A method for determining the iron content in polyvinyl butyral resin

Abstract

This invention discloses a method for determining the iron content in polyvinyl butyral resin. The method involves digesting the PVB resin sample with an inorganic acid, diluting the digest with a mixture of amide organic compounds and water, then using inductively coupled plasma atomic emission spectrometry (ICP-AES) to measure the spectral intensity of the sample. The iron content of the PVB resin sample is then calculated using a standard iron content curve. This method for determining the iron content in PVB resin offers advantages such as high precision, high accuracy, simple and rapid operation, low reagent consumption, and minimal environmental pollution. Furthermore, it has low equipment and maintenance costs, making it easy to promote and popularize.

Description

Technical Field

[0001] This invention belongs to the field of analytical testing technology and provides a method for determining the iron content in polyvinyl butyral resin. Background Art

[0002] Polyvinyl butyral resin (PVB resin) is non-toxic, odorless, non-corrosive, and non-flammable. Due to its special molecular structure, it has high tensile strength and impact resistance, excellent transparency and elasticity, and good adhesion to glass, metal, wood, ceramics, and fiber products. It is a synthetic resin material with broad development and utilization prospects.

[0003] A novel process for producing PVB resin involves adding water-based PVB resin powder or an emulsifier to polyvinyl alcohol (PVA), adding an antioxidant to butyraldehyde, and using an acid solution as a catalyst. The process is followed by an acetalization reaction to prepare PVB resin. The addition of the antioxidant improves the antioxidant properties of the PVB butyraldehyde resin, enhancing product stability and significantly increasing its added value. However, PVB resin contains trace amounts of iron ions introduced from raw materials and the manufacturing process. When the iron ion content exceeds 10 ppm, it affects the viscosity stability of the PVB resin, reduces its whiteness and optical properties, and ultimately impacts product quality. Therefore, accurately measuring and strictly controlling the iron content in PVB resin is crucial.

[0004] Currently, the main methods for detecting iron content at home and abroad are volumetric method, spectrophotometry, atomic absorption spectrometry, and inductively coupled plasma atomic emission spectrometry.

[0005] Although the capacity method is a classic method, it is mainly applicable to constant analysis.

[0006] The spectrophotometric determination of iron content in organic matter generally involves complex pretreatment processes such as carbonization and ashing to remove organic matter, followed by acidification with inorganic acids to prepare an aqueous solution. The pH of the solution is then adjusted with acid or alkali solutions, and after color development with a colorimetric reagent, the iron content is determined by colorimetric measurement using a spectrophotometer. This method is time-consuming (at least 8 hours), cumbersome, requires many types of reagents, has high blank values, and significant analytical errors.

[0007] Atomic absorption spectrometry (AAS) and inductively coupled plasma atomic emission spectrometry (ICP-AES) for determining iron content require low viscosity of the test solution. High viscosity can lead to several problems: first, it can clog the nebulizer and damage the instrument; second, it affects nebulization, sample injection rate, and spectral line intensity, resulting in large fluctuations in the measurement results and poor repeatability and accuracy. Due to its unique molecular structure, PVB resin is soluble in most organic solvents but insoluble in water. Furthermore, the higher the molecular weight of the organic solvent, the higher the viscosity of the PVB solution. Therefore, PVB solutions directly dissolved in organic solvents cannot be used for iron content determination using the aforementioned spectroscopic methods.

