A method for rapid detection of non-sulfonated oil content in aes by chemical derivation and fluorescence

Abstract

This invention provides a rapid chemical derivatization-fluorescence detection method for the content of unsulfonated oil in AES (Alternative Ester Extraction), comprising the following steps: S1: Dissolving the AES sample to be tested in anhydrous ethanol to prepare an AES ethanol solution; S2: Passing the AES ethanol solution obtained in step S1 through a strong anion exchange solid-phase extraction column and collecting the eluent containing AEO; S3: Removing the solvent from the eluent collected in step S2 to obtain AEO residue; S4: Dissolving the AEO residue obtained in step S3 in an organic solvent, adding a fluorescent derivatizing reagent and a pH buffer solution to cause the primary hydroxyl groups at the ends of the AEO molecules to undergo a derivatization reaction to generate a derivatized product with a fluorescent signal; S5: Extracting the fluorescent derivatized product obtained in step S4; Step S6: Calculating the content of unsulfonated oil in the AES sample based on the fluorescence signal value measured in step S5 and a pre-established standard curve. The method is simple to operate, highly sensitive, and rapid in detection.

Description

Technical Field

[0001] This invention belongs to the field of surfactant analysis and detection technology, specifically relating to a chemical derivatization-fluorescence rapid detection method for the content of unsulfonated oil in fatty alcohol polyoxyethylene ether sulfate (AES). Background Technology

[0002] AES is an important anionic nonionic surfactant widely used in daily chemical, textile, and printing and dyeing industries. AES is produced through the sulfonation / sulfation reaction of fatty alcohol polyoxyethylene ether (AEO). Unreacted AEO constitutes the "unsulfonated oil" component in AES products. Excessive unsulfonated oil content not only affects the product's color and transparency but may also lead to odor deterioration, making it one of the important indicators for evaluating AES product quality.

[0003] Currently, the determination of unsulfonated oil content mainly adopts the national standard GB / T 17830-1999 "Determination of Polyethylene Glycol Content in Polyethoxylated Nonionic Surfactants". This method is based on quantification by gravimetric method after separation with ion exchange resin. This method has the following technical defects: ① The operation process is complex, requiring multiple steps such as ion exchange, distillation, and drying, taking about 2.5-3 hours in total, which is difficult to meet the needs of rapid detection; ② The gravimetric method has low sensitivity, and for samples with low unsulfonated oil content, the weighing error is large, resulting in poor precision of the measurement results; ③ There are many human operation steps, which are easy to introduce errors, and the reproducibility between different operators is poor.

[0004] In recent years, although chromatographic detection methods (such as differential refractive index detection and evaporative light scattering detection) have been applied in this field, differential refractive index detection requires gradient elution conditions and has limited sensitivity, while evaporative light scattering detection equipment is expensive and has high maintenance costs. Therefore, there is an urgent need to develop a new method for detecting the content of unsulfonated oil in AES that is easy to operate, highly sensitive, fast in detection, and cost-effective. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a chemical derivatization-fluorescence rapid detection method for the content of unsulfonated oil in AES that is simple to operate, highly sensitive, fast to detect, and cost-controllable, so as to replace the traditional gravimetric and chromatographic detection methods.

[0006] This invention provides a chemically derived fluorescence rapid detection method for the content of unsulfonated oil in AES, comprising the following steps:

[0007] Step S1: Dissolve the AES sample to be tested in anhydrous ethanol to prepare an AES ethanol solution;

[0008] Step S2: Pass the AES ethanol solution obtained in step S1 through a strong anion exchange solid phase extraction column to adsorb and retain AES, while unsulfonated neutral AEO molecules flow out with the solution, and collect the eluent containing AEO.

[0009] Step S3: Remove the solvent from the effluent collected in step S2 to obtain AEO residue;

[0010] Step S4: Dissolve the AEO residue obtained in step S3 in an organic solvent, add a fluorescent derivatizing reagent and a pH buffer solution, and react at a certain temperature for a certain time to allow the primary hydroxyl groups at the ends of the AEO molecules to undergo a derivatization reaction to generate a derivatized product with a fluorescent signal.

