The status quo of formaldehyde determination methods in water-based coatings

Formaldehyde is a colorless, strong irritating odor gas, soluble in water, alcohol and ether, 35% to 40% of formaldehyde solution called Formarin. Formaldehyde is an important chemical raw material, is widely used in coatings (container wall coatings, interior wall coatings), artificial boards, plastics and other industrial products. Formaldehyde has an important impact on human health, the human respiratory mucosa and skin has a strong stimulating effect, will lead to headache, tears, nausea, vomiting, weakness and other symptoms, long-term exposure to low-dose formaldehyde will cause chronic respiratory diseases, memory loss, chromosomal abnormalities, immune function abnormalities, such as
C.
. In recent years, formaldehyde has become one of the main pollutants in the indoor environment due to the extensive use of decorative materials (inner wall coatings, adhesives and other materials containing formaldehyde).
In order to protect the environment and human health, the State has issued and implemented the mandatory standard "GB 18582-2008 Interior Wall Coatings limit", requiring formaldehyde content of ≤ 0.1 g/kg, the World Health Organization (WTO) and the United States Environmental Protection Agency (EPA) have listed formaldehyde as a potentially dangerous carcinogen and important environmental pollutants. Therefore, it is important to study the determination method of formaldehyde in coatings to reduce indoor pollution. At present, a lot of research work has been done in the analysis and determination of formaldehyde at home and abroad, mainly in spectro-optical method, gas chromatography (GC), liquid chromatography (HPLC), catalytic dynamics and so on. At present, the literature reports that the analysis methods of formaldehyde in coatings are different, and this paper analyzes and compares the pre-treatment methods and measurement methods of formaldehyde in water-based coatings.
1 pre-treatment method
sample pre-treatment is a process of formaldehyde extraction, which directly affects the accuracy and accuracy of formaldehyde content determination in the sample. At present, the pre-treatment methods of water-based coatings mainly include distillation method, static top-air method and solid-phase micro-extraction method.
1.1 distillation method
distillation method as a traditional method, simple equipment, low cost, the general laboratory can meet its experimental conditions, so widely used. GB18582-2008 uses the pre-treatment method of distillation to water the coating and absorb the steamed formaldehyde with distilled water. Gb18582-2008 Compared with GB 18582-2001, the former reduces the amount of samples and water used and shortens the distillation time. There are problems such as long time-consuming, unstable distilled substances and certain safety hazards in ordinary distillation methods. Shen Wenjie and others used nitrogen fixation instrument to distill formaldehyde in water-based coatings, with distilled water absorption and then determination, reducing the volume of distillation, improve sensitivity and distillation efficiency, shorten the distillation time, with easy to operate, safe, fast and other advantages.
1.2 Static top-empty method
-air method is a convenient and fast sample pre-treatment method in gas chromatography, the principle is to put the sample to be tested in a closed container, heating up by heating The volatile components are waved from the sample base, balanced in the two phases of the gas-liquid (or gas-solid), and the top gas is extracted directly for chromatography analysis to test the composition and content of the volatile components in the sample. The use of top-empty sample technology can eliminate the long and cumbersome sample pre-processing process, with easy operation, short time and other advantages.
1.3 Solid Phase MicroExtraction
Solid Phase Microextraction (SPME) is a fast, sensitive, convenient and solvent-free sample pre-treatment technology that emerged and developed in the late 1980s. Basic solid-phase micro-extraction is the extraction and pre-concentration of organic molecules in the sample through a polymer layer coated on the surface of the quartz fiber head, which is then directly pyration in the gas chromatography sampler. It simplifies the pre-processing of samples and improves detection speed and sensitivity. Yang Xiupei et al. established a SPME/GC determination method for free formaldehyde in water-based coatings by using a solid phase micro-extraction probe of 16ol/hethyl glycol polyester (CA/PGA). The use of solid-phase micro-extraction technology eliminates the interference of complex substations in coatings and improves selectivity and accuracy.
of the above three methods, distillation method is the standard method and classical method stipulated in the national standard, the method is simple, but it takes a long time, and the distillation time, distillation temperature and other factors have a greater impact on the results. If the temperature is too high in the distillation process, white foam is easy to produce in the distillation bottle, and the coking of the distilled sample solution may break down formaldehyde, thus affecting the accuracy of the measurement results. The overhead method is simple to operate and takes a short time, but the purity of the gas is high, and the interference of impurity gas needs to be avoided. Solid-phase micro-extraction method is used in association with chromatography, which is easy to operate and easy to automate. Solid phase micro-extraction is an extremely complex mass transfer process, which should strictly control the extraction temperature, extraction time, stirring rate and other factors.
