Method for determining dimethyl phthalate in DMC catalyst by HPLC (High Performance Liquid Chromatography) method

Abstract

The invention belongs to the technical field of detection and analysis, and discloses a method for determining dimethyl phthalate in a DMC catalyst by an HPLC (High Performance Liquid Chromatography) method. The method comprises the following steps: mixing a DMC catalyst to be detected with an ethylenediamine tetraacetic acid tetrasodium salt solution, performing ultrasonic treatment, extracting with ethyl acetate, and collecting extract liquor to prepare a sample solution to be detected; the method comprises the following steps: weighing a dimethyl phthalate standard substance, and dissolving in a solvent to prepare a standard working solution; performing chromatographic analysis on the standard working solution and the to-be-detected sample solution by adopting a liquid chromatograph to obtain a standard substance solution HPLC (High Performance Liquid Chromatography) chromatogram and a to-be-detected sample solution HPLC chromatogram, drawing a standard curve graph according to the standard substance solution HPLC chromatogram, and calculating the content of dimethyl phthalate in the to-be-detected sample solution. The method provided by the invention is simple to operate, good in accuracy, high in sensitivity and good in stability; and the analysis time is short, and the detection can be completed only in 8 minutes.

Description

Technical Field

[0001] The invention belongs to the technical field of detection and analysis, and particularly relates to a method for determining dimethyl phthalate in a DMC catalyst by using an HPLC method. Background Art

[0002] DMC (double metal cyanide complex) catalyzer is based on double metal cyanide complex, a kind of complicated complex compound of complexing other organic or inorganic ligands, is a kind of conventional catalyst that is used for oxyethane, propylene oxide etc. and carries out ring-opening polymerization.The polyether glycol with this catalyst preparation has the advantages such as relative molecular mass is high, unsaturation degree is low, relative molecular mass distribution is narrow, viscosity is low, therefore is widely used in organic synthesis field.And dimethyl phthalate is as common organic ligand in the DMC catalyzer, and the control of its content will directly affect the quality of catalyst performance, too much or too little all can cause catalyst activity to descend, and the polyether glycol of preparation can't obtain the characteristics such as above-mentioned relative molecular mass is high, unsaturation degree is low, viscosity is low.So in producing DMC catalyzer process, often take detecting dimethyl phthalate content as one of product internal control quality index, detecting dimethyl phthalate content in the DMC catalyzer is very necessary.

[0003] Currently, there is no method for detecting the content of dimethyl phthalate in DMC catalysts reported in the prior art. Therefore, there is an urgent need to establish a detection method that is simple to operate, has good accuracy, high sensitivity, and good stability for detecting the content of dimethyl phthalate in DMC catalysts. Summary of the Invention

[0004] The present invention is intended to solve at least one of the technical problems existing in the above-mentioned prior art. To this end, the present invention provides a method for determining dimethyl phthalate in a DMC catalyst by HPLC. The method provided by the present invention is simple to operate, has good accuracy, high sensitivity, and good stability.

[0005] The invention provides a method for determining dimethyl phthalate in a DMC catalyst by using an HPLC method.

[0006] Specifically, the method for determining dimethyl phthalate in a DMC catalyst by HPLC comprises the following steps:

[0007] The DMC catalyst to be tested is mixed with a tetrasodium salt solution of ethylenediaminetetraacetic acid, subjected to ultrasonic treatment, extracted with ethyl acetate, and the extract is collected to prepare a sample solution to be tested;

[0008] Weigh dimethyl phthalate standard and dissolve it in solvent to prepare standard working solutions of different concentrations;

[0009] The standard working solution and the sample solution to be tested are subjected to chromatographic analysis by a liquid chromatograph to obtain an HPLC chromatogram of the standard solution and an HPLC chromatogram of the sample solution to be tested, a standard curve is drawn according to the HPLC chromatogram of the standard solution, and the content of dimethyl phthalate in the sample solution to be tested is calculated;

[0010] The conditions of the chromatographic analysis include:

[0011] Chromatographic column: C18 column;

[0012] Elution mode: isocratic elution;

[0013] Mobile phase: by volume, methanol: water = (55-90): (10-45);

[0014] Detection wavelength: 275-280nm.

[0015] In some embodiments of the present invention, the solvent is methanol.

[0016] In some embodiments of the present invention, the concentration of the standard working solution is 1-120 μg / mL.

[0017] In some embodiments of the present invention, the mass percentage of the tetrasodium salt of ethylenediaminetetraacetic acid solution is 5%-15%, such as 8%, 10%, 12%, etc.

[0018] In some embodiments of the present invention, the pH value of the tetrasodium salt of EDTA solution is 6.5-7.5.