[0011] Step S5: Extract the fluorescent derivative obtained in step S4, detect it using a fluorescence detector, and record the fluorescence signal value;

[0012] Step S6: Based on the fluorescence signal value measured in step S5 and combined with the pre-established standard curve, calculate the content of unsulfonated oil in the AES sample.

[0013] Preferably, the strong anion exchange solid-phase extraction column in step S2 is a SAX solid-phase extraction column bonded with quaternary ammonium salt functional groups; the SAX solid-phase extraction column is activated and equilibrated sequentially with methanol, pure water and 0.1 mol / L sodium acetate buffer containing 30% methanol before sample loading; after sample loading, it is washed with 0.1 mol / L sodium acetate buffer containing 30% methanol.

[0014] Preferably, the fluorescent derivatizing reagent in step S4 is selected from any one of dansyl chloride, 5-di-n-butylaminonaphthalene-1-sulfonyl chloride, or 10-ethylacridone-2-sulfonyl chloride; the organic solvent is acetonitrile; the pH buffer solution is a sodium carbonate-sodium bicarbonate buffer solution with a pH of 10.0-12.5; the reaction temperature is 50-80℃; and the reaction time is 5-60 min.

[0015] Preferably, the fluorescent derivatizing reagent in step S4 is dansyl chloride with a concentration of 7-11 mg / mL (dissolved in acetonitrile); the pH buffer solution is a sodium carbonate-sodium bicarbonate buffer solution with a pH of 11.5-12.5; the reaction temperature is 65-75℃; and the reaction time is 20-40 min.

[0016] Preferably, the excitation wavelength of the fluorescence detector in step S5 is 335-345 nm and the emission wavelength is 510-520 nm; the solvent used for product extraction is ethyl acetate.

[0017] Preferably, the formula for calculating the unsulfonated oil content in step S6 is:

[0018] ,

[0019] Where w is the mass fraction (%) of unrefined oil in the AES sample, C is the AEO concentration (mg / L) obtained from the standard curve, V is the final volume (mL), D is the dilution factor, and m is the mass (g) of the AES sample.

[0020] Preferably, the concentration of the AES ethanol solution in step S1 is 1-100 mg / mL.

[0021] Preferably, the packing particle size of the strong anion exchange solid phase extraction column in step S2 is 40-60 μm.

[0022] Preferably, the fluorescent derivatizing reagent in step S4 is 10-ethylacridone-2-sulfonyl chloride with a concentration of 3-5 mg / mL (dissolved in acetonitrile); the pH buffer solution is a sodium carbonate-sodium bicarbonate buffer solution with a pH of 11.0-12.0; the reaction temperature is 60-70℃; and the reaction time is 15-30 min.

[0023] Preferably, the method for establishing the standard curve in step S6 is as follows: using a series of AEO standards, processing and measuring them according to the same derivatization method and fluorescence detection conditions as in steps S1-S5, and performing linear fitting with AEO concentration as the abscissa and fluorescence signal value as the ordinate to obtain the standard curve equation; the concentration range of the AEO standards is 0.1-100 mg / L, and the correlation coefficient R² of the standard curve is ≥0.999.

[0024] The beneficial effects of this invention are as follows:

[0025] 1. High sensitivity: This invention uses a fluorescence derivatization method to convert non-fluorescent AEO molecules into derivatives with strong fluorescent signals, which are then detected by a fluorescence detector. The detection limit can reach below 0.05 mg / L, which is far superior to traditional gravimetric and differential refractive index detection methods.

[0026] 2. Fast analysis speed: The entire detection process of this invention (including pretreatment, solid phase extraction, derivatization, and detection) can be completed within 1.5 hours, which significantly shortens the analysis time compared with the traditional gravimetric method (2.5-3 hours) and meets the needs of rapid detection.

[0027] 3. High specificity: This invention uses a SAX solid-phase extraction column to effectively separate AES and AEO. Combined with fluorescence derivatization reaction and fluorescence detection at a specific wavelength, the method has strong anti-interference ability and effectively avoids interference from other impurities in the matrix on the detection results.

[0028] 4. Simple operation and controllable cost: This invention does not require expensive large-scale analytical equipment, and all reagents used are conventional reagents. The operation steps are clear and easy to standardize and promote. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the process of the present invention. Detailed Implementation

[0030] To further understand the features, technical means, and specific objectives and functions achieved by the present invention, the present invention will be described in further detail below with reference to specific embodiments and accompanying drawings.

