QACs probe solution, probes and methods for rapid screening and accurate analysis of qacs

Abstract

The application provides a new method for rapidly screening and accurately analyzing quaternary ammonium salt surfactants. In view of the problems of weak selectivity or long time consumption and high cost of the detection methods in the prior art, the application adopts a sodium tetraphenylborate-bromocresol purple-phosphate buffer salt mixed solution as a probe solution, and rapidly identifies the quaternary ammonium salt surfactants in the sample through a probe reaction. For a positive sample, further liquid chromatography-mass spectrometry analysis is carried out through high-speed centrifugation and dissolution and precipitation, so that accurate qualitative and quantitative analysis of the quaternary ammonium salt surfactants is realized. The application can effectively meet the demand for rapid screening and accurate analysis, has important practical value and wide application prospect, and can significantly improve work efficiency and reduce analysis cost, especially in the fields of environmental protection and daily chemical management.

Description

Technical Field

[0001] This invention relates to the field of surfactant product analysis and detection technology, and particularly to a quaternary ammonium salt surfactant probe solution, its preparation, and its application. Furthermore, this invention also relates to rapid detection and precise quantification techniques for quaternary ammonium salt surfactants using this probe solution. Technical Background

[0002] Quaternary ammonium cationic surfactants (QACs), widely used industrial additives in detergents, disinfectants, and fabric softeners, have raised concerns about their environmental behavior. Some varieties, such as D1821 (disaccharide dimethyl ammonium chloride), are difficult to degrade in the environment and exhibit significant ecotoxicity to the ecosystem and aquatic communities, thus requiring strict restrictions on their use and dosage. While some industry regulations and standards have standardized the use of QACs and provided testing methods, many commercially available products or regulatory scenarios still lack applicable QAC testing methods.

[0003] Currently reported methods for detecting QACs mainly include two-phase titration, spectrophotometry, liquid chromatography, and liquid chromatography-mass spectrometry. Two-phase titration is more suitable for product-specific quality control; spectrophotometry is only applicable to specific product types. Both methods lack qualitative capabilities and have limitations in analyzing unknown samples. While liquid chromatography and liquid chromatography-mass spectrometry are advanced analytical methods, they are difficult to apply to rapid on-site screening and testing, and their analytical costs are high for large-scale screening. Therefore, developing detection methods that combine rapid screening with accurate qualitative and quantitative functions has significant application value in environmental monitoring and analysis of products in circulation. However, there is currently a lack of probe solutions that can rapidly screen for QACs, resulting in the inability to perform accurate qualitative and quantitative analysis. Summary of the Invention

[0004] To address the problems existing in the prior art, the first objective of this invention is to provide a probe solution for rapidly indicating or screening quaternary ammonium surfactants (QACs). The probe solution is a mixed solution of sodium tetraphenylborate, bromocresol purple, and phosphate buffer, wherein the total molar concentration of sodium tetraphenylborate and bromocresol purple is 2 mmol / L to 20 mmol / L, and the molar ratio of sodium tetraphenylborate to bromocresol purple is 100:1 to 500:1; the phosphate buffer solution is composed of sodium dihydrogen phosphate and disodium hydrogen phosphate, with a pH of 7 to 8; when the probe solution encounters a sample containing quaternary ammonium surfactants, it will exhibit at least one of the following phenomena due to the presence of QACs: turbidity, precipitation, or fading, indicating the presence of quaternary ammonium surfactants in the sample.

[0005] The present invention provides a method for preparing a probe solution for rapid indication or screening of QACs as follows: (1) Prepare solution A: Weigh sodium tetraphenylborate, dissolve it in water, and prepare a solution with a concentration of 2 mmol / L to 20 mmol / L; (2) Prepare solution B: Weigh bromocresol purple, dissolve it in a small amount of ethanol, dilute it with water, and prepare a solution with a concentration of 0.2 mmol / L to 2 mmol / L; (3) Prepare solution C: Weigh sodium dihydrogen phosphate and disodium hydrogen phosphate, dissolve them in water, and prepare a mixed buffer salt solution with a pH of 7-8 and a total concentration of 10 mmol / L-100 mmol / L. (4) Take an appropriate amount of solution A and an appropriate amount of solution B and mix them. The molar ratio of sodium tetraphenylborate to bromocresol violet in the mixed solution should be controlled at 100:1 to 500:1. Then add an appropriate amount of solution C to maintain the pH value of the final solution at 7 to 8, thus obtaining the probe solution.

[0006] The second objective of this invention is to provide a method for rapidly screening quaternary ammonium salt surfactants, comprising: taking a sample to be tested, dissolving it if necessary, and adding it dropwise to the probe solution described in this invention to obtain a sample solution; if the sample solution shows turbidity, precipitation, or fading, then the sample contains quaternary ammonium salt surfactants; if the appearance of the sample solution does not change significantly, then the sample does not contain quaternary ammonium salt surfactants.