[0008] Currently, the main pretreatment methods for polymer compounds are dry ashing and wet digestion. Dry ashing, as mentioned earlier, is time-consuming, and the loss of analytes due to adsorption by the vessel and high temperatures during the process leads to large errors, low recovery rates, and poor repeatability. Wet digestion involves using one or more inorganic acids as digesting agents to treat the polymer sample before analysis. Direct digestion or microwave digestion methods are commonly used in sample preparation. The general process of direct digestion is as follows: Weigh approximately 0.3g of sample, add 8mL of nitric acid, and heat in a hot plate or oil bath to decompose and oxidize the organic matter in the sample, causing it to escape in a gaseous state. Acid must be added promptly during the reaction to prevent carbonization. After heating until the sample solution becomes a transparent liquid (approximately 2 hours), heating continues to remove the acid. When only a small amount of solution remains (approximately 1.5 hours), dilute with water to the final volume for analysis. The general procedure for microwave digestion is as follows: Weigh approximately 0.3g of sample into a digestion vessel, add 6-8mL of nitric acid, cover, and pre-digest for several minutes. Place the digestion vessel into the oven cavity of a microwave digestion apparatus and perform microwave digestion according to the temperature program. After the program is completed, cool the vessel and open the lid (approximately 1 hour). Transfer the solution to an acid removal apparatus for acid removal. When only a small amount of solution remains (approximately 1.5 hours), transfer it to a volumetric flask, dilute with water to the final volume, and prepare for analysis. The above two methods are not suitable for determining the iron content in PVB resin samples because: (1) Due to its special molecular structure, PVB resin, after being digested with inorganic acid, produces a clear and transparent digestion solution with no visible impurities. However, after dilution with pure water or dilute acid solution, a large number of fine and irregular suspended matter appears in the solution. This indicates that some small molecules remain after the PVB resin sample is digested with inorganic acid. When it comes into contact with water, it becomes fine and irregular suspended matter in the solution. Some iron is trapped in the solution and cannot be dissolved. At the same time, these suspended matter need to be filtered before injection, otherwise it will easily clog and contaminate the nebulizer, causing large fluctuations in the measurement results. (1) Low yield and large error; (2) During the acid removal process, it is difficult to ensure that the final amount of the solution is consistent, resulting in inconsistent acidity of the solution after volume adjustment; on the other hand, due to open evaporation, it is easy to cause sample volatilization loss and cross-contamination between samples, which will bring errors to the subsequent analysis, resulting in poor precision and accuracy; (3) The test container is changed multiple times during the sample pretreatment process, and the sample solution is easily damaged during multiple transfers, which also results in low precision and accuracy of the measurement results; (4) High temperature, high pressure and strong acid vapors brought by acid removal, on the one hand, bring psychological pressure to the experimenter in terms of safety, and on the other hand, cause environmental pollution. Summary of the Invention

[0009] This invention addresses the shortcomings of existing technologies by providing a rapid and accurate method for determining the iron content in PVB resin to meet product quality control needs. The key technical challenge lies in selecting the appropriate solvent and eliminating interference, particularly from small molecule suspended particles. This method consumes minimal reagents, causes minimal environmental pollution, is simple to operate, rapid and efficient, possesses high precision and accuracy, and has low instrument and maintenance costs, making it easy to promote and widely adopt.

[0010] To solve the technical problem, the present invention adopts the following technical solution:

[0011] The method for determining the iron content in PVB resin according to the present invention includes the following steps:

[0012] (1) Weigh the PVB resin sample to be tested into a threaded digestion tube with a cap, add inorganic acid, seal the reaction at room temperature, and then transfer it into an oil bath for heating and digestion to obtain the digestion solution.

[0013] (2) Prepare a mixed solution of amide organic compounds and water;

[0014] (3) Dilute the digestion solution from step (1) with the mixed solution prepared in step (2) to obtain the sample solution;

[0015] (4) Dilute the iron standard working solution with the mixed solution prepared in step (2) to obtain a series of iron standard solutions;

[0016] (5) Turn on the inductively coupled plasma atomic emission spectrometer and set the test conditions for the inductively coupled plasma atomic emission spectrometer;

[0017] (6) Under the conditions set in step (5), test the spectral intensity of the iron standard series solutions, and plot the iron content standard working curve with the iron content of the iron standard series solutions as the abscissa and the corresponding spectral intensity as the ordinate.

[0018] (7) Under the conditions set in step (5), test the spectral intensity of the sample solution obtained in step (3);

[0019] (8) Obtain a sample solution with a content of 0 PVB resin sample as a blank sample solution according to the methods in steps (1), (2), and (3), and then test the spectral intensity of the blank sample solution under the conditions set in step (5).

[0020] (9) Based on the spectral intensity of the sample solution and the blank sample solution, the iron content of the PVB resin sample to be tested is calculated according to the iron content standard working curve in step (6).

[0021] Further, in step (1), the ratio of the amount of PVB resin sample to inorganic acid is 0.10-0.50g:0.8-1.2mL, preferably 0.30g:1.0mL.

[0022] Further, in step (1), the inorganic acid is high-purity concentrated hydrochloric acid, high-purity concentrated sulfuric acid, or high-purity concentrated nitric acid, preferably high-purity concentrated nitric acid with a mass concentration of 65.0-68.0%.