[0031] like Figure 1 As shown in Example 1: This example provides a chemically derived fluorescence rapid detection method for the content of unsulfonated oil in AES, and the specific operation is as follows:

[0032] (1) Sample pretreatment

[0033] Weigh 100.0 mg (accurate to 0.1 mg) of the AES sample to be tested, place it in a 10 mL volumetric flask, dissolve it in anhydrous ethanol and dilute to volume to prepare an AES ethanol solution with a concentration of 10 mg / mL.

[0034] (2) Anion exchange solid-phase extraction separation

[0035] Take an SAX strong anion exchange solid-phase extraction column (3 mL / 200 mg, packing particle size 40-60 μm) and activate and equilibrate it sequentially with 3 mL of methanol, 3 mL of pure water, and 3 mL of 0.1 mol / L sodium acetate buffer (pH 5.0) containing 30% methanol. Take 1 mL of the AES ethanol solution prepared in step (1), dilute it with 1 mL of deionized water, and load it at a flow rate of 1 mL / min, collecting the eluent. Then, wash with 3 mL of 0.1 mol / L sodium acetate buffer containing 30% methanol, collect the eluent, and combine it with the eluent.

[0036] (3) Solvent removal

[0037] The combined liquid collected in step (2) was rotary evaporated to dryness in a 50°C water bath to obtain AEO residue.

[0038] (4) Fluorescent derivatization reaction

[0039] Add 2 mL of acetonitrile to the AEO residue obtained in step (3) to dissolve it, then add 1 mL of dansyl chloride acetonitrile solution (9 mg / mL) and 1 mL of sodium carbonate-sodium bicarbonate buffer solution with pH=12.0, mix well, and react in a 70℃ water bath for 30 min. After the reaction is complete, cool to room temperature.

[0040] (5) Product extraction and detection

[0041] Add 3 mL of ethyl acetate to the reaction solution from step (4), shake to extract for 1 min, allow to stand for layering, take the organic phase, dry it under nitrogen, dissolve the residue in 1 mL of acetonitrile, filter through a 0.45 μm filter membrane, and use the filtrate for fluorescence detection. Use a fluorescence spectrophotometer, set the excitation wavelength to 340 nm and the emission wavelength to 515 nm, and measure the fluorescence intensity value.

[0042] (6) Content Calculation

[0043] AEO standards (0.1, 0.5, 1.0, 5.0, 10.0, 50.0, 100.0 mg / L) were pre-treated using the same derivatization method as in steps (1)-(5), and a standard curve was plotted. The linear equation obtained was Y=125.6X+36.2 (R²=0.9996), where X is the AEO concentration (mg / L) and Y is the fluorescence intensity. The AEO concentration was calculated by substituting the fluorescence intensity measured in step (5) into the linear equation, and then the content of unsulfonated oil in the AES sample was calculated according to the following formula:

[0044] ;

[0045] Where w is the mass fraction (%) of untreated oil, C is the AEO concentration (mg / L) obtained from the standard curve in step (5), V is the final volume (mL), D is the dilution factor (1 in this embodiment), and m is the mass (mg) of AES actually involved in the calculation in step (1).

[0046] Example 2: This example is basically the same as Example 1, except that: in step (4), the fluorescent derivatizing reagent is 5-di-n-butylaminonaphthalene-1-sulfonyl chloride (Bns-Cl), with a concentration of 5 mg / mL (dissolved in acetonitrile); the pH buffer solution is pH=11.5-12.0; the reaction temperature is 65-70℃; and the reaction time is 30-45 min. The other conditions are the same as in Example 1.

[0047] Example 3: This example is basically the same as Example 1, except that: in step (4), the fluorescent derivatizing reagent is 10-ethylacridinone-2-sulfonyl chloride (EASC), with a concentration of 3 mg / mL (dissolved in acetonitrile); the pH buffer solution is pH=11.0-12.0; the reaction temperature is 60-70℃; and the reaction time is 15-30 min. The other conditions are the same as in Example 1.

