Method for analyzing purity of o-phthalic anhydride by using gas chromatography

Abstract

The invention relates to the field of substance purity analysis methods, and discloses a method for analyzing the purity of o-phthalic anhydride by using gas chromatography, which comprises the following steps: firstly, preparing a standard solution of which the concentration of each component is close to that of each component in crude phthalic anhydride to be analyzed, and analyzing the standard solution for more than three times; calculating a correction factor of each substance after the peak area repeatability error of each substance is less than 3%; and inputting the correction factor into a method-component table, comparing the spectrogram of the to-be-detected sample solution with the spectrogram of the standard substance solution, determining peak localization of corresponding substances in the to-be-detected sample solution according to retention time, and calculating the purity of phthalic anhydride in the to-be-detected sample by adopting an area correction normalization method. The method is simple to operate, short in analysis time and good in stability and reproducibility.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of analysis methods for the purity of substances, in particular to a method for analyzing the purity of phthalic anhydride by gas chromatography. BACKGROUND

[0002] Phthalic anhydride (chemical formula C8H4O3) is an organic compound, which is a white crystalline powder. It is insoluble in cold water, slightly soluble in hot water, diethyl ether, soluble in ethanol, acetone, benzene, carbon disulfide, etc. Phthalic anhydride is an important organic chemical raw material, mainly used for the preparation of phthalate plasticizers, coatings, saccharin, dyes, and as an important raw material for the production of dyes and pigments, coatings, etc., and its purity directly affects the performance and quality of downstream products. However, phthalic anhydride is prone to introduce impurities during production due to improper control of raw material purity, reaction conditions, or storage environment. The presence of these impurities not only reduces product purity, but also may cause safety hazards. Therefore, it is of great significance to establish an efficient and accurate purity detection method to ensure product quality and production safety.

[0003] Currently, the detection methods for the purity of phthalic anhydride mainly include chemical titration, infrared spectroscopy, and gas chromatography. Chemical titration measures the total acid content through acid-base neutralization reaction, although it is simple to operate, but it cannot distinguish different acidic impurities, and its sensitivity is low, which is difficult to meet the demand of modern industry for trace impurity detection. The infrared spectroscopy method is based on the characteristic absorption peak of molecular vibration for qualitative analysis, but the quantitative accuracy is limited by factors such as sample state and instrument resolution, especially for low concentration impurity detection. In contrast, gas chromatography has become the mainstream technology for phthalic anhydride purity detection due to its high separation efficiency, high sensitivity, and quantitative accuracy.

[0004] Gas chromatography separates each component in the sample through a chromatographic column, and combines with a detector (such as a hydrogen flame ionization detector, FID) to realize quantitative analysis. The early standard (such as SN / T 4373-2015) uses packed column gas chromatography to determine the content of maleic anhydride in phthalic anhydride, but the packed column has low column efficiency and poor separation degree, which limits the detection sensitivity and reproducibility. With the progress of chromatographic technology, capillary chromatographic column gradually replaces packed column as the mainstream due to its small inner diameter, high column efficiency, and fast analysis speed.

[0005] The current national standard GB / T 15336-2013, "Phytocyanic Anhydride," provides a method for determining the purity of phthalic anhydride in section 6.7. This method utilizes gas chromatography and employs the area normalization method to determine purity. However, this requires the detector to have completely uniform sensitivity to phthalic anhydride and all impurities, thus directly assuming that peak area represents mass. This assumption is invalid. Some methods have limited detection capabilities for low-concentration impurities (such as maleic anhydride <0.1%), making it difficult to meet the quality control requirements for high-purity products.

[0006] In addition, due to the different raw materials used in the production of phthalic anhydride, the impurities in phthalic anhydride vary. The main raw materials for existing processes are o-xylene or naphthalene. Since the o-xylene process for producing phthalic anhydride is relatively clean and the impurities are relatively simple, while the naphthalene process for producing phthalic anhydride has relatively more impurities, poor separation effect, and it is not easy to obtain all the correction factors. Summary of the Invention

[0007] To overcome the shortcomings of existing technologies, we use a "correction factor" to correct the differences in response sensitivity of different substances, making the analytical results more accurate. We have also invented a more precise method for detecting the purity of ortho-phthalic anhydride.

[0008] The technical solution adopted by this invention to solve its technical problem is as follows: A method for analyzing the purity of phthalic anhydride using gas chromatography involves first preparing standard solutions with concentrations close to those of the components in the crude phthalic anhydride to be analyzed. The concentration of each component is calculated using the area normalization method. Then, a correction factor for each component is calculated and input into the method-component table. The gas chromatograms of the sample solution and the standard solution are compared. The peak locations of the corresponding substances in the sample solution are determined based on the retention time. Finally, the purity of the phthalic anhydride in the sample is calculated using the area correction normalization method.