[0007] As a preferred technical solution, based on the principle of the above-mentioned method for rapid screening of quaternary ammonium salt surfactants, the probe solution of the present invention can also be prepared into a droplet probe for rapid indication or screening of quaternary ammonium salt surfactants, which is more convenient to use.

[0008] A third objective of this invention is to provide a method for rapid screening and accurate analysis of quaternary ammonium surfactants using the aforementioned probe solution, comprising the following steps: (1) Rapid screening: Take the sample to be tested, dissolve it if necessary, and add it dropwise to the probe solution described in this invention to obtain the sample solution. If the sample solution shows turbidity, precipitation or fading, it is judged as positive and the sample contains quaternary ammonium salt surfactants; if the appearance of the sample solution does not change significantly, it is judged as negative and the sample does not contain quaternary ammonium salt surfactants. (2) Accurate analysis: a. Take the sample solution that was quickly screened as positive in step (1), and separate it by high-speed centrifugation. The supernatant should remain purple. If obvious fading occurs, reduce the sample amount and repeat step (1) until the positive sample solution is separated by high-speed centrifugation and the supernatant remains purple. b. After centrifugation of the sample solution, discard the supernatant, add an appropriate amount of solvent to dissolve the precipitate, and then send it to a liquid chromatography-mass spectrometry system for accurate qualitative and quantitative analysis.

[0009] Preferably, in step (1), the sample amount is 1g to 5g, and if necessary, 1mL to 5mL of solvent is added to dissolve it to obtain a transparent solution; the solvent is selected from one or more of water, methanol, ethanol, and isopropanol.

[0010] Preferably, the solvent used to dissolve the precipitate in step (2) is one of benzene, ketone, alcohol, or chloroalkane solvents, or an aqueous solution thereof, or a liquid chromatography mobile phase. More preferably, the solvent is one of benzene, toluene, acetone, isopropanol, or carbon tetrachloride, or an aqueous solution thereof; and the liquid chromatography mobile phase is an ammonium acetate aqueous solution-acetonitrile-water system.

[0011] Preferably, in step (2), the analytical conditions of the liquid chromatography-mass spectrometry system are as follows: the chromatographic column is a ThermoAcclaim Surfactant Plus column; the mobile phase is an ammonium acetate aqueous solution-acetonitrile-water system, using gradient elution mode; the mass spectrometer is equipped with an electrospray ionization source, and the characteristic target ions are selectively monitored or extracted in positive ion mode. More preferably, the concentration of the ammonium acetate aqueous solution in the mobile phase combination is 50 mmol / L to 100 mmol / L, and the pH value is 4.5 to 5.5. The gradient program is set as follows: the ammonium acetate aqueous solution is used as mobile phase A, acetonitrile is used as mobile phase B, and water is used as mobile phase C. The volume ratio of mobile phase A is maintained at a fixed value of 5% to 10% throughout the gradient program. Elution separation is achieved by adjusting the ratio of mobile phase B to mobile phase C. During the initial time period of 1 min to 2 min, the volume ratio of mobile phase B is maintained at 50% to 60%. Subsequently, during the time period of 2 min to 10 min, the volume ratio gradient of mobile phase B is increased to 80% to 90%, while the volume ratio gradient of mobile phase C is simultaneously reduced to 15% to 0% to achieve complete elution of the target component.

[0012] The innovative aspects of the technical solution of this invention are:

[0013] (1) Innovation of probe solution: Sodium tetraphenylborate, bromocresol purple and phosphate buffer are combined in a specific ratio and form a synergistic effect under specific conditions, which produces new properties, making the probe solution highly sensitive and easy to observe. These properties cannot be presented when the reagent is used alone and have not been reported.

[0014] (2) Innovation of integrated probe identification and enrichment separation: Quaternary ammonium salt surfactants are identified and precipitated and enriched at the same time. After high-speed centrifugation, they are separated from most impurities. The analytical method realizes the integration of identification and enrichment separation.

[0015] (3) Innovative method design: This scheme combines the probe solution method and the instrumental analysis method, so that the scheme as a whole has both the ability to quickly identify and the ability to further accurately determine and quantify. Compared with existing methods, the method of this invention combines the high efficiency of the rapid indication method and the accuracy of the instrumental analysis method, which can provide the detection results of QACs in a short time, and has a low cost and significant advancement.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] (1) Rapid screening, cost reduction and efficiency improvement: Through the rapid reaction mechanism of the specially designed probe solution, the presence of quaternary ammonium salt surfactants in samples can be detected quickly, significantly shortening the initial screening time and making it suitable for rapid on-site identification. At the same time, it can effectively exclude a large number of negative samples, significantly improving work efficiency and reducing analysis costs.

