Method for detecting content of isophthalic acid

Abstract

The invention discloses a method for detecting the content of isophthalic acid. The method comprises the following steps: S1, preparing a transesterification solution; weighing a set amount of tetraethylene glycol dimethyl ether and zinc acetate, and dissolving and diluting the tetraethylene glycol dimethyl ether and the zinc acetate with methanol; s2, preparing an isophthalic acid stock solution; the preparation method comprises the following steps: weighing dimethyl isophthalate and methanol according to a set amount, and uniformly mixing; step S3, preparing a dimethyl isophthalate correction solution; respectively weighing a set mass of calibration solution from the isophthalic acid stock solution, adding a set amount of ester exchange liquid into the calibration solution, uniformly mixing, and filtering; step S6, analyzing different filtrates obtained in the step S3 by using gas chromatography to obtain corresponding data; and step S7, calculating the content of the isophthalic acid according to the data obtained in the step S6 and the test result of the gas chromatograph in the step S7. The method for detecting the content of the isophthalic acid, provided by the invention, can detect the content of the isophthalic acid, and is simple to operate and high in accuracy of the test result.

Description

Technical Field

[0001] The present invention belongs to the technical field of detection, and relates to a detection method, in particular to a detection method for the content of isophthalic acid. Background Art

[0002] National standard GB / T 14190-2017 is a methanol alcoholysis standard, which states that: the sample undergoes transesterification reaction under high temperature and in the presence of methanol, and diglycol is liberated, and then the content of diglycol in the filtrate is detected by gas chromatography. The above standard is used for determining the content of diglycol, and there is no method description for determining the content of isophthalic acid.

[0003] The IS Indian standard is applicable to the determination of the content of isophthalic acid in polyethylene terephthalate samples. The polymer sample is digested and depolymerized in benzyl alcohol, and then esterified into dibenzyl isophthalate, dibenzyl terephthalate and ethylene glycol ester. Isopropyl titanate is added as a depolymerization catalyst; the sample is analyzed by gas chromatography, and the weight percentage of dimethyl isophthalate is estimated using the peak areas of the two esters with an internal standard. This method is relatively cumbersome, with more steps, a longer overall test time, and a higher temperature set for the gas chromatograph.

[0004] In view of this, there is an urgent need to design a new detection method for the content of isophthalic acid today, so as to overcome at least some of the above defects existing in the existing detection methods. Summary of the Invention

[0005] The present invention provides a detection method for the content of isophthalic acid, which can detect the content of isophthalic acid, is simple to operate, and has high accuracy of test results.

[0006] To solve the above technical problems, according to one aspect of the present invention, the following technical solution is adopted:

[0007] A detection method for the content of isophthalic acid, the detection method for the content of isophthalic acid comprising:

[0008] Step S1, preparing a transesterification solution; weighing a set amount of tetraethylene glycol dimethyl ether and zinc acetate, dissolving and diluting with methanol;

[0009] Step S2, preparing an isophthalic acid stock solution; weighing a set amount of dimethyl isophthalate and methanol, and mixing evenly;

[0010] Step S3, preparing a dimethyl isophthalate calibration solution; respectively weighing a set mass of calibration solution from the isophthalic acid stock solution, adding a set amount of transesterification solution to the calibration solution, mixing evenly, and filtering;

[0011] Step S6, analyzing the different filtrates obtained in Step S3 by gas chromatography to obtain a coefficient K;

[0012] Step S7: Weigh a sample of a set mass into a reaction vessel, add a transesterification solution to the reaction vessel, seal the reaction vessel, and place it in a heating device; after reacting at a set temperature for a set time, take it out, cool it to a set temperature, filter it, aspirate a set filtrate, and test it with a gas chromatograph; calculate the isophthalic acid content based on the data obtained in step S6 and the results of the test performed with the gas chromatograph in this step.