[0048] Methodological Validation

[0049] (1) Linear range and sensitivity

[0050] The AEO standard solution was determined according to the method described in Example 1. The linear range was 0.1-100 mg / L, and the correlation coefficient R² ≥ 0.999. The limit of detection (LOD) calculated at 3 times the signal-to-noise ratio was 0.04 mg / L, and the limit of quantitation (LOQ) calculated at 10 times the signal-to-noise ratio was 0.15 mg / L.

[0051] (2) Precision

[0052] The same AES sample (containing approximately 1.5% unsulfonated oil) was tested according to the method in Example 1. Six consecutive measurements were taken on the same day, and the intra-day precision RSD was calculated to be 3.2%. Six measurements were taken on each of three consecutive days, and the inter-day precision RSD was calculated to be 5.6%. The results indicate that this method has good precision.

[0053] (3) Spike recovery rate

[0054] AEO standards at three levels—low (1 mg / L), medium (10 mg / L), and high (50 mg / L)—were added to AES samples with known unsulfonated oil content. The recoveries were determined and calculated according to the method in Example 1. The average recoveries at the three levels were 96.8%, 101.2%, and 99.5%, respectively, all within the range of 95%–105%, indicating good accuracy of the method.

[0055] (4) Interference test

[0056] Impurities that may be present during the AES production process (unreacted fatty alcohols and polyethylene glycol) were treated under the same derivatization conditions as in Example 1 and then subjected to fluorescence detection. The results showed that the fluorescence signal intensity of the derivatives of these impurities at wavelengths of 340 nm and 515 nm was less than 0.5% of the signal intensity of the AEO derivatives, and did not significantly interfere with the quantitative detection of AEO.

[0057] Key Parameter Description

[0058] (1) Explanation of the organic phase ratio of the SAX solid phase extraction column eluent in step S2

[0059] AEO molecules are nonionic surfactants, and they may exhibit a certain degree of nonspecific adsorption on SAX solid-phase extraction columns. This invention uses a sodium acetate buffer containing 30% methanol as the loading and eluent. The methanol effectively weakens the hydrophobic interaction between AEO and the stationary phase, while the acetate ion, as a competitive anion, saturates the ion exchange sites on the SAX column, thereby minimizing the nonspecific adsorption of AEO and ensuring a recovery rate of over 95% of AEO in the effluent.

[0060] (2) Explanation of the selection of derivatization pH conditions in step S4

[0061] The efficiency of fluorescence derivatization is significantly affected by pH. When the pH is too low (<10), the nucleophilicity of the terminal hydroxyl group of AEO is insufficient to react effectively with dansyl chloride; when the pH is too high (>12.5), the hydrolysis side reaction rate of dansyl chloride increases significantly, leading to a decrease in the concentration of the derivatizing reagent and a reduction in derivatization efficiency. This invention, through experimental optimization, determined that the suitable pH range for AEO primary hydroxyl derivatization is 11.5-12.5, under which both reaction efficiency and reagent stability can be balanced.

[0062] (3) Explanation of alternative fluorescent derivatizing reagents

[0063] This invention also covers Bns-Cl and EASC as alternative fluorescent derivatizing reagents. Bns-Cl has a higher fluorescence quantum efficiency than dansyl chloride, and its derivatives are more easily extracted by low-polarity solvents, which is beneficial for pre-detection purification steps. EASC has an even higher fluorescence quantum efficiency, approximately 43 times that of dansyl chloride, and can be used for the quantitative detection of lower concentrations of unsulfonated oils. The suitability of these alternative reagents needs to be selected based on actual application requirements and preliminary experiments.

[0064] The embodiments described above merely illustrate the optimal implementation of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A rapid chemical derivatization-fluorescence detection method for the content of unsulfonated oil in AES, characterized in that, Includes the following steps: Step S1: Dissolve the AES sample to be tested in anhydrous ethanol to prepare an AES ethanol solution; Step S2: Pass the AES ethanol solution obtained in step S1 through a strong anion exchange solid phase extraction column to adsorb and retain AES, while unsulfonated neutral AEO molecules flow out with the solution, and collect the eluent containing AEO. Step S3: Remove the solvent from the effluent collected in step S2 to obtain AEO residue; Step S4: Dissolve the AEO residue obtained in step S3 in an organic solvent, add a fluorescent derivatizing reagent and a pH buffer solution, and react at a certain temperature for a certain time to allow the primary hydroxyl groups at the ends of the AEO molecules to undergo a derivatization reaction to generate a derivatized product with a fluorescent signal. Step S5: Extract the fluorescent derivative obtained in step S4, detect it using a fluorescence detector, and record the fluorescence signal value; Step S6: Based on the fluorescence signal value measured in step S5 and combined with the pre-established standard curve, calculate the content of unsulfonated oil in the AES sample.

