Method for determining composition of amide thickening agent

Abstract

The invention relates to the field of chemical analysis, and discloses an amide thickening agent composition determination method, which comprises: (1) mixing an amide thickening agent, an internal standard substance and a solvent A to obtain a mixed solution B; (2) determining each component in the amide thickening agent in the mixed solution B, the characteristic peak area of the internal standard substance and the proton number corresponding to the characteristic peak; (3) calculating the mass percentage content of each component in the amide thickening agent according to the area of the characteristic peak and the number of protons corresponding to the characteristic peak; wherein the amide thickening agent contains a metal salt of N-alkyl terephthalic acid monoacyl sodium salt. The method is easy and convenient to operate, high in accuracy and high in detection efficiency, the composition of the amide thickening agent can be determined through the method, quantitative analysis of amide compounds is achieved, and therefore data support is provided for adjustment of the synthesis reaction material proportion of the amide thickening agent, adjustment of an application investigation formula and the like.

Description

Technical Field

[0001] The present invention relates to the field of chemical analysis, and in particular to a method for determining the composition of an amide thickener. Background Art

[0002] Amide thickeners, primarily composed of sodium N-alkyl terephthalate monoacyl salts, offer advantages such as a high dropping point, excellent radiation resistance, long life, and good oxidative and mechanical stability. They are primarily used in the manufacture of high-performance greases for use in various industrial equipment, aviation, aerospace, automotive, food processing, bearings, gearboxes, and other applications requiring high lubrication. Their primary functions include providing lubrication, reducing friction, preventing wear, and reducing heat and noise.

[0003] The synthesis of sodium salts of N-alkyl terephthalic acid monoacyl groups primarily involves aminolysis of esters with amines, followed by saponification. This is accompanied by other side reactions, resulting in complex byproducts. Understanding the absolute content of byproducts and unreacted raw materials during the synthesis of amide salts provides accurate data support for optimizing the material ratios in the synthesis reaction and regulating the process formulation.

[0004] Since amide thickener products have an amide structure, gas chromatography, liquid chromatography, and gas-mass spectrometry are often used for qualitative analysis of amide compound products.

[0005] CN101692074A proposes a liquid chromatography method for analyzing and determining C8-C 24 The method of fatty amide compounds is characterized by: using high-purity spherical silica particles, using reverse-phase bonding C 18 The chromatographic column is filled with water-organic polar solvent as mobile phase, wherein the mobile phase includes organic acid; the volume ratio of water-organic polar solvent is 80:20-50:50; comprising the following steps: (1) taking C 8- C 24 An appropriate amount of fatty amide compound sample is dissolved in water to prepare a sample solution with a concentration of 0.1-5 mg / mL; (2) the flow rate of the mobile phase is set to 0.5-1.5 ml / min, the detection wavelength is 200-260 nm, and the column box temperature is 25-50 ° C; (3) 10-40 μL of the sample solution of (1) is taken and injected into the high performance liquid chromatograph to complete C 8- C 24 Qualitative analysis of fatty amide compounds.

[0006] CN103512996A discloses an analytical method for amide compounds, which is analyzed by gas chromatography-mass spectrometry. Under the analytical conditions optimized by the present invention, five amide compounds can obtain good chromatographic peaks within 15 minutes and can obtain good separation effects; all target compounds have good linearity within the concentration range of 0.01-10 mg / L, with correlation coefficients greater than 0.9995, detection limits of 0.01 mg / kg, relative standard deviations <2.5%, and spiked recoveries of 80%-105%. This method can only achieve relative quantitative analysis of amide compounds, and the amide compounds in this method include formamide, N, N-dimethylformamide, N-methylacetamide, N, N-dimethylacetamide, and acrylamide, which are different from the structures of the substances to be measured in the present invention.

[0007] The above methods calculate the trend of product component content by identifying the characteristic peaks of the components. However, they are unable to use the characteristic peak ratio of sodium monoacyl to diamide to determine the relative content of amide in different sample compositions, and thus are unable to promote process improvement and quality control of amide thickeners. When using nuclear magnetic resonance to quantitatively analyze the content of synthetic amide salt thickeners, due to the poor solubility of sodium N-alkyl terephthalate monoacyl salt in solvents (solubility decreases with carbon chain length), there are problems with solvent peak interference and inaccurate internal standard calibration, which interfere with the measurement results. It is impossible to accurately quantitatively analyze sodium N-alkyl terephthalate monoacyl salt, amide synthesis reaction byproducts, and unreacted raw materials, resulting in the inability to evaluate and determine the reaction process and yield of the synthetic amide thickener.