[0013] As an embodiment of the present invention, in step S6, using a chromatographic separation analysis method with a gas as the mobile phase, the vaporized filtrate is carried into the chromatographic column by the carrier gas (mobile phase). The stationary phase in the chromatographic column has different molecular interaction forces with each component in the sample, and each component flows out of the chromatographic column at different times, and the components are separated.

[0014] Adopt an FID detector to make a chromatogram marking the time and concentration of each component flowing out of the chromatographic column; according to the peak emergence time and sequence shown in the figure, perform qualitative analysis on the compound; according to the height and area of the peak, perform quantitative analysis on the compound.

[0015] As an embodiment of the present invention, in step S7, weigh a sample of a set mass into a reaction vessel, add a transesterification solution to the reaction vessel, seal the reaction vessel, and place it in a heating device; after reacting at a set temperature for a set time, take it out, cool it to a set temperature, filter it, aspirate a set filtrate, and test it with a gas chromatograph.

[0016] As an embodiment of the present invention, in step S7, weigh about 1 g of the sample, accurate to 0.1 mg, into a reaction tube, accurately add 25 mL of the transesterification solution, tighten the reaction tube with a wrench, place it in a heating device, take it out after reacting at 210 °C for 2 h, cool it to room temperature with tap water, filter it into a bottle, aspirate 1 μL of the filtrate, and test it with a gas chromatograph.

[0017] As an embodiment of the present invention, in step S7, calculate the isophthalic acid content in the sample:

[0018]

[0019] Among them, X1 is the isophthalic acid content, K is the slope of the working curve, A1 is the area of dimethyl isophthalate, A ST is the area of tetraethylene glycol dimethyl ether, m is the mass of the sample, and 0.855 is the ratio of the relative molecular weights of isophthalic acid and dimethyl isophthalate.

[0020] As an embodiment of the present invention, before step S6 and after step S3, the detection method further includes step S4: constructing a mathematical model of gas chromatography parameters; extracting the characteristics of the substance to be detected, using the extracted characteristics as the input of the mathematical model of gas chromatography parameters, and constructing the mathematical model of gas chromatography parameters based on this; the output of the mathematical model of gas chromatography parameters includes: column inner diameter, column length, film thickness, stationary phase composition, and flow rate.

[0021] As an embodiment of the present invention, before step S6 and after step S4, the detection method further includes step S5: extracting the characteristic data of isophthalic acid and using this as the input data to input into the mathematical model of gas chromatography parameters; obtaining the corresponding key gas chromatography parameters: inlet temperature, column temperature, detector temperature, nitrogen flow rate, air flow rate, and split ratio, and setting them in the gas chromatograph based on this.

[0022] As an embodiment of the present invention, in step S6, gas chromatography analysis is performed on the filtrate using the key gas chromatography parameters set in the gas chromatograph in step S5 to obtain corresponding data.

[0023] As an embodiment of the present invention, the detection method further includes: plotting a calibration curve;

[0024] Using the mass of diethylene glycol in the calibration solution as the ordinate and the ratio of the peak area of dimethyl isophthalate to the peak area of the internal standard as the abscissa, linearly regress to plot the calibration curve, and the correlation coefficient is higher than 0.99.

[0025] As an embodiment of the present invention, in step S1, the steps for preparing the transesterification solution include: weighing 240 mg of tetraethylene glycol dimethyl ether and 36 mg of zinc acetate, dissolving and diluting them with methanol to 1 L; the concentration of the internal standard in this solution is 0.24 mg / ml, and the concentration of zinc acetate is 0.036 mg / ml;

[0026] In step S2, the steps for preparing the isophthalic acid stock solution include: weighing 2.0 g of dimethyl isophthalate and 100 g of methanol, mixing them thoroughly for use;

[0027] In step S3, the steps for preparing the dimethyl isophthalate calibration solution include: weighing the calibration solution with a set mass respectively, adding 25 ml of the transesterification solution to the calibration solution, shaking it thoroughly, and filtering it into a bottle; in step S6, 1 μL of the filtrate is taken for gas chromatography analysis.