[0018] (2) The method is simple, sensitive and accurate: After a simple separation operation, the quaternary ammonium salt surfactant is effectively enriched, providing high-quality test samples for subsequent liquid chromatography-mass spectrometry analysis, making the overall scheme simpler, more sensitive and accurate. Attached Figure Description

[0019] Figure 1 The extracted ion chromatogram is obtained by liquid chromatography-mass spectrometry analysis of the D1821 component in the fabric softener product in Example 1. Detailed Implementation

[0020] Quaternary ammonium cationic surfactants (QACs) are cationic surfactants formed by replacing all four hydrogen atoms of the ammonium cation [H4N+] with organic groups. They mainly include alkyltrimethylammonium salt cationic surfactants, dialkyldimethylammonium salt cationic surfactants, alkyldimethylbenzylammonium salt cationic surfactants, pyridinium salt cationic surfactants, alkylisoquinolineium salt cationic surfactants, and benzyl chlorideium salt cationic surfactants, etc.

[0021] The inventors accidentally discovered that a specific combination of sodium tetraphenylborate, bromocresol purple, and phosphate buffer, under specific conditions, exhibits a new property: when this mixed solution encounters a sample containing quaternary ammonium surfactants, it displays at least one of the following changes in appearance: turbidity, precipitation, or fading. This makes it a highly sensitive and easily observable indicator for the rapid screening of quaternary ammonium surfactants (QACs). The basic principle is as follows:

[0022]

[0023] Wherein: NaB(C6H5)4 represents sodium tetraphenylborate, R represents bromocresol purple, Q+ represents quaternary ammonium cationic surfactant, and PBS represents phosphate buffer.

[0024] The reaction of sodium tetraphenylborate with QACs is a fundamental principle of commonly used two-phase titration methods. However, the inventors discovered that under specific conditions, sodium tetraphenylborate and bromocresol purple can produce a synergistic effect, reacting with QACs to form a complex precipitate. This precipitate reaction is sensitive, rapid, and complete, and the precipitate can be separated by simple centrifugation, achieving the goal of enriching and separating QACs. Furthermore, once the sodium tetraphenylborate is consumed, QACs will individually combine with bromocresol purple to form a complex, causing the bromocresol purple solution to decolorize. Therefore, the decolorization phenomenon can indicate that the concentration of QACs in the sample solution is too high, requiring a reduction in the sample amount; otherwise, incomplete enrichment will occur.

[0025] QACs are identified through the above operations and, after being enriched and separated, are separated from most impurities, providing high-quality samples for further liquid chromatography-mass spectrometry analysis. Under optimized chromatographic conditions, QACs peaks are undisturbed and have high sensitivity.

[0026] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments. It should be noted that the following embodiments are only some preferred embodiments of the present invention. All embodiments obtained by combining, simple transformation, or modifying parameter ranges under the guidance of the spirit of the present invention fall within the scope of protection of the present invention.

[0027] Example 1: Screening and detection of D1821 in a commercially available fabric softener product

[0028] (a) Preparation of probe solution: Solution A: Weigh out sodium tetraphenylborate, dissolve it in water, and prepare a solution with a concentration of 15 mmol / L; Solution B: Weigh out bromocresol purple, dissolve it in a small amount of ethanol, dilute it with water, and prepare a solution with a concentration of 0.2 mmol / L; Solution C: Weigh out sodium dihydrogen phosphate and disodium hydrogen phosphate, dissolve them in water, and prepare a mixed buffer salt solution with a pH of 7 and a total concentration of 100 mmol / L. Take 5 mL of solution A and solution B and place them in a 15 mL transparent centrifuge tube. After mixing, the molar ratio of sodium tetraphenylborate to bromocresol violet in the solution is 100:1. Add 5 mL of solution C. The final pH of the solution is 7, which is the probe solution.

[0029] (II) Measurement process: Take 5g of commercially available sample, dissolve it in water to form a clear solution, and transfer it to a 5mL volumetric flask and dilute to volume. Take 1mL of the sample solution and add it dropwise to the probe solution prepared above. A purple precipitate will immediately appear in the probe solution, indicating a positive sample. Centrifuge at 4000 rpm; the supernatant will show a significant fading compared to the probe solution.

[0030] Take another 2g sample and repeat the above steps. After centrifugation, the supernatant remains purple and shows no fading. Discard the supernatant, dissolve the precipitate in 50% acetone-water solution, and bring the volume to 10mL. Send the solution to a liquid chromatography-mass spectrometry (LC-MS) system for further analysis.