[0023] Furthermore, in step (1), the time for the closed reaction at room temperature is 3-10 min, preferably 5-6 min.

[0024] Further, in step (1), the heating and digestion temperature is 150-190℃ (preferably 165-175℃), and the time is 20-35min (preferably 25-30min).

[0025] Further, in step (2), the amide organic compound is dimethylacetamide or dimethylformamide (preferably dimethylacetamide), and the volume ratio of the amide organic compound to water is 4-5:1 (preferably 4:1).

[0026] Furthermore, in step (4), the concentration range of the iron standard series solutions is between 0 and 2.5 mg / kg.

[0027] Further, in step (5), the test conditions of the inductively coupled plasma emission spectrometer are set as follows: argon cylinder outlet pressure 0.68MPa, high frequency generator power 1.4kW, cooling gas 25L / min, auxiliary gas 0.3L / min, nebulizer 45PSI, injection speed 0.8mL / min, and characteristic wavelength of iron 259.940nm.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] 1. This invention first digests the sample with an inorganic acid, and then further dissolves and dilutes the digest with a mixed solution of amide organic solvent and water. Only two reagents are selected for sample pretreatment, and the reagent consumption is low, reducing interference from impurities introduced by the reagents. Therefore, this invention has a low blank value and high accuracy. Amide organic compounds can dissolve residual small molecules in the digest. After dilution with the mixed solution of amide organic solvent and water, the test solution is clear and transparent, without visible impurities (suspended matter). Therefore, the test solution does not require filtration. The viscosity of the test solution, measured using a Brookfield viscometer at 20°C, is 1.28 mPa·s, comparable to the viscosity of a 2.5% nitric acid solution at the same temperature. Therefore, direct injection of the test solution (ICP-OES) will not affect the atomization efficiency and thus the results.

[0030] 2. This invention uses a closed container with assisted oil bath heating as a sample pretreatment method, which can completely digest the sample in just 20-35 minutes without the need for subsequent acid removal. The acidity of the digested sample solution is tested to be below 0.35 mol / L. Therefore, the pretreatment of this invention is fast, efficient and environmentally friendly.

[0031] 3. This invention uses inductively coupled plasma optical emission spectrometry (ICP-OES) and employs a direct sample introduction method for organic systems to determine the iron content in PVB resin samples, and quantifies it using the external standard method. ICP-OES features high excitation temperature, inert atmosphere, good atomization conditions, effective elimination of self-absorption phenomena by the "skin effect," low background interference from Ar gas, good stability of ICP torch discharge, electrode-free discharge, and no electrode contamination. Therefore, compared with atomic absorption spectrometry, it has the advantages of high sensitivity, good selectivity, wide linear range, and high analytical precision and accuracy.

[0032] 4. The single-hole constant temperature oil bath and the threaded digestion tube with a cap used in this invention are both commonly used laboratory equipment; the heating medium in the oil bath is glycerol, which is a commonly used laboratory reagent; a stainless steel test tube rack that matches the oil bath can be set up to assist digestion, so that multiple samples can be processed at the same time. Therefore, the pretreatment equipment of this invention has low cost and maintenance expenses and low energy consumption.

[0033] 5. The method of the present invention can also simultaneously determine the content of heavy metals such as copper, zinc, chromium, and nickel in PVB resin. Attached Figure Description

[0034] Figure 1 The standard working curves of the iron standard series solutions (concentration range of 0 to 2.5 μg / g) of Example 1 at characteristic wavelengths are shown.

[0035] Figure 2 This is the standard working curve of the iron standard series solutions (concentration range of 0 to 2.5 μg / g) of Comparative Example 1 at the characteristic wavelength. Detailed Implementation

[0036] The technical solution of the present invention will be described in detail below through embodiments. The samples used in the following embodiments and comparative tests are all PVB resin samples produced by Anhui Wanwei High-Tech Materials Co., Ltd.

[0037] The tools used in the following embodiments and comparative examples are as follows:

[0038] 1. Instruments and reagents:

[0039] Plasma emission spectrometer: TELEDYNE Leeman Labs, Model: PRODIGY-SPEC;

[0040] Electronic analytical balance: accuracy 0.1 mg;

[0041] Digital display single-hole constant temperature oil bath: temperature control accuracy ±0.5℃, temperature fluctuation ±0.5℃.