[0008] Therefore, there is an urgent need to provide a detection method for quantitative analysis of the composition of amide thickeners. Summary of the Invention

[0009] The purpose of the present invention is to overcome the problems of poor solubility of amide salt thickeners in the prior art and inaccurate quantitative detection results, and to provide a method for determining the composition of an amide thickener.

[0010] In order to achieve the above object, the present invention provides a method for determining the composition of an amide thickener, wherein the method comprises:

[0011] (1) mixing an amide thickener, an internal standard substance, and a solvent A to obtain a mixed solution B;

[0012] (2) determining the characteristic peak areas of the components of the amide thickener and the internal standard in the mixed solution B and the number of protons corresponding to the characteristic peaks;

[0013] (3) calculating the mass percentage of each component in the amide thickener based on the characteristic peak area and the number of protons corresponding to the characteristic peak;

[0014] Wherein, the amide thickener contains a metal salt of sodium N-alkyl terephthalate.

[0015] Through the above technical solution, the present invention achieves the following beneficial effects:

[0016] The present invention adopts a nuclear magnetic resonance method to perform quantitative analysis of amide compounds. During the analysis process, complicated pretreatment of samples and provision of standard samples of the components to be tested are not required. Only the area of ​​the absorption peak of each component and the number of protons corresponding to the absorption peak need to be used for calculation, thereby eliminating the influence of the pretreatment on the detection result. The method is simple to operate, has high accuracy and high detection efficiency. The composition of the amide thickener can be determined by the method, and the quantitative content of each component (sodium octadecanoyl, bisamide, residual raw material dimethyl terephthalate, residual raw material octadecylamine, etc.) can be obtained by analysis at the same time, thereby providing data support for adjusting the ratio of synthetic reaction materials of the amide thickener, adjusting the application investigation formula, and the like. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is the nuclear magnetic resonance identification spectrum of the main component of the amide thickener in Example 1.

[0018] Figure 2 is the hydrogen nuclear magnetic resonance spectrum of the amide thickener in Example 1. DETAILED DESCRIPTION

[0019] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0020] The present invention provides a method for determining the composition of an amide thickener, wherein the method comprises:

[0021] (1) mixing an amide thickener, an internal standard substance, and a solvent A to obtain a mixed solution B;

[0022] (2) determining the characteristic peak areas of the components of the amide thickener and the internal standard in the mixed solution B and the number of protons corresponding to the characteristic peaks;

[0023] (3) calculating the mass percentage of each component in the amide thickener based on the characteristic peak area and the number of protons corresponding to the characteristic peak;

[0024] Wherein, the amide thickener contains a metal salt of sodium N-alkyl terephthalate.

[0025] In the present invention, the synthesis process of the amide thickener is accompanied by side reactions, and the generated by-products (such as bisamide) and unreacted raw materials (such as octadecylamine and dimethyl terephthalate) are mixed in the target product. The main component of the amide thickener finally obtained is a metal salt containing N-alkyl terephthalic acid monoamide.

[0026] In the present invention, preferably, the metal salt of sodium N-alkyl terephthalate is sodium octadecanoyl.

[0027] In the present invention, the preparation method of sodium octadecanoyl comprises: mixing octadecylamine and dimethyl terephthalate, keeping the mixture at a constant temperature of 180-190° C. for 6-10 hours, then saponifying the mixture at 95-100° C. with a sodium hydroxide solution having a mass percentage concentration of 6-7% for 4-6 hours, and finally centrifuging and washing with water.

[0028] In the present invention, dimethyl terephthalate is the raw material for the synthesis of sodium octadecanoyl. In the actual production process, the present invention can reduce or even eliminate the residual dimethyl terephthalate raw material in the amide thickener by controlling the corresponding process method.

[0029] According to some embodiments of the present invention, the amide thickener further comprises bisamide, octadecylamine and optionally dimethyl terephthalate.

[0030] In the present invention, the bisamide is obtained by self-production. The preparation method of the bisamide comprises: reacting diformic acid with octadecylamine at high temperature and high pressure and then dehydrating the bisamide.

