A method for determining the critical micelle concentration of sodium alkylbenzenesulfonate

Abstract

The application provides a method for determining the critical micelle concentration of sodium alkyl benzene sulfonate, comprising the following steps: step 1, dissolving 1-4 parts of sodium alkyl benzene sulfonate in 300-600 parts of water to obtain a sodium alkyl benzene sulfonate solution with a target concentration; step 2, gradient diluting the sodium alkyl benzene sulfonate solution with the target concentration to obtain a plurality of solutions with different concentrations; step 3, qualitatively and quantitatively analyzing the plurality of solutions with different concentrations under the action of an asymmetric flow field flow fractionation instrument to construct a standard line; and step 4, determining the critical micelle concentration of sodium alkyl benzene sulfonate based on the standard line. The method for determining the critical micelle concentration of sodium alkyl benzene sulfonate by using an asymmetric flow field flow fractionation instrument (AF4, hereinafter referred to as a field flow fractionation instrument) has the advantages of convenient operation, strong universality, high sensitivity, small required sample amount and good compatibility compared with the prior art.

Description

Technical Field

[0001] This invention relates to the field of critical micelle concentration determination, and in particular to a method for determining the critical micelle concentration of sodium alkylbenzene sulfonate using a combination of asymmetric flow field meter and flow field analyzer. Background Technology

[0002] Sodium alkylbenzene sulfonate is a typical anionic surfactant with a benzene ring structure. Currently, commonly used methods for determining critical micelle concentration include: surface tension method, conductivity method, light scattering method, dye method, pyrene fluorescent probe method, turbidimetric method, and direct spectrophotometry. Because different physicochemical properties have varying response ranges and sensitivities to changes in surfactant concentration, the CMC values ​​obtained by different methods will differ.

[0003] Existing surface tension methods are generally applicable to various surfactants. However, if the sample contains highly surface-active polar organic compounds such as long-chain alcohols, higher amines, and fatty acids, the inflection point of the surface tension-concentration curve becomes less distinct, making it difficult to determine the critical micelle concentration. Furthermore, surface tension measurements are easily affected by ambient temperature and the cleanliness of the container. In addition, the time required for surfactant solutions to reach surface equilibrium is very long (international standards specify 3 hours), making the testing process cumbersome.

[0004] Existing conductivity methods cannot be used to determine the critical micelle concentration of nonionic surfactants.

[0005] The existing pyrene fluorescent probe method requires a toxic benzene solution to prepare the pyrene probe, and the operation process is cumbersome.

[0006] Existing direct spectrophotometry methods are not suitable for surfactants that do not contain benzene rings. Summary of the Invention

[0007] This invention provides a method for determining the critical micelle concentration of sodium alkylbenzene sulfonate using asymmetric flow-field coupling technology, which at least solves the problems of inconvenient operation and low sensitivity in the prior art for determining the critical micelle concentration of sodium alkylbenzene sulfonate.

[0008] This invention provides a method for determining the critical micelle concentration of sodium alkylbenzene sulfonate, comprising:

[0009] Step 1: Take 1-4 parts by weight of sodium alkylbenzene sulfonate, dissolve it in 300-600 parts by weight of water, mix well, and obtain a sodium alkylbenzene sulfonate solution of the target concentration.

[0010] Step 2: The sodium alkylbenzene sulfonate solution of the target concentration is serially diluted to obtain multiple solutions of different concentrations;

[0011] Step 3: Perform qualitative and quantitative analysis on the multiple solutions of different concentrations under the action of an asymmetric fluid field analyzer to construct a standard line;

[0012] Step 4: Determine the critical micelle concentration of sodium alkylbenzene sulfonate based on the standard line conditions.

[0013] Furthermore, the sodium alkylbenzene sulfonate is a long-chain saturated sodium alkylbenzene sulfonate.

[0014] Furthermore, the sodium alkylbenzene sulfonate is sodium dodecylbenzene sulfonate.

[0015] Further, the solutions of different concentrations are, in sequence, 0.1, 0.3, 0.5, 0.7, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0, and 3.5 mM sodium alkylbenzene sulfonate solutions.