[0031] The analytical conditions for liquid chromatography-mass spectrometry are as follows: The chromatographic column used was a Thermo Acclaim Surfactant Plus column (4.6 mm × 150 mm, 3 μm); The mobile phase was an ammonium acetate aqueous solution-acetonitrile-water system, using gradient elution mode at a flow rate of 1.0 mL / min; The mass spectrometer is equipped with an electrospray ionization source and is monitored in positive ion mode; characteristic target ions are extracted, such as hexadecyl dimethyl ammonium chloride (m / z 494.6), hexadecyl octadecyl dimethyl ammonium chloride (m / z 522.6), and hexadecyl dimethyl ammonium chloride (m / z 550.7).

[0032] Elution program: Mobile phase A is 100 mmol / L ammonium acetate aqueous solution (pH adjusted to 5.0 with acetic acid), mobile phase B is acetonitrile, and mobile phase C is water. The gradient elution program is shown in the table below:

[0033] Table 1 Gradient elution program 0 5 55 40 2 5 55 40 8 5 85 10 10 5 55 40 Under the above conditions, the extraction ion chromatogram of the D1821 standard working solution is shown in the appendix. Figure 1 .

[0034] The content of D1821 in this fabric softener product was determined to be 6%.

[0035] Example 2: Screening of D1821 surfactant in a commercially available laundry detergent

[0036] (a) Preparation of probe solution: Solution A: Weigh sodium tetraphenylborate, dissolve it in water, and prepare a solution with a concentration of 20 mmol / L; Solution B: Weigh out bromocresol purple, dissolve it in a small amount of ethanol, dilute it with water, and prepare a solution with a concentration of 2 mmol / L; Solution C: Weigh out sodium dihydrogen phosphate and disodium hydrogen phosphate, dissolve them in water, and prepare a mixed buffer salt solution with a pH of 7.5 and a total concentration of 20 mmol / L. Take 6 mL of solution A and solution B and place them in a 20 mL transparent centrifuge tube. After mixing, the molar ratio of sodium tetraphenylborate to bromocresol violet in the solution is 500:1. Add 6 mL of solution C. The final pH of the solution is 7.5, which is the probe solution.

[0037] (II) Measurement process: Take 2g of commercially available sample, dissolve it in isopropanol to form a clear solution, and transfer it to a 5mL volumetric flask and dilute to volume. Take 1mL of the sample solution and add it dropwise to the probe solution prepared above. If the probe solution shows no obvious reaction, it is determined to be a negative sample, and the sample does not contain the D1821 surfactant.

[0038] Example 3: Troubleshooting Missed Detections Take another 2g of sample from Example 2, dissolve it in isopropanol to form a clear solution, transfer it to a 5mL volumetric flask and make up to volume, then send it to a liquid chromatography-mass spectrometry system for missed detection.

[0039] The same liquid chromatography-mass spectrometry (LC-MS) detection conditions as in Example 1 were used for detection. No molecular weight information characteristic of D1821 was found, proving that the rapid screening method of this scheme has a low false negative rate and accurate judgment results.

[0040] Example 4: Screening and Detection of Quaternary Ammonium Salt Surfactants in a Commercially Available Disinfectant Product

[0041] (a) Preparation of probe solution: Solution A: Weigh out sodium tetraphenylborate, dissolve it in water, and prepare a solution with a concentration of 5 mmol / L; Solution B: Weigh out bromocresol purple, dissolve it in a small amount of ethanol, dilute it with water, and prepare a solution with a concentration of 2 mmol / L; Solution C: Weigh sodium dihydrogen phosphate and disodium hydrogen phosphate, dissolve them in water, and prepare a mixed buffer salt solution with a pH of 8 and a total concentration of 10 mmol / L. Take 10 mL of solution A and solution B and place them in a 25 mL transparent centrifuge tube. After mixing, the molar ratio of sodium tetraphenylborate to bromocresol violet in the solution is 200:1. Add 10 mL of solution C. The final pH of the solution is 8, which is the probe solution.

[0042] (II) Measurement process: Take 3g of commercially available sample, dissolve it in water to form a clear solution, and transfer it to a 5mL volumetric flask and dilute to volume. Take 1mL of the sample solution and add it dropwise to the probe solution prepared above. A purple precipitate immediately appears in the probe solution, indicating a positive sample. Centrifuge at 3000 rpm; the supernatant shows no significant fading compared to the probe solution.

[0043] The supernatant was discarded, the precipitate was dissolved in acetone, and the mobile phase was diluted to 5 mL and sent to a liquid chromatography-mass spectrometry system for further analysis.