[0042] 19-hole stainless steel test tube rack: The height of the upper and lower test tube rack plates is adjustable. The diameter of the upper plate of the test tube rack is larger than the diameter of the oil bath. The positioning hole diameter of the digestion tube on the upper plate of the test tube rack is ∅17mm, and the positioning hole diameter of the digestion tube on the lower plate of the test tube rack is ∅14mm.

[0043] 16×150mm threaded digestion tube with cap (10mL);

[0044] Graduated pipettes: 10 mL, 1 mL; injection needles: 250 μL, 50 μL;

[0045] Volumetric flasks: 500mL, 50mL, 25mL;

[0046] Glycerol;

[0047] Nitric acid (65.0–68.0%): GR;

[0048] Dimethylacetamide: AR;

[0049] Iron standard solution (GSB 04-1726-2004): 1000 μg / mL;

[0050] 2. Prepare the required solution:

[0051] (1) Mixed solvent 1: Measure 400 mL of dimethylacetamide (AR) into a 500 mL volumetric flask, dilute with high-purity water to the mark, shake well, and set aside for use.

[0052] (2) Mixed solvent 2: Measure 12.5 mL of nitric acid (GR) into a 500 mL volumetric flask, dilute to the mark with high-purity water, and shake well.

[0053] (3) Preparation of iron standard working solution 1: Accurately pipette 5.0 mL of iron standard solution into a dry, clean 50 mL volumetric flask that has been accurately weighed (to the nearest 0.0001 g). Weigh the solution (to the nearest 0.0001 g), dissolve and dilute it to the mark with mixed solvent 1, weigh the solution (to the nearest 0.0001 g), shake well, and set aside for use. The concentration of this solution is 105 μg / g.

[0054] (4) Preparation of iron standard working solution 2: Accurately pipette 5.0 ml of iron standard solution (same as the iron standard solution in the example) into a dry, clean 50 mL volumetric flask that has been accurately weighed (to the nearest 0.0001 g). Weigh the solution (to the nearest 0.0001 g), dissolve and dilute it to the mark with mixed solvent 2, weigh the solution (to the nearest 0.0001 g), shake well, and set aside for use. The concentration of this solution is 100 μg / g.

[0055] Example 1

[0056] The following method is used in this embodiment of the invention to detect the iron content in PVB resin:

[0057] S1. Place the single-hole constant-temperature oil bath in a fume hood, remove the oil bath lid, place the stainless steel test tube rack, and adjust the height of the upper and lower test tube rack plates so that the upper test tube rack plate is precisely locked onto the oil bath orifice, keeping the oil bath sealed. Adjust the height of the lower test tube rack plate to 30-40mm from the oil bath partition. Inject glycerol (approximately 2 / 3 of the oil bath volume), cover the oil bath, open the oil bath, and set the oil bath temperature to 170℃.

[0058] S2. Preparation of blank solution for sample: Take a dry, clean, and numbered threaded cap digestion tube, accurately add 1.00 mL of nitric acid (GR), place it in the test tube rack of the oil bath that has been heated to 170°C, evaporate it with the opening open for 30 min, take it out, let it cool slightly, put on the screw cap, wash away the glycerol adhering to the outer wall of the digestion reaction tube with running water, accurately add 4.0 mL of mixed solvent 1, put on the screw cap, shake well, and let it stand for later use.

[0059] S3. Preparation of Sample Solution: Take another dry and clean threaded digestion tube with a cap, label it, and weigh it (accurate to 0.0001g), recording it as m0. Weigh 0.30g of PVB resin sample, place it at the bottom of the digestion tube, weigh it (accurate to 0.0001g), recording it as m1. Accurately add 1.00mL of nitric acid (GR), immediately cap it and tighten it, digest at room temperature for 5min, then tighten the cap again and transfer it to an oil bath test tube rack heated to 170℃ for 25min. Remove it, let it cool slightly, wash away the glycerol adhering to the outer wall of the digestion tube, unscrew the cap, accurately add 4.0mL of mixed solvent 1, cap it and tighten it, wipe the outer wall clean, let it reach room temperature, weigh it (accurate to 0.0001g), recording it as m2. After fully dissolving and shaking, set aside for later use; this is the sample solution to be tested.

