Detection method and application of monochloroacetic acid content in cocamidopropyl betaine

Abstract

The present application embodiment proposes a detection method and use of the content of monochloroacetic acid in cocamidopropyl betaine. The detection method includes: under alkaline conditions, reacting a monochloroacetic acid standard solution of different concentrations with 4-nitrothiophenol in a water bath to obtain standard samples of different concentrations; performing high performance liquid chromatography ultraviolet detection on the standard samples of different concentrations to obtain the peak area of ​​monochloroacetic acid in the standard samples of different concentrations; and obtaining a linear equation of the corresponding relationship between concentration x and peak area y; performing high performance liquid chromatography ultraviolet detection on the sample to be tested to obtain the peak area of ​​monochloroacetic acid in the sample to be tested, and calculating the content of monochloroacetic acid in the sample to be tested; The detection method of the present application embodiment can effectively improve the detection accuracy and precision of the content of monochloroacetic acid in cocamidopropyl betaine.

Description

Technical Field

[0001] The present application relates to the technical field of analytical chemistry, and in particular to a method for detecting the content of monochloroacetic acid in cocamidopropyl betaine and a use thereof. Background Art

[0002] Cocamidopropyl betaine (CAB) is a mild amphoteric surfactant with excellent performance, which is often used in combination with anionic, cationic and nonionic surfactants. Because it has low irritation to eyes and skin, has a care effect on hair and skin and produces a large amount of stable foam, and has excellent foaming and washing properties in soap and hard water, it is widely used in washing products such as shampoo and foam bath.

[0003] At present, in industrial production, monochloroacetic acid (or chloroacetic acid) is often used as a raw material to produce cocamidopropyl betaine. However, monochloroacetic acid is a moderately toxic substance and is highly corrosive to the skin and mucous membranes. Therefore, when using monochloroacetic acid as a raw material to produce cocamidopropyl betaine, the residual amount in the product should be limited. In the index content analysis of cocamidopropyl betaine products, the content of monochloroacetic acid is generally required to be less than 20ppm.

[0004] In the prior art, the detection method of residual monochloroacetic acid mainly includes high performance liquid phase method, gas chromatography and ion chromatography. In high performance liquid phase method detection, due to the shorter detection wavelength of monochloroacetic acid, at about 200nm, at this wavelength, almost all substances have response, and the interference is serious when the sample composition is complicated, and it is not detected when the content is low with evaporative light scattering detector and differential detector. And gas chromatography needs to dry the sample first, then esterify with butanol, and then perform gas phase analysis after extraction, but the method has great defects, and the sample can decompose or volatilize after high temperature drying, resulting in low results, and cocamidopropyl betaine has emulsification, and extraction is also more difficult.

[0005] In view of this, the present application embodiment proposes a method for detecting the content of monochloroacetic acid in cocamidopropyl betaine. Summary of the invention

[0006] The purpose of the embodiments of the present application is to provide a method for detecting the content of monochloroacetic acid in cocamidopropyl betaine and its use.

[0007] To achieve the above objectives, the present application proposes the following technical solutions:

[0008] In a first aspect, the present application provides a method for detecting the content of monochloroacetic acid in cocamidopropyl betaine, the detection method comprising:

[0009] Prepare monochloroacetic acid standard solutions of different concentrations; react the monochloroacetic acid standard solutions of different concentrations with 4-nitrothiophenol in a water bath under alkaline conditions to obtain standard samples of different concentrations;

[0010] Performing high performance liquid chromatography ultraviolet detection on standard samples of different concentrations to obtain the peak areas of monochloroacetic acid in the standard samples of different concentrations; obtaining a linear equation of the corresponding relationship between concentration x and peak area y based on the peak areas corresponding to the standard samples of different concentrations;

[0011] A cocamidopropyl betaine solution is prepared; under alkaline conditions, the cocamidopropyl betaine solution is reacted with 4-nitrothiophenol in a water bath to obtain a sample to be tested;

[0012] The sample to be tested is subjected to high performance liquid chromatography ultraviolet detection to obtain the peak area of ​​monochloroacetic acid in the sample to be tested; the peak area of ​​monochloroacetic acid in the sample to be tested is substituted into a linear equation to calculate the content of monochloroacetic acid in the sample to be tested.

[0013] As an embodiment, under alkaline conditions, reacting monochloroacetic acid standard solutions of different concentrations with 4-nitrothiophenol in a water bath to obtain standard samples of different concentrations comprises:

[0014] Add alkali reagent and 4-nitrothiophenol to monochloroacetic acid standard solutions of different concentrations, and place them in a 70℃ water bath for reaction;

[0015] After the reaction, phosphoric acid and acetonitrile were added, the volume was fixed with distilled water, and bubbles were removed by ultrasonic wave. Standard samples of different concentrations were obtained after filtration.