[0019] In some embodiments of the present invention, the mass ratio of the DMC catalyst to be tested to the tetrasodium salt of ethylenediaminetetraacetic acid solution is 1:(50-200); preferably, the mass ratio of the DMC catalyst to be tested to the tetrasodium salt of ethylenediaminetetraacetic acid solution is 1:(80-150); further preferably, the mass ratio of the DMC catalyst to be tested to the tetrasodium salt of ethylenediaminetetraacetic acid solution is 1:(80-120).

[0020] In some embodiments of the present invention, the volume ratio of the mobile phase is methanol:water=(55-80):(20-45).

[0021] In some embodiments of the present invention, the conditions for the chromatographic analysis further include:

[0022] Column temperature: 40-50°C;

[0023] Injection volume: 10-20 μL;

[0024] Flow rate: 0.8-1.0mL / min.

[0025] In some embodiments of the present invention, the detection wavelength is 277 nm.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The HPLC method provided by the present invention for determining dimethyl phthalate in DMC catalyst not only fills the technical gap in this field, but also has the advantages of simplicity, accuracy, reproducibility and high precision, and is suitable for routine detection and actual production product quality control.

[0028] (2) In the method provided by the present invention, ethylenediaminetetraacetic acid tetrasodium salt is first used to replace the complexed dimethyl phthalate in the DMC catalyst, and then ethyl acetate is used for extraction to prepare a sample solution to be tested. During this pre-treatment process, the coordinating atoms (oxygen or nitrogen) in the ethylenediaminetetraacetic acid tetrasodium molecule can provide lone pairs of electrons, which combine with metal ions to form stable coordination bonds, so that the ethylenediaminetetraacetic acid tetrasodium and the metal ions are tightly combined, thereby completely replacing the dimethyl phthalate complexed with the DMC bimetallic complex. And because the substituted dimethyl phthalate is insoluble in the ethylenediaminetetraacetic acid tetrasodium salt aqueous solution but soluble in ethyl acetate, the dimethyl phthalate can be extracted into ethyl acetate by ethyl acetate extraction for detection and analysis. This pre-treatment method, combined with the HPLC detection method provided by the present invention, can accurately detect the content of dimethyl phthalate in the DMC catalyst.

[0029] (3) The method provided by the present invention has a short analysis time, requiring only 8 minutes to complete the determination; and there is no interference, and the content detection accuracy is high. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a standard curve diagram of dimethyl phthalate in Example 1 of the present invention;

[0031] Figure 2 This is an HPLC chromatogram of a standard solution of dimethyl phthalate in Example 1 of the present invention;

[0032] Figure 3 HPLC chromatogram of dimethyl phthalate in the DMC catalyst in Example 1 of the present invention. DETAILED DESCRIPTION

[0033] In order to make the technical solution of the present invention more clearly understood by those skilled in the art, the following examples are given for illustration. It should be noted that the following examples do not limit the scope of protection claimed by the present invention.

[0034] Unless otherwise specified, the raw materials, reagents, or devices used in the following experimental examples and embodiments can be obtained from conventional commercial sources or by existing known methods.

[0035] Example 1

[0036] The method for determining dimethyl phthalate in a DMC catalyst by HPLC provided in this embodiment comprises the following steps:

[0037] (1) Preparation of a standard curve: A commercially available dimethyl phthalate standard was used. In this example, a standard reagent produced by Aladdin was used, with a content of 99%. Accurately weigh 0.1 g of the dimethyl phthalate standard and add 10 mL of methanol to prepare a standard stock solution. The standard working solution was then diluted sequentially to 100 μg / mL, 50 μg / mL, 10 μg / mL, 5 μg / mL, and 1 μg / mL. The standard solution was then stored in a dark place.

[0038] (2) Drawing of standard working curve: The above standard working solutions were sequentially introduced into the HPLC system and tested under the following chromatographic conditions: chromatographic column: C18 column (4.6*250mm 5μm); column temperature: 40°C; flow rate: 1.0mL / min; wavelength: 277nm; injection volume: 20μL; mobile phase: methanol: ultrapure water = 60:40; the standard curve (y = 7.3229x - 0.1017, R 2 =0.9999)(e.g. Figure 1 ) and HPLC chromatogram of standard solution (as shown Figure 2 shown).

[0039] (3) Preparation of ethylenediaminetetraacetic acid tetrasodium salt solution: Weigh 10 g of ethylenediaminetetraacetic acid tetrasodium salt, add 90 g of water, dissolve under ultrasonication, and adjust the pH to neutral with acid.

