Method for detecting urea-formaldehyde resin in melamine-formaldehyde materials

Abstract

The present invention discloses a method for detecting urea-formaldehyde resin in melamine-formaldehyde materials, comprising the following steps: washing a sample powder with a hydrochloric acid solution, hydrolyzing the sample at 110°C ± 5°C for 60 min ± 5 min, filtering the sample through a polyethersulfone filter membrane to obtain a test solution; and subjecting the test solution to high-performance liquid chromatography-mass spectrometry. The detection method of the present invention achieves highly specific and sensitive identification of the presence of urea-formaldehyde resin in melamine-formaldehyde materials, providing excellent technical support for quality control and safety monitoring of food contact materials and products, and having significant economic and social benefits.

Description

Technical Field

[0001] The present invention relates to the technical field of material analysis, and more particularly to a method for detecting whether urea-formaldehyde resin is mixed in a melamine-formaldehyde material. Background Art

[0002] Melamine-formaldehyde resin (also known as melamine resin) and melamine tableware produced with it as the main raw material are widely used in homes and restaurants due to their advantages such as lightness, non-fragility, high heat deformation temperature, poor thermal conductivity, impact resistance, appearance similar to porcelain, and long service life. The main product and raw material standards involved in melamine tableware include GB / T41001-2021 "Melamine Plastic Tableware" and GB / T13451 "Plastic Powdered Melamine-Formaldehyde Molding Compounds (MF-PMCs)". Melamine tableware has also been the focus of market supervision departments and media at all levels in recent years, and product failures occur frequently.

[0003] Urea-formaldehyde resin is a resin produced by the polymerization of urea and formaldehyde. Relevant standards include the GB / T3403-2008 series of standards, "Plastic Powdered Urea-Formaldehyde and Urea / Melamine-Formaldehyde Molding Compounds (UF and UF / MF-PMCs)." Because urea-formaldehyde resin and urea / melamine-formaldehyde products appear similar to melamine-formaldehyde resin products, and urea-formaldehyde resin is significantly cheaper than melamine resin, some manufacturers, to reduce costs, add urea-formaldehyde resin (or urea) to the raw materials or use a "core coating" process to produce melamine tableware, combining a urea-formaldehyde resin base with melamine-formaldehyde resin powder as the surface material. These products have poor resistance to moisture and heat and are more likely to release harmful substances during use, potentially endangering human health. GB 4806.6-2016, "National Food Safety Standard for Plastic Resins for Food Contact," also does not list urea-formaldehyde resin as a food contact plastic resin.

[0004] Currently, the main methods for identifying melamine tableware mixed with urea-formaldehyde resin include infrared spectroscopy, nuclear magnetic resonance, thermogravimetry, etc. These methods have played a certain role in the identification of melamine tableware, but these methods have poor specificity for the analysis and identification of complex mixture systems, especially when the target content is low, it is difficult to make an accurate judgment, and the detection limit is generally above 5%.

[0005] Therefore, there is an urgent need to provide a method with strong specificity and high sensitivity for identifying whether urea-formaldehyde resin is mixed in melamine-formaldehyde material. Summary of the Invention

[0006] Based on this, the object of the present invention is to provide a method for detecting urea-formaldehyde resin in melamine-formaldehyde material.

[0007] The technical solutions for achieving the above-mentioned invention objectives include the following.

[0008] The invention provides a method for detecting urea-formaldehyde resin in a melamine-formaldehyde material, comprising the following steps: washing melamine-formaldehyde material powder to be tested with a hydrochloric acid solution, hydrolyzing the powder at 110°C±5°C for 60min±5min, and filtering the powder through a polyethersulfone filter membrane to obtain a test solution; and performing high performance liquid chromatography-mass spectrometry on the test solution. The liquid chromatography conditions include: an amino column; a gradient elution program: 0 min, 10±2% A; 1.0 min, 10±2% A; 6.0 min, 30±5% A; 10.0 min, 30±5% A; 11.0 min, 10±2% A; and 15.5 min, 10±2% A. The mass spectrometry conditions include: GAS1: 60±2psi; GAS2: 60±2psi; Curtaingas: 40±2psi; and a temperature of 650°C±20°C.

[0009] The present invention achieves highly specific and sensitive identification of urea-formaldehyde resin in melamine-formaldehyde materials by controlling key technical parameters such as the hydrolysis temperature and time during sample solution preparation, the liquid chromatography gradient elution mobile phase and elution procedure, and mass spectrometry detection conditions. Therefore, the detection method of the present invention provides excellent technical support for the quality control and safety monitoring of food contact materials and products, with significant economic and social benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 This is the extracted ion chromatogram of the characteristic hydrolysis product 61.040±0.02Da of the positive sample in Example 2 of the present invention.