[0016] As an embodiment, the cocamidopropyl betaine solution is prepared; under alkaline conditions, the cocamidopropyl betaine solution is reacted with 4-nitrothiophenol in a water bath to obtain a sample to be tested, comprising:

[0017] Prepare a cocamidopropyl betaine solution, add an alkali reagent and 4-nitrothiophenol to the cocamidopropyl betaine solution, and place the solution in a 70°C water bath for reaction;

[0018] After the reaction, phosphoric acid and acetonitrile were added, the volume was fixed with distilled water, and bubbles were removed by ultrasonic wave. The sample to be tested was obtained after filtration.

[0019] As an embodiment, the alkaline agent is sodium carbonate.

[0020] As an implementation method, the linear equation is:

[0021] y=56.6280x-2.1918, correlation coefficient R 2 =0.99842.

[0022] As an embodiment, the chromatographic column used in the high performance liquid chromatography ultraviolet detection is Agilent SB-C8.

[0023] As an embodiment, the column temperature of the chromatographic column is 30°C.

[0024] As an embodiment, the chromatographic conditions of the high performance liquid chromatography ultraviolet detection include:

[0025] The detection wavelength was 250-260 nm, and the injection volume was 20 μL;

[0026] Mobile phase A was acetonitrile;

[0027] The mobile phase B was a mixed solution of acetonitrile, water and phosphoric acid in a volume ratio of 100:898:2.

[0028] As an embodiment, the gradient elution program of mobile phase A and mobile phase B is:

[0029] Elution was performed with mobile phase A and mobile phase B in a volume ratio of 20:80 for 8 min;

[0030] Elution was performed with mobile phase A and mobile phase B in a volume ratio of 80:20 for 5 min;

[0031] Elution was performed with mobile phase A and mobile phase B in a volume ratio of 20:80 for 5 min;

[0032] Among them, the flow rate is 1.0mL / min.

[0033] In a second aspect, the embodiments of the present application provide the use of the detection method described in the first aspect in the quality control of cocamidopropyl betaine products.

[0034] The embodiments of the present application have at least the following beneficial effects:

[0035] In the embodiment of the present application, 4-nitrothiophenol is used as a derivatization reagent. Under alkaline conditions, monochloroacetic acid and 4-nitrothiophenol undergo a nucleophilic substitution reaction in a water bath to generate 2-(4-nitrophenylthio)acetic acid. Among them, the 2-(4-nitrophenylthio)acetic acid generated by derivatization is very easy to separate in high performance liquid chromatography, and can achieve the purpose of separation and detection through high performance liquid chromatography, so it is easy to eliminate the interference of matrix effects and improve the detection accuracy; therefore, the detection method of the embodiment of the present application is not only easy to operate, but also can effectively improve the separation effect, detection accuracy and precision.

[0036] The detection method provided in the embodiment of the present application can more accurately detect the content of monochloroacetic acid in cocamidopropyl betaine, and the detection method is highly efficient; thus, the embodiment of the present application solves the problem of impurity interference in the existing detection method of monochloroacetic acid, and has a better application prospect in the quality control of cocamidopropyl betaine.

[0037] Additional aspects and advantages of the present application will be partially given in the following description, which will become apparent from the following description, or will be understood through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a schematic diagram showing the effect of the derivatization reaction temperature on the peak area of ​​monochloroacetic acid;

[0039] Figure 2 is the liquid chromatogram of monochloroacetic acid;

[0040] Figure 3 Schematic diagram of the linear equation of monochloroacetic acid concentration and peak area. DETAILED DESCRIPTION

[0041] The technical scheme in the embodiments will be clearly and completely described below in combination with the embodiments of the present application and the accompanying drawings. Obviously, the embodiments described below are only part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0042] It should be understood that when used in this specification and the appended claims, the terms "include" and "comprises" indicate the presence of described features, integers, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or combinations thereof.

[0043] It should also be understood that the terms used in this specification of the embodiments of the present application are only for the purpose of describing specific embodiments and are not intended to limit the embodiments of the present application. As used in the specification of the embodiments of the present application and the appended claims, unless the context clearly indicates otherwise, the singular forms of "a", "an" and "the" are intended to include plural forms.

[0044] The following is a detailed description of the method for detecting the content of monochloroacetic acid in cocamidopropyl betaine according to the embodiments of the present application and its use.

[0045] First, the detection method of this embodiment is described.

[0046] Detection Methods

[0047] This embodiment provides a method for detecting the content of monochloroacetic acid in cocamidopropyl betaine.