2 Quantitative measurement method
2.1 dlight photometric method
dicing photometric method is the traditional method of quantitative determination of formaldehyde, the free formaldehyde in the sample is collected by distillation of the absorbed liquid, under certain conditions, with a color agent color, through a specific wavelength of absorbent measurement. The method mainly includes acetyl acetone method, phenol reagent method, by-pintain method and so on.
2.1.1 acetylacetone method
this method is the preferred method for determining formaldehyde content in coatings in national standards, which is less expensive, widely used and highly selective.
principle: formaldehyde and acetyl acetone in excess of ammonium salt conditions to produce yellow 2,5- diacetyl-1,4- dihydrohydrogenic yellow compounds, the compound at a wavelength of 412 nm has the maximum absorption, with acetylacetone color, after coloring with phosphorescometer, to determine formaldehyde content.method
: After first water vapor distillation collection, in the ammonium acetate-ammonium acetate buffer solution with acetyl acetone, in a temperature bath at 60 degrees C after 0.5 h to produce a stable yellow compound, at a wavelength of 412 nm to determine the absorbance value, its absorbance value and content in line with Lambeberbier's law. Acetyl acetone method is an ideal analytical method for determining formaldehyde content, which has been widely used in various fields. The advantage of this method is not disturbed by acetaldehyde, and good stability, small error, than color fluid can stabilize 12 h unchanged. The disadvantage is that the induction period of about 60 min is required to produce a stable biochrome material. In addition, the method has some effect on the measurement results in an SO2-containing environment, and the use of NaHSO3 as a protective agent or ammonium tetrachlorocurate as an absorbent can eliminate the effect.
acetyl acetone color agent is relatively stable, linear relationship is better, the linear range is wider, suitable for determining the higher content of formaldehyde, but because of the need for distillation, to the operator brings great inconvenience, and there is a certain toxicity, the distillation process has safety risks. When determining formaldehyde content in the inner wall coating by acetyl acetone dphosphorescication method, Wang Weiyi et al. made a correlation between the color agent acetyl acetone distillation and non-distillation treatment. Through the examination of the blank experimental calibration curve and the labeling recovery experiment of the sample, it is proved that there is a difference in color between acetylacetone reagents used without distillation and distillation, and acetylacetone without distillation cannot obtain the same accuracy as distillation. This method is suitable for coatings with free formaldehyde content of 0.005 to 0.5 g/kg, and coatings exceeding this content can be determined by this method after being diluted in moderate.
2.1.2 Phenol reagent color comparison
formaldehyde and phenolic reagent (MBTH) reaction to produce in the acidic solution by high-speed rail ions oxidized into blue compound gin, its color depth and formaldehyde content is directly related to the standard sample comparison for quantification. The compound solution has the maximum absorption peak near 635 nm, the absorbance and formaldehyde content obey the law of absorbance within a certain range, and formaldehyde can be effectively determined by hydrolight method. Phenol reagent method is simple to operate, high sensitivity, lower detection limit and lower measurement limit, better accuracy, solvent interference to the determination is small, more suitable for measuring trace formaldehyde. Generally a small amount of phenol, ethanol, other aldehyde interference determination is less, but sulfur dioxide co-existence will make the measurement results low. Phenol reagent stability is poor, Song Jianhua and others found that the measurement process is limited by time and temperature. Kei Toda et al. have improved this method by using light-emitting secondary tubes over a period of 5 min to reduce formaldehyde detection limits and improve detection sensitivity. Acid overspending will inhibit the color-showing reaction, pH to 3 to 5 best.
2.1.3 Sub-masion method
the sub-mascarin method was proposed by Schiff's as early as 1866. The method is simple to operate, has a wide range of measurements and is suitable for applications with high formaldehyde content. The principle is that sulphate and by-red produce colorless Shiv reagents, and then with aldehyde to produce fuchsia compounds, sulfuric acid to produce blue compounds, is a unique reaction of formaldehyde. The advantage of side-red method is that the specificity of formaldehyde is good, and other aldehyde and phenol do not interfere with the determination. The disadvantages are fast fading, low sensitivity, poor reproducibleness, vulnerability to temperature, the use of toxic mercury reagents, and the use of raw compounds at room temperature at least 60 min to achieve stable absorption. Munoz et al. use flow injection technology to eliminate the disadvantages of slow trachromic color, low sensitivity, and poor stability. Li Wanhai proposed an improved method to change the order of adding reagents, first adding acidic by-red, then adding sodium sulfate, eliminating the use of toxic mercury reagents, and improving the stability and sensitivity of the method. The method is used to determine formaldehyde in the air, and the desired results can be obtained.
2.2 chromatography
chromatography is a widely used formaldehyde content determination method, including gas chromatography (GC) and high-efficiency liquid chromatography (HPLC).
2.2.1 gas chromatography
gas chromatography (GC) sensitivity is high, no interference, good separation. Gas chromatography mainly has direct method, derived gas chromatography and top air chromatography.