[0016] Furthermore, the mixing process in step 1 includes:

[0017] Dissolve sodium alkylbenzene sulfonate in water, sonicate for 5-20 minutes, and let stand to obtain a sodium alkylbenzene sulfonate solution.

[0018] Furthermore, the qualitative and quantitative analysis process includes:

[0019] Sodium alkylbenzene sulfonate solution was separated using an asymmetric flow field analyzer;

[0020] Obtain test data;

[0021] The detection data includes at least one of ultraviolet absorption data and particle size detection data.

[0022] Furthermore, the separation of sodium alkylbenzene sulfonate solution using an asymmetric flow field analyzer includes:

[0023] During the injection phase, the parameters are set as follows: Delay Time 0.5 min, Injection Flow 0.3 mL / min, Injection Time 10 min, Cross Flow 2.50 mL / min, Focus Pump 2.70 mL / min, and Transition Time 1 min.

[0024] The elution phase includes:

[0025] In the first stage, the parameters were: Cross Flow 2.50 mL / min, Time 1 min; Type constant, Exponent 0.00;

[0026] The second stage parameters were: Cross Flow 2.50 mL / min, Time 20 min, Type Power, Exponent 0.20;

[0027] The parameters for the third stage were: Cross Flow 0.15 mL / min, Time 10 min, Type Power, Exponent 0.80;

[0028] The fourth stage had the following parameters: Cross Flow 0 mL / min, Time 30 min, Type constant, Exponent 0.20;

[0029] During the rinsing phase, the parameters are set as follows: Tip Pump 0.05 mL / min, Focus Pump 0.05 mL / min, Skx Pump 0.00 mL / min, and Time 0.5 min.

[0030] Furthermore, the asymmetric flow field instrument includes an AF4 flow field instrument, and the detection data is obtained using a UV-Vis spectrophotometer and a multi-angle static laser particle size analyzer. The wavelengths of the UV-Vis spectrophotometer are selected as 230nm and 260nm.

[0031] Furthermore, the AF4 flow meter is equipped with an AF4 channel semi-permeable membrane, which is a 300kDa polyethersulfone membrane, and the rinsing mobile phase used in the AF4 flow meter is 25μM sodium chloride.

[0032] This invention uses an asymmetric flow field analyzer (AF4, hereinafter referred to as the flow field analyzer) to determine the critical micelle concentration of sodium alkylbenzene sulfonate. Compared with the prior art, it has the advantages of convenient operation, strong versatility, high sensitivity, small sample amount required and good compatibility. Taking sodium dodecylbenzene sulfonate as an example, the CMC of this typical anionic surfactant is in good agreement with the classical method, and it has a relatively broad application prospect. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the sample in the channel before separation;

[0034] Figure 2 Schematic diagram of particle size and flow velocity distribution

[0035] Figure 3 Peak data of sodium dodecylbenzenesulfonate in a field flow meter: (a), (b) UV-vis at 230 nm; (c) y-shifted packing plot; (d) MALS.

[0036] Figure 4The calibration curve for MALS particle size change over time at a 90° scattering angle;

[0037] Figure 5 The surface tension of sodium dodecylbenzenesulfonate was measured using a surface tension meter. Detailed Implementation

[0038] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0039] It should be noted that the terms "first," "second," etc., in the specification, claims, and drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0040] The asymmetric flow field analyzer (Poatnova, EAF2000MT, GERMAN), hereinafter referred to as the flow field analyzer, is used for separation involving various force fields, including asymmetric fields and electric fields. Different force fields can be applied perpendicular to the separation channel, depending on the applied flow field separation method. Under the influence of these force fields and the opposing diffusion field, different equilibrium layers are formed in the sample.

[0041] The field flow analyzer utilizes the pressure generated by cross-flow to trap colloidal substances on a dialysis membrane that allows only ions to pass through. Based on the characteristics of different colloids, such as size and density, the colloids diffuse vertically; larger and denser particles diffuse more slowly, thus separating colloidal particles of different sizes and densities. Before separation begins, the incoming sample colloidal particles are trapped in the lower part of the channel, where the channel flow and the focusing flow meet and are flushed. Figure 1 As shown. The dialysis membrane impedes the passage of colloidal particles but allows the solvent to pass through the channel easily. After sample injection, the focusing flow rate returns to zero, and the colloidal particles are eluted from the channel by the channel flow in the direction towards the detector. According to boundary layer theory, the fluid velocity is slower near the channel wall and faster near the channel center. The fluid velocity exhibits a parabolic streamline along the cross-section. Smaller particles are located on the faster streamlines of the laminar flow within the channel, while larger particles are located on the slower streamlines, such as... Figure 2As shown, this allows smaller particles to pass through the channel faster than larger particles during elution and preferentially enter the detector. Simultaneously, the diffusion flux of the sample is related to its hydrodynamic diameter; the smaller the hydrodynamic diameter, the greater the diffusion flux. Therefore, the order of sample elution can characterize the size of its hydrodynamic diameter. The field flow meter can be coupled with many detectors such as UV-Vis spectrophotometers, multi-angle static laser particle size analyzers, fluorescence detectors, differential detectors, and inductively coupled plasma mass spectrometers. By analyzing different characteristics of colloidal particles using different detectors, simultaneous online detection, separation, and characterization of colloidal particles can be achieved.

[0042] To further illustrate the effectiveness of the present invention, taking sodium dodecylbenzenesulfonate as an example, a method for determining the critical micelle concentration of sodium dodecylbenzenesulfonate using an asymmetric flow field analyzer is provided, comprising the following steps:

[0043] Dissolve 3.88 g of sodium dodecylbenzenesulfonate (MACKLIN, Shanghai, AR, >90%) in 500 mL of ultrapure water, sonicate for 10 min, and allow to stand to obtain a 20 mM sodium dodecylbenzenesulfonate solution. Dilute 12.5 mL of the 20 mM sodium dodecylbenzenesulfonate solution to 500 mL, sonicate for 10 min, and allow to stand to obtain a 1 mM sodium dodecylbenzenesulfonate solution.

[0044] Sodium dodecylbenzenesulfonate was prepared with concentration gradients of 0.1, 0.3, 0.5, 0.7, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0, and 3.5 mM. Approximately 1.5 mL of sample was transferred to the flowmeter sample vial, and the samples were then placed sequentially on the flowmeter sample rack. The operating method was then set in the flowmeter software, with specific parameters shown in Table 1. The operating method consisted of three steps: sample introduction, elution, and rinsing. In this embodiment, an AF4 flowmeter separation system coupled with a UV-Vis spectrophotometer and a multi-angle static laser particle size analyzer (MALS) was used for qualitative and quantitative analysis of the prepared sodium dodecylbenzenesulfonate sample. The UV-Vis spectrophotometer wavelengths were selected at 230 nm and 260 nm. The AF4 channel semipermeable membrane used in the experiment was a 300 Da polyethersulfone (PES) membrane, and the rinsing mobile phase was 25 μM sodium chloride.

[0045] Table 1. Operating Procedure Parameters for Asymmetric Flow Field Meter

[0046]

[0047] The field flow analyzer effectively separated sodium dodecylbenzenesulfonate micelles from other dissolved substances. Detection using a UV-Vis spectrophotometer revealed two main absorption peaks: one at 11 min, which exceeded the detection limit even at low concentrations; and another around 15 min, showing no significant absorption peak at concentrations of 1.0 mM and below, but exhibiting an absorption peak at 1.2 mM, indicating micelle formation at this concentration, meaning the critical micelle concentration is between 1.0 and 1.2 mM. Subsequent absorption peaks increased with increasing concentration. This pattern was observed at both 230 nm and 260 nm, but the second absorption peak signal was not significant at 260 nm.

[0048] The surface tension of sodium dodecylbenzenesulfonate gradient samples was measured using a surface tensiometer. It was found that before 1.2 mM, the surface tension of sodium dodecylbenzenesulfonate decreased rapidly with increasing concentration. After exceeding 1.2 mM, the surface tension gradually stabilized with a slight decrease, indicating that micelles had formed in the solution, meaning the critical micelle concentration was around 1.2 mM. Fitting the two sets of surface tension data separately yielded a critical micelle concentration of 1.23 mM for sodium dodecylbenzenesulfonate. This data is similar to the results obtained using a field-flow analyzer, demonstrating that the field-flow analyzer technique can be used as a method for quantitatively determining the critical micelle concentration of sodium dodecylbenzenesulfonate.