[0048] Specifically, the detection method comprises:

[0049] (1) preparing monochloroacetic acid standard solutions of different concentrations; reacting the monochloroacetic acid standard solutions of different concentrations with 4-nitrothiophenol in a water bath under alkaline conditions to obtain standard samples of different concentrations;

[0050] (2) performing high performance liquid chromatography ultraviolet detection on standard samples of different concentrations to obtain the peak areas of monochloroacetic acid in the standard samples of different concentrations; based on the peak areas corresponding to the standard samples of different concentrations, obtaining a linear equation for the corresponding relationship between concentration x and peak area y;

[0051] (3) preparing a cocamidopropyl betaine solution; under alkaline conditions, reacting the cocamidopropyl betaine solution with 4-nitrothiophenol in a water bath to obtain a sample to be tested;

[0052] (4) performing high performance liquid chromatography ultraviolet detection on the sample to be tested to obtain the peak area of ​​monochloroacetic acid in the sample to be tested; substituting the peak area of ​​monochloroacetic acid in the sample to be tested into a linear equation to calculate the content of monochloroacetic acid in the sample to be tested.

[0053] It can be understood that, in this embodiment, under alkaline conditions, monochloroacetic acid and 4-nitrothiophenol undergo a nucleophilic substitution reaction in a water bath to generate 2-(4-nitrophenylthio)acetic acid. Among them, the 2-(4-nitrophenylthio)acetic acid generated by derivatization is very easy to separate in high performance liquid chromatography, and can achieve the purpose of separation and detection through high performance liquid chromatography, so it is easy to eliminate the interference of matrix effect and improve the detection accuracy.

[0054] Therefore, the detection method of this embodiment is not only easy to operate, but also can effectively improve the separation effect, detection accuracy and precision.

[0055] Next, the relevant steps of the above detection method will be further described.

[0056] Step (1), preparing monochloroacetic acid standard solutions of different concentrations; reacting the monochloroacetic acid standard solutions of different concentrations with 4-nitrothiophenol in a water bath under alkaline conditions to obtain standard samples of different concentrations; can be:

[0057] Weigh 0.1 g of monochloroacetic acid standard, dissolve it in distilled water, dilute to 100 mL, and shake well; use a pipette to transfer 10 mL into another 100 mL volumetric flask, dilute to volume, mix well, and obtain a stock solution.

[0058] In this embodiment, after obtaining the stock solution, different concentrations of monochloroacetic acid standard solutions can be prepared based on the stock solution, and an alkali reagent and 4-nitrothiophenol are added to the monochloroacetic acid standard solution, which is placed in a water bath for reaction to obtain standard samples of different concentrations.

[0059] It can be understood that the alkaline conditions described in this embodiment are pH values ​​greater than 7, and in this embodiment, an alkaline environment is created by adding an alkaline reagent, sodium carbonate.

[0060] Specifically, under alkaline conditions, monochloroacetic acid standard solutions of different concentrations are reacted with 4-nitrothiophenol in a water bath to obtain standard samples of different concentrations, including:

[0061] Alkaline reagent and 4-nitrothiophenol were added to monochloroacetic acid standard solutions of different concentrations respectively, and the solutions were placed in a 70°C water bath for reaction. After the reaction, phosphoric acid and acetonitrile were added, the solution was fixed to volume with distilled water, and bubbles were removed by ultrasonication. Standard samples of different concentrations were obtained after filtration.

[0062] For example, after the above-mentioned stock solution (monochloroacetic acid stock solution with a concentration of 100 mg / L) is prepared, 0.50 mL, 1.00 mL, 2.00 mL, 3.00 mL, 4.00 mL and 5.00 mL of the stock solution are respectively measured and put into a 50 mL volumetric flask, and the volume is filled up to 20 mL with distilled water, and 0.5 mL of 5% sodium carbonate is added, and 0.5 mL of 0.5% 4-nitrothiophenol is added dropwise, and the flasks are placed in a water bath at 70° C. for 1-3 hours; after the reaction is completed, 0.5 mL of 10% phosphoric acid is added to terminate the reaction, 10 mL of acetonitrile is added, the volume is adjusted to the mark with distilled water, bubbles are removed by ultrasound, and a series of standard samples are obtained by filtering with a syringe filter.

[0063] Usually, the ultrasonication time is 3 to 5 minutes, preferably 5 minutes.

[0064] In this example, 4-nitrothiophenol was added in the form of a 4-nitrothiophenol solution.

[0065] The preparation method of the 4-nitrothiophenol solution is as follows: weigh 0.5 g of 4-nitrothiophenol, add 49.5 g of acetonitrile, and dissolve by ultrasonication to obtain a 4-nitrothiophenol solution with a mass concentration of 1%.

[0066] This embodiment found through relevant experiments that the peak area of ​​monochloroacetic acid increases with increasing temperature, and after reaching the peak value, it decreases with increasing temperature. When the temperature is 70°C, the peak area is the largest, and this temperature has a good derivation effect, which is conducive to reflecting the test results.