[0044] The analytical conditions for liquid chromatography-mass spectrometry are as follows: The chromatographic column used was a Thermo Acclaim Surfactant Plus column (4.6 mm × 250 mm, 3 μm); The mobile phase was an ammonium acetate aqueous solution-acetonitrile-water system, using gradient elution mode at a flow rate of 1.0 mL / min; The mass spectrometer is equipped with an electrospray ionization source and is monitored in positive ion mode; characteristic target ions are extracted, such as dodecyltrimethylammonium chloride (m / z 228.3), dodecyldimethylbenzylammonium chloride (m / z 304.3), dihexadecyldimethylammonium chloride (m / z 494.6), hexadecyloctadecyldimethylammonium chloride (m / z 522.6), and dioctadecyldimethylammonium chloride (m / z 550.7).

[0045] Elution program: Mobile phase A is 50 mmol / L ammonium acetate aqueous solution (pH adjusted to 4.5 with acetic acid), mobile phase B is acetonitrile, and mobile phase C is water. The gradient elution program is shown in the table below:

[0046] Table 2 Gradient elution program 0 10 50 40 1 10 50 40 10 10 80 10 Analysis revealed that the product contains dodecyltrimethylammonium chloride and dodecyldimethylbenzylammonium chloride. The content of dodecyltrimethylammonium chloride was 0.52% and that of dodecyldimethylbenzylammonium chloride was 0.15% by external standard method.

[0047] The sample was prepared repeatedly 6 times, and the results are as follows:

[0048] Table 3 Precision Assessment 1 0.52% 0.14% 2 0.54% 0.15% 3 0.54% 0.13% 4 0.50% 0.15% 5 0.56% 0.14% 6 0.51% 0.14% RSD / % 4.2 5.3 A relative standard deviation (RSD) of less than 6% indicates that the measurement method has good precision.

[0049] Example 5: Screening and Detection of Quaternary Ammonium Surfactants in Wastewater from a Factory

[0050] Prepare the probe solution in advance, using the same method as in Example 4.

[0051] Measurement process: Wastewater from a factory's discharge outlet was added dropwise to the probe solution prepared above. The probe solution immediately produced a purple precipitate, indicating a positive sample. Centrifugation at 5000 rpm revealed no significant fading of the supernatant compared to the probe solution. The supernatant was discarded, the precipitate was dissolved in acetone, and the mobile phase was diluted to 5 mL. The solution was then sent to a liquid chromatography-mass spectrometry (LC-MS) instrument for further analysis.

[0052] The analytical conditions for liquid chromatography-mass spectrometry are as follows: The chromatographic column used was a Thermo Acclaim Surfactant Plus column (4.6 mm × 100 mm, 3 μm); The mobile phase was an ammonium acetate aqueous solution-acetonitrile-water system, using gradient elution mode at a flow rate of 1.0 mL / min; The mass spectrometer is equipped with an electrospray ionization source and is monitored in positive ion mode. It adopts SCAN mode and scans in the molecular weight range of 100 to 1000.

[0053] Elution program: Mobile phase A is 80 mmol / L ammonium acetate aqueous solution (pH adjusted to 5.5 with acetic acid), mobile phase B is acetonitrile, and mobile phase C is water. The gradient elution program is shown in the table below:

[0054] Table 4 Gradient elution program 0 5 60 35 2 5 60 35 10 5 90 5 Analysis revealed that the wastewater contained diecryldimethylammonium chloride, with a content of 0.1% determined by the external standard method.

[0055] Example 6: Identification and Detection of Quaternary Ammonium Salt Surfactants in a Commercially Available Disinfectant Product

[0056] (a) Preparation of probe solution: Solution A: Weigh out sodium tetraphenylborate, dissolve it in water, and prepare a solution with a concentration of 15 mmol / L; Solution B: Weigh bromocresol purple, dissolve it in a small amount of ethanol, dilute it with water, and prepare a solution with a concentration of 0.4 mmol / L; Solution C: Weigh out sodium dihydrogen phosphate and disodium hydrogen phosphate, dissolve them in water, and prepare a mixed buffer salt solution with a pH of 7 and a total concentration of 100 mmol / L. Take 5 mL of solution A and solution B and place them in a 15 mL transparent centrifuge tube. After mixing, the molar ratio of sodium tetraphenylborate to bromocresol violet in the solution is 100:1. Add 5 mL of solution C. The final pH of the solution is 7, which is the probe solution.

[0057] (II) Measurement process: Take 5g of a commercially available disinfectant sample, dissolve it in water to form a clear solution, and transfer it to a 5mL volumetric flask and dilute to volume. Pipette 1mL of the sample solution into the probe solution prepared above. The probe solution immediately forms a purple precipitate, indicating a positive sample. Centrifuge at 4000 rpm. The supernatant shows no significant fading compared to the probe solution. Discard the supernatant, dissolve the precipitate in 50% acetone-water solution, and dilute to 10mL. Send the solution to a liquid chromatography-mass spectrometry (LC-MS) system for further accurate identification and analysis.