(1) direct method.
directly into the sample generally using acid distillation method, formaldehyde distillation out, water absorption, and then sample. This method is generally used for the constant determination of formaldehyde, direct sample, the method is simple, fast and direct, avoiding the classic analysis of the need for sample pre-treatment, cumbersome operation, large reagent consumption, method selectivity and other shortcomings.
(2) derived gas chromatography.
2,4- Dinitrobenzene (DNPH) and formaldehyde react under certain conditions to produce 2,4-dinitrobenzene , which is then extracted with a very small solvent (cyclohexane, chloroform, etc.), and then separated by a column of chromatography and detected by a detector. Li Jing et al. used dichloromethane extraction in water-soluble paint to produce , qualitative and quantitative with gas chromatography-mass spectrometrometrometrometrography (GC-MS), sample repeated assay, RSD (relative standard deviation) of 3.2% to 4.8%, the detection limit is less than 5 μg/mL. Gu Xiuying et al. used derivative gas chromatography to determine the content of formaldehyde in beer, plus positive hexane extraction, using the gas chromatography of ECD detector to determine formaldehyde 2,4- dinitrobenzene derivatives, indirectly determine formaldehyde content. The detection limit is 0.014 mg/L, the accuracy is 8.0%, and the recovery rate is 92.4% to 106.0%. Huang Huiling and others established a gas chromatography detection method for trace formaldehyde in food packaging materials. After the sample is derived by DNPH and the positive hexane extracts the derivative reactant, the gas chromatography-electronic capture detector method is determined. The detection limit is 0.05 mg/kg, the relative standard deviation is 2.7% to 5.0%, and the recovery rate is 88.6% to 98.0%. Derivative gas chromatography is generally used for micro-determination of formaldehyde. The derived re-in sample has good selectivity, and between inorganic ions and some organic matter will not interfere with the experiment. Methanol, ethanol, acetic acid and so on will not interfere with the experiment, and acetaldehyde and derivative reactions, as well as formaldehyde and derivative reactions can be very good separation on the column, do not interfere with the determination. The method has the advantages of fast, high sensitivity, simple pre-treatment, low detection limit, stable derivatives, strong anti-jamming ability and easy preservation of reagents, but this method requires a high standard of equipment.
(3) top air chromatography.
top air chromatography is a new quantitative analysis of formaldehyde method, take the appropriate amount of samples in the top empty bottle, water content, sealing, constant temperature water bath for a period of time, insulation conditions to take the top gas injection gas chamber in the sample bottle, measure its peak area quantitative. Qin Guoqiang et al. used the top air chromatography system (capillary chromatography column, electronic capture detector) to detect the content of free formaldehyde in interior coatings and adhesives. Top-empty sample, calculated by external standard method, has a good linear relationship in the range of 0 to 5 g/kg concentration, and the experimental recovery rate is 101.0% to 107.7%. Mary-Anne et al. established a top-air mass spectrometry method to measure both foryic acid and formaldehyde, with a detection limit of 0.2 mg/L and a relative standard deviation (RSD) of ≤ 10%. Wu Mengli et al. studied formaldehyde in the determination of formaldehyde in sewage by automatic static top-air-capillary gas chromatography. The experimental results show that the method has a wide linear range and good correlation in the range of 0 to 10.0 mg/L (r>0.999 0); Between.0% and 3.2%, the sample's mark-up recovery rate is between 94.7% and 104.0%, the method sensitivity is high, and the detection limit is 0.69 μg/L. This method is simple, fast and highly sensitive.
2.2.2 High-efficiency liquid chromatography
formaldehyde and 2,4-dinitrobenzene (DNPH) reaction to generate , derivative product aldehyde after extraction with organic solvent enrichment, evaporated at a certain temperature, concentrated, and then dissolved or diluted with methanol or acetylene, and finally with efficient liquid chromatography to determine the content of formaldehyde in the solution.
, Zhao Jingzen and others established an intra-column derived high-efficiency liquid chromatography method of formaldehyde in interior wall coatings. The linear range is 30 to 300 mg/L, the detection limit is 5 μg/mL, the RSD of the sample test is between 1.02% and 1.51%, and the sample recovery rate is 95.90% to 102.49%. The method is simple, fast, reproducible and satisfactory in accuracy, and can be used as an effective method to determine the formaldehyde content in the inner wall coating. Wang Shengqing et al. used pre-column derived high-efficiency liquid chromatography to determine trace formaldehyde in beer, the recovery rate was between 96.1% and 102.8%, and the relative standard deviation (RSD) of sample analysis was in the range of 1.7% to 4.2%. The use of high-efficiency liquid chromatography to determine formaldehyde content, has a high sensitivity, but because the instrument is expensive, difficult to popularize.
2.3 Catalytic Dynamics
formaldehyde can catalyde certain in acidic media