[0067] In step (1), in this embodiment, 4-nitrothiophenol is used as a derivatization reagent to cause a nucleophilic substitution reaction between monochloroacetic acid and 4-nitrothiophenol to generate 2-(4-nitrophenylthio)acetic acid. The 2-(4-nitrophenylthio)acetic acid generated by derivatization is very easy to separate in high performance liquid chromatography, and can be separated and detected by high performance liquid chromatography, so that the interference of matrix effect can be easily eliminated, thereby improving the detection accuracy and precision.

[0068] In this embodiment, the CAS number of monochloroacetic acid is 79-11-8.

[0069] In step (2), after the standard samples of different concentrations are prepared, high performance liquid chromatography ultraviolet detection is performed on the standard samples of different concentrations to obtain the peak areas of monochloroacetic acid in the standard samples of different concentrations; and based on the peak areas corresponding to the standard samples of different concentrations, a linear equation of the corresponding relationship between the concentration x and the peak area y is obtained;

[0070] In other words, in this embodiment, the concentration of monochloroacetic acid is used as the abscissa x and the peak area is used as the ordinate y to perform linear regression and obtain the corresponding linear equation.

[0071] Specifically, the above linear equation is: y=56.6280x-2.1918, and the correlation coefficient R 2 =0.99842.

[0072] In step (2), the standard sample after the derivatization reaction is separated and detected by high performance liquid chromatography ultraviolet; wherein the 2-(4-nitrophenylthio)acetic acid generated by derivatization is very easy to separate in high performance liquid chromatography, and the purpose of separation and detection can be achieved by high performance liquid chromatography, so it is easy to eliminate the interference of matrix effect and improve the detection accuracy.

[0073] At the same time, in step (2), based on the above test result (peak area of ​​monochloroacetic acid), a linear equation (calibration model) of the corresponding relationship between concentration x and peak area y can be obtained; based on the linear equation, when the content of the sample to be tested is tested, the content (concentration) of monochloroacetic acid in the cocamidopropyl betaine solution can be quickly calculated according to the peak area of ​​the sample to be tested.

[0074] It is understandable that the ultraviolet detection of the high performance liquid chromatography of this embodiment can be performed in a high performance liquid chromatograph, such as an Agilent 1260 liquid chromatograph.

[0075] In step (3), a cocamidopropyl betaine solution is prepared; under alkaline conditions, the cocamidopropyl betaine solution is reacted with 4-nitrothiophenol in a water bath to obtain a sample to be tested, comprising:

[0076] Prepare a cocamidopropyl betaine solution, add an alkali reagent and 4-nitrothiophenol to the cocamidopropyl betaine solution, and place the solution in a 70°C water bath for reaction;

[0077] After the reaction, phosphoric acid and acetonitrile were added, the volume was fixed with distilled water, and bubbles were removed by ultrasonic wave. The sample to be tested was obtained after filtration.

[0078] Specifically, the above steps may be:

[0079] Weigh 5g (accurate to 1mg) of cocamidopropyl betaine, put it into a 50mL volumetric flask, add 15mL of distilled water, add 0.5mL of 5% sodium carbonate, add 0.5mL of 0.5% 4-nitrothiophenol dropwise, shake the bottle while dropping to make full reaction; put it in a 70℃ water bath for 1-3 hours to carry out derivatization reaction; after the reaction is completed, add 0.5mL of 10% phosphoric acid solution to terminate the reaction, add 10mL of acetonitrile, distilled water to 50mL, remove bubbles by ultrasound, and filter with a syringe filter to obtain the sample to be tested.

[0080] As mentioned above, the alkaline conditions described in this embodiment are pH values ​​greater than 7. In this embodiment, an alkaline environment is created by adding an alkaline reagent, sodium carbonate.

[0081] Usually, the ultrasonication time is 3 to 5 minutes, preferably 5 minutes.

[0082] It can be understood that step (3) is to allow monochloroacetic acid in the cocamidopropyl betaine solution to undergo a nucleophilic substitution reaction with 4-nitrothiophenol to generate 2-(4-nitrophenylthio)acetic acid. The 2-(4-nitrophenylthio)acetic acid generated by derivatization is very easy to separate in the subsequent high performance liquid chromatography, which can effectively eliminate the interference of matrix effect and improve the accuracy of the detection result.