[0028] The beneficial effects of the present invention are as follows: The detection method for the content of isophthalic acid proposed by the present invention can detect the content of isophthalic acid, is simple to operate, and has high test result accuracy. Description of the Drawings

[0029] Figure 1Flow chart of the detection method for isophthalic acid content in an embodiment of the present invention.

[0030] Figure 2 Chromatogram of the test results of the regenerated chip of cord fabric in an embodiment of the present invention.

[0031] Figure 3 Schematic diagram of the sample injection result of the regenerated chip of cord fabric in an embodiment of the present invention.

[0032] Figure 4 Chromatogram of the test results of the regenerated chip of cord fabric in an embodiment of the present invention.

[0033] Figure 5 Schematic diagram of the sample injection result of the regenerated chip of cord fabric in an embodiment of the present invention. Detailed implementation manners

[0034] The preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0035] To further understand the present invention, the preferred implementation manners of the present invention will be described below in conjunction with embodiments. However, it should be understood that these descriptions are only for further explaining the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0036] The description of this part is only for several typical embodiments, and the present invention is not limited to the scope described in the embodiments. The mutual replacement of the prior art means similar or identical to some technical features in the embodiments is also within the scope of the description and protection of the present invention.

[0037] The expression of the steps in each embodiment in the specification is only for convenience of description, and the implementation manner of the present application is not limited by the order of step implementation.

[0038] The present invention discloses a detection method for isophthalic acid content. Figure 1 For the flow chart of the detection method for isophthalic acid content in an embodiment of the present invention; please refer to Figure 1 , the detection method for isophthalic acid content includes:

[0039]

Step S1

[0040] In one embodiment, in step S1, the step of preparing the transesterification solution includes: weighing 240 mg of tetraethylene glycol dimethyl ether and 36 mg of zinc acetate, dissolving and diluting to 1 L with methanol; the internal standard substance concentration in this solution is 0.24 mg / ml, and the zinc acetate concentration is 0.036 mg / ml.

[0041]

Step S2

[0042] In one embodiment, in step S2, preparing the isophthalic acid stock solution includes: weighing 2.0 g of dimethyl isophthalate and 100 g of methanol, mixing well, and setting aside for use;

[0043]

Step S3

[0044] In one embodiment, in step S3, the steps of configuring the dimethyl isophthalate calibration solution include: weighing out a set mass of the calibration solution respectively, adding 25 ml of the transesterification solution to the calibration solution, shaking well, and filtering into a bottle; in step S6, aspirate 1 μL of the filtrate and analyze it by gas chromatography.

[0045]

Step S4

[0046]

Step S5

[0047]

Step S6

[0048] In one embodiment of the present invention, the filtrate is analyzed by gas chromatography using the key gas chromatography parameters set in the gas chromatograph in step S5 to obtain corresponding data.

[0049] In one embodiment of the present invention, in step S6, using the chromatographic separation analysis method with gas as the mobile phase, the vaporized sample is carried into the chromatographic column by the carrier gas (mobile phase). The stationary phase in the chromatographic column has different molecular interactions with each component in the sample, and each component flows out of the chromatographic column at different times, and the components are separated;

[0050] An FID detector is used to make a chromatogram marking the time and concentration of each component flowing out of the chromatographic column; according to the peak emergence time and order shown in the figure, qualitative analysis of the compound is carried out; according to the height and area of the peak, quantitative analysis of the compound is carried out.

[0051]

Step S7

[0052] In an embodiment of the present invention, in the chromatographic separation analysis method using a gas as the mobile phase, the vaporized sample is carried into the chromatographic column by the carrier gas (mobile phase). The stationary phase in the chromatographic column has different molecular interaction forces with each component in the sample, and each component flows out of the chromatographic column at different times, achieving component separation. An FID detector is used to produce a chromatogram marking the time and concentration of each component flowing out of the chromatographic column; according to the peak emergence time and sequence shown in the figure, qualitative analysis of the compound is performed; according to the height and area of the peaks, quantitative analysis of the compound is performed.

