Formaldehyde detection of formaldehyde content in indoor air environment can be divided into:
(1) AHMT spectrophotometry
The main method for spectrophotometric determination is acetylacetone Method, chromium acidification method, MBTH method, parafuchsin method, AHMT method, etc. 1.1 Acetylacetone method The principle of the acetylacetone method is to use formaldehyde, acetylacetone and ammonia to generate the yellow compound diacetyldihydrolutidine, and then perform spectrophotometric measurement at 412nm. The biggest advantage of this method is that it is easy to operate, has stable performance, small error, and is not interfered by acetaldehyde. The colored solution can exist stably for 12 hours. The disadvantage is that the sensitivity is low, and the minimum detection concentration is 0.25 mg/L, which is only suitable for higher Determination of the concentration of formaldehyde; the disadvantage of the method is that the reaction is slow and takes about 60 minutes; SO2 interferes with the determination (this can be eliminated by using NaHSO3 as a protective agent). This method is very traditional and widely used. 1.2 Chromotropic acid method (CTA method) Chromotropic 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 form a purple compound. The maximum absorption wavelength of this compound is at 580nm, which can be analyzed and determined by spectrophotometry. Changing the concentration of chromotropic acid and using different sampling methods can meet the needs of different concentrations of formaldehyde detection. Using 0.1 chromotropic acid-86 sulfuric acid solution as the absorption liquid, the detection limit can reach 20 μg/L; using 1 1 sodium sulfite solution to absorb formaldehyde, and changing the chromotropic acid concentration to 5, the method is more stable and sensitive. The advantage of this method is that it is easy to operate, fast and sensitive; the disadvantage is that it is carried out in concentrated sulfuric acid medium, which is difficult to control, and aldehydes, alkenes and NO2 may interfere with the determination. 1.3 Phenol Reagent Method The principle of the phenol reagent method is that formaldehyde reacts with the phenol reagent to form an azine. The azine is oxidized by ferric ions in an acidic solution to form a blue-green compound. The color depth is proportional to the formaldehyde content. The molar absorption coefficient of this compound at 630 nm can reach ε. 7.0×104, this method is very sensitive to the determination of formaldehyde, and the lowest detection limit is 0.015mg/L. The disadvantage of the method is that the presence of acetaldehyde and propionaldehyde will interfere with the measurement results. When sulfur dioxide is present, the measurement results are low. The reaction is limited by temperature. The room temperature is lower than 15, and the color development is incomplete. The color development is most complete in 15 minutes between 20 and 35. , leave it for 4 hours, and the absorption will be stable. 1.4 Parafuchsin method (PRA) The principle of the Parafuchsin method is that in the presence of formaldehyde, sulfite ions and Parafuchsin form a purple complex with a maximum absorption peak at 570nm and a detection limit of 50μg/L. The advantage of this method is that it is simple and sensitive, and other aldehydes and phenols do not interfere with the determination; the disadvantage is that it fades quickly, is not highly sensitive, is easily affected by temperature, uses toxic mercury reagents, and requires at least 60 minutes for chromogenic compounds to achieve stable absorption. The use of flow injection technology can eliminate the shortcomings of slow color development, low sensitivity and poor stability of spectrophotometry. 1.5AHMT method The principle of AHMT method is that formaldehyde and 4-amino-3-hydrazine-5-mercapto-1,2,3-triazole (AHMT) are condensed under alkaline conditions, and then oxidized by potassium periodate to form 6-yl-5-triazole[4,3-b]-S-tetraazabenzene purple-red compound, colorimetric quantification. The advantage of this method is that it has strong anti-interference ability. Hexamine, which seriously interferes with the acetylacetone method, MBTH method and parafuchsin method, has no interference with this determination method. Therefore, this method is an effective method for measuring the formaldehyde released during the resin cross-linking process. Sensitivity Higher, the lowest detection limit is 0.01mg/m3, which is more suitable for indoor air detection under normal circumstances; the disadvantage is that the color gradually deepens with time, requiring that the color reaction time of the standard solution and the color reaction time of the sample solution must be strictly unified , measured at the maximum absorption wavelength of 550nm in the chromogenic system, Co2 and Cu2 interfere with the measurement. 1.6 Potassium bromate-methylene blue method The principle of the potassium bromate-methylene blue method is that in acidic media, formaldehyde can promote the oxidation of methylene blue by potassium bromate and reduce the absorbance of the system to quickly determine the formaldehyde content.
