阅读说明：本技术 基于电位滴定法测定表面活性剂碱度的方法 (Method for measuring alkalinity of surfactant based on potentiometric titration method ) 是由 观文娜 李凯伦 季双琦 关彤 潘翔宇 刘婷婷 于 2021-08-26 设计创作，主要内容包括：本发明公开了一种基于电位滴定法测定表面活性剂碱度的方法,涉及表面活性剂性能测定技术领域。本发明包括称取3-5g样品,加入100mL水中置于高精度光热电位分析仪上,加入磁性转子搅拌均匀；滴定方法选择动态滴定,最大溃液体积为0.4mL,最小溃液体积为0.02mL；使用pH复合电极,将电极及溃液管没入液面后,用配制好的0.1mol/L盐酸滴定溶液滴定至终点,读取滴定体积。本发明通过采用pH复合电极,通过电位突跃判断滴定终点,滴定体系中无需加入指示剂,通过电位电极检测滴定曲线的突跃点来判断滴定终点,滴定终点的判断更准确；解决深色或不透光样品使用光度电极滴定终点判断不准确的问题。(The invention discloses a method for measuring alkalinity of a surfactant based on a potentiometric titration method, and relates to the technical field of performance measurement of the surfactant. Weighing 3-5g of sample, adding the sample into 100mL of water, placing the sample on a high-precision photothermal potential analyzer, adding a magnetic rotor, and uniformly stirring; dynamic titration is selected by a titration method, the maximum collapsing liquid volume is 0.4mL, and the minimum collapsing liquid volume is 0.02 mL; and (3) immersing the electrode and the liquid feed pipe into the liquid surface by using a pH composite electrode, titrating by using prepared 0.1mol/L hydrochloric acid titration solution to an end point, and reading the titration volume. According to the invention, the titration end point is judged by adopting the pH composite electrode and potential jump, no indicator is required to be added into a titration system, and the titration end point is judged by detecting the jump point of a titration curve through the potential electrode, so that the titration end point is more accurately judged; the problem of inaccurate judgment of the titration end point of a dark color or light-tight sample by using a photometric electrode is solved.)

1. A method for measuring the alkalinity of a surfactant based on a potentiometric titration method, characterized in that the method comprises the following steps:

step S001: weighing 3-5g of sample, adding the sample into 100mL of water, and placing the sample on a high-precision photothermal potential analyzer;

step S002: adding a magnetic rotor and uniformly stirring;

step S003: dynamic titration is selected by a titration method, the maximum collapsing liquid volume is 0.4mL, and the minimum collapsing liquid volume is 0.02 mL;

step S004: and (3) immersing the PH composite electrode and the liquid feed pipe into the liquid level by using the PH composite electrode, titrating the solution to the end point by using prepared 0.1mol/L hydrochloric acid titration solution, and reading the titration volume.

2. The method for measuring the alkalinity of the surfactant according to claim 1, wherein the hydrochloric acid titration solution is prepared by the following method:

s1: accurately measuring 0.986mL of 37% hydrochloric acid, and adding the hydrochloric acid into a beaker with 200mL of ultrapure water;

s2: after being mixed evenly, the mixture is moved into a volumetric flask with the volume of 1000mL, and the wall of the beaker is repeatedly washed by ultrapure water;

s3: adding the washing solution into a volumetric flask, fixing the volume to 1000mL, and ultrasonically mixing uniformly;

s4: to prepare a hydrochloric acid titration solution.

3. The potentiometric titration-based method for determining the alkalinity of a surfactant according to claim 1, further comprising a calibration method of a hydrochloric acid titration solution, wherein the calibration method comprises:

SS 1: accurately weighing 0.2g of anhydrous sodium carbonate which is burnt to constant weight in a muffle furnace at a high temperature of 300 ℃, and dissolving the anhydrous sodium carbonate in 50mL of water;

SS 2: adding two drops of bromocresol green-methyl red indicator;

SS 3: dripping the prepared hydrochloric acid titration solution until the solution changes from green to dark red, heating and boiling for 2min, cooling, dripping the solution to dark red, simultaneously carrying out a blank experiment, and calculating the accurate concentration of the hydrochloric acid titration solution according to the following formula:

wherein: m is the mass of anhydrous sodium carbonate, g;

v1 is the volume of solution consumed for titration, mL;

v0 is the volume of solution consumed for the blank experiment, mL;

SS 4: until the concentration of the titrated solution is 0.0983mol/L through calibration hydrochloric acid.