[0053] In one embodiment, weigh approximately 1 g of the sample, accurate to 0.1 mg, into a reaction tube, accurately add 25 mL of the transesterification solution, tighten the reaction tube with a wrench, place it in a heating device, take it out after reacting at 210 °C for 2 h, cool it to room temperature with tap water, filter it into a bottle, and aspirate 1 μL of the filtrate for testing with a gas chromatograph.

[0054] In an embodiment of the present invention, in Step S7, the calculation of the isophthalic acid content in the sample:

[0055]

[0056] Among them, X1 is the isophthalic acid content, K is the slope of the working curve, A1 is the area of dimethyl isophthalate, A ST is the area of tetraethylene glycol dimethyl ether, m is the mass of the sample, and 0.855 is the ratio of the relative molecular weights of isophthalic acid and dimethyl isophthalate.

[0057] In the above steps, Step S4 and Step S5 are optional steps; in some embodiments, Step S4 or / and Step S5 may not be set.

[0058] In an embodiment of the present invention, the detection method further includes: drawing a calibration curve;

[0059] Taking the mass of diethylene glycol in the calibration solution as the ordinate and the ratio of the peak area of dimethyl isophthalate to the peak area of the internal standard as the abscissa, linearly regress to draw the calibration curve, and the correlation coefficient is higher than 0.99.

[0060] In a usage scenario of the present invention, the raw materials, process steps, process conditions (time, temperature, pressure, flow rate, melting point, refractive index, etc.), special equipment, etc. involved in the present invention are as follows.

[0061] Instruments and Equipment

[0062] Gas chromatograph: equipped with a hydrogen flame ionization detector, for example: Agilent GC8860 installed with an FID detector

[0063] Chromatographic column: capillary column; for example: DB-WAXer 30m 0.53mm 1.50μm

[0064] Balance: minimum division value of 0.1mg

[0065] Heating device: temperature controlled at 210±10°C, reaction tube 50ml bench vice wrench

[0066] Automatic pipetting device or pipette 25ml

[0067] Microsyringe or autosampler 1μL

[0068] Reagents

[0069] Dimethyl isophthalate internal standard (ST) in methanol: tetraethylene glycol dimethyl ether zinc acetate

[0070] Transesterification solution: Weigh 240mg of tetraethylene glycol dimethyl ether and 36mg of zinc acetate, dissolve with methanol and dilute to 1L. The concentration of the internal standard in this solution is 0.24mg / ml, and the concentration of zinc acetate is 0.036mg / ml. (Actual concentration needs to be calculated)

[0071] Preparation of dimethyl isophthalate stock solution: Weigh 2.0g of dimethyl isophthalate and 100g of methanol, accurate to 0.1mg, mix well and set aside (actual concentration needs to be calculated).

[0072] Recommended gas chromatography test conditions when using the capillary column of the above specifications

[0073] Nitrogen flow rate: 25mL / min; hydrogen flow rate 40mL / min; air flow rate 300mL / min

[0074] Column temperature: 180°C (30min); inlet temperature 250°C; detector temperature 280°C; injection volume 1μL

[0075] Preparation of calibration solution

[0076] It is recommended to prepare the dimethyl isophthalate calibration solution according to Table 1

[0077]

[0078] Weigh the calibration solutions of the above masses respectively. Add 25 ml of the transesterification solution to the above calibration solutions, shake well, filter into a bottle, take 1 μL of the filtrate and analyze it by gas chromatography;

[0079] Drawing of the calibration curve

[0080] Taking the mass of diethylene glycol (in milligrams) in the calibration solution as the ordinate and the ratio of the peak area of dimethyl isophthalate to the peak area of the internal standard as the abscissa, draw the calibration curve by linear regression, and the correlation coefficient is higher than 0.99;

[0081] Note: According to the content of isophthalic acid reagent in the sample, the range of use of the standard curve needs to be adjusted reasonably;

