The main methods of spectrophotometric determination are acetylacetone method, chromic acid method, MBTH method, magenta method, AHMT method and so on.
2. Acetylacetone method
The principle of acetylacetone method is that formaldehyde, acetylacetone and ammonia are used to generate yellow compound diacetyl dihydrodimethylpyridine, and then the yellow compound diacetyl dihydrodimethylpyridine is determined by spectrophotometry at 4 12nm.
3. Chromogenic acid method (CTA method)
Chromogenic acid method is also called chromic acid method. Formaldehyde can react with chromotropic acid (1, 8- dihydroxynaphthalene-3,6-disulfonic acid) in concentrated sulfuric acid solution to generate purple compounds. The maximum absorption wavelength of this compound is 580nm, which can be determined by spectrophotometry. Changing the concentration of chromotropic acid and adopting different sampling methods can meet the needs of formaldehyde detection with different concentrations.
4. Phenol reagent method
The principle of phenol reagent method is that formaldehyde reacts with phenol reagent to produce azine, which is oxidized by ferric ion in acidic solution to produce blue-green compounds. The color depth is directly proportional to the formaldehyde content, and the molar absorption coefficient ε of the compound at 630nm can reach 7.0× 104. This method is very sensitive to the determination of formaldehyde, and the minimum detection limit is 0.015 mg/L/L.
5.Paramagenta method
The principle of parafuchsin method is that sulfite ion and parafuchsin form purple complex in the presence of formaldehyde, and its maximum absorption peak is at 570nm, and the detection limit is 50 μ g/L.
6.AHMT method
The principle of AHMT method is that formaldehyde is condensed with 4- amino -3- hydrazine -5- mercapto-1, 2,3- triazene (AHMT) under alkaline conditions, and then oxidized by potassium periodate to 6- yl -5- triazene [4,3-b]-s-tetraazabenzene purple compound.
7. Potassium bromate-methylene blue method?
The principle of potassium bromate-methylene blue method is that in acidic medium, formaldehyde can promote the oxidation of methylene blue by potassium bromate and reduce the absorbance of the system to quickly determine the formaldehyde content.
8. Silver-iron zine method?
The principle of silver-iron zine method is that hydrated silver oxide can oxidize formaldehyde and reduce it to Ag.
Extended data
Removal method
1, open the window for ventilation to keep indoor air circulation. It is more effective for nature to purify indoor air than any product to open the window for ventilation. We should believe that the power of nature is infinite. Even if air purification products are used, it is necessary to keep indoor ventilation, which is not only helpful for natural purification, but also helpful for air purification products to play their own adsorption role.
2. Indoor green plants, such as chlorophytum, can purify indoor air. Green plants, such as Hupilan, Chlorophytum, cactus, etc., all have the function of adsorbing formaldehyde. Putting some green plants at home can not only remove formaldehyde but also beautify the living environment. This is a way to kill two birds with one stone.
Although plants can adsorb formaldehyde, their adsorption capacity is limited, so it is not realistic to rely solely on plant in addition to formaldehyde. It can only play an auxiliary role.
Put some pineapples indoors to improve the clarity of the air.
4. Nano-adsorption: The pore size of the pores is between 0.27 and 0.98 nm, showing crystal arrangement. At the same time, there is weak electricity. The molecular diameters of formaldehyde, ammonia, benzene, toluene and xylene are all between 0.4 and 0.62 nm, and they are all polar molecules, which have the characteristics of preferentially adsorbing harmful gases such as formaldehyde, benzene and TVOC, thus achieving the effect of purifying indoor air.
5. Activated carbon adsorption
Activated carbon, bamboo charcoal and coconut charcoal all have adsorption potential, and adsorption potential is formed by the mutual attraction of carbon molecules and adsorbed molecules. The smaller the aperture, the stronger the adsorption potential. In addition, according to the theory of molecular motion, all objects are composed of molecules or atoms, and there are gaps between them, and at the same time they are in an endless state of random thermal motion, and molecules collide frequently.
According to relevant data, in the standard state, the free movement speed of formaldehyde molecule is about 450m/s, and one formaldehyde molecule collides with other molecules 109 times per second. At this time, if the diameter of the collision molecule matches the pore of the activated carbon, it is adsorbed.
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