[0011] Figure 2 This is the extracted ion chromatogram of the characteristic hydrolysis product 613.266±0.02Da of the positive sample in Example 2 of the present invention.

[0012] Figure 3 This is the extracted ion chromatogram of the characteristic hydrolysis product 479.183±0.02Da of the positive sample in Example 2 of the present invention.

[0013] Figure 4 This is the extracted ion chromatogram of the characteristic hydrolysis product 331.147±0.02Da of the positive sample in Example 2 of the present invention.

[0014] Figure 5 This is the extracted ion chromatogram of the characteristic hydrolysis product 155.054±0.02Da of the positive sample in Example 2 of the present invention.

[0015] Figure 6This is the extracted ion chromatogram of the characteristic hydrolysis product 145.072±0.02Da of the positive sample in Example 2 of the present invention.

[0016] Figure 7 This is the extracted ion chromatogram of the characteristic hydrolysis product 217.104±0.02Da of the positive sample in Example 2 of the present invention.

[0017] Figure 8 This is the extracted ion chromatogram of the characteristic hydrolysis product 299.119±0.02Da of the positive sample in Example 2 of the present invention.

[0018] Figure 9 This is the extracted ion chromatogram of the characteristic hydrolysis product 329.129±0.02Da of the positive sample in Example 2 of the present invention.

[0019] Figure 10 This is the extracted ion chromatogram of the characteristic hydrolysis product 185.065±0.02Da of the positive sample in Example 2 of the present invention.

[0020] Figure 11 This is the extracted ion chromatogram of the characteristic hydrolysis product 371.153±0.02Da of the positive sample in Example 2 of the present invention.

[0021] Figure 12 This is the extracted ion chromatogram of the characteristic hydrolysis product 61.040±0.02Da when urea-formaldehyde:melamine-formaldehyde = 90:10 in Example 3 of the present invention.

[0022] Figure 13 This is the extracted ion chromatogram of the characteristic hydrolysis product 613.266±0.02Da when urea-formaldehyde:melamine-formaldehyde = 90:10 in Example 3 of the present invention.

[0023] Figure 14 This is the extracted ion chromatogram of the characteristic hydrolysis product 479.183±0.02Da when urea-formaldehyde:melamine-formaldehyde = 90:10 in Example 3 of the present invention.

[0024] Figure 15 This is the extracted ion chromatogram of the characteristic hydrolysis product 331.147±0.02Da when urea-formaldehyde:melamine-formaldehyde = 90:10 in Example 3 of the present invention.

[0025] Figure 16 This is the extracted ion chromatogram of the characteristic hydrolysis product 155.054±0.02Da when urea-formaldehyde:melamine-formaldehyde = 90:10 in Example 3 of the present invention.

[0026] Figure 17This is the extracted ion chromatogram of the characteristic hydrolysis product 145.072±0.02Da when urea-formaldehyde:melamine-formaldehyde = 90:10 in Example 3 of the present invention.

[0027] Figure 18 This is the extracted ion chromatogram of the characteristic hydrolysis product 217.104±0.02Da when urea-formaldehyde:melamine-formaldehyde = 90:10 in Example 3 of the present invention.

[0028] Figure 19 This is the extracted ion chromatogram of the characteristic hydrolysis product 299.119±0.02Da when urea-formaldehyde:melamine-formaldehyde = 90:10 in Example 3 of the present invention.

[0029] Figure 20 This is the extracted ion chromatogram of the characteristic hydrolysis product 329.129±0.02Da when urea-formaldehyde:melamine-formaldehyde = 90:10 in Example 3 of the present invention.

[0030] Figure 21 This is the extracted ion chromatogram of the characteristic hydrolysis product 185.065±0.02Da when urea-formaldehyde:melamine-formaldehyde = 90:10 in Example 3 of the present invention.

[0031] Figure 22 This is the extracted ion chromatogram of the characteristic hydrolysis product 371.153±0.02Da when urea-formaldehyde:melamine-formaldehyde = 90:10 in Example 3 of the present invention. DETAILED DESCRIPTION

[0032] To facilitate understanding of the present invention, the present invention will be described more fully below. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art to which this invention pertains. The terms used in this specification are for the purpose of describing specific embodiments only and are not intended to limit the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0034] Experimental methods in the following examples, where specific conditions are not specified, generally followed conventional conditions, such as those described in Green and Sambrook et al., Molecular Cloning: A Laboratory Manual (2013), or according to manufacturer recommendations. All commonly used chemical reagents used in the examples were commercially available.