[0049] Sodium dodecylbenzenesulfonate is just one specific substance among sodium alkylbenzenesulfonates, but sodium alkylbenzenesulfonate compounds have similar functional groups and can all be applied to the solutions of the embodiments of the present invention.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that after reading this application specification, they can still modify or make equivalent substitutions to the specific implementation of the present invention, but these modifications or changes do not depart from the protection scope of the pending claims of the present invention.

Claims

1. A method for determining the critical micelle concentration of sodium alkylbenzene sulfonate, characterized in that, include: Step 1: Take 1-4 parts by weight of sodium alkylbenzene sulfonate, dissolve it in 300-600 parts by weight of water, mix well, and obtain a sodium alkylbenzene sulfonate solution of the target concentration. Step 2: The sodium alkylbenzene sulfonate solution of the target concentration is serially diluted to obtain multiple solutions of different concentrations; Step 3: Perform qualitative and quantitative analysis on the multiple solutions of different concentrations under the action of an asymmetric fluid field analyzer to construct a standard line; The qualitative and quantitative analysis process includes: Sodium alkylbenzene sulfonate solution was separated using an asymmetric flow field analyzer; Obtain test data; The detection data includes at least one of ultraviolet absorption data and particle size detection data; The asymmetric flow field instrument includes an AF4 flow field instrument. The detection data is obtained using a UV-Vis spectrophotometer and a multi-angle static laser particle size analyzer. The wavelengths of the UV-Vis spectrophotometer are selected as 230nm and 260nm. The AF4 field flow meter is equipped with an AF4 channel semi-permeable membrane, which is a 300kDa polyethersulfone membrane. After detection by a UV-Vis spectrophotometer, two main absorption peaks were found. One peak was at 11 min, which exceeded the detection limit at low concentrations. The other peak was around 15 min, with no obvious absorption peak in the concentration range of 1.0 mM and below, but an absorption peak appeared at a concentration of 1.2 mM. Step 4: Determine the critical micelle concentration of sodium alkylbenzene sulfonate based on the standard line conditions; The sodium alkylbenzene sulfonate is a long-chain saturated sodium alkylbenzene sulfonate, and the sodium alkylbenzene sulfonate is sodium dodecylbenzene sulfonate; The solutions of different concentrations were, in order, 0.1, 0.3, 0.5, 0.7, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4, 2.6, 2.8, 3.0, and 3.5 mM sodium alkylbenzene sulfonate solutions.

2. The method for determining the critical micelle concentration of sodium alkylbenzene sulfonate according to claim 1, characterized in that, The mixing process in step 1 includes: Dissolve sodium alkylbenzene sulfonate in water, sonicate for 5-20 minutes, and let stand to obtain a sodium alkylbenzene sulfonate solution.

3. The method for determining the critical micelle concentration of sodium alkylbenzene sulfonate according to claim 1, characterized in that, The separation of sodium alkylbenzene sulfonate solution using an asymmetric flow field analyzer includes: During the injection phase, the parameters are set as follows: DelayTime 0.5 min, InjectionFlow 0.3 mL / min, InjectionTime 10 min, CrossFlow 2.50 mL / min, FocusPump 2.70 mL / min, and TransitionTime 1 min. The elution phase includes: The parameters for the first stage are: CrossFlow 2.50 mL / min, Time 1 min; Type constant, Exponent 0.00; The parameters for the second stage were: CrossFlow 2.50 mL / min, Time 20 min, Type Power, Exponent 0.20; The parameters for the third stage were: CrossFlow 0.15 mL / min, Time 10 min, Type Power, Exponent 0.80; The fourth stage had the following parameters: CrossFlow 0 mL / min, Time 30 min, Type constant, Exponent 0.

20. During the rinsing phase, the parameters are set as follows: TipPump 0.05 mL / min, FocusPump 0.05 mL / min. SkxPump0.00mL / min, Time0.5min.

4. The method for determining the critical micelle concentration of sodium alkylbenzene sulfonate according to claim 1, characterized in that, The AF4 field flow meter uses 25 μM sodium chloride as the rinsing mobile phase.

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