[0060] S4. Preparation of iron standard series solutions

[0061] Take six dry, clean 25mL volumetric flasks, label them, and weigh them (accurate to 0.0001g). Pipette 0.00, 0.02, 0.06, 0.15, 0.35, and 0.60mL of iron standard working solution 1 (105μg / g) into the corresponding numbered volumetric flasks, weigh them (accurate to 0.0001g), dilute to the mark with mixed solvent 1, weigh them (accurate to 0.0001g), and shake well before use. The concentrations of this series of iron standard solutions are 0.0, 0.1, 0.3, 0.7, 1.5, and 2.5μg / g, respectively.

[0062] S5. Set the operating parameters of the plasma emission spectrometer.

[0063] Argon cylinder outlet pressure: 0.68 MPa

[0064] High-frequency generator power: 1.4kW

[0065] Cooling gas: 25L / min

[0066] Auxiliary gas: 0.3L / min

[0067] Atomizer: 45PSI

[0068] Injection rate: 0.8 mL / min

[0069] Characteristic wavelength of iron: 259.940 nm

[0070] S6. Draw the standard working curve.

[0071] Follow the operating procedures for the plasma atomic emission spectrometer to start the instrument for warm-up. Set all operating parameters as described above. Once the instrument is running stably, measure the spectral intensities of the iron standard series solutions sequentially. Each standard solution is measured three times, and the average values ​​of the three measurements are recorded, as shown in Table 1. Plot the iron content of the iron standard series solutions on the x-axis and the corresponding spectral intensities on the y-axis using the instrument's software, as shown in Table 1. Figure 1 As shown.

[0072] Table 1. Iron content and corresponding spectral intensities of standard series solutions from the examples.

[0073]

[0074] S7. Measure the spectral intensity of the blank solution and the sample solution. Repeat the measurement three times and take the average value of the three measurement results. According to the iron content standard working curve plotted by the instrument software, obtain the iron content of the blank solution and the sample solution, and record them as C0 and C1, respectively.

[0075] Calculation of iron content in S8 and PVB resin samples:

[0076]

[0077] Where: C—derived from the iron content standard working curve ( Figure 1 The iron content in the sample solution was found to be in micrograms per gram (μg / g).

[0078] C0: Derived from the iron content standard working curve ( Figure 1 The iron content in the blank solution of the sample was found to be in micrograms per gram (μg / g).

[0079] m2-m0: Total mass of the sample solution, in grams (g);

[0080] m1-m0: Mass of PVB resin sample, in grams (g).

[0081] Comparative Example 1

[0082] This comparative example uses a MARS6 microwave digester and its matching acid removal instrument manufactured by CEM Corporation, USA. First, a concentrated inorganic acid is used to digest the PVB resin sample. Then, a certain volume of a mixed solvent of inorganic acid and water is added to dissolve, dilute, and filter the sample digest. Finally, the spectral intensity of iron at a specific wavelength is measured using ICP-OES (the same plasma emission spectrometer used in this embodiment). Based on the working curve between spectral line intensity and the concentration of iron standard solutions, the iron content in the sample solution is obtained, and the iron content in the PVB resin sample is calculated. The specific implementation is as follows:

[0083] S1. Weigh 0.30g of PVB resin sample (accurate to 0.0001g) and place it in a numbered digestion vessel. In an acid-proof fume hood, add 6.0mL of concentrated nitric acid (GR) and pre-digest for 5 minutes. Tighten the digestion vessel lid. Simultaneously, perform a blank test using a separate dry and clean digestion vessel. After placing the digestion vessel into the digestion vessel holder, place it in the oven cavity of the microwave digestion apparatus. Confirm that the instrument is functioning properly and perform microwave digestion according to the temperature rise program in Table 2. After the program is completed, cool the vessel until the internal temperature drops to room temperature. Remove the digestion vessel from the acid-proof fume hood and slowly release the pressure (Note: the opening of the digestion vessel must not face the experimenter). Open the digestion vessel lid.

[0084] Table 2 Microwave Digestion Program Temperature Rise Parameter Settings

[0085]

[0086] S2. Place the acid removal instrument in an acid-proof fume hood, then transfer the digestion vessel to the acid removal instrument. Wash the digestion vessel lid with a small amount of high-purity water, then pour it into the digestion vessel to remove the acid. When a small amount of solution remains, remove it and let it cool slightly. Wash the walls of the digestion vessel with a small amount of high-purity water, then transfer it to a dry, clean, and accurately weighed 10mL volumetric flask. Dilute to the mark with mixed solvent 2, weigh accurately, mix well, and filter through a 0.45μm filter membrane. This filtrate is the test solution. At the same time, prepare a blank solution for the sample.