[0035] In some embodiments of the present invention, a method for detecting urea-formaldehyde resin in a melamine-formaldehyde material is disclosed. The method comprises the following steps: washing a powder of the melamine-formaldehyde material to be tested with a hydrochloric acid solution, hydrolyzing the powder at 110°C±5°C for 60 min±5 min, and filtering the powder through a polyethersulfone filter membrane to obtain a test solution; and subjecting the test solution to high performance liquid chromatography-mass spectrometry. The liquid chromatography conditions include: an amino column; a gradient elution program of: 0 min, 10±2% A; 1.0 min, 10±2% A; 6.0 min, 30±5% A; 10.0 min, 30±5% A; 11.0 min, 10±2% A; and 15.5 min, 10±2% A. The mass spectrometry conditions include: GAS1: 60±2 psi; GAS2: 60±2 psi; Curtaingas: 40±2 psi; and a temperature of 650°C±20°C.

[0036] In some embodiments, the gradient elution program is: 0 min, 10% A; 1.0 min, 10% A; 6.0 min, 30% A; 10.0 min, 30% A; 11.0 min, 10% A; 15.5 min, 10% A.

[0037] In some embodiments, the liquid chromatography conditions include mobile phase A is ammonium acetate aqueous solution, and mobile phase B is acetonitrile.

[0038] In some embodiments, the mass concentration of the ammonium acetate aqueous solution is 0.36 g / L to 0.40 g / L.

[0039] In some embodiments, the mass spectrometry conditions include: GAS1: 60 psi; GAS2: 60 psi; Curtaingas: 40 psi; Temperature: 650°C.

[0040] In some embodiments, the hydrolysis temperature is 110°C ± 2°C, and the hydrolysis time is 60 min ± 2 min.

[0041] In some embodiments, the liquid chromatography conditions further include: injection volume: 2±1 μL; flow rate: 0.4±0.1 mL / min.

[0042] In some embodiments, the mass spectrometry conditions further include:

[0043] CADGAS: 7±1

[0044] Sprayvotage: 3500±50V

[0045] TOFMS start mass: 50 ± 5 Da

[0046] TOFMS stopmass: 1000±50Da

[0047] TOFMSAccumulationTime: 0.3±0.05s

[0048] TOFMSDeclusteringPotential: 60±5V

[0049] TOFMSDPspread: 0V

[0050] TOFMSCollisionenergy:10±1V

[0051] TOFCEspread: 0V

[0052] TOFMSMSstartmass: 50±5Da

[0053] TOFMSMS stopmass: 1000±50Da

[0054] TOFMSMSAccumulationTime: 0.1±0.01s

[0055] TOFMSMSDeclusteringPotential: 60±5V

[0056] TOFMSMSDPspread: 0V

[0057] TOFMSMSCollisionenergy: 20±2V

[0058] TOFMSMSCEspread0V.

[0059] In some embodiments, after the HPLC-MS detection, a step of detecting chromatographic peaks is further included. When one or more chromatographic peaks 1 to 11 appear in the test solution, urea-formaldehyde resin is present in the test solution:

[0060] Chromatographic peak 1: mass spectrometry molecular weight 61.040±0.02Da, retention time 1.0-2.0min;

[0061] Chromatographic peak 2: mass spectrometry molecular weight 613.266±0.02Da, retention time 0.8-7.5min;

[0062] Chromatographic peak 3: mass spectrometry molecular weight 479.183±0.02Da, retention time 2.0-8.0min;

[0063] Chromatographic peak 4: mass spectrometry molecular weight 331.147±0.02Da, retention time 1.5-6.0min;

[0064] Chromatographic peak 5: mass spectrometry molecular weight 155.054±0.02Da, retention time 1.5-4.0min;

[0065] Chromatographic peak 6: mass spectrometry molecular weight 145.072±0.02Da, retention time 1.0-6.5min;

[0066] Chromatographic peak 7: mass spectrometry molecular weight 217.104±0.02Da, retention time 1.0-6.5min;

[0067] Chromatographic peak 8: mass spectrometry molecular weight 299.119±0.02Da, retention time 1.5-6.5min;

[0068] Chromatographic peak 9: mass spectrometry molecular weight 329.129±0.02Da, retention time 1.5-6.0min;

[0069] Chromatographic peak 10: mass spectrometry molecular weight 185.065±0.02Da, retention time 1.0-4.0min;

[0070] Chromatographic peak 11: mass spectrometry molecular weight 371.153±0.02Da, retention time 1.5-7.0min.

