Formaldehyde is a colorless gas with a strong pungent odor. As a carcinogen, it is the key control object of many laws and regulations. If people live in a room contaminated with formaldehyde for a long time, it can cause a decline in immunity, infertility or fetal malformation, respiratory diseases, depression, leukemia, cancer and other diseases. Sources of formaldehyde in daily life: (1) Formaldehyde in the air mainly comes from industrial production and plastic parts, rubber products, urea-formaldehyde foam, automobile exhaust, etc.; (2) Indoor formaldehyde mainly comes from decorative materials, such as wood, Adhesives and wallpaper, etc.; (3) Formaldehyde can also come from cosmetics, preservatives, printing inks, paper, textile fibers, etc. Formaldehyde has a wide range of uses. Synthetic resins, surfactants, plastics, rubber, leather, papermaking, dyes, pharmaceuticals, pesticides, photographic films, explosives, building materials, and disinfection, fumigation and antiseptic processes all use formaldehyde. It can be said Formaldehyde is a generalist in the chemical industry, but the use of anything must be controlled in a limited amount and standard. Once the use exceeds the standard and limit, it will bring disadvantages. Formaldehyde detection method: The chemical properties of formaldehyde are very active, so there are many methods for quantitative analysis of formaldehyde, which can be summarized into five categories: titration, gravimetric method, colorimetry, gas chromatography and liquid chromatography. Among them, titration and gravimetric methods are suitable for the quantitative analysis of high concentrations of formaldehyde, and colorimetry, gas chromatography and liquid chromatography are suitable for the quantitative analysis of trace formaldehyde. 1. Colorimetry Colorimetry is a classic method for the determination of formaldehyde, as well as a standard method for the determination of formaldehyde in the environment. The analysis method using ultraviolet-visible light absorption spectrophotometer (UV-VIS) has great advantages in terms of analysis limit, accuracy and reproducibility. It's just that the operation is more cumbersome. The colorimetric method can be divided into different color developing reagents: (1) Acetylacetone method Acetylacetone method is an equimolar reaction of formaldehyde and acetylacetone in the presence of excess ammonium acetate to produce light yellow 2,6- Dimethyl-3,5-diacetylpyridine is colorimetrically measured at its maximum absorption wavelength of 412～415nm. The method has high precision, good reproducibility, stable color developing solution and little interference. (2) The sulfite fuchsin method (Schiff reagent method) sulfite fuchsin method is to react fuchsin (rose bengal aniline) hydrochloride with acidic sodium sulfite and concentrated salt to form fuchsin-acid sulfite. Then Under strong acid (sulfuric acid or hydrochloric acid) conditions, it reacts with acetylacetone formaldehyde to form a rose red (violet) salt. The colorimetric determination is carried out at the maximum absorption wavelength of 552～554nm. This method is simple to operate, but the sensitivity is low, the color developing solution is unstable, and the reproducibility is poor. It is suitable for quantitative analysis of higher formaldehyde content. (3) Phloroglucinol method Phloroglucinol method uses formaldehyde and phloroglucinol to generate orange-red compounds under alkaline (2.5mol/L sodium hydroxide) conditions, and performs color comparison at the maximum absorption wavelength of 460nm analysis. The advantages and disadvantages of this method are similar to the Schiff method. (4) Chromotropic acid method The chromotropic acid method is in the sulfuric acid medium, formaldehyde reacts with chromotropic acid (1,8-dihydroxynaphthalene-3,6-disulfonic acid) to generate a purple compound at the maximum absorption wavelength of 568～ Colorimetric analysis is performed at 570nm. This method has high sensitivity and good stability of the color developing solution. It is suitable for the determination of samples with low formaldehyde content, but this method is susceptible to interference and is suitable for sample processing methods for gas phase extraction. 2. In chromatographic method, because the formaldehyde molecule is too small, the peak is too fast when directly entering the GC analysis, and there is no response in the FID detector; the liquid chromatography method also flows out at the same time as the solvent peak due to the too large polarity of formaldehyde, and there is no Absorption cannot be detected. Therefore, when using chromatography to determine formaldehyde, the formaldehyde is generally derivatized first, and then determined by GC or LC. 2,4-Dinitrophenylhydrazine is a relatively stable formaldehyde derivatizing agent, which is widely used in the chromatographic determination of formaldehyde. The reaction formula of formaldehyde and 2,4-dinitrophenylhydrazine is as follows: The reaction needs to be under strong acid conditions. Then, the reaction product is extracted by organic solvent liquid extraction or solid phase extraction. Because liquid-liquid extraction or solid-phase extraction not only increases the operation steps, but also causes the loss of derivatives. Usually, formaldehyde and 2,4-dinitrophenylhydrazine are directly used for liquid chromatographic analysis under weakly acidic conditions, and no organic solvent extraction is required, which avoids the loss of the extraction process. This method is applied to the determination of formaldehyde in actual samples, with simple operation and accurate results. The test
of formaldehyde content is based on the requirements of the standard, and the operating methods are not the same. It should be considered in conjunction with the test standards and samples. If necessary, colorimetry and liquid chromatography should be used for comparison and verification to ensure the accuracy of the data. The test of formaldehyde content is a highly technically demanding project. It not only requires the operator to be proficient in the standard, but also requires the operator to have certain chemical expertise and skills. Therefore, the project should attract more attention during the operation and implementation process. More about leather testing equipment: http://www.standard-groups.com/LeatherShoes/
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