[0087] S3, Preparation of iron standard series solutions

[0088] Take six dry, clean 25mL volumetric flasks, label them, and weigh them (accurate to 0.0001g). Pipette 0.00, 0.02, 0.06, 0.15, 0.35, and 0.60mL of iron standard working solution 2 (100 μg / g) into the corresponding numbered volumetric flasks, weigh them (accurate to 0.0001g), dilute to the mark with mixed solvent 2, weigh them (accurate to 0.0001g), and shake well before use. The concentrations of this series of iron standard solutions are 0.0, 0.1, 0.3, 0.7, 1.5, and 2.5 μg / g, respectively.

[0089] S4. Set the operating parameters of the plasma emission spectrometer.

[0090] Argon cylinder outlet pressure setting: 0.68MPa

[0091] High-frequency generator power: 1.2kW

[0092] Cooling gas: 20L / min

[0093] Auxiliary gas: 0.2L / min

[0094] Atomizer: 50PSI

[0095] Injection rate: 1.3 mL / min

[0096] Characteristic wavelength of iron: 259.940 nm

[0097] S5. Draw the standard working curve.

[0098] Follow the operating procedures for the plasma atomic emission spectrometer to start the instrument for warm-up. Set all operating parameters as described above. Once the instrument is running stably, measure the spectral intensities of the iron standard series solutions sequentially. Each standard solution is measured three times, and the average values ​​of the three measurements are recorded, as shown in Table 3. Plot the iron content of the iron standard series solutions on the x-axis and the corresponding spectral intensities on the y-axis using the instrument's software to create a standard working curve for iron content, as shown in Table 3. Figure 2 As shown.

[0099] Table 3 Iron content and corresponding spectral intensities of comparative standard solutions

[0100]

[0101] S6. Measure the spectral intensity of the blank solution and the sample solution. Repeat the measurement three times and take the average value of the three measurement results. According to the iron standard working curve drawn by the instrument software, obtain the iron content of the blank solution and the sample solution, and record them as C0 and C1 respectively.

[0102] Calculation of iron content in S7 PVB resin samples:

[0103]

[0104] Where: C—derived from the iron content standard working curve ( Figure 2 The iron content in the sample solution was found to be in micrograms per gram (μg / g).

[0105] C0—derived from the iron content standard working curve ( Figure 2 The iron content in the blank solution of the sample was found to be in micrograms per gram (μg / g).

[0106] m1-m0 — Total mass of the sample solution, in grams (g);

[0107] m—Sample mass of PVB resin, in grams (g).

[0108] Method verification in examples and comparative examples:

[0109] 1. Linearity of methods

[0110] The linear relationship and correlation coefficient of the iron content standard working curves plotted in the above embodiments and comparative examples are shown in Table 4.

[0111] Table 4. Linearity test results of the two methods

[0112]

[0113] As shown in Table 4, within the linear range of 0–2.5 μg / g, the iron content and spectral line intensity of both methods exhibit a good linear relationship. The correlation coefficient r is 0.9999 for both methods.

[0114] 2. Method precision test

[0115] Accurately weigh 14 equal-mass PVB resin samples from the same batch, with 7 samples per group. Add an equal-mass iron standard working solution 1 or iron standard working solution 2 to each group. Determine the iron content of each group using the corresponding method (Example 1 or Comparative Example 1). Calculate the standard deviation based on the test results. The results are shown in Tables 5 and 6.

[0116] Table 5 Precision Test of Method in Example 1

[0117]

[0118] Table 6. Precision test of method in Comparative Example 1

[0119]

[0120] As shown in Tables 5 and 6, the standard deviation of the method in Example 1 of the present invention is 1.18%, while the standard deviation of the method in Comparative Example 1 is 12.50%, indicating that there is a significant difference in the precision test between the two methods. The method of the present invention has stable results and good precision in determining the iron content in PVB resin.

[0121] 4. Spike Recovery Test

[0122] Accurately weigh 6 PVB resin samples with known iron content of equal mass, and divide them into groups of three. Add a certain mass of iron standard working solution 1 or iron standard working solution 2 to each group and determine the iron content using the corresponding method (Example 1 or Comparative Example 2). Calculate the spiked recovery rate based on the test results. The results are shown in Table 7.