[0071] In some embodiments, the concentration of the hydrochloric acid solution is 0.10 mol / L to 0.15 mol / L.

[0072] In some embodiments, each 10 mL of the test solution contains 0.05 g to 0.07 g of the sample powder to be tested.

[0073] The method for detecting urea-formaldehyde resin in melamine-formaldehyde material of the present invention is to use high performance liquid chromatography-quadrupole time-of-flight mass spectrometry instrument (a mass spectrometry analysis technology using liquid chromatography as a separation system, electrospray or atmospheric pressure chemical ionization source as an ionization mode, and quadrupole tandem time-of-flight as a mass analyzer. Its multi-dimensional analysis parameter setting, high sensitivity, high resolution, and high acquisition speed give it extremely high chemical composition acquisition and analysis capabilities. Combined with the huge data processing function and statistical analysis function of the software, it can achieve specific screening and identification effects that conventional spectral methods cannot achieve) to detect characteristic hydrolysis products of urea-formaldehyde resin. In the preparation of the test solution, suitable water is added. With the overall coordination of key technical parameters such as decomposition temperature, liquid chromatography gradient elution mobile phase and elution procedure, and mass spectrometry detection conditions, the technical effect of highly specific and sensitively identifying whether urea-formaldehyde resin is mixed in melamine-formaldehyde materials is achieved. The detection limit of urea, the characteristic hydrolysis product of urea-formaldehyde resin, reaches 1%, with excellent sensitivity, and it can provide an accurate molecular weight (accurate to four decimal places) for the characteristic hydrolysis product. Therefore, the chromatogram will not be affected by the components contained in the matrix, and the identification method is not easily cracked by new mixing technologies. It provides excellent technical support for the quality control and safety monitoring of food contact materials and products, and has good economic and social benefits.

[0074] In the following examples, the chromatographic column used was a Yuexu Ultimate HILIC Amide 100 mm × 2.1 mm, 5 μm chromatographic column; the liquid chromatograph used was a Waters Acquity UPLC H-CLASS PLUS; and the mass spectrometer used was a Sciex X500B quadrupole time-of-flight mass spectrometer.

[0075] Example 1 A method for detecting whether urea-formaldehyde resin is mixed in melamine-formaldehyde material

[0076] The following steps are involved:

[0077] 1. Prepare standard solution

[0078] Weigh approximately 10 mg of urea standard into a 10 mL volumetric flask, dilute with water, and dilute to the mark. Mix thoroughly. The concentration of this standard stock solution is 1000 mg / L. Use a graduated pipette to transfer 2 mL of the standard stock solution to a 100 mL volumetric flask, dilute to the mark with water, and mix thoroughly. The concentration of this standard working solution is 20.0 mg / L. Then, transfer 0 mL, 0.25 mL, 0.50 mL, 1.00 mL, 2.50 mL, and 5.00 mL of the 20 mg / L standard working solution into six 10 mL volumetric flasks, dilute to the mark with water, and mix thoroughly. The concentrations of these working solutions are 0 mg / L, 0.50 mg / L, 1.00 mg / L, 2.00 mg / L, 5.00 mg / L, and 10.0 mg / L, respectively. This standard working solution is used to confirm the instrument status.

[0079] 2. Prepare the test solution

[0080] Powder the sample to be tested using a tool and mix thoroughly. Weigh 0.06g of the sample into a 2mL plastic centrifuge tube and wash the powder with 4.5mL of 0.12mol / L hydrochloric acid solution three times, discarding the washing solution. Use 4.5mL of 0.12mol / L hydrochloric acid solution to completely transfer the powder to the polytetrafluoroethylene inner tank of a 25mL hydrothermal reactor and seal the tank. Place the hydrothermal reactor in a 110°C oven for 60min±5min. Remove the reactor, cool it to room temperature, open the tank, and completely transfer the powder and liquid in the tank to a 10mL colorimetric tube. Wash the inner wall of the tank with water, transfer the washing solution to the same colorimetric tube, dilute to the mark with water, and vortex to mix thoroughly. Pass approximately 1mL of the solution through a polyethersulfone filter membrane to obtain the test solution.

[0081] At the same time, prepare a blank test solution.

[0082] 3. High performance liquid chromatography-quadrupole time-of-flight mass spectrometry detection

[0083] The standard solution, blank solution and test solution are tested on the machine to obtain the original data.