[0082] Experimental procedure

[0083] Weigh about 1 g of the sample accurately to 0.1 mg into the reaction tube, accurately add 25 mL of the transesterification solution, tighten the reaction tube with a wrench, put it into the heating device, take it out after reacting at 210 °C for 2 h, cool it to room temperature with tap water, filter into a bottle, take 1 μL of the filtrate and test it with a gas chromatograph;

[0084] Result calculation

[0085] Calculation of the isophthalic acid content in the sample:

[0086]

[0087] X1 —— Isophthalic acid content;

[0088] K —— Slope of the working curve, in milligrams mg;

[0089] A1 —— Area of dimethyl isophthalate, in square centimeters cm 2 ;

[0090] A ST —— Area of tetraethylene glycol dimethyl ether, in square centimeters cm 2 ;

[0091] m —— Mass of the sample, in grams g;

[0092] 0.855 —— Ratio of the relative molecular weights of isophthalic acid and dimethyl isophthalate.

[0093] Figure 2 This is the chromatogram of the test results of the regenerated slice of cord fabric in an embodiment of the present invention, Figure 3 This is the schematic diagram of the injection results of the test of the regenerated slice of cord fabric in an embodiment of the present invention, Figure 4 This is the chromatogram of the test results of the regenerated slice of cord fabric in an embodiment of the present invention, Figure 5Schematic diagram of the test sample injection result of the regenerated chip of the cord fabric in an embodiment of the present invention; please refer to Figures 2 to 5 , calculated according to the solution result of the present invention:

[0094]

[0095] In summary, the detection method of isophthalic acid content proposed by the present invention can detect the isophthalic acid content, has simple operation and high test result accuracy.

[0096] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the various technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope described in this specification.

[0097] The description and application of the present invention here are illustrative and do not intend to limit the scope of the present invention to the above embodiments. The effects or advantages involved in the embodiments may not be reflected in the embodiments due to various factors. The description of the effects or advantages is not used to limit the embodiments. The deformations and changes of the embodiments disclosed here are possible, and the substitutions and equivalent various components of the embodiments are well known to those of ordinary skill in the art. Those skilled in the art should clearly understand that the present invention can be implemented in other forms, structures, arrangements, proportions, and with other components, materials and parts without departing from the spirit or essential characteristics of the present invention. Other deformations and changes can be made to the embodiments disclosed here without departing from the scope and spirit of the present invention.

Claims

1. A method for detecting the content of isophthalic acid, characterized in that, The detection method for the content of isophthalic acid includes: Step S1: Prepare the transesterification solution; weigh a set amount of tetraethylene glycol dimethyl ether and zinc acetate, dissolve and dilute with methanol. Step S2: Prepare the isophthalic acid stock solution; weigh a set amount of dimethyl isophthalate and methanol, and mix evenly. Step S3: Configure the dimethyl isophthalate calibration solution; weigh a set mass of calibration solution from the isophthalic acid stock solution, add a set amount of transesterification solution to the calibration solution, mix evenly, and filter. Step S6: Analyze the different filtrates obtained in Step S3 by gas chromatography to obtain the coefficient K. Step S7: Weigh a set mass of the sample into a reaction vessel, add the transesterification solution to the reaction vessel, seal the reaction vessel, and place it in a heating device; after reacting at a set temperature for a set time, take it out, cool it to a set temperature, filter, and aspirate a set filtrate for testing with a gas chromatograph; calculate the content of isophthalic acid based on the data obtained in Step S6 and the results of the test with the gas chromatograph in this step.

2. The detection method for the content of isophthalic acid according to claim 1, characterized in that: In Step S6, using a chromatographic separation analysis method with a gas as the mobile phase, the vaporized filtrate is carried into the chromatographic column by the carrier gas. The stationary phase in the chromatographic column has different molecular interactions with the components in the sample, and the components flow out of the chromatographic column at different times, achieving component separation. An FID detector is used to produce a chromatogram indicating the time and concentration of each component flowing out of the chromatographic column; according to the peak time and order shown in the figure, qualitative analysis of the compound is performed; according to the height and area of the peak, quantitative analysis of the compound is performed.