[0123] Table 7 Comparison of Spike Recovery Tests for the Two Methods

[0124]

[0125] As shown in Table 7, the spiked recovery rate of Example 1 of the present invention is between 97.2% and 101.0%, and the spiked recovery rate of Comparative Example 1 is between 59.3% and 80.8%. The spiked recovery rate range of the method of Example 1 of the present invention meets the specification requirements (the content of the analyte is between 1-100 mg / kg, and the recovery rate range is 90-110%), indicating that the method of the present invention for determining the iron content in PVB resin is reliable and has high accuracy.

[0126] 5. Method detection limit test

[0127] The precision and spiked recovery comparison data of the two methods above show that the method of Example 1 of this invention has high precision in determining the iron content in PVB resin, and the results are accurate and reliable. The following is only a method detection limit test of the method of this invention, and the specific operation is as follows:

[0128] Seven equal masses of the same PVB resin sample were weighed, and sample solutions were prepared according to the method in Example 1 of this invention. The samples were then tested under the corresponding spectral conditions. The method detection limit was calculated according to formula (A1), and the results are shown in Table 8.

[0129] MDL=S×t(n-1,0.99)........................(A1)

[0130] Where: MDL — method detection limit, μg / g;

[0131] n—Number of parallel determinations of the sample;

[0132] S — Standard deviation of n parallel measurements;

[0133] t(n-1, 0.99) — t-distribution (one-sided) with n-1 degrees of freedom and a 99% confidence level. From the t-test table, with a 99% confidence level, t(6, 0.99) = 3.143.

[0134] Table 8 Method Detection Limit Test

[0135]

[0136] As shown in Table 8, the detection limit of the method in Example 1 of this invention is 0.014 μg / g.

[0137] As can be seen from the above, the method of the present invention for determining the iron content in PVB resin has the advantages of good precision, high accuracy, simple and fast operation, small amount of reagents, and low environmental pollution. In addition, the equipment cost and maintenance cost are low, making it easy to promote and popularize.

Claims

1. A method for determining the iron content in polyvinyl butyral resin, characterized in that, Includes the following steps: (1) Weigh the PVB resin sample to be tested into a threaded digestion tube with a cap, add inorganic acid, put on the threaded cap and tighten it, and react in a sealed environment at room temperature for 3-10 min. Tighten the threaded cap again and transfer it to an oil bath at 150-190℃ for heating and digestion for 20-35 min to obtain the digestion solution. The ratio of the amount of PVB resin to be tested to the amount of inorganic acid is 0.10-0.50 g: 0.8-1.2 mL. The inorganic acid is supercritical concentrated hydrochloric acid, supercritical concentrated sulfuric acid or supercritical concentrated nitric acid. (2) Prepare a mixed solution of amide organic compound and water; wherein the amide organic compound is dimethylacetamide or dimethylformamide, and the volume ratio of amide organic compound to water is 4-5:1; (3) Dilute the digestion solution from step (1) with the mixed solution prepared in step (2) to obtain the sample solution; (4) Dilute the iron standard working solution with the mixed solution prepared in step (2) to obtain a series of iron standard solutions; (5) Turn on the inductively coupled plasma emission spectrometer and set the test conditions of the inductively coupled plasma emission spectrometer as follows: argon cylinder outlet pressure 0.68MPa, high frequency generator power 1.4kW, cooling gas 25L / min, auxiliary gas 0.3L / min, nebulizer 45PSI, injection speed 0.8mL / min, characteristic wavelength of iron 259.940nm; (6) Under the conditions set in step (5), test the spectral intensity of the iron standard series solutions, and plot the iron content standard working curve with the iron content of the iron standard series solutions as the abscissa and the corresponding spectral intensity as the ordinate. (7) Under the conditions set in step (5), test the spectral intensity of the sample solution obtained in step (3); (8) Obtain a sample solution with a content of 0 PVB resin sample as a blank sample solution according to the methods in steps (1), (2), and (3), and then test the spectral intensity of the blank sample solution under the conditions set in step (5). (9) Based on the spectral intensity of the sample solution and the blank sample solution, the iron content of the PVB resin sample to be tested is calculated according to the iron content standard working curve in step (6).

2. The method for determining the iron content in polyvinyl butyral resin according to claim 1, characterized in that: In step (4), the concentration range of the iron standard series solutions is between 0 and 2.5 mg / kg.

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