[0009] Furthermore, the crude phthalic anhydride contains several standard substances, including maleic anhydride (MA), benzoic acid (BA), phthalic anhydride (PA), and phthalyl phthalide (PD), which are added to a solvent to prepare standard samples. Furthermore, the correction factor F for each component is... ; Furthermore, both the test sample solution and the standard solution were nearly saturated solutions, and the solvent was acetone.

[0010] Further, the analytical conditions for gas chromatography are as follows: the column temperature is increased using a gradient method, starting at 60-70℃ and holding for 3 min, then increasing to 180℃ at a rate of 10-20℃ / min and holding for 5 min, then increasing to 220-270℃ at a rate of 10-20℃ / min and holding for 5 min; the carrier gas flow rate is 1.0-1.6 mL / min, the injector temperature is 290-300℃, the detector temperature is 290-300℃, the hydrogen-air ratio is 1:10-20, the make-up flow rate is 30-40 mL / min, and the split ratio is 10-20:1.

[0011] Furthermore, gas chromatography detection employs a flame ionization detector.

[0012] Furthermore, the gas chromatography used a quartz capillary column, specification SE-54, model 30m×0.32mm×1.0μm column.

[0013] Furthermore, the gas chromatography run time is 20-30 minutes.

[0014] Furthermore, the injection volume of both the test sample solution and the standard solution was 0.2-0.8 μL.

[0015] More specifically, accurately weigh a grams of maleic anhydride (MA), b grams of benzoic acid (BA), c grams of phthalic anhydride (PA), and d grams of phthalyl phthalate (PD) into a 100 mL volumetric flask, add acetone to the mark, and sonicate to dissolve, thus preparing a standard sample solution. The purity of MA is e%, the purity of BA is f%, the purity of PD is g%, and the content of each component in PA is MA: u%, BA: v%, PA: w%, PD: y%. Then, the true concentrations of each component in the standard solution are Z. MA = Z BA = Z PA = Z PD = Inject this standard sample solution into a gas chromatograph 3-6 times, and calculate the concentrations of each component (MA) using the area normalization method. x :i x %,BA x :j x %, PA x :k x %, PD x :l x % (x represents the xth injection), calculate the average value of each component: MA: m%, BA: n%, PA: p%, PD: q%, and the correction factors for each component are F1= F2= F3= F4= Enter this correction factor into the method-component table, i.e., the method-component table of the Shimadzu GCsolutionLite gas chromatography workstation in Japan. When analyzing the sample again, the corrected concentration will be obtained.

[0016] Compared with the prior art, the beneficial effects of the present invention include: This invention separates phthalic anhydride and solvent using gas chromatography, determines impurities present in phthalic anhydride under normal conditions, and calculates the purity of phthalic anhydride using the single-point correction area normalization method. First, standard solutions with concentrations close to those of each component in the crude phthalic anhydride to be analyzed are prepared. The standard solutions are analyzed at least three times, and after calculating the peak area repeatability error of each substance to be less than 3%, correction factors are calculated for each substance. These correction factors are input into the method-component table. The spectra of the test sample solution and the standard solution are compared, and the peak locations of the corresponding substances in the test sample solution are determined based on the retention time. The purity of phthalic anhydride in the test sample is calculated using the area correction normalization method. This invention is simple to operate, has a short analysis time, and exhibits good stability and reproducibility.

[0017] This method is particularly suitable for impurities with a mass content of 0.001-5.000 wt%, i.e., phthalic anhydride with a mass content higher than 95.00 wt%.

[0018] (1) High accuracy: By preparing standard solutions with concentrations close to those of each component of the crude phthalic anhydride to be analyzed and calculating correction factors, the purity is calculated using the area correction normalization method. This effectively reduces the impact of factors such as instrument response differences and sample matrix effects on the detection results, improves the accuracy of the detection results, and can more accurately reflect the actual purity of phthalic anhydride.

[0019] (2) Good stability: The specific gas chromatography analysis conditions are adopted, including the column temperature program of gradient temperature rise, appropriate carrier gas flow rate, injector temperature, detector temperature and other parameter settings, as well as the selection of quartz capillary columns of specific specifications, so that each component can be well separated on the chromatographic column, with sharp and symmetrical peaks, reducing peak overlap and tailing, ensuring the stability and repeatability of the analysis process, and high consistency of detection results of different batches.