Methylene blue has a maximum absorption peak at 665nm. Adding KBrO3 to H2SO4 medium can slightly decrease the absorption peak. When formaldehyde is added, the absorbance will decrease significantly. The decrease in △A is proportional to the formaldehyde concentration. 1.7 Silver-Ferrozine method The principle of the silver-Ferrozine method is that hydrated silver oxide can oxidize formaldehyde and be reduced to Ag. The generated Ag reacts with Fe3 quantitatively to generate Fe2. Fe2 forms a colored complex with Ferrozine, which is measured at 562nm. Absorbance. The Fe2-Ferrozine complex is proportional to the formaldehyde concentration, the molar absorption coefficient ε=5.5 8×104, and the sensitivity is 3.5 times higher than the chromium acidification method.
(2) Phenol reagent spectrophotometry
(3) Gas chromatography
(4) Acetylacetone spectrophotometry
(5) Electrochemical sensor method
In electronic sensing equipment detection (including interscan4160 PPM400 BG FM-06 BRAMC air-328 and other equipment), the electrochemical sensor is subject to greater interference and the quantitative detection data has larger errors.
(6) Formaldehyde self-test box detection method
Formaldehyde self-test box, also known as formaldehyde test box, is commonly known as formaldehyde self-test box. It is a fast, simple and low-cost method. A semi-quantitative detection product that detects the concentration or treatment effect of formaldehyde in the air in specific spaces such as indoors and furniture.
The formaldehyde self-test box is simple to operate and easy to use, and is suitable for personal home testing of formaldehyde. The formaldehyde self-test box is small in size and easy to place. It is used to compare the formaldehyde concentration before and after furniture treatment to judge the treatment effect. Its biggest feature is that consumers can detect formaldehyde by themselves, and the operation method is simple.
The detection principle of the formaldehyde self-test kit is the nationally recommended and approved phenol reagent colorimetric method. Judging from the display results of formaldehyde detection, the formaldehyde self-test box is a semi-quantitative detection product that can fully meet people's needs for detecting formaldehyde concentration in indoor air.
Whether the results of the formaldehyde self-test box are accurate is related to many factors such as whether the reactants and color developers are stable, whether the packaging is tight, and whether the operation is correct. Different manufacturers will also have differences. Formaldehyde self-test boxes are not necessarily equally accurate. You should choose formaldehyde self-test box products from professional and regular manufacturers and big brands.
When choosing a formaldehyde self-test box, you should pay attention to the following two points:
⑴. You should choose qualified products developed by professional institutions and produced by regular large manufacturers. When purchasing online, it is best to choose brand stores with direct sales from manufacturers.
⑵. Product packaging is tight and solid. When purchasing online, don’t just look at price and sales, but also look at the results of reviews and feedback. Pay more attention to product reviews.
The basic steps for operating the formaldehyde detection box are as follows:
① Before testing, please close the doors and windows of the room to be tested for 1 hour or 2 hours (different products have different requirements). When sealing, please close it at the same time. Turn off air conditioning equipment such as air conditioners and purifiers. If necessary, open furniture cabinet doors, drawers and other suspected pollutants. (If it has been a closed space before the test, it is recommended to ventilate it for a period of time before closing it).
②Pour all the diluent liquid in the formaldehyde self-test box into the absorption box;
③Place the absorption box at the pre-selected location to be tested and expose it for 30-40 Minutes;
④ Pour the chromogen liquid completely into the absorption box and close the lid; be sure to place it out of reach of light to avoid interference from ultraviolet rays that will affect the accuracy of the results.
⑤Observe the color after 10 minutes, compare with the color chart, and read the test results; be careful to observe in a place where light cannot reach to avoid the influence of ultraviolet rays.
It is recommended to conduct post-closure testing according to the required time. First of all, formaldehyde detection method products are based on scientific principles and experimental data verification. In order to ensure the validity of the detection results, a reasonable sealing time before detection is specified.
Secondly, we test formaldehyde to clearly know the true indoor formaldehyde concentration. If the sealing time exceeds the required time, the test results may be higher than the actual pollution situation, making it inconvenient to judge.
Pay attention to the following two points when comparing colors:
First, when comparing colors with color charts, you should choose a darker place and cannot read under sunlight. , because ultraviolet rays will cause the color to turn blue, causing the color to not match, and in severe cases affecting the test results.
Secondly, when comparing colors with color comparison cards, due to individual differences of each person, the results of the same color may come to different conclusions. It is recommended to detect the formaldehyde concentration in different places at the same time with multiple different colors. It is easier to accurately identify the formaldehyde concentration range by comparing the colors. This makes the comparison clearer.