[0058] The analytical conditions for liquid chromatography-mass spectrometry are as follows: The chromatographic column used was a Thermo Acclaim Surfactant Plus column (4.6 mm × 150 mm, 3 μm); The mobile phase was an ammonium acetate aqueous solution-acetonitrile-water system, using gradient elution mode at a flow rate of 1.0 mL / min; The mass spectrometer was equipped with an electrospray ionization source and monitored in positive ion mode. Characteristic target ions were extracted, including: dihexadecyl dimethyl ammonium chloride (m / z 494.6), hexadecyl octadecyl dimethyl ammonium chloride (m / z 522.6), dioctadecyl dimethyl ammonium chloride (m / z 550.7), hexadecyl trimethyl ammonium bromide (284.3), dodecyl trimethyl ammonium chloride (228.3), octadecyl trimethyl ammonium chloride (312.4), benzalkonium chloride (304.3), and hexadecylpyridinium chloride (340.0).

[0059] Elution program: Mobile phase A is 100 mmol / L ammonium acetate aqueous solution (pH adjusted to 5.0 with acetic acid), mobile phase B is acetonitrile, and mobile phase C is water. The gradient elution program is shown in the table below:

[0060] Table 5 Gradient elution program 0 5 55 40 2 5 55 40 8 5 85 10 10 5 55 40 Under the above conditions, the disinfectant was accurately identified to contain cetyltrimethylammonium bromide and benzalkonium chloride.

[0061] The contents of cetyltrimethylammonium bromide and benzalkonium chloride in the disinfectant product were determined to be 0.5% and 0.3%, respectively.

[0062] Example 7: Identification and Detection of Quaternary Ammonium Salt Surfactants in a Commercially Available Pet Shampoo Product

[0063] (a) Preparation of probe solution: Solution A: Weigh out sodium tetraphenylborate, dissolve it in water, and prepare a solution with a concentration of 10 mmol / L; Solution B: Weigh bromocresol purple, dissolve it in a small amount of ethanol, dilute it with water, and prepare a solution with a concentration of 0.8 mmol / L; Solution C: Weigh out sodium dihydrogen phosphate and disodium hydrogen phosphate, dissolve them in water, and prepare a mixed buffer salt solution with a pH of 7 and a total concentration of 80 mmol / L. Take 5 mL of solution A and solution B and place them in a 15 mL transparent centrifuge tube. After mixing, the molar ratio of sodium tetraphenylborate to bromocresol violet in the solution is 150:1. Add 5 mL of solution C. The final pH of the solution is 7, which is the probe solution.

[0064] (II) Measurement process: Take 5g of commercially available sample, dissolve it in water to form a clear solution, and transfer it to a 5mL volumetric flask and dilute to volume. Pipette 1mL of the sample solution into the probe solution prepared above. A purple precipitate immediately appears in the probe solution, indicating a positive sample. Centrifuge at 4000 rpm. The supernatant shows no significant fading compared to the probe solution. Discard the supernatant, dissolve the precipitate in 80% acetone-water solution, and dilute to 10mL with the initial mobile phase. Send the solution to a liquid chromatography-mass spectrometry (LC-MS) system for further accurate identification and analysis.

[0065] The analytical conditions for liquid chromatography-mass spectrometry are as follows: The chromatographic column used was a Thermo Acclaim Surfactant Plus column (4.6 mm × 150 mm, 3 μm); The mobile phase was an ammonium acetate aqueous solution-acetonitrile-water system, using gradient elution mode at a flow rate of 1.0 mL / min; The mass spectrometer is equipped with an electrospray ionization source and is monitored in positive ion mode. It adopts SCAN mode and scans in the molecular weight range of 100 to 1000.

[0066] Elution program: Mobile phase A is 100 mmol / L ammonium acetate aqueous solution (pH adjusted to 5.0 with acetic acid), mobile phase B is acetonitrile, and mobile phase C is water. The gradient elution program is shown in the table below:

[0067] Table 6 Gradient elution program 0 5 60 35 2 5 60 35 10 5 90 5 Under the above conditions, the product was accurately identified to contain: octadecyl dimethyl ammonium chloride.

[0068] The product was found to contain 0.8% octadecyl dimethyl ammonium chloride.

[0069] Example 8: Detection of residual quaternary ammonium surfactants in the degradation tank of a wastewater treatment plant

[0070] Prepare the probe solution in advance, using the same method as in Example 6.

[0071] Measurement process: Take 200 mL of sample from the sampling port of the degradation cell, shake well, take 1 mL, and add it to the probe solution prepared above. If there is no obvious reaction in the probe solution, it is determined to be a negative sample.

[0072] Take another 5 mL sample, dilute it to 5 mL with the initial mobile phase, and send it to a liquid chromatography-mass spectrometry system for missed detection confirmation.