[0083] In step (4), high performance liquid chromatography ultraviolet detection is performed on the sample to be tested to obtain the peak area of ​​monochloroacetic acid in the sample to be tested; the peak area of ​​monochloroacetic acid in the sample to be tested is substituted into a linear equation to calculate the content of monochloroacetic acid in the sample to be tested, which specifically includes:

[0084] The sample to be tested obtained in step (3) is injected into a high performance liquid chromatograph for high performance liquid ultraviolet detection to obtain the peak area of ​​monochloroacetic acid; the peak area of ​​monochloroacetic acid obtained is substituted into the linear equation obtained in step (2) to calculate the content of monochloroacetic acid.

[0085] Therefore, in this embodiment, the sample to be tested after the above-mentioned derivatization reaction is separated and detected by high performance liquid chromatography ultraviolet; the peak area of ​​monochloroacetic acid in the sample to be tested is obtained. At the same time, based on the linear equation (calibration model) obtained in step (2), the content of monochloroacetic acid in the cocamidopropyl betaine solution can be quickly obtained according to the peak area of ​​the sample to be tested.

[0086] Therefore, the testing scheme of this embodiment has better detection accuracy, and the testing process is more convenient and faster.

[0087] It is understandable that in the test processes in steps (2) and (4), the sample (standard sample or sample to be tested) is injected into a high performance liquid chromatograph for high performance liquid ultraviolet detection.

[0088] As an implementation mode, the chromatographic column used in the above-mentioned high performance liquid chromatography ultraviolet detection is Agilent SB-C8, and the column temperature of the chromatographic column is 30°C.

[0089] As an embodiment, the chromatographic conditions of the above-mentioned high performance liquid chromatography ultraviolet detection include:

[0090] The detection wavelength is 250-260 nm (e.g., 256 nm), and the injection volume is 20 μL;

[0091] Mobile phase A was acetonitrile;

[0092] The mobile phase B is a mixed solution of acetonitrile, water and phosphoric acid (such as phosphoric acid with a mass concentration of 85%) in a volume ratio of 100:898:2.

[0093] In this embodiment, the gradient elution program of mobile phase A and mobile phase B is:

[0094] Elution was performed with mobile phase A and mobile phase B in a volume ratio of 20:80 for 8 min;

[0095] Elution was performed with mobile phase A and mobile phase B in a volume ratio of 80:20 for 5 min;

[0096] Elution was performed with mobile phase A and mobile phase B in a volume ratio of 20:80 for 5 min;

[0097] Among them, the flow rate is 1.0mL / min.

[0098] In summary, in this embodiment, 4-nitrothiophenol is used as a derivatization reagent. Under alkaline conditions, monochloroacetic acid and 4-nitrothiophenol undergo a nucleophilic substitution reaction in a water bath to generate 2-(4-nitrophenylthio)acetic acid. Among them, the 2-(4-nitrophenylthio)acetic acid generated by derivatization is very easy to separate in high performance liquid chromatography, and can achieve the purpose of separation and detection through high performance liquid chromatography, so it is easy to eliminate the interference of matrix effects and improve the detection accuracy; that is, the detection method of this embodiment is not only easy to operate, but also can effectively improve the separation effect, detection accuracy and precision.

[0099] Next, the use of the above detection method in the quality control of cocamidopropyl betaine will be explained.

[0100] use

[0101] It is understandable that since there is a certain amount of monochloroacetic acid residue in the cocamidopropyl betaine produced using monochloroacetic acid as a raw material, and cocamidopropyl betaine is usually used as a cleaning agent or food additive, it is easy for the residual monochloroacetic acid to be directly or indirectly contacted or ingested by the human body. Therefore, when using monochloroacetic acid as a raw material to produce cocamidopropyl betaine, the residual amount in cocamidopropyl betaine should be limited.

[0102] As mentioned above, the detection method provided in this embodiment can detect the content of monochloroacetic acid in cocamidopropyl betaine more accurately and quickly, and the detection method is highly efficient; therefore, it can meet the needs of safety risk screening of monochloroacetic acid in cocamidopropyl betaine, and can provide good technical support for the quality control and safety monitoring of cocamidopropyl betaine, suggesting that the detection method has better application prospects in the quality control of cocamidopropyl betaine.

[0103] The present application will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate / explain the present application and are not used to limit the scope of the present application.

[0104] In the following examples, the materials, reagents and instruments used can be purchased from commercial sources unless otherwise specified.

[0105] It should be noted that, in the following examples, unless otherwise specified, the method and conditions for analysis (separation and detection) using a high performance liquid chromatograph are as follows:

[0106] The preparation method of 4-nitrothiophenol solution is as follows: weigh 0.5 g of 4-nitrothiophenol, add 49.5 g of acetonitrile, and dissolve by ultrasonication to obtain a 4-nitrothiophenol solution with a mass concentration of 1%.

[0107] Agilent 1260 liquid chromatograph was used for high performance liquid chromatography, and the concentration of phosphoric acid solution in mobile phase B was 85%.

