, the starch should not appear blue.
3. 1+5 sulfuric acid solution.
4. 1% (m/V) starch solution: Weigh 1 g of soluble starch, make a paste with a small amount of water, and dilute to 100 mL with freshly boiled water. After cooling, 0.1 g of salicylic acid or 0.4 g of zinc chloride was added to preserve the corrosion.
5, 0.02500mol / L (1/6K2Cr2O7) potassium dichromate standard solution: Weighed at 105-110 ° C for 2h, and cooled 1.2258g potassium dichromate, dissolved in water, transferred to a 1000mL volumetric flask, with water Dilute to the mark and shake well.
6. Sodium thiosulfate solution: Weigh 6.2g sodium thiosulfate (Na2S2O3•5H2O) dissolved in boiling water, add 0.2g sodium carbonate, dilute to 1000mL with water, store in brown bottle, use 0.02500 before use. Calibration of mol/L potassium dichromate standard solution.
7. Sulfuric acid, ρ = 1.84.
3. Measurement step 1. Fixation of dissolved oxygen: Insert the liquid pipe into the surface of the dissolved oxygen bottle, add 1 mL of manganese sulfate solution, 2 mL of alkaline potassium iodide solution, cover the stopper, and mix for several times, and let stand. Usually fixed at the sampling site.
2. Open the stopper and immediately add 2.0 mL of sulfuric acid by inserting a pipette into the liquid surface. Cover the stopper, shake it upside down, shake until the sediment is completely dissolved, and let it stand in the dark for 5 min.
3. Pipette 100.00 mL of the above solution into a 250 mL Erlenmeyer flask, titrate with a sodium thiosulfate standard solution until the solution is light yellow, add 1 mL of the starch solution, continue titration until the blue color just recedes, and record the amount of sodium thiosulfate solution.
Fourth, in the calculation formula: M - the concentration of sodium thiosulfate standard solution (mol / L);
V - titration consumes sodium thiosulfate standard solution volume (mL).
V. Cautions 1. When the water sample contains nitrite, it will interfere with the determination. Sodium azide can be added to decompose the nitrite in the water to eliminate interference. This is added by adding sodium azide to an alkaline potassium iodide solution in advance.
2. If the water sample contains Fe3+ up to 100-200mg/L, 1mL 40% potassium fluoride solution can be added to eliminate the interference.
3. If the water sample contains oxidizing substances (such as free chlorine), it should be removed by adding a considerable amount of sodium thiosulfate.
Edit this paragraph dissolved oxygen meter portable dissolved oxygen meter has stable and reliable, easy to operate (can be operated by one hand), suitable for oxygen concentration (mg / L or ppm) and oxygen saturation percentage (%) in aqueous solutions of various industries And the temperature (T) of the measured medium is measured, and the imported oxygen electrode is used as standard, and the polarographic method is used for measurement, and the oxygen film is not required to be replaced. Technical indicators:
1. Measurement range:
Dissolved oxygen (DO): 0.0 to 20.0 mg / L
:0~100%
Temperature (T): 0 ~ 100 ° C2. Measurement accuracy:
Dissolved oxygen: ±0.2mg/L (the system to be tested is isothermal with the calibration system)
±0.5mg/L (when the system to be tested and the calibration system are ±10°C)
Temperature: ±1°C3. Automatic temperature compensation range: 0~40°C 4. Calibration point: 1 or 2 points 5. Salinity compensation setting: 0~35g/L
6. Atmospheric pressure setting: 0.5 to 1.5 atmospheres 7. Battery type: 9V battery 1 section 8. Dimensions: 75mm × 140mm × 38mm
9. Weight: less than 220g
Features:
1. Micro-processing technology, easy to operate 2. One or two-button automatic calibration 3. Automatic/manual temperature compensation and temperature measurement 4. Salinity coefficient and atmospheric pressure can be set 5. Data lock function 6. Long electrode life 7. Can store 99 sets of data 8. Data will not be lost when power is off

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