[0073] The analytical conditions for liquid chromatography-mass spectrometry are as follows: The chromatographic column used was a Thermo Acclaim Surfactant Plus column (4.6 mm × 100 mm, 3 μm); The mobile phase was an ammonium acetate aqueous solution-acetonitrile-water system, using gradient elution mode at a flow rate of 1.0 mL / min; The mass spectrometer is equipped with an electrospray ionization source and is monitored in positive ion mode. It adopts SCAN mode and scans in the molecular weight range of 100 to 1000.

[0074] Elution program: Mobile phase A is 100 mmol / L ammonium acetate aqueous solution (pH adjusted to 5.0 with acetic acid), mobile phase B is acetonitrile, and mobile phase C is water. The gradient elution program is shown in the table below:

[0075] Table 7 Gradient elution program 0 5 60 35 2 5 60 35 10 5 90 5 As a result, no characteristic ion peaks of common quaternary ammonium salt surfactants were detected in the molecular weight range of 100–1000, proving that the conclusion that the probe solution identified negative results was accurate.

[0076] Comparative Example 1:

[0077] Take 5g of the sample from Example 1, dissolve it in water to form a transparent solution, and transfer it to a 5mL volumetric flask and make up to volume.

[0078] 1 mL of sample solution was transferred and added dropwise to a 15 mmol / L sodium tetraphenylborate solution. The probe solution became turbid, but the precipitation was not obvious. After centrifugation at 4000 r / min, the supernatant was clear, and the precipitate was white. The supernatant was discarded, and analysis was performed using the same liquid chromatography-mass spectrometry method as in Example 1. The results showed that the content of D1821 in the product was 2%, which was significantly lower than the actual content of 6%.

[0079] The comparative example shows that when sodium tetraphenylborate is used as the probe solution alone, the precipitation reaction is relatively slow, the precipitate is white and difficult to observe, and it is impossible to determine whether the precipitation is complete, resulting in lower measurement results.

[0080] Comparative Example 2:

[0081] Solution B: Weigh bromocresol purple, dissolve it in a small amount of ethanol, dilute it with water, and prepare a solution with a concentration of 2 mmol / L; Solution C: Weigh sodium dihydrogen phosphate and disodium hydrogen phosphate, dissolve them in water, and prepare a mixed buffer solution with a pH of 8 and a total concentration of 10 mmol / L. Take 10 mL of solution B and place it in a 25 mL transparent centrifuge tube. Add 10 mL of solution C. The final solution has a pH of 8 and can be used as the probe solution.

[0082] Take 3g of the sample from Example 4, dissolve it in water to form a clear solution, and transfer it to a 5mL volumetric flask and dilute to volume. Take 1mL of the sample solution and add it dropwise to the probe solution prepared above. The probe solution shows fading, but no obvious precipitation is observed. This solution is used as the test solution and sent to a liquid chromatography-mass spectrometry (LC-MS) instrument for analysis using the same analytical conditions and procedures as in Example 4. The results show that quaternary ammonium surfactants were not detected.

[0083] This comparative example shows that, although using only bromocresol purple-phosphate buffer as a probe solution can indicate the presence of quaternary ammonium salt surfactants, it cannot achieve separation and enrichment through precipitation reaction. As a result, the concentration of the analyte in the sample solution is lower than the instrument detection limit, and accurate results for further analysis cannot be obtained.

[0084] Comparative Example 3:

[0085] Dodecyl dimethyl benzyl ammonium chloride (1227), a commercially available water treatment agent raw material, was analyzed using QB / T 1915-2021 and the method described in this paper. The results are compared below:

[0086] Table 8 Comparison of Results Analysis 1 30.1% 30.4% 2 30.3% 30.5% 3 30.2% 30.3% mean 30.2% 30.4% The comparison shows that the results of this method are similar to those of the standard method.

[0087] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A probe solution for rapidly indicating or screening quaternary ammonium salt surfactants, characterized in that, The probe solution is a mixed solution of sodium tetraphenylborate, bromocresol purple, and phosphate buffer, wherein the total molar concentration of sodium tetraphenylborate and bromocresol purple is 2 mmol / L to 20 mmol / L and the molar ratio of sodium tetraphenylborate to bromocresol purple is 100:1 to 500:1; the phosphate buffer solution is composed of sodium dihydrogen phosphate and disodium hydrogen phosphate, and its pH value is 7 to 8; the pH value of the probe solution is maintained at 7 to 8; if the probe solution exhibits at least one of the following phenomena when it encounters a sample containing quaternary ammonium salt surfactants: turbidity, precipitation, or fading, then the sample is determined to contain quaternary ammonium salt surfactants.