[0040] (4) Preparation of the sample solution: Weigh 0.1 g of the DMC catalyst sample, add 10 g of the above-mentioned tetrasodium ethylenediaminetetraacetic acid solution, and sonicate for 10 min. Extract twice with 5 g of ethyl acetate, and combine the two extracts (upper layer). Weigh 0.1 g of the extract, dilute to 10 mL with methanol, and sonicate to obtain the sample solution to be tested. Filter with a 0.25 μm microporous filter membrane.

[0041] (5) Determination of dimethyl phthalate in the sample solution: Take the above sample solution into the HPLC system, and obtain the dimethyl phthalate spectrum of the sample solution according to the above chromatographic conditions (such as Figure 3 As shown), the peak area of ​​dimethyl phthalate in the test solution was substituted into the standard curve y = 7.3229x-0.1017 to calculate the phthalic acid content in the test solution, and then the dimethyl phthalate content in the DMC catalyst was calculated based on the extraction amount and the sample amount, and the result was 7.50%.

[0042] Experimental Example 1: Methodological investigation of the determination of dimethyl phthalate in DMC catalyst by HPLC, including the following contents:

[0043] (1) Linear correlation investigation

[0044] The standard working solutions of 100 μg / mL, 50 μg / mL, 10 μg / mL, 5 μg / mL, and 1 μg / mL in Example 1 were injected according to the chromatographic conditions in Example 1. A standard curve was drawn with the concentration of the standard solution as the abscissa and the corresponding peak area as the ordinate. The curve y = 7.3229x-0.1017 was obtained. R 2 =0.9999, showing a linear relationship, which meets the actual detection requirements, as shown in Table 1.

[0045] Table 1 Linear correlation of dimethyl phthalate

[0046] Concentration (μg / mL) Peak area (mV) 1 7.6 5 38 10 74.5 50 360 100 735

[0047] (2) Precision and repeatability investigation

[0048] The 10 μg / mL standard working solution in Example 1 was injected six times continuously under the chromatographic conditions in Example 1. The relative standard deviation was calculated based on the six peak areas. The RSD was 0.80%, indicating good precision, meeting the actual detection requirements. The calculation results are shown in Table 2.

[0049] Table 2 Precision test of dimethyl phthalate

[0050] Number of injections Peak area (mV) 1 74.5 2 74.0 3 75.1 4 74.9 5 74.2 6 73.5 Relative standard deviation RSD 0.80％

[0051] Take the sample to be tested in Example 1, prepare 6 copies in parallel according to the pretreatment method of Example 1, and inject according to the chromatographic conditions in Example 1. The peak area of ​​dimethyl phthalate in the test solution is substituted into the standard curve y = 7.3229x-0.1017 to calculate the phthalic acid content in the test solution. Then, the dimethyl phthalate content in the DMC catalyst is calculated based on the extraction amount and the sample amount. The relative standard deviation is calculated, and the RSD is 1.30%, which has good repeatability and meets the actual detection requirements. The calculation results are shown in Table 3 below.

[0052] Table 3 Repeatability test of dimethyl phthalate

[0053] DMC catalyst sample content(%) Parallel 1 7.65 Parallel 2 7.50 Parallel 3 7.41 Parallel 4 7.38 Parallel 5 7.55 Parallel 6 7.49 Relative standard deviation RSD 1.30％

[0054] (3) Sensitivity investigation

[0055] The sample was injected according to the chromatographic conditions in Example 1, and a stepwise dilution method was used. At a signal-to-noise ratio of 3, a method detection limit of 0.14 μg / mL was obtained for dimethyl phthalate.

[0056] (4) Recovery rate investigation

[0057] Using the spiked recovery method, 6 portions of a test sample with a known content were spiked with dimethyl phthalate at three concentrations: low, medium, and high. The sample was injected according to the pretreatment method and chromatographic conditions described in Example 1. The recovery rate was calculated to be between 80% and 120%, which is a good recovery rate that meets practical testing requirements. The results are shown in Table 4 below.

[0058] Table 4 Recovery test of dimethyl phthalate spiked

[0059]

[0060] Experimental Example 2

[0061] Different pretreatment methods were used to detect dimethyl phthalate in DMC catalysts. The specific test was as follows: (1) Preparation of standard curve: Same as in Example 1;

[0062] (2) Drawing of standard working curve: same as in Example 1;

[0063] (3) Preparation of ethylenediaminetetraacetic acid tetrasodium salt solution: same as in Example 1;

[0064] (4) Preparation of ethylenediaminetetraacetic acid disodium salt solution: Weigh 10 g of ethylenediaminetetraacetic acid disodium salt, add 90 g of water, dissolve under ultrasonication, and adjust the pH to neutral with acid.

[0065] (5) Preparation of test sample solutions: The same batch of samples was treated with four different pretreatment methods to obtain test sample solutions.