2. The chemical derivatization-fluorescence rapid detection method for the content of unsulfonated oil in AES according to claim 1, characterized in that, The strong anion exchange solid-phase extraction column mentioned in step S2 is an SAX solid-phase extraction column bonded with quaternary ammonium salt functional groups; the SAX solid-phase extraction column is activated and equilibrated sequentially with methanol, pure water and 0.1 mol / L sodium acetate buffer containing 30% methanol before sample loading; after sample loading, it is washed with 0.1 mol / L sodium acetate buffer containing 30% methanol.

3. The chemical derivatization-fluorescence rapid detection method for the content of unsulfonated oil in AES according to claim 1, characterized in that, The fluorescent derivatizing reagent in step S4 is selected from any one of dansyl chloride, 5-di-n-butylaminonaphthalene-1-sulfonyl chloride, or 10-ethylacridone-2-sulfonyl chloride; the organic solvent is acetonitrile; the pH buffer solution is a sodium carbonate-sodium bicarbonate buffer solution with a pH of 10.0-12.5; the reaction temperature is 50-80℃; and the reaction time is 5-60 min.

4. The chemical derivatization-fluorescence rapid detection method for the content of unsulfonated oil in AES according to claim 3, characterized in that, The fluorescent derivatizing reagent in step S4 is dansyl chloride with a concentration of 7-11 mg / mL (dissolved in acetonitrile); the pH buffer solution is a sodium carbonate-sodium bicarbonate buffer solution with a pH of 11.5-12.5; the reaction temperature is 65-75℃; and the reaction time is 20-40 min.

5. The chemical derivatization-fluorescence rapid detection method for the content of unsulfonated oil in AES according to claim 1, characterized in that, The excitation wavelength of the fluorescence detector in step S5 is 335-345 nm, and the emission wavelength is 510-520 nm; the solvent used for product extraction is ethyl acetate.

6. The chemical derivatization-fluorescence rapid detection method for the content of unsulfonated oil in AES according to claim 1, characterized in that, The formula for calculating the unsulfonated oil content in step S6 is: ； Where w is the mass fraction (%) of unrefined oil in the AES sample, C is the AEO concentration (mg / L) obtained from the standard curve, V is the final volume (mL), D is the dilution factor, and m is the mass (g) of the AES sample.

7. The chemical derivatization-fluorescence rapid detection method for the content of unsulfonated oil in AES according to claim 1, characterized in that, The concentration of the AES ethanol solution in step S1 is 1-100 mg / mL.

8. The chemical derivatization-fluorescence rapid detection method for the content of unsulfonated oil in AES according to claim 1, characterized in that, The packing material of the strong anion exchange solid phase extraction column described in step S2 has a particle size of 40-60 μm.

9. The chemical derivatization-fluorescence rapid detection method for the content of unsulfonated oil in AES according to claim 1, characterized in that, The fluorescent derivatizing reagent in step S4 is 10-ethylacridone-2-sulfonyl chloride with a concentration of 3-5 mg / mL (dissolved in acetonitrile); the pH buffer solution is a sodium carbonate-sodium bicarbonate buffer solution with a pH of 11.0-12.0; the reaction temperature is 60-70℃; and the reaction time is 15-30 min.

10. A rapid chemical derivatization-fluorescence detection method for the content of unsulfonated oil in AES according to any one of claims 1-9, characterized in that, The method for establishing the standard curve in step S6 is as follows: AEO standards of a series of concentrations are used, and the same derivatization method and fluorescence detection conditions as in steps S1-S5 are applied for processing and measurement. A linear fit is performed with AEO concentration as the abscissa and fluorescence signal value as the ordinate to obtain the standard curve equation. The concentration range of the AEO standards is 0.1-100 mg / L, and the correlation coefficient R² of the standard curve is ≥0.999.

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