4. The potentiometric titration-based method for determining the alkalinity of a surfactant according to claim 3, wherein the bromocresol green-methyl red indicator is prepared by a method comprising:

p01: weighing 1g of methyl red, and dissolving in 100mL of methanol;

p02: weighing 2g of bromocresol green and dissolving in 100mL of methanol;

p03: and mixing the methyl red solution and the bromocresol green solution according to the ratio of 2: 3, uniformly mixing in proportion;

p04: the bromocresol green-methyl red indicator is prepared.

5. The potentiometric titration-based method for determining the alkalinity of a surfactant according to claim 1, wherein the sample is an anionic surfactant or a nonionic surfactant.

6. The potentiometric titration-based method for determining the alkalinity of a surfactant according to claim 5, wherein the anionic surfactant is sodium fatty alcohol-polyoxyethylene ether sulfate or sodium dodecyl sulfate and the nonionic surfactant is cocomethyl monoethanolamide.

7. The potentiometric titration-based method for determining the alkalinity of a surfactant according to claim 6, wherein the alkalinity of the sample is expressed as a mass percentage X of sodium oxide, and is calculated according to the following formula:

in the formula: v is the volume of 0.1mol/L hydrochloric acid titration solution consumed by titration, mL;

c is the accurate concentration of the hydrochloric acid titration solution (the concentration of the hydrochloric acid titration solution used in the experiment is calibrated to be 0.0983mol/L), and mol/L;

m is the sample mass, g.

8. The potentiometric titration-based method for determining the alkalinity of a surfactant according to claim 6, wherein the alkaline substance in the sodium dodecyl sulfate is reacted with the hydrochloric acid titration solution twice, and the second jump is taken as the titration endpoint.

Technical Field

The invention belongs to the technical field of surfactant performance measurement, and particularly relates to a method for measuring the alkalinity of a surfactant based on a potentiometric titration method.

Background

The surfactant is a general term for substances which can obviously change the surface state of a solution system, is used as one of additives commonly used in the petrochemical industry and is widely applied to the fields of oil field tertiary recovery, cosmetic products and the like, and the alkalinity is used as an important performance index of the surfactant, so that the use performance of the surfactant product, such as the irritation of the cosmetic to the skin, the selection of cosurfactant and the like, can be influenced, and the subsequent wastewater treatment process is influenced.

The alkalinity in the surfactant is measured mainly according to a national standard 'titration method for measuring the alkalinity of the surfactant' (GB/T7378-.

For another example, photometric titration is the detection of a change in color of an indicator by a photometric electrode to determine the endpoint of titration. At present, commercial photometric electrodes can accurately detect absorbance change under specific wavelength, and are used for titration experiments to judge titration end points, namely photometric titration, so that errors caused by color change observed by human eyes in national standard titration can be avoided.

Disclosure of Invention

The invention aims to provide a method for determining the alkalinity of a surfactant based on a potentiometric titration method, which adopts a pH composite electrode, judges a titration end point through potential jump, does not need to add an indicator into a titration system, and solves the problem of inaccurate judgment of the titration end point of a dark or opaque sample.

In order to solve the technical problems, the invention is realized by the following technical scheme:

the invention relates to a method for measuring the alkalinity of a surfactant based on a potentiometric titration method, which comprises the following steps:

step S001: weighing 3-5g of sample, adding the sample into 100mL of water, and placing the sample on a high-precision photothermal potential analyzer;

step S002: adding a magnetic rotor and uniformly stirring;

step S003: dynamic titration is selected by a titration method, the maximum collapsing liquid volume is 0.4mL, and the minimum collapsing liquid volume is 0.02 mL;

step S004: and (3) immersing the PH composite electrode and the liquid feed pipe into the liquid level by using the PH composite electrode, titrating the solution to the end point by using prepared 0.1mol/L hydrochloric acid titration solution, and reading the titration volume.

Further, the preparation method of the hydrochloric acid titration solution comprises the following steps:

s1: accurately measuring 0.986mL of 37% hydrochloric acid, and adding the hydrochloric acid into a beaker with 200mL of ultrapure water;

s2: after being mixed evenly, the mixture is moved into a volumetric flask with the volume of 1000mL, and the wall of the beaker is repeatedly washed by ultrapure water;

s3: adding the washing solution into a volumetric flask, fixing the volume to 1000mL, and ultrasonically mixing uniformly;

s4: to prepare a hydrochloric acid titration solution.