[0031] In the present invention, octadecylamine and dimethyl terephthalate can be purchased commercially or prepared in-house. The preparation method for octadecylamine comprises: continuously and quantitatively feeding stearic acid and ammonia into a liquid-phase reaction tower, and aminating at 300-360°C to produce octadecanonitrile. The intermediate product is washed and refined with water, then added to an autoclave, where it is hydrogenated at 125-135°C and 3-4 MPa under the action of a nickel catalyst to produce octadecylamine. The hydrogenated product is precipitated to remove the catalyst to obtain the finished product. Methods for preparing dimethyl terephthalate include terephthalic acid (TPA) methyl esterification, PET alcoholysis, and the Witten-Hercules process.

[0032] In the present invention, the amount of the amide thickener can be adjusted accordingly according to the molecular weight of the analyte, the field strength, and the detection method (such as hydrogen spectrum, carbon spectrum).

[0033] In the present invention, adopt nuclear magnetic resonance internal standard method to carry out quantitative analysis. Internal standard method is a kind of indirect or relative calibration method, when analyzing the content of a certain component in the sample, adds a kind of internal standard substance to calibrate and eliminate the influence produced due to operating conditions, thereby determines the zero point of the chemical shift of nuclear magnetic resonance spectrum. And the selection of internal standard substance has a great influence on the accuracy of the quantitative detection result of the test substance, therefore, the selection of internal standard substance and its important. In the experiment process, the inventor found that when the internal standard substance meets the following conditions, the absorption peak of the internal standard substance and the test analyte substance does not overlap, and has less proton equivalent, and the measurement result is accurate. a. The internal standard should be a substance not present in the analyte to be measured, and the internal standard should be a known compound with high purity, good stability, and low volatility; b. The components of the internal standard and the analyte to be measured should be essentially the same or as consistent as possible, such as having similar physical or chemical properties (chemical structure, polarity, volatility, and solubility in the solvent); c. The internal standard must be completely soluble in the analyte to be measured (or solvent), not chemically react with the analyte to be measured, and be completely separable from the chromatographic peaks of each component in the analyte; d. The amount of the internal standard should be close to that of the analyte to be measured; e. The chromatographic behavior and response characteristics of the internal standard should preferably be homologous to the analyte to be measured. Specifically, the position of the internal standard chromatographic peak should be close to that of the analyte chromatographic peak, or between several chromatographic peaks of the analyte to be measured, in order to avoid sensitivity differences caused by instrument instability; f. The peak area matching between the internal standard and the analyte should be greater than 75% to avoid sensitivity deviations caused by different response value regions of the internal standard and the analyte.

[0034] According to some embodiments of the present invention, the internal standard is selected from 2,4,6-trichloropyridine and / or tetrafluorobenzene, preferably 2,4,6-trichloropyridine.

[0035] In the present invention, when the type of the internal standard satisfies the above-mentioned limited range, the position of the characteristic peak of the internal standard in the present invention is close to the position of the characteristic peak of each component in the analyte to be measured or in the middle of the characteristic peak of the component to be measured, and the characteristic peak of the internal standard can be completely separated from the characteristic peak of each component in the amide thickening agent. The characteristic peaks of the internal standard and the components in the amide thickening agent will not overflow together, thereby avoiding the difference in sensitivity caused by the instability of the instrument.

[0036] In the present invention, if there are too many impurities in the internal standard, the impurities in the internal standard will interfere with the detection results during nuclear magnetic resonance detection, resulting in a large error in the calibration of the internal standard. Preferably, the purity of the internal standard is ≥99wt%.

[0037] According to some embodiments of the present invention, the mass ratio of the amide thickener to the internal standard is (0.8-1.2):1.

[0038] In the present invention, if the ratio of the amount of the amide thickener (analyte) to the internal standard is not appropriate, quantitative analysis cannot be performed. When the amount of the internal standard meets the above-defined range, the matching of the characteristic peak areas of the internal standard and each component of the amide thickener is greater than 75%, thereby avoiding sensitivity deviation caused by their different response value regions.

[0039] According to some embodiments of the present invention, the solvent A is deuterated trifluoroacetic acid.

[0040] In the present invention, during the nuclear magnetic resonance test, slight fluctuations in magnetic field intensity can cause changes in the chemical shift of the compound's characteristic peak, resulting in a shift in the chemical shift of the characteristic peak across the entire hydrogen spectrum. When the present invention employs solvent A for quantitative nuclear magnetic resonance analysis of an amide thickener, the chemical shift of the characteristic peak of solvent A can be completely distinguished from the chemical shifts of the various components in the amide thickener, without obscuring the sample peak. Furthermore, the field can be accurately locked, ensuring that a highly uniform and stable magnetic field intensity is maintained throughout the nuclear magnetic resonance test, thereby obtaining accurate test data.

[0041] In the present invention, if there are too many impurities in the solvent, the impurities will affect the test results during the nuclear magnetic resonance test. Preferably, the purity of the solvent A is ≥99.5wt%.

[0042] According to some embodiments of the present invention, the volume mass ratio of the solvent A to the amide thickener is (0.15-0.3): 1 mL / mg.

[0043] In the present invention, the volume mass ratio of solvent A to amide thickener is (0.15-0.3):1 mL / mg, wherein "mL / mg" means that the volume of solvent A added to 1 mg of amide thickener is 0.15-0.3 mL.

[0044] In the present invention, the inventors have also found that the type, concentration and dosage of the solvent will also have a great impact on the quantitative detection results of the content of each component in the amide thickener. For example, when dichloromethane is selected as the solvent, the polarity of the solvent is reduced, and the phenomenon of poor solubility will occur, resulting in inaccurate quantitative results. The influence of the solvent is also reflected in the concentration. As the solvent concentration increases, the degree of dilution of the amide increases, resulting in a decrease in the ability to form hydrogen bonds between the amide molecules, and the ratio of isomers also changes accordingly. The cis and trans protons between the amide molecules are all displaced to high field. In addition, too little solvent will affect the automatic field averaging effect, thereby affecting the experimental speed and the effect of the hydrogen spectrum; too much solvent will cause waste, and because the sample is diluted, the effective sample amount in the corresponding coil on the instrument fixed depth graduated cylinder is reduced.

[0045] In the present invention, when the type, concentration and amount of the solvent A meet the above-defined ranges, the solubility of the amide thickener in the solvent A is very high, and the solvent peak does not overlap with the sample peak, thus not interfering with the determination.

[0046] According to some embodiments of the present invention, the characteristic peak area and the number of protons corresponding to the characteristic peak are measured using nuclear magnetic resonance hydrogen spectroscopy.

[0047] In the present invention, the main principle involved in the determination of the components and content of the amide thickener by the nuclear magnetic resonance hydrogen method is that in a strong magnetic field, the magnetic properties inherent in the atomic nuclei and electron energy of certain elements are split into two or more quantized energy levels. By absorbing electromagnetic radiation of appropriate frequencies, transitions can occur between the generated magnetically induced energy levels. In the magnetic field, such molecules or atomic nuclei with nuclear magnetism absorb the energy difference between the two energy levels transitioning from a low energy state to a high energy state, generating a resonance spectrum that can be used to determine the number, type, and relative position of certain atoms in the molecule, thereby performing qualitative and quantitative analysis.

[0048] In the present invention, the sample to be tested and the internal standard of known purity are accurately weighed, mixed, and dissolved in a deuterated reagent to prepare a test solution. After nuclear magnetic resonance analysis, the characteristic peaks of the test components and the internal standard and the corresponding proton numbers are obtained, and the content of the test sample is calculated according to the absolute quantitative formula.

[0049] In the present invention, in order to fully dissolve the amide thickener and internal standard in solvent A, the acylated compound, internal standard and solvent A can be mixed and then ultrasonically treated. Preferably, the ultrasonic treatment conditions include: ultrasonic frequency of 20-40 KHz, temperature of 35-40° C., and time of 5-10 min.

[0050] According to some embodiments of the present invention, the detection conditions of the nuclear magnetic resonance spectroscopy include: a pulse sequence of 30-degree excitation angle, a delay time ≥ 6s, a blank scan number ≥ 4, and a scan number ≥ 32.