[0084] The conditions for chromatographic determination include:

[0085] Chromatographic column: amino column, 100 mm × 2.1 mm, 5 μm;

[0086] Mobile phase combination: A: 0.38 g ammonium acetate + 1 L water, B: acetonitrile;

[0087] Injection volume: 2 μL;

[0088] Flow rate: 0.4 mL / min;

[0089] Mobile phase elution program 1: 0 min, 10% A; 1.0 min, 10% A; 6.0 min, 30% A; 10.0 min, 30% A; 11.0 min, 10% A; 15.5 min, 10% A.

[0090] The mass spectrometry conditions include (using TOFMS or IDA scanning mode, electrospray ionization source, positive ion ionization mode):

[0091] GAS1: 60psi

[0092] GAS2: 60psi

[0093] Curtaingas: 40psi

[0094] CADGAS: 7

[0095] Temperature: 650℃

[0096] Sprayvotage: 3500V

[0097] TOFMS startmass: 50Da

[0098] TOFMS stopmass: 1000Da

[0099] TOFMSAccumulationTime: 0.3s

[0100] TOFMSDeclusteringPotential: 60V

[0101] TOFMSDPspread: 0V

[0102] TOFMSCollisionenergy:10V

[0103] TOFCEspread: 0V

[0104] TOFMSMSstartmass: 50Da

[0105] TOFMSMS stopmass: 1000Da

[0106] TOFMSMSAccumulationTime: 0.1s

[0107] TOFMSMSDeclusteringPotential: 60V

[0108] TOFMSMSDPspread: 0V

[0109] TOFMSMSCollisionenergy:20V

[0110] TOFMSMSCEspread0V.

[0111] 4. Results Analysis

[0112] When the urea peak, or one or more of the urea and other chromatographic peaks appear in the chromatogram of the test solution, it can be determined that the test solution contains mixed urea-formaldehyde resin:

[0113] Chromatographic peak 1 (urea): mass spectrometry molecular weight 61.040±0.02Da, retention time 1.0-2.0min;

[0114] Chromatographic peak 2: mass spectrometry molecular weight 613.266±0.02Da, retention time 0.8-7.5min;

[0115] Chromatographic peak 3: mass spectrometry molecular weight 479.183±0.02Da, retention time 2.0-8.0min;

[0116] Chromatographic peak 4: mass spectrometry molecular weight 331.147±0.02Da, retention time 1.5-6.0min;

[0117] Chromatographic peak 5: mass spectrometry molecular weight 155.054±0.02Da, retention time 1.5-4.0min;

[0118] Chromatographic peak 6: mass spectrometry molecular weight 145.072±0.02Da, retention time 1.0-6.5min;

[0119] Chromatographic peak 7: mass spectrometry molecular weight 217.104±0.02Da, retention time 1.0-6.5min;

[0120] Chromatographic peak 8: mass spectrometry molecular weight 299.119±0.02Da, retention time 1.5-6.5min;

[0121] Chromatographic peak 9: mass spectrometry molecular weight 329.129±0.02Da, retention time 1.5-6.0min;

[0122] Chromatographic peak 10: mass spectrometry molecular weight 185.065±0.02Da, retention time 1.0-4.0min;

[0123] Chromatographic peak 11: mass spectrometry molecular weight 371.153±0.02Da, retention time 1.5-7.0min.

[0124] Example 2: Detecting whether urea-formaldehyde resin is mixed in melamine-formaldehyde material sample using the method of Example 1

[0125] Seventeen food-contact melamine-formaldehyde samples (trays, plates, bowls, and dishes) were drilled out of powder using an electric drill. After the powder was collected, the test solution was prepared and tested according to the method of Example 1.

[0126] Among the 17 samples to be tested, 16 samples did not detect the characteristic hydrolysis product chromatographic peaks, and one tray sample detected all the characteristic hydrolysis product chromatographic peaks. The characteristic hydrolysis product extracted ion chromatograms are as follows: Figures 1 to 11 As shown, the chromatographic peak area × 10 -5 They are: chromatographic peak 1 (urea): 31.1, chromatographic peak 2: 5.52, chromatographic peak 3: 18.1, chromatographic peak 4: 14.6, chromatographic peak 5: 34.0, chromatographic peak 6: 21.8, chromatographic peak 7: 6.38, chromatographic peak 8: 3.99, chromatographic peak 9: 17.4, chromatographic peak 10: 29.5, chromatographic peak 11: 3.08.

[0127] Example 3 Detection limit and precision of the detection method of the present invention

[0128] Melamine-formaldehyde resin and urea-formaldehyde resin (both purchased from Guangdong Shunde Hengye Synthetic Materials Co., Ltd.) were thoroughly mixed in varying ratios. The prepared samples had mixing ratios (urea-formaldehyde:melamine-formaldehyde) of 1:99, 2:98, 5:95, 10:90, 30:70, 50:50, 70:30, and 90:10.