Further, the method also comprises a calibration method of the hydrochloric acid titration solution, wherein the calibration method comprises the following steps:

SS 1: accurately weighing 0.2g of anhydrous sodium carbonate which is burnt to constant weight in a muffle furnace at a high temperature of 300 ℃, and dissolving the anhydrous sodium carbonate in 50mL of water;

SS 2: adding two drops of bromocresol green-methyl red indicator;

SS 3: dripping the prepared hydrochloric acid titration solution until the solution changes from green to dark red, heating and boiling for 2min, cooling, dripping the solution to dark red, simultaneously carrying out a blank experiment, and calculating the accurate concentration of the hydrochloric acid titration solution according to the following formula:

wherein: m is the mass of anhydrous sodium carbonate, g;

v1 is the volume of solution consumed for titration, mL;

v0 is the volume of solution consumed for the blank experiment, mL;

SS 4: until the concentration of the titrated solution is 0.0983mol/L through calibration hydrochloric acid.

Further, the preparation method of the bromocresol green-methyl red indicator comprises the following steps:

p01: weighing 1g of methyl red, and dissolving in 100mL of methanol;

p02: weighing 2g of bromocresol green and dissolving in 100mL of methanol;

p03: and mixing the methyl red solution and the bromocresol green solution according to the ratio of 2: 3, uniformly mixing in proportion;

p04: the bromocresol green-methyl red indicator is prepared.

Further, the sample is an anionic surfactant or a nonionic surfactant.

Further, the anionic surfactant is sodium fatty alcohol-polyoxyethylene ether sulfate or sodium dodecyl sulfate, and the nonionic surfactant is coconut methyl monoethanolamide.

Further, the method expresses the alkalinity of the sample according to the mass percent X of the sodium oxide, and the alkalinity is calculated according to the following formula:

in the formula: v is the volume of 0.1mol/L hydrochloric acid titration solution consumed by titration, mL;

c is the accurate concentration of the hydrochloric acid titration solution (the concentration of the hydrochloric acid titration solution used in the experiment is calibrated to be 0.0983mol/L), and mol/L;

m is the sample mass, g.

Further, the alkaline substance in the sodium dodecyl sulfate reacts with the hydrochloric acid titration solution twice, and the second jump is taken as the titration end point.

The invention has the following beneficial effects:

the invention adopts the pH composite electrode, judges the titration end point through potential jump, does not need to add an indicator into a titration system, and can solve the problem that the titration end point of a dark color or opaque sample is not accurately judged by using a photometric electrode.

Of course, it is not necessary for any product in which the invention is practiced to achieve all of the above-described advantages at the same time.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to the drawings without creative efforts.

FIG. 1(a) is a photometric titration curve for determining the alkalinity of sodium alcohol ether sulfate;

FIG. 1(b) is a photometric titration curve for determining the alkalinity of sodium dodecyl sulfate;

FIG. 1(c) is a photometric titration curve for determining the alkalinity of cocoate methyl monoethanolamide;

FIG. 2(a) is a potentiometric titration curve for determining alkalinity of sodium alcohol ether sulfate;

FIG. 2(b) is a potentiometric titration curve for measuring alkalinity of sodium dodecyl sulfate

FIG. 2(c) is a potentiometric titration curve for determining the alkalinity of cocomethyl monoethanolamide.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Experimental samples:

surfactant sample: sodium fatty alcohol polyoxyethylene ether sulfate (anionic surfactant), sodium lauryl sulfate (anionic surfactant) and coconut methyl monoethanolamide (nonionic surfactant) were purchased from Shandong Youguo chemical science and technology, Inc.

Experimental apparatus and reagents:

high-precision opto-thermo potentiometric analyzers (beijing maritime optical instruments ltd); pH compliant electrodes (beijing pioneer weofeng technologies development corporation); photometric electrodes (Thyss Wantong China Co., Ltd.); one in ten thousand balance (mertler-toledo, switzerland); 20mL acid burette (national pharmaceutical group chemical reagents, Inc.);

methanol (national chemical group chemical reagent limited, analytical grade); 37% hydrochloric acid solution (national pharmaceutical group chemical reagent limited, analytical purity); bromocresol green (national drug group chemical reagents ltd); methyl red (national pharmaceutical group chemical agents limited); bromophenol blue (national pharmaceutical group chemical agents limited).

The first embodiment is as follows:

the method for measuring the alkalinity of the surfactant based on the potentiometric titration method comprises the following steps:

step S001: 3 ~ 5g samples are weighed, add 100mL aquatic and place in high accuracy light and heat potential analyzer on, high accuracy light and heat potential analyzer: beijing Hai Guang instruments Inc., the samples were weighed on a ten thousandth balance: Mettler-Torlodo Switzerland;

step S002: adding a magnetic rotor and uniformly stirring;

step S003: dynamic titration is selected by a titration method, the maximum collapsing liquid volume is 0.4mL, and the minimum collapsing liquid volume is 0.02 mL;

step S004: immersing the PH composite electrode and the liquid feed pipe into the liquid level by using a PH composite electrode, titrating to the end point by using prepared 0.1mol/L hydrochloric acid titration solution, and reading the titration volume; pH composite electrode: beijing pioneer Weifeng technology development company.