[0108] Mobile phase A was acetonitrile; mobile phase B was acetonitrile: water: phosphoric acid = 100: 898: 2 (volume ratio).

[0109] The gradient elution program is shown in Table 1 below:

[0110] Table 1:

[0111] Time (min) Mobile phase A(%) Mobile phase B(%) Flow rate (mL / min) 0.00 20 80 1 8.00 20 80 1 9.00 80 20 1 14.00 80 20 1 15.00 20 80 1 20.00 20 80 1

[0112] Among them, the chromatographic column selected is Agilent ZORBAX SB-C8, the chromatographic column length is 250mm, the chromatographic column inner diameter is 4.6mm, and the chromatographic column filler particle diameter is 5μm; the detection wavelength is set to 256 nm, the column temperature is 30℃, and the injection volume is 20μL.

[0113] Embodiment 1-10:

[0114] This example found that the derivatization temperature of monochloroacetic acid would affect its peak area. Therefore, by setting a gradient water bath temperature, the peak area of ​​monochloroacetic acid was detected, specifically:

[0115] Weigh 0.1016 g of monochloroacetic acid standard, dissolve it in distilled water, dilute to 100 mL, and shake well; use a pipette to transfer 10 mL to another 100 mL volumetric flask, dilute to volume, mix well, and obtain a stock solution with a concentration of 101.6 mg / L.

[0116] Take 10 50mL volumetric flasks, transfer 101.6mg / L monochloroacetic acid into the volumetric flasks, fill up to 20mL with distilled water, add 0.5mL of 5% sodium carbonate and 0.5mL of 0.5% 4-nitrothiophenol, mix well; place in a water bath at 40, 45, 50, 55, 60, 65, 70, 75, 80, 85℃ for 1 hour; after the reaction, take out the volumetric flask, add 0.5mL of 10% phosphoric acid to terminate the reaction, add 10mL of acetonitrile, fill up to the mark with distilled water, and remove bubbles by ultrasound for 5 minutes; filter into a sample bottle with a syringe filter, inject into a high performance liquid chromatograph for separation and detection, and the test results are shown in Table 2.

[0117] The water bath temperature is the horizontal axis and the peak area is the vertical axis. The test results are as follows: Figure 1 shown.

[0118] Table 2: Water bath temperature and resolution

[0119] Example Water bath temperature (℃) Peak area Example 1 40 89.7 Example 2 45 123.2 Example 3 50 200.9 Example 4 55 320.6 Example 5 60 392.4 Example 6 65 429.3 Example 7 70 440.6 Example 8 75 431.2 Example 9 80 410.3 Example 10 85 364.6

[0120] Based on Table 2 and Figure 1 The test results show that the peak area of ​​monochloroacetic acid increases with the increase of temperature. After reaching the peak value, it decreases with the increase of temperature. Among them, when the temperature is 70℃, the peak area is the largest, and the derivatization effect is good at this temperature. Therefore, the derivatization temperature is determined to be 70℃.

[0121] Among them, the liquid chromatogram after separation is as follows Figure 2 As shown. Combined Figure 2 It can be seen from the liquid chromatogram that there is basically no interference peak in the liquid chromatogram; that is, this embodiment uses 4-nitrothiophenol as a derivatization reagent to effectively eliminate the interference of matrix effects and improve the accuracy of the detection results.

[0122] Accuracy experiment

[0123] Embodiment 11-16:

[0124] Weigh 0.1020 g of monochloroacetic acid standard into a 100 mL volumetric flask, dilute to the mark with distilled water, and the concentration is 1000 mg / L; transfer 10 mL into another 100 mL volumetric flask, dilute to the mark with distilled water, and use as a stock solution (102.0 mg / L) for later use;

[0125] 0.50mL, 1.00mL, 2.00mL, 3.00mL, 4.00mL and 5.00mL of the stock solution were respectively measured in 6 50mL volumetric flasks, and filled to 20mL with distilled water; 0.5mL of 5% sodium carbonate and 0.5mL of 0.5% 4-nitrothiophenol were added, and the mixture was placed in a water bath at 70°C for 1 hour; after the reaction was completed, the volumetric flask was taken out, 0.5mL of 10% phosphoric acid was added to terminate the reaction, 10mL of acetonitrile was added, and the mixture was filled to the mark with distilled water, and the bubbles were removed by ultrasound for 5 minutes; the mixture was filtered into a sample bottle with a syringe filter, and the sample was injected into a high performance liquid chromatograph for ultraviolet spectrum detection to obtain the peak area of ​​monochloroacetic acid. The test results are shown in Table 3:

[0126] Table 3: Peak area for detection of monochloroacetic acid

[0127] Example Monochloroacetic acid (mg / L) Peak area Embodiment 11 1.020 55.88 Example 12 2.040 114.27 Example 13 4.080 223.89 Embodiment 14 6.120 351.75 Embodiment 15 8.16 443.91 Example 16 10.200 585.54

[0128] Combined with the test results in Table 3, linear regression was performed with the concentration of monochloroacetic acid as the abscissa and the peak area as the ordinate, and the linear equation was obtained as follows: y=56.6280x-2.1918, and the correlation coefficient R 2 =0.99842, the linear equation is Figure 3 As shown in Table 3 and Figure 3 The test results show that monochloroacetic acid has good linearity in the concentration range of 0-10 mg / L.

[0129] Embodiment 17-19:

[0130] Accurately weigh 3 parts of cocamidopropyl betaine, the weight is shown in Table 4 (accurate to 1 mg), and they are placed in 50 mL volumetric flasks, and 15 mL of distilled water is added; 0.5 mL of sodium carbonate with a mass concentration of 5% is added, and 0.5 mL of 4-nitrothiophenol with a mass concentration of 0.5% is added dropwise, and the mixture is placed in a water bath at 70° C. for 1 hour; after the reaction is completed, the volumetric flask is taken out, 0.5 mL of phosphoric acid with a mass concentration of 10% is added to terminate the reaction, 10 mL of acetonitrile is added, and distilled water is filled to the scale line, and bubbles are removed by ultrasound for 5 minutes; the mixture is filtered into a sample bottle with a syringe filter, and the obtained sample is injected into a high performance liquid chromatograph for ultraviolet spectrum detection to obtain the peak area of ​​monochloroacetic acid; the concentration of monochloroacetic acid in each sample is calculated, which is the content of the target substance contained in Examples 17-19, and is recorded as A value.

[0131] Embodiment 20-22:

[0132] Accurately weigh 3 parts of cocamidopropyl betaine, the weight is shown in Table 4 (accurate to 1 mg), and place them in 50 mL volumetric flasks respectively. Take the stock solution (102.0 mg / L) prepared in Example 11-16 as a reference substance (known concentration), add 0.5 mL (parallel group 1), 1 mL (parallel group 2), and 2 mL (parallel group 3) respectively, add 15 mL of distilled water, add 0.5 mL of 5% mass concentration of sodium carbonate, add 0.5 mL of 0.5% mass concentration of 4-nitrothiophenol dropwise, and place in a 70°C water bath for 1 hour;

[0133] After the reaction is completed, the volumetric flask is taken out, 0.5 mL of 10% mass concentration phosphoric acid is added to terminate the reaction, 10 mL of acetonitrile is added, and the scale is filled with distilled water, and the bubbles are removed by ultrasound for 5 minutes; the sample is filtered into a sample bottle with a syringe filter, and the obtained sample is injected into a high performance liquid chromatograph for ultraviolet spectrum detection to obtain the peak area of ​​monochloroacetic acid, which is substituted into the linear equation obtained in the above Examples 11-16 to calculate the concentration of monochloroacetic acid in the sample, which is the content of the target substance contained in Examples 20-22, recorded as C value.

[0134] The recovery rate is calculated based on the A value and the C value, where the recovery rate formula is: .

[0135] In the above formula: A is the content of the target substance contained in Examples 17-19; B is the increase in sample concentration after adding the reference substance; C is the content of the target substance contained in Examples 20-22.

[0136] The calculation formula of B value is:

[0137] (Concentration of stock solution*volume of stock solution added) / weight of the corresponding test sample in Examples 20-22.

[0138] Among them, each concentration was prepared in triplicate, and three groups of parallel experiments were performed. The recovery rates were determined under the content determination item, and the test results are shown in Table 4 below; among them, for the recovery rate calculation in Table 4, the A value was calculated by taking the average value of the A value (i.e., 15.03 mg / kg) and substituting it into the above recovery rate calculation formula.

[0139] Table 4: Accuracy test results

[0140]

[0141] According to the test results in Table 4, the average recovery rate of the three parallel group experiments is greater than 96%, indicating that the loss of the analyte during the processing of the sample is extremely small. The detection method has excellent accuracy and high precision (RSD is 0.84%).

[0142] Precision experiment

[0143] Embodiment 23-28:

[0144] The monochloroacetic acid solution of Example 15 was taken and injected 6 times continuously, the peak area of ​​the main component was recorded, and the precision was calculated. The test results are shown in Table 5 below:

[0145] Table 5: Precision test results

[0146]

[0147] According to the test results in Table 5, it is shown that the detection method of this embodiment has excellent precision and repeatability.

[0148] Solution stability test

[0149] Examples 29-33:

[0150] The monochloroacetic acid solution of Example 15 was taken and injected at room temperature for 4, 8, 12, 24 and 48 hours, and the peak area change of the main component was recorded. The test results are shown in Table 6 below:

[0151] Table 6: Solution stability test results

[0152]

[0153] According to the test results in Table 6, it is shown that the detection method of this embodiment has excellent stability of the derivatization solution within 48 hours at room temperature.

[0154] In summary, in this embodiment, 4-nitrothiophenol is used as a derivatization reagent. Under alkaline conditions, monochloroacetic acid and 4-nitrothiophenol undergo a nucleophilic substitution reaction in a water bath to generate 2-(4-nitrophenylthio)acetic acid. Among them, the 2-(4-nitrophenylthio)acetic acid generated by derivatization is very easy to separate in high performance liquid chromatography, and can achieve the purpose of separation and detection through high performance liquid chromatography, so it is easy to eliminate the interference of matrix effects and improve the detection accuracy; at the same time, the detection method of this embodiment is not only easy to operate, but also can effectively improve the separation effect, detection accuracy and precision.

[0155] The technical solutions provided in the embodiments of the present application are introduced in detail above. Specific examples are used herein to illustrate the principles and implementation methods of the embodiments of the present application. The description of the above embodiments is only applicable to help understand the principles of the embodiments of the present application. At the same time, for those skilled in the art, according to the embodiments of the present application, there will be changes in the specific implementation methods and application scopes. In summary, the contents of this specification should not be understood as limiting the present application.

Claims

1. A method for detecting the content of monochloroacetic acid in cocamidopropyl betaine, characterized in that, The detection method comprises: Prepare monochloroacetic acid standard solutions of different concentrations; react the monochloroacetic acid standard solutions of different concentrations with 4-nitrothiophenol in a water bath under alkaline conditions to obtain standard samples of different concentrations; Performing high performance liquid chromatography ultraviolet detection on standard samples of different concentrations to obtain the peak areas of monochloroacetic acid in the standard samples of different concentrations; obtaining a linear equation of the corresponding relationship between concentration x and peak area y based on the peak areas corresponding to the standard samples of different concentrations; A cocamidopropyl betaine solution is prepared; under alkaline conditions, the cocamidopropyl betaine solution is reacted with 4-nitrothiophenol in a water bath to obtain a sample to be tested; Performing high performance liquid chromatography ultraviolet detection on the sample to be tested to obtain the peak area of ​​monochloroacetic acid in the sample to be tested; substituting the peak area of ​​monochloroacetic acid in the sample to be tested into a linear equation to calculate the content of monochloroacetic acid in the sample to be tested; Wherein, under alkaline conditions, reacting monochloroacetic acid standard solutions of different concentrations with 4-nitrothiophenol in a water bath to obtain standard samples of different concentrations includes: Add alkali reagent and 4-nitrothiophenol to monochloroacetic acid standard solutions of different concentrations, and place them in a 70℃ water bath for reaction; After the reaction, phosphoric acid and acetonitrile were added, the volume was fixed with distilled water, and bubbles were removed by ultrasonic wave. Standard samples of different concentrations were obtained after filtration. The method comprises preparing a cocamidopropyl betaine solution; reacting the cocamidopropyl betaine solution with 4-nitrothiophenol in a water bath under alkaline conditions to obtain a sample to be tested, comprising: Prepare a cocamidopropyl betaine solution, add an alkali reagent and 4-nitrothiophenol to the cocamidopropyl betaine solution, and place the solution in a 70°C water bath for reaction; After the reaction, phosphoric acid and acetonitrile were added, the volume was fixed with distilled water, and bubbles were removed by ultrasonic wave, and the sample to be tested was obtained after filtration; The alkaline reagent is sodium carbonate; the chromatographic column used in the high performance liquid chromatography ultraviolet detection is Agilent SB-C8; The chromatographic conditions of the high performance liquid chromatography ultraviolet detection include: The detection wavelength was 250-260 nm, and the injection volume was 20 μL; Mobile phase A was acetonitrile; Mobile phase B was a mixed solution of acetonitrile, water, and phosphoric acid in a volume ratio of 100:898:2; The gradient elution program of the mobile phase A and the mobile phase B is: Elution was performed with mobile phase A and mobile phase B in a volume ratio of 20:80 for 8 min; Elution was performed with mobile phase A and mobile phase B in a volume ratio of 80:20 for 5 min; Elution was performed with mobile phase A and mobile phase B in a volume ratio of 20:80 for 5 min; Among them, the flow rate is 1.0mL / min.

2. The detection method according to claim 1, characterized in that: The linear equation is: y=56.6280x-2.1918, correlation coefficient R 2 =0.99842.

3. The detection method according to claim 1, characterized in that: The column temperature of the chromatographic column is 30°C.

4. according to the purposes of the detection method described in any one of claims 1-3 in cocamidopropyl betaine product quality control.

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