[0051] According to some embodiments of the present invention, the method for calculating the mass percentage of each component in the amide thickener includes: calculating the mass percentage of each component in the amide thickener according to the characteristic peak area I a , the number of protons N corresponding to the characteristic peaks of each component in the amide thickener a , the relative molecular mass M of each component in the amide thickener a and the mass W of amide thickener a And the characteristic peak area of ​​the internal standard I s , the number of protons N corresponding to the characteristic peak of the internal standard s , the relative molecular mass M of the internal standard s , the mass of the internal standard W sand the purity Ps of the internal standard, calculate the mass percentage P of each component in the amide thickener a .

[0052] In the present invention, the characteristic peak area of ​​each component in the amide thickener and the characteristic peak area of ​​the internal standard are automatically integrated and calculated by a nuclear magnetic resonance instrument. Before performing the integral calculation, phase correction and baseline leveling are required, and the corresponding integral interval of the quantitative peak is selected. Each peak is integrated 3-4 times to ensure that the integral area tends to be stable and the signal-to-noise ratio (S / N) of each quantitative peak is ≥150. When the relative standard deviation (RSD) of the repeated integrated peak areas is less than 1%, the average is taken to obtain the characteristic peak area of ​​each component in the amide thickener and the characteristic peak area of ​​the internal standard.

[0053] According to some embodiments of the present invention, the mass percentage of each component in the amide thickener is P a Satisfies the following formula:

[0054]

[0055] Among them, I a is the characteristic peak area of ​​each component in the amide thickener;

[0056] Among them, N a is the number of protons corresponding to the characteristic peaks of each component in the amide thickener;

[0057] Among them, M a is the molar mass of each component in the amide thickener;

[0058] Among them, W a is the mass of the amide thickener, in mg;

[0059] Among them, I s is the characteristic peak area of ​​the internal standard;

[0060] Among them, N s is the number of protons corresponding to the characteristic peak of the internal standard;

[0061] Among them, M s is the molar mass of the internal standard;

[0062] Among them, W s is the mass of the internal standard, in mg;

[0063] Wherein, Cs is the purity of the internal standard, and the unit is mass %.

[0064] In the present invention, the chemical shift of the characteristic peak of octadecylamine in the amide thickener in the H NMR spectrum overlaps with that of other components in the amide thickener (sodium octadecanoyl, bisamide and dimethyl terephthalate), which is not conducive to the calculation of the characteristic peak area. The difference method is used for calculation. The mass percentage content of octadecylamine in the amide thickener P a (Octadecanamine) satisfies the following formula:

[0065] P a (Octadecanamine)=100-P a (Sodium octadecanoyl)-P a (dimethyl terephthalate)-

[0066] P a (bisamide).

[0067] The present invention will be described in detail below through examples.

[0068] 2,4,6-Trichloropyridine was purchased from Chongqing Southwest Chemical Reagent Co., Ltd. with a purity of 99.9% by mass.

[0069] Deuterated trifluoroacetic acid was purchased from Chongqing Southwest Chemical Reagent Co., Ltd. with a purity of 99.5% by mass.

[0070] The mass percentages of sodium octadecanoyl, bisamide and dimethyl terephthalate were all determined using a nuclear magnetic resonance spectrometer (ASCEND 400) produced by BRUKER.

[0071] The mass percentage of each component in the amide thickener P a (sodium octadecanoyl, bisamide, dimethyl terephthalate) satisfies the following formula:

[0072]

[0073] Among them, I a is the characteristic peak area of ​​each component in the amide thickener;

[0074] Among them, N a is the number of protons corresponding to the characteristic peaks of each component in the amide thickener;

[0075] Among them, M a is the molar mass of each component in the amide thickener;

[0076] Among them, W a is the mass of the amide thickener, in mg;

[0077] Among them, I s is the characteristic peak area of ​​the internal standard;

[0078] Among them, N sis the number of protons corresponding to the characteristic peak of the internal standard;

[0079] Among them, M s is the molar mass of the internal standard;

[0080] Among them, W s is the mass of the internal standard, in mg;

[0081] Wherein, Cs is the purity of the internal standard, expressed in mass %;

[0082] Among them, the chemical shifts of the characteristic peaks of sodium octadecanoyl, bisamide and dimethyl terephthalate in the nuclear magnetic resonance hydrogen spectrum are 8.32 / 8.34, 7.98 and 8.22 ppm, respectively.