[0066] DMC catalyst sample 1: same as Example 1 (pre-treated with ethylenediaminetetraacetic acid tetrasodium salt);

[0067] DMC catalyst sample 2: Weigh 0.1 g of DMC catalyst sample, add 10 g of the above-mentioned disodium salt of ethylenediaminetetraacetic acid solution, and sonicate for 10 min. Extract twice with 5 g of ethyl acetate, and combine the two extracts (upper layer). Weigh 0.1 g of the extract, dilute to 10 mL with methanol, and sonicate to obtain the sample solution to be tested. Filter through a 0.25 μm microporous filter membrane.

[0068] DMC catalyst sample 3: Weigh 0.1 g of DMC catalyst sample, add 5 g of carbon tetrachloride, and sonicate for 10 min. Weigh 0.1 g of the solution, dilute to 10 mL with methanol, and sonicate to obtain the sample solution to be tested. Filter with a 0.25 μm microporous filter membrane.

[0069] DMC catalyst sample 4: Weigh 0.1 g of DMC catalyst sample, dilute to 10 mL with methanol, and ultrasonically vibrate to obtain a sample solution to be tested, which is then filtered through a 0.25 μm microporous filter membrane.

[0070] (6) Determination of dimethyl phthalate in the test solution: The test sample solution was injected sequentially according to the chromatographic conditions of Example 1. The dimethyl phthalate peak area in the test solution was substituted into the standard curve y = 7.3229x-0.1017 to calculate the phthalic acid content in the test solution. The dimethyl phthalate content in the DMC catalyst was then calculated based on the extraction amount and the sample amount. The results showed that under the pretreatment method of tetrasodium ethylenediaminetetraacetic acid, the dimethyl phthalate content in the DMC catalyst could be completely detected. That is, tetrasodium ethylenediaminetetraacetic acid could completely replace the complexed dimethyl phthalate in the DMC catalyst, while disodium ethylenediaminetetraacetic acid, carbon tetrachloride, and methanol could not completely replace the complexed dimethyl phthalate in the DMC catalyst. The specific results are shown in Table 5.

[0071] Table 5 Dimethyl phthalate content in DMC catalyst

[0072]

[0073]

[0074] It can be seen from the above embodiments and experimental examples that the detection method provided by the embodiments of the present invention has the characteristics of simple operation, good precision and accuracy, etc., is suitable for the determination of the dimethyl phthalate content in DMC catalysts, and provides a good characterization method for the preparation of DMC catalysts.

[0075] 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 present invention. 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 present invention shall be determined by the appended claims.

Claims

1. The method for determining dimethyl phthalate in DMC catalyst by HPLC, characterized in that: The following steps are involved: The DMC catalyst to be tested is mixed with a tetrasodium salt solution of ethylenediaminetetraacetic acid, subjected to ultrasonic treatment, extracted with ethyl acetate, and the extract is collected to prepare a sample solution to be tested; Weigh dimethyl phthalate standard and dissolve it in solvent to prepare standard working solutions of different concentrations; The standard working solution and the sample solution to be tested are subjected to chromatographic analysis by a liquid chromatograph to obtain an HPLC chromatogram of the standard solution and an HPLC chromatogram of the sample solution to be tested, a standard curve is drawn according to the HPLC chromatogram of the standard solution, and the content of dimethyl phthalate in the sample solution to be tested is calculated; The conditions of the chromatographic analysis include: Chromatographic column: C18 column; Elution mode: isocratic elution; Mobile phase: by volume, methanol: water = (55-90): (10-45); Detection wavelength: 275-280nm.

2. The method according to claim 1, characterized in that The solvent is methanol.

3. The method according to claim 1, characterized in that The concentration of the standard working solution is 1-120 μg / mL.

4. The method according to claim 1, wherein The mass percentage of the tetrasodium salt of ethylenediaminetetraacetic acid solution is 5%-15%.

5. The method according to claim 4, characterized in that The pH value of the tetrasodium salt of ethylenediaminetetraacetic acid solution is 6.5-7.

5.

6. The method according to claim 4 or 5, characterized in that The mass ratio of the DMC catalyst to be tested to the tetrasodium salt of ethylenediaminetetraacetic acid solution is 1:(50-200).

7. The method according to claim 6, characterized in that The mass ratio of the DMC catalyst to be tested to the tetrasodium salt of ethylenediaminetetraacetic acid solution is 1:(80-150).

8. The method according to claim 1, characterized in that The volume ratio of the mobile phase is methanol:water=(55-80):(20-45).

9. The method according to claim 1, characterized in that The conditions of the chromatographic analysis also include: Column temperature: 40-50°C; Injection volume: 10-20 μL; Flow rate: 0.8-1.0mL / min.

10. The method according to claim 1, characterized in that The detection wavelength is 277 nm.

Images