3. The detection method for the content of isophthalic acid according to claim 1, characterized in that: In Step S7, the calculation of the isophthalic acid content in the sample: Wherein, X1 is the content of isophthalic acid, K is the slope of the working curve, A1 is the area of dimethyl isophthalate, A ST is the area of tetraethylene glycol dimethyl ether, m is the mass of the sample, and 0.855 is the ratio of the relative molecular weights of isophthalic acid and dimethyl isophthalate.

4. The detection method for the content of isophthalic acid according to claim 1, characterized in that: In Step S7, using a chromatographic separation analysis method with a gas as the mobile phase, the vaporized sample is carried into the chromatographic column by the carrier gas. The stationary phase in the chromatographic column has different molecular interactions with the components in the sample, and the components flow out of the chromatographic column at different times, achieving component separation. An FID detector is used to produce a chromatogram indicating the time and concentration of each component flowing out of the chromatographic column; according to the peak time and order shown in the figure, qualitative analysis of the compound is performed; according to the height and area of the peak, quantitative analysis of the compound is performed.

5. The detection method for the content of isophthalic acid according to claim 1, characterized in that: In Step S7, weigh about 1 g of the sample, accurate to 0.1 mg, into a reaction tube, accurately add 25 mL of the transesterification solution, tighten the reaction tube with a wrench, place it in a heating device, take it out after reacting at 210 °C for 2 h, cool it to room temperature with tap water, filter it into a bottle, and aspirate 1 μL of the filtrate for testing with a gas chromatograph.

6. The detection method for the content of isophthalic acid according to claim 1, characterized in that: Before step S6 and after step S3, the detection method further includes step S4: constructing a mathematical model of gas chromatography parameters; extracting the characteristics of the substance to be detected, using the extracted characteristics as the input of the mathematical model of gas chromatography parameters, and constructing the mathematical model of gas chromatography parameters accordingly. The outputs of the mathematical model of gas chromatography parameters include: column inner diameter, column length, film thickness, stationary phase composition, and flow rate.

7. The detection method for the content of isophthalic acid according to claim 6, characterized in that: Before step S6 and after step S4, the detection method further includes step S5: extracting the characteristic data of isophthalic acid, and using this as input data to input into the mathematical model of gas chromatography parameters; obtaining the corresponding key gas chromatography parameters: inlet temperature, column temperature, detector temperature, nitrogen flow rate, air flow rate, and split ratio, and setting them in the gas chromatograph accordingly.

8. The detection method for the content of isophthalic acid according to claim 6, characterized in that: In step S6, gas chromatography analysis is performed on the filtrate using the key gas chromatography parameters set in the gas chromatograph in step S5 to obtain corresponding data.

9. The detection method for the content of isophthalic acid according to claim 1, characterized in that: The detection method further includes: plotting a calibration curve; Taking the mass of diethylene glycol in the calibration solution as the ordinate and the ratio of the peak area of dimethyl isophthalate to the peak area of the internal standard as the abscissa, linearly regressing to plot the calibration curve, and the correlation coefficient is higher than 0.

99.

10. The detection method for the content of isophthalic acid according to claim 1, characterized in that: In step S1, the steps for preparing the transesterification solution include: weighing 240 mg of tetraethylene glycol dimethyl ether and 36 mg of zinc acetate, dissolving with methanol and diluting to 1 L; the concentration of the internal standard in this solution is 0.24 mg / ml, and the concentration of zinc acetate is 0.036 mg / ml. In step S2, the steps for preparing the isophthalic acid stock solution include: weighing 2.0 g of dimethyl isophthalate and 100 g of methanol, mixing well for use. In step S3, the steps for preparing the dimethyl isophthalate calibration solution include: weighing the calibration solution with a set mass respectively, adding 25 ml of the transesterification solution to the calibration solution, shaking well, and filtering into a bottle; in step S6, 1 μL of the filtrate is aspirated for gas chromatography analysis.

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