[0083] The mass percentage of octadecylamine in the amide thickener P a (Octadecanamine) satisfies the following formula:

[0084] P a (Octadecanamine)=100-P a (Sodium octadecanoyl)-P a (dimethyl terephthalate)-

[0085] P a (bisamide).

[0086] In the following examples and comparative examples, unless otherwise specified, all reagents were commercially available.

[0087] Preparation Example

[0088] Octadecanoyl sodium thickener was prepared by mixing octadecylamine and dimethyl terephthalate in a molar ratio of 1:1.3, keeping the mixture at a constant temperature of 185°C for 8 hours, then saponifying the mixture with a 7% sodium hydroxide solution at 100°C for 4 hours, and finally centrifuging and washing with water.

[0089] Example 1

[0090] (1) Weigh 11 mg of the amide thickener (Preparation Example 1), add 10 mg of 2,4,6-trichloropyridine (purity: 99.9%), and then add 2 mL of deuterated trifluoroacetic acid reagent (purity: 99.5%). Ultrasonicate for 1 min to completely dissolve the mixture. Then transfer the mixture into a 5 mm NMR tube, seal, and label for later use.

[0091] Among them, the chemical shift of the characteristic peak of 2,4,6-trichloropyridine in the H NMR spectrum is 7.53 ppm;

[0092] Among them, the chemical shift of the characteristic peak of deuterated trifluoroacetic acid in the nuclear magnetic resonance hydrogen spectrum is 11.72ppm;

[0093] (2) The mixed solution was subjected to nuclear magnetic resonance analysis to determine the characteristic peak areas of sodium monoacyl, bisamide, octadecylamine, dimethyl terephthalate and the internal standard, as well as the number of protons corresponding to the characteristic peaks. The mass percentage of each component in the amide thickener was calculated according to the above formula. The specific data are shown in Table 1;

[0094] The detection conditions of the nuclear magnetic resonance spectrometer were set as follows: the pulse sequence was 30-degree excitation angle, the delay time was 6 s, the number of blank scans was 4, and the number of scans was 32.

[0095] Example 2

[0096] (1) Weigh 10 mg of amide thickener, add 9 mg of 2,4,6-trichloropyridine (purity 99.9%), and then add 2 mL of deuterated trifluoroacetic acid reagent (purity 99.5%). Ultrasonicate for 1 min to completely dissolve the mixture. Then transfer the mixture into a 5 mm NMR tube, seal and label it for later use.

[0097] Among them, the chemical shift of the characteristic peak of 2,4,6-trichloropyridine in the H NMR spectrum is 7.53 ppm;

[0098] Among them, the chemical shift of the characteristic peak of deuterated trifluoroacetic acid in the nuclear magnetic resonance hydrogen spectrum is 11.72ppm;

[0099] (2) The mixed solution was subjected to nuclear magnetic resonance analysis to determine the characteristic peak areas of sodium monoacyl, bisamide, octadecylamine, dimethyl terephthalate and the internal standard, as well as the number of protons corresponding to the characteristic peaks. The mass percentage of each component in the amide thickener was calculated according to the above formula. The specific data are shown in Table 1;

[0100] The detection conditions of the nuclear magnetic resonance spectrometer were set as follows: the pulse sequence was 30-degree excitation angle, the delay time was 6 s, the number of blank scans was 5, and the number of scans was 32.

[0101] Example 3

[0102] (1) Weigh 10 mg of amide thickener, add 10 mg of 2,4,6-trichloropyridine (purity 99.9%), then add 2 mL of deuterated trifluoroacetic acid reagent (purity 99.5%), sonicate for 1 min to completely dissolve, then transfer the mixture into a 5 mm NMR tube, seal and label for later use;

[0103] Among them, the chemical shift of the characteristic peak of 2,4,6-trichloropyridine in the H NMR spectrum is 7.53 ppm;

[0104] Among them, the chemical shift of the characteristic peak of deuterated trifluoroacetic acid in the nuclear magnetic resonance hydrogen spectrum is 11.72ppm;

[0105] (2) The mixed solution was subjected to nuclear magnetic resonance analysis to determine the characteristic peak areas of sodium monoacyl, bisamide, octadecylamine, dimethyl terephthalate and the internal standard, as well as the number of protons corresponding to the characteristic peaks. The mass percentage of each component in the amide thickener was calculated according to the above formula. The specific data are shown in Table 1;

[0106] The detection conditions of the nuclear magnetic resonance spectrometer were set as follows: the pulse sequence was 30-degree excitation, the delay time was 7 s, the number of blank scans was 6, and the number of scans was 33.

[0107] Example 4

[0108] The method of Example 1 was followed, except that the internal standard was 1,3,5-trimethoxybenzene. The results are shown in Table 1.

[0109] Example 5

[0110] The method of Example 1 was followed, except that solvent A was deuterated sulfuric acid. The results are shown in Table 1.

[0111] Comparative Example 1

[0112] The content of sodium octadecanoyl was determined according to the detection method of Example 1 in CN103512996A. The results are shown in Table 1.

[0113] Test Example 1

[0114] Accuracy test:

[0115] The measurement was repeated three times according to the method of Example 1. The results are shown in Table 2.

[0116] Table 1

[0117]

[0118] Table 2

[0119]

[0120] As can be seen from the results in Table 1-2, the nuclear magnetic resonance spectroscopy method of Examples 1-3 of the present invention can quantitatively analyze the content of each component in the amide thickener (mainly a metal salt of sodium N-alkyl terephthalate), with simple operation, high accuracy and reasonable data.

[0121] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for determining the composition of an amide thickener, characterized in that: The method includes: (1) mixing an amide thickener, an internal standard substance, and a solvent A to obtain a mixed solution B; (2) determining the characteristic peak areas of the components of the amide thickener and the internal standard in the mixed solution B and the number of protons corresponding to the characteristic peaks; (3) calculating the mass percentage of each component in the amide thickener based on the characteristic peak area and the number of protons corresponding to the characteristic peak; Wherein, the amide thickener contains a metal salt of sodium N-alkyl terephthalate.

2. The method according to claim 1, wherein The amide thickener also includes bisamide, octadecylamine and optionally dimethyl terephthalate; And / or, the internal standard is selected from 2,4,6-trichloropyridine and / or tetrafluorobenzene, preferably 2,4,6-trichloropyridine.

3. The method according to claim 1 or 2, wherein The mass ratio of the amide thickener to the internal standard is (0.8-1.2):

1.

4. The method according to any one of claims 1 to 3, wherein: The solvent A is deuterated trifluoroacetic acid.

5. The method according to any one of claims 1 to 4, wherein: The purity of the solvent A is ≥99.5 wt %.

6. The method according to any one of claims 1 to 5, wherein: The volume mass ratio of the solvent A to the amide thickener is (0.15-0.3): 1 mL / mg.

7. The method according to any one of claims 1 to 6, wherein: In step (2), the characteristic peak area and the number of protons corresponding to the characteristic peak are measured using nuclear magnetic resonance spectroscopy.

8. The method according to claim 7, wherein: The detection conditions of the nuclear magnetic resonance spectroscopy method include: a pulse sequence of 30-degree excitation angle, a delay time of ≥6s, a blank scan number of ≥4, a scan number of ≥32, and a signal-to-noise ratio of a quantitative peak of ≥150.

9. The method according to claim 1, wherein The method for calculating the mass percentage of each component in the amide thickener includes: calculating the mass percentage of each component in the amide thickener according to the characteristic peak area I a , the number of protons N corresponding to the characteristic peaks of each component in the amide thickener a , the relative molecular mass M of each component in the amide thickener a and the mass W of amide thickener a And the characteristic peak area of ​​the internal standard I s , the number of protons N corresponding to the characteristic peak of the internal standard s , the relative molecular mass M of the internal standard s , the mass of the internal standard W s and the purity Ps of the internal standard, calculate the mass percentage P of each component in the amide thickener a .

10. The method according to claim 9, wherein: The mass percentage of each component in the amide thickener is P a Satisfies the following formula: Among them, I a is the characteristic peak area of ​​each component in the amide thickener; Among them, N a is the number of protons corresponding to the characteristic peaks of each component in the amide thickener; Among them, M a is the molar mass of each component in the amide thickener; Among them, W a is the mass of the amide thickener, in mg; Among them, I s is the characteristic peak area of ​​the internal standard; Among them, N s is the number of protons corresponding to the characteristic peak of the internal standard; Among them, M s is the molar mass of the internal standard; Among them, W s is the mass of the internal standard, in mg; Wherein, Cs is the purity of the internal standard, and the unit is mass %.

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