[0020] (3) High sensitivity: By optimizing various conditions of gas chromatography, such as appropriate hydrogen-air ratio, tail blow flow rate and split ratio, combined with the high sensitivity of flame ionization detector, it can detect low concentration of impurity components in phthalic anhydride. It has significant advantages for the detection of products with high purity requirements and can meet the needs of high-precision quality control.

[0021] (4) Simple operation: Both the sample solution and the standard solution are prepared into near-saturated solutions using acetone as solvent. The sample pretreatment process is relatively simple, which reduces the errors and operational difficulties that may be introduced by complex pretreatment steps. At the same time, the preparation method of the standard solution is clear, which is easy for operators to master and implement, thus improving the detection efficiency. Attached Figure Description

[0022] Figure 1 This is the gas chromatogram of Example 1; Figure 2 This is the gas chromatogram of Example 2. Detailed Implementation

[0023] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0025] The MA reagent used in this embodiment is Aladdin M16389 with a purity of 99.675%; the BA reagent is Comio analytical grade with a purity of 99.500%; the PD reagent is Aladdin P104476 with a purity of 98.000%; and the PA reagent is Sinopharm 10015617. The contents of each component are as follows: MA: 0.022%, BA: 0.091%, PA: 99.880%, and PD: 0.005%.

[0026] Example 1 A method for determining the purity of pyromellitic dianhydride using liquid chromatography, comprising the following steps: 1.1 Accurately weigh 0.0045g MA (Aladdin M16389), 0.0043g BA (Comio AR), 5.6200g PA (Sinopharm 10015617), and 0.0005g PD (Aladdin P104476) into a 100mL volumetric flask. Add an appropriate amount of acetone to dissolve them, and finally dilute to the mark. The actual mass concentrations of each component in the standard solution prepared from the above reagents are: MA: 0.102%, BA: 0.167%, PA: 99.718%, PD: 0.014%. The standard solution was injected 6 times, and the concentration of each component was calculated by the area normalization method, and then the average concentration of each component was obtained: MA: 0.0436%, BA: 0.1716%, PA: 99.956%. 2%, PD: 0.0154%; further, the correction factors for each component were calculated as F1: 0.427, F2: 1.028, F3: 1.002, F4: 1.100, and the correction factors were entered into the Method-Component Table; accurately weigh 0.0055g MA (Aladdin M16389), 0.0058g BA (Comio AR), 6.1000g PA (Sinopharm 10015617), and 0.0001g PD (Aladdin P104476) into a 100ml volumetric flask, add an appropriate amount of acetone to dissolve them, and finally dilute to the mark. This is the sample solution to be tested, and the actual mass concentrations of each component are MA: 0.112%, BA: 0.185%, PA: 99.697%, PD: 0.007%.

[0027] 1.2 The sample solution was analyzed using a gas chromatograph (GC). The injection volume was 0.4 μL. The chromatographic conditions were as follows: gradient temperature increase, starting at 70 °C and holding for 3 min, then increasing to 180 °C at a rate of 10 °C / min and holding for 5 min, followed by increasing to 270 °C at a rate of 20 °C / min and holding for 5 min; carrier gas flow rate was 1.0–1.6 mL / min, injector temperature was 300 °C, detector temperature was 290 °C, hydrogen-air ratio was 1:10, make-up flow rate was 30 mL / min, and split ratio was 10:1. The GC run time was 28.5 min.

[0028] 1.3 Locate the corresponding chromatogram of the sample to be tested in the chromatography workstation, such as... Figure 1 As shown, after removing the solvent peak, the location of each component peak in the chromatogram of the sample solution is determined based on the retention time. The purity of phthalic anhydride in the sample is calculated using the area correction normalization method based on the correction factor in the method-component table.

[0029] The concentrations of each component, measured using the existing area normalization method, were: MA: 0.260%, BA: 0.177%, PA: 99.558%, and PD: 0.004%. The concentrations of each component, measured using the area correction normalization method, were: MA: 0.111%, BA: 0.182%, PA: 99.702%, and PD: 0.005%.

[0030] Example 2 The actual mass concentrations of each component in the sample solution to be tested were: MA: 0.047%, BA: 0.137%, PA: 99.806%, PD: 0.010%, and other steps were the same as in Example 1.

[0031] The concentrations of each component, measured using the existing area normalization method, were MA: 0.112%, BA: 0.127%, PA: 99.755%, and PD: 0.005%. The concentrations of each component, measured using the area correction normalization method, were MA: 0.048%, BA: 0.131%, PA: 99.816%, and PD: 0.006%.

