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.
The biggest advantages of this method are simple operation, stable performance, small error, and no interference from acetaldehyde. The chromogenic solution can exist stably for 65438±02hr；. . The disadvantage is that the sensitivity is low, and the minimum detection concentration is 0.25mg/L, which is only suitable for the determination of higher concentration formaldehyde.
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. Using 0. 1% chromotropic acid -86% sulfuric acid solution as absorption solution, the detection limit can reach 20μ g/L; Using 1% sodium sulfite solution to absorb formaldehyde and changing the concentration of chromotropic acid to 5%, the method is more stable and sensitive.
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. The method is simple and sensitive, and other aldehydes and phenols do not interfere with the determination.
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-ferrous zine method is that hydrated silver oxide can oxidize formaldehyde and be reduced to Ag, and the generated Ag reacts quantitatively with Fe3+ to generate Fe? +，Fe？ +forms a colored complex with ferrizine, and the absorbance is determined at 562nm.
Extended data:
In the air:
1, all kinds of phenolic resin glue wood-based panels are used as decorative materials such as wallboard and ceiling, such as plywood, blockboard, fiberboard and particleboard.
2. Decorative materials that contain formaldehyde and may be emitted to the outside world, such as wall covering, wallpaper, paint and painted pipes.
3. Indoor furnishings and daily necessities that may emit formaldehyde, such as furniture, chemical fiber carpets, foam plastics, etc.
4. Some substances that emit formaldehyde after burning, such as cigarettes and some organic substances.
Some perfumes and mosquito killing liquids also contain formaldehyde.
Dressed:
White or non-ironing clothes, especially some jeans, underwear advertised as 100% crease-resistant and shrink-resistant or all-cotton non-ironing shirts are all shaped with glyoxal resin and all contain formaldehyde. Formaldehyde has a strong stimulating effect on human skin, which can cause skin eczema and systemic allergy.
References:
Baidu encyclopedia-formaldehyde detection