2. A method for preparing a probe solution for rapid indication or screening of quaternary ammonium salt surfactants, comprising the following steps: (1) Preparation of solution A: Weigh sodium tetraphenylborate, dissolve it in water, and prepare a solution with a concentration of 5 mmol / L to 20 mmol / L; (2) Preparation of solution B: Weigh bromocresol purple, dissolve it in a small amount of ethanol, dilute it with water, and prepare a solution with a concentration of 0.2 mmol / L to 2 mmol / L; (3) Preparation of solution C: Weigh sodium dihydrogen phosphate and disodium hydrogen phosphate, dissolve them in water, and prepare a mixed buffer salt solution with a pH of 7-8 and a total concentration of 10 mmol / L-100 mmol / L. (4) Take an appropriate amount of solution A and an appropriate amount of solution B and mix them together. The molar ratio of sodium tetraphenylborate to bromocresol violet in the mixed solution should be controlled at 100:1 to 500:

1. Then add an appropriate amount of solution C so that the total molar concentration of sodium tetraphenylborate and bromocresol violet in the final solution is 2 mmol / L to 20 mmol / L and the pH value of the final solution is maintained at 7 to 8. The probe solution is obtained.

3. A method for rapid screening of quaternary ammonium surfactants, characterized in that, Take the sample to be tested, dissolve it, and add it dropwise to the probe solution described in claim 1 to obtain a sample solution. If the sample solution shows at least one of the following phenomena: turbidity, precipitation, or fading, then the sample contains quaternary ammonium salt surfactants. If the appearance of the sample solution does not change significantly, then the sample does not contain quaternary ammonium salt surfactants.

4. A droplet probe for rapid indication or screening of quaternary ammonium salt surfactants prepared using the probe solution of claim 1.

5. A method for rapid screening and accurate analysis of quaternary ammonium surfactants, characterized in that, Includes the following steps: Step (1) Rapid screening: Take the sample to be tested, dissolve it, and add it dropwise to the probe solution described in claim 1 to obtain the sample solution. If the sample solution shows turbidity, precipitation or fading, it is judged as positive and the sample contains quaternary ammonium salt surfactants; if the appearance of the sample solution does not change significantly, it is judged as negative and the sample does not contain quaternary ammonium salt surfactants. Step (2) Accurate analysis: a. Take the sample solution that was determined to be positive in the rapid screening in step (1), and separate it by high-speed centrifugation. The supernatant should remain purple. If obvious fading occurs, reduce the sample amount and repeat the operation of step (1) until the positive sample solution is separated by high-speed centrifugation and the supernatant remains purple. b. After centrifugation of the sample solution, discard the supernatant, add an appropriate amount of solvent to dissolve the precipitate, and then send it to a liquid chromatography-mass spectrometry system for accurate qualitative and quantitative analysis.

6. The method according to claim 5, characterized in that, In step (1), the sample amount is 1g~5g, and 1mL~5mL of solvent is added to dissolve it to obtain a transparent solution; the solvent is selected from one or more of water, methanol, ethanol, and isopropanol.

7. The method according to claim 5, characterized in that, The solvent used to dissolve the precipitate in step (2) is one of the following: benzene, ketone, alcohol or chloroalkane solvents or their corresponding aqueous solutions, or liquid chromatography mobile phase.

8. The method according to claim 7, characterized in that, The solvent is one of benzene, toluene, acetone, isopropanol or carbon tetrachloride or an aqueous solution thereof; the liquid chromatography mobile phase is an ammonium acetate aqueous solution-acetonitrile-water system.

9. The method according to claim 5, characterized in that, The analytical conditions for the liquid chromatography-mass spectrometry (LC-MS) instrument in step (2) are as follows: the chromatographic column is a Thermo Acclaim Surfactant Plus column; the mobile phase is an ammonium acetate aqueous solution-acetonitrile-water system, using gradient elution mode; the mass spectrometer is equipped with an electrospray ionization source, and the characteristic target ions are selectively monitored or extracted in positive ion mode.

10. The method according to claim 9, characterized in that: The concentration of the ammonium acetate aqueous solution in the mobile phase combination is 50 mmol / L to 100 mmol / L, and the pH value is 4.5 to 5.5; The gradient program of the gradient elution mode is set as follows: ammonium acetate aqueous solution is used as mobile phase A, acetonitrile as mobile phase B, and water as mobile phase C. The volume ratio of mobile phase A is maintained at a fixed value of 5% to 10% throughout the gradient program. Elution separation is achieved by adjusting the ratio of mobile phase B to mobile phase C. During the initial time period of 1 min to 2 min, the volume ratio of mobile phase B is maintained at 50% to 60%. Subsequently, during the time period of 2 min to 10 min, the volume ratio gradient of mobile phase B is increased to 80% to 90%, while the volume ratio gradient of mobile phase C is simultaneously reduced to 15% to 0% to achieve complete elution of the target component.

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