[0032] The purity analysis results of phthalic anhydride in Examples 1-2 are shown in the table below: Table 1. Purity analysis results of phthalic anhydride in two examples Clearly, the methods used in the two embodiments are closer to the actual mass concentrations of each component, indicating that the method of the present invention has high accuracy in detecting the purity of phthalic anhydride.

[0033] Comparative Example 1 The current national standard GB / T 15336-2013 "Phytocyanic Anhydride" 6.7 provides a method for determining the purity of phthalic anhydride, which is gas chromatography detection and the purity is determined by the area normalization method. However, this method requires that the detector has the same response sensitivity to phthalic anhydride and all impurities, so the peak area is directly considered to represent the mass. But this assumption is not valid.

[0034] This invention uses a "correction factor" to correct for differences in the response sensitivity of different substances, making the analytical results more accurate. We prepared test solutions with known concentrations: MA: 0.112%, BA: 0.185%, PA: 99.697%, PD: 0.007%. The purity was measured using both the national standard area normalization method and the corrected area normalization method of this invention. The area normalization method results in: MA: 0.260%, BA: 0.177%, PA: 99.558%, PD: 0.004%. The corrected area normalization method results in: MA: 0.111%, BA: 0.182%, PA: 99.702%, PD: 0.005%. The results show that the detection results corrected by this invention are closer to the true values.

[0035] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for analyzing the purity of phthalic anhydride by gas chromatography, characterized by, It comprises the following steps: (1) Preparation of standard solution: a grams of MA, b grams of BA, c grams of PA, d grams of PD are weighed into a volumetric flask, and then solvent is added to the mark, ultrasonic dissolution, and standard sample solution is prepared; (2) Calculation of correction factor: the standard sample solution is injected into the gas chromatograph, the concentration of each component is calculated by area normalization method, the average value of the concentration of each component is calculated, and then the correction factor of each component is calculated, and the correction factor is input into the method-component table, that is, the computer workstation software, which can automatically convert the corrected concentration; (3) Sample analysis: the chromatograms of the sample solution and the standard sample solution are compared, the peak positioning of the corresponding substance in the sample solution is determined according to the retention time, and the purity of phthalic anhydride in the sample is calculated by area correction normalization method.

2. The method for analyzing the purity of phthalic anhydride by gas chromatography according to claim 1, characterized by, The sample solution and the standard sample solution are both near-saturated solutions, and the solvent is acetone.

3. The method for analyzing the purity of phthalic anhydride by gas chromatography according to claim 1, characterized by, The analysis conditions of the gas chromatograph are as follows: The column temperature is in the form of gradient heating, the initial temperature is 60-70 DEG C, the temperature is kept for 3 min, the temperature is raised to 180 DEG C at a rate of 10-20 DEG C / min, the temperature is kept for 5 min, and then the temperature is raised to 220-270 DEG C at a rate of 10-20 DEG C / min, and the temperature is kept for 5 min; The carrier gas flow is 1.0-1.6 mL / min; The injector temperature is 290-300 DEG C; The detector temperature is 290-300 DEG C; The hydrogen to air ratio is 1:10-20; The tail blow flow is 30-40 mL / min; The split ratio is 10-20:

1.

4. The method for analyzing the purity of phthalic anhydride by gas chromatography according to claim 1, characterized by, The gas chromatograph uses a flame ionization detector.

5. The method for analyzing the purity of phthalic anhydride by gas chromatography according to claim 1, characterized by, The gas chromatograph uses a quartz capillary column, the specification is SE-54, the model is 30 m*0.32 mm*1.0 mu m chromatographic column.

6. The method for analyzing the purity of phthalic anhydride by gas chromatography according to claim 1, characterized by, The running time of the gas chromatograph is 20-30 min.

7. The method for analyzing the purity of phthalic anhydride by gas chromatography according to claim 1, characterized by, The injection amount of the sample solution and the standard sample solution is 0.2-0.8 mu L.

8. The method for analyzing the purity of phthalic anhydride by gas chromatography according to claim 1, characterized by, The correction factor of each component is calculated as follows: F = 1 - (1 - 0.01) = 0.99 .

9. The method for analyzing the purity of phthalic anhydride by gas chromatography according to claim 1, characterized by, The standard sample solution is injected into the gas chromatograph 3-6 times, and the concentrations of the components are calculated by area normalization method, respectively MA x : i x %, BA x : j x %, PA x : k x %, and PD x : l x % (x represents the xth injection), and the average values of the components MA: m%, BA: n%, PA: p%, and PD: q% are obtained.

10. The method for analyzing the purity of phthalic anhydride by gas chromatography according to claim 1, characterized by, When the sample is analyzed again, the purity of phthalic anhydride in the sample is obtained based on the correction factor input into the method-component table.

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