[0129] Weigh 5.00g each of melamine-formaldehyde resin, urea-formaldehyde resin, and mixed resins of varying proportions into ten 50mL beakers lined with tin foil. Compact with stainless steel sheets and wrap the tin foil securely. Place the beakers in a 130°C oven for 1 hour. Remove the samples and grind and mix thoroughly.

[0130] Prepare the standard working solution according to step 1 of Example 1, prepare the test solution according to step 2, and perform HPLC-QTFMS detection according to step 3. The raw data of each compound were processed according to Table 1. The extracted ion chromatograms of the characteristic hydrolysis products 12 to 22 when urea-formaldehyde:melamine-formaldehyde = 90:10 are shown as follows: Figures 1 to 11 shown.

[0131] Table 1

[0132]

[0133] 1. Urea detection limit and working curve

[0134] The urea working solution concentration is 0.5 mg / L, the chromatographic peak signal-to-noise ratio (S / N) is greater than 4, and the instrument detection limit of urea can reach 0.5 mg / L.

[0135] Urea working curve concentration range 1.0-20.0mg / L, urea working curve Area×10 -5 =0.021×Concentration 2 +1.222×Concentration+0.7538, correlation coefficient r=0.9988.

[0136] 2. Peak area and precision of characteristic hydrolysis products

[0137] Peak area of ​​each characteristic hydrolysis product × 10 -5 The values ​​are shown in Tables 2 through 12. Six replicates were performed for each of the 1% urea-formaldehyde, 5% urea-formaldehyde, 30% urea-formaldehyde, and 70% urea-formaldehyde resins. The 30% urea-formaldehyde resin was additionally measured twice on the second and third days. ND indicates no peak.

[0138] Table 2 Peak area of ​​characteristic hydrolysis product chromatographic peak 1 (urea)

[0139]

[0140] Table 3 Peak area of ​​chromatographic peak 2 of characteristic hydrolysis products

[0141]

[0142] Table 4 Peak area of ​​chromatographic peak 3 of characteristic hydrolysis products

[0143]

[0144] Table 5 Peak area of ​​chromatographic peak 4 of characteristic hydrolysis products

[0145]

[0146] Table 6 Peak area of ​​characteristic hydrolysis product chromatographic peak 5

[0147]

[0148] Table 7 Peak area of ​​characteristic hydrolysis product chromatographic peak 6

[0149]

[0150] Table 8 Peak area of ​​characteristic hydrolysis product chromatographic peak 7

[0151]

[0152] Table 9 Peak area of ​​characteristic hydrolysis product chromatographic peak 8

[0153]

[0154] Table 10 Peak area of ​​characteristic hydrolysis product chromatographic peak 9

[0155]

[0156] Table 11 Characteristic hydrolysis product chromatographic peak 10 peak area

[0157]

[0158] Table 12 Peak area of ​​characteristic hydrolysis product chromatographic peak 11

[0159]

[0160] As shown in Tables 2 to 12, the method of the present invention achieves a detection limit of 1% for urea, 2% for peaks 5 and 10, 5% for peak 6, 30% for peaks 3, 4, 7, 8, 9, and 11, and 50% for peak 2. Method stability (relative standard deviation) ranges from 4.1% to 44.9%. Detected components are reproducible across multiple tests.

[0161] Experimental Example 1 Effect of the Preparation Method of the Test Solution on the Test Results

[0162] 1. Hydrolysis temperature and time

[0163] Powder the sample to be tested using a tool and mix thoroughly. Weigh 0.06g of the sample into a 2mL plastic centrifuge tube and wash the powder with 4.5mL of 0.12mol / L hydrochloric acid solution three times, discarding the wash solution. Transfer the powder completely to the polytetrafluoroethylene inner tank of a 25mL hydrothermal reactor using 4.5mL of 0.12mol / L hydrochloric acid solution and seal the tank. The hydrothermal reactor was subjected to the following five treatment conditions: ① 110℃, 1 hour; ② 120℃, 1 hour; ③ 110℃, 1.5 hours; ④ 110℃, 2.5 hours; ⑤ 110℃, 3.5 hours.

[0164] After processing, remove the sample and cool to room temperature. Open the can and transfer all the powder and liquid in the can to a 10mL colorimetric tube. Wash the inside of the can with water. Transfer the wash solution to the same colorimetric tube, dilute to the mark with water, and vortex to mix. Pass approximately 1mL of the solution through a polyethersulfone filter to obtain the test solution.

[0165] The urea peak response in the urea-formaldehyde sample hydrolyzate was measured using a high-performance liquid chromatography-ultraviolet detector. The hydrolysis condition with the highest urea peak response was used as the final sample hydrolysis condition. The peak areas under the five conditions were: ① 32.6 mAu*s; ② 30.2 mAu*s; ③ 24.1 mAu*s; ④ 23.2 mAu*s; and ⑤ 19.4 mAu*s. Therefore, 110°C for 1 hour was used as the hydrolysis condition for sample solution preparation.

[0166] 2. Quality of the sample to be tested

[0167] The responses of the urea chromatographic peaks in 0.06g, 0.12g, and 0.18g melamine sample hydrolyzates mixed with 1% (wt / wt) urea-formaldehyde resin were compared. After comparison, the urea chromatographic peak responses in the three sample hydrolyzates were slightly different, with peak areas of 6.8E5cps*s, 6.4E5cps*s, and 7.4E5cps*s, respectively. In order to reduce the content of dissolved matter in the test solution and improve the stability of the method, 0.06g was selected as the sample mass for preparing the test solution.

[0168] Experimental Example 2: Effect of Mass Spectrometry Conditions on Detection Results

[0169] With the main goal of improving the mass spectrometry peak area of ​​urea, the following mass spectrometry ion source parameters were optimized by single factor comparison (using 10 mg / L urea standard solution as the test solution), and other detection conditions were the same as in Example 1.

[0170] 1. Temperature

[0171] Comparison of 550℃, 650℃, and 700℃

[0172] The peak areas are 1.9E5cps*s, 2.3E5cps*s, and 2.3E5cps*s, respectively.

[0173] 2. GAS1

[0174] Comparison of 55psi, 60psi, 65psi, and 70psi

[0175] The peak areas are 2.0E5cps*s, 2.2E5cps*s, 1.8E5cps*s, and 1.6E5cps*s, respectively.

[0176] 3. GAS2

[0177] Comparison of 55psi, 60psi, 65psi, and 70psi

[0178] The peak areas are 2.0E5cps*s, 2.2E5cps*s, 2.2E5cps*s, and 2.1E5cps*s, respectively.

[0179] 4. Curtaingas

[0180] Comparison of 35psi, 40psi, and 45psi

[0181] The peak areas are 2.1E5cps*s, 2.1E5cps*s, and 2.1E5cps*s, respectively.

[0182] Finally, the mass spectrometry ion source conditions of the present invention were selected: Temperature 650°C, GAS 160psi, GAS 260psi, and Curtaingas 40psi.

[0183] Experimental Example 3 Effect of Chromatographic Conditions on Detection Results

[0184] Commonly used reversed-phase liquid chromatography columns do not retain polar compounds such as urea and are therefore unsuitable for this method. Using an amino column and 5 mmol / L ammonium acetate as the aqueous mobile phase can improve compound chromatographic peak shape and enhance method stability.

[0185] After optimization of the mobile phase gradient, urea was well retained (retention time 1.5 min) and well separated from melamine, the main hydrolysis product of melamine resin (melamine retention time 2.5 min), thus avoiding interference of melamine in the determination.

[0186] Test Example 4: Effect of Identification Standards on Test Results

[0187] In addition to urea, more than 30 components (chromatographic peaks) different from those in the hydrolyzate of melamine products can be extracted from the hydrolyzate of urea-formaldehyde products. In addition to the chromatographic peaks selected by the present invention, there are also chromatographic peaks with the following mass spectrometry molecular weights: 445.201 (3.0 min, RSD is 45.9%), 289.137 (3.8 min), 529.238 (2.3 min, RSD is 123.2%), 467.187 (3.8 min), 341.131 (3.5 min, RSD is 55.2%), 353.112 (2.7 min, RSD is 48.2%), 311.108 (3.7 min), 407.154 (2.6 min, RSD is 120.5%), etc.

[0188] After comparing the component responses and investigating the stability of the method, 11 components (including urea, Table 1) were selected as target components for identifying melamine products mixed with urea-formaldehyde resin.

[0189] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0190] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be determined by the appended claims.

Claims

1. A method for detecting urea-formaldehyde resin in melamine-formaldehyde material, characterized in that: The following steps are involved: Wash the melamine-formaldehyde material powder to be tested with hydrochloric acid solution, place it at 105℃~115℃ for hydrolysis for 55min~65min, and filter it through a polyethersulfone filter membrane to obtain the test solution; The test solution was subjected to high performance liquid chromatography-mass spectrometry detection; When the test solution shows chromatographic peak 1, or chromatographic peak 1 and one or more of chromatographic peaks 2 to 11, urea-formaldehyde resin is present in the test solution: Chromatographic peak 1: mass spectrometry molecular weight 61.040±0.02 Da, retention time 1.0-2.0 min; the chromatographic peak 1 is a urea peak; Chromatographic peak 2: mass spectrometry molecular weight 613.266±0.02 Da, retention time 0.8-7.5 min; Chromatographic peak 3: mass spectrometry molecular weight 479.183±0.02 Da, retention time 2.0-8.0 min; Chromatographic peak 4: mass spectrometry molecular weight 331.147±0.02 Da, retention time 1.5-6.0 min; Chromatographic peak 5: mass spectrometry molecular weight 155.054±0.02 Da, retention time 1.5-4.0 min; Chromatographic peak 6: mass spectrometry molecular weight 145.072±0.02 Da, retention time 1.0-6.5 min; Chromatographic peak 7: mass spectrometry molecular weight 217.104±0.02 Da, retention time 1.0-6.5 min; Chromatographic peak 8: mass spectrometry molecular weight 299.119±0.02 Da, retention time 1.5-6.5 min; Chromatographic peak 9: mass spectrometry molecular weight 329.129±0.02 Da, retention time 1.5-6.0 min; Chromatographic peak 10: mass spectrometry molecular weight 185.065±0.02 Da, retention time 1.0-4.0 min; Chromatographic peak 11: mass spectrometry molecular weight 371.153±0.02 Da, retention time 1.5-7.0 min; The liquid chromatography conditions include: an amino column; mobile phase A is an aqueous ammonium acetate solution, and mobile phase B is acetonitrile; a gradient elution program: 0 min, 10±2% A; 1.0 min, 10±2% A; 6.0 min, 30±5% A; 10.0 min, 30±5% A; 11.0 min, 10±2% A; 15.5 min, 10±2% A; The mass spectrometry conditions include: GAS 1: 60±2 psi; GAS 2: 60±2 psi; Curtain gas: 40±2 psi; Temperature: 650℃±20℃; TOF MS start mass: 50±5 Da; TOF MS stop mass: 1000±50Da; TOF MSMS start mass: 50±5 Da; TOF MSMS stop mass: 1000±50 Da.

2. The method for detecting urea-formaldehyde resin in melamine-formaldehyde material according to claim 1, characterized in that: The gradient elution program was: 0 min, 10% A; 1.0 min, 10% A; 6.0 min, 30% A; 10.0 min, 30% A; 11.0 min, 10% A; 15.5 min, 10% A.

3. The method for detecting urea-formaldehyde resin in melamine-formaldehyde material according to claim 1, characterized in that: The mass concentration of the ammonium acetate aqueous solution is 0.36 g / L~0.40 g / L.

4. The method for detecting urea-formaldehyde resin in melamine-formaldehyde material according to claim 1, characterized in that: The mass spectrometry conditions include: GAS 1: 60 psi; GAS 2: 60 psi; Curtain gas: 40 psi; Temperature: 650°C.

5. The method for detecting urea-formaldehyde resin in melamine-formaldehyde material according to any one of claims 1 to 4, characterized in that The liquid chromatography conditions also include: injection volume: 2±1 μL; flow rate: 0.4±0.1 mL / min.

6. The method for detecting urea-formaldehyde resin in melamine-formaldehyde material according to any one of claims 1 to 4, characterized in that The mass spectrometry conditions also include: CAD GAS: 7±1 Spray votage: 3500±50V TOF MS Accumulation Time: 0.3±0.05 s TOF MS Declustering Potential: 60±5V TOF MS DP spread: 0V TOF MS Collision energy: 10±1V TOF CE spread: 0V TOF MSMS Accumulation Time: 0.1±0.01 s TOF MSMS Declustering Potential: 60±5V TOF MSMS DP spread: 0V TOF MSMS Collision energy: 20±2V TOF MSMS CE spread 0 V.

7. The method for detecting urea-formaldehyde resin in melamine-formaldehyde material according to any one of claims 1 to 4, characterized in that: The hydrolysis temperature is 110°C ± 2°C, and the hydrolysis time is 60 min ± 2 min.

8. The method for detecting urea-formaldehyde resin in melamine-formaldehyde material according to any one of claims 1 to 4, characterized in that The concentration of the hydrochloric acid solution is 0.10 mol / L~0.15 mol / L.

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