As an embodiment provided by the present invention, preferably, the preparation method of the hydrochloric acid titration solution comprises:

s1: accurately measuring 0.986mL of 37% hydrochloric acid, and adding the hydrochloric acid into a beaker with 200mL of ultrapure water;

s2: after being mixed evenly, the mixture is moved into a volumetric flask with the volume of 1000mL, and the wall of the beaker is repeatedly washed by ultrapure water;

s3: adding the washing solution into a volumetric flask, fixing the volume to 1000mL, and ultrasonically mixing uniformly;

s4: to prepare a hydrochloric acid titration solution.

As an embodiment provided by the present invention, preferably, the method further includes a calibration method of the hydrochloric acid titration solution, where the calibration method includes:

SS 1: accurately weighing 0.2g of anhydrous sodium carbonate which is burnt to constant weight in a muffle furnace at a high temperature of 300 ℃, and dissolving the anhydrous sodium carbonate in 50mL of water;

SS 2: adding two drops of bromocresol green-methyl red indicator;

SS 3: dripping the prepared hydrochloric acid titration solution until the solution changes from green to dark red, heating and boiling for 2min, cooling, dripping the solution to dark red, simultaneously carrying out a blank experiment, and calculating the accurate concentration of the hydrochloric acid titration solution according to the following formula:

wherein: m is the mass of anhydrous sodium carbonate, g;

v1 is the volume of solution consumed for titration, mL;

v0 is the volume of solution consumed for the blank experiment, mL;

SS 4: until the concentration of the titrated solution is 0.0983mol/L through calibration hydrochloric acid.

As an embodiment provided by the present invention, preferably, the preparation method of the bromocresol green-methyl red indicator comprises:

p01: weighing 1g of methyl red, and dissolving in 100mL of methanol;

p02: weighing 2g of bromocresol green and dissolving in 100mL of methanol;

p03: and mixing the methyl red solution and the bromocresol green solution according to the ratio of 2: 3, uniformly mixing in proportion;

p04: the bromocresol green-methyl red indicator is prepared.

As an embodiment provided by the present invention, preferably, the method expresses the alkalinity of the sample according to the mass percentage X of sodium oxide, and the alkalinity is calculated according to the following formula:

in the formula: v is the volume of 0.1mol/L hydrochloric acid titration solution consumed by titration, mL;

c is the accurate concentration of the hydrochloric acid titration solution (the concentration of the hydrochloric acid titration solution used in the experiment is calibrated to be 0.0983mol/L), and mol/L;

m is the sample mass, g.

As an embodiment provided by the present invention, preferably, the alkaline substance in the sodium dodecyl sulfate reacts with the hydrochloric acid titration solution twice, and the second jump is taken as the titration endpoint.

Wherein:

methanol: chemical reagent of national drug group, Inc., analytically pure;

37% hydrochloric acid solution: chemical reagent of national drug group, Inc., analytically pure;

bromocresol green: chemical agents of the national drug group, ltd;

methyl red: chemical agents of the national drug group, ltd;

bromophenol blue: chemical agents of the national drug group, ltd.

The titration end point is judged by adopting the pH composite electrode through potential jump, and an indicator does not need to be added into a titration system, so that the problem that the titration end point of a dark color or opaque sample is not accurately judged by using a photometric electrode can be solved. Measuring the alkalinity of three surfactant samples of fatty alcohol-polyoxyethylene ether sodium sulfate, lauryl sodium sulfate and coconut acid methyl monoethanolamide by a potentiometric titration method; the potentiometric titration curves are shown in fig. 2(a), (b) and (c), and all three surfactants have significant potential jump at the titration endpoint, wherein the alkaline substance in the sodium dodecyl sulfate reacts with hydrochloric acid twice, so the second jump is taken as the titration endpoint.

Comparative example one:

a national standard titration method is adopted:

weighing 3-5g of sample, adding the sample into 100mL of water, placing the sample on an electromagnetic stirring table, adding two drops of bromophenol blue indicator after the sample is fully dissolved, adding a magnetic rotor, and uniformly stirring; adding 15mL of prepared 0.1mol/L hydrochloric acid titration solution into a 20mL acid burette, slowly dripping the solution until the solution turns blue to yellow as a titration end point, and reading the scale on the burette;

the alkalinity of the samples was expressed in terms of the mass percent X (%) of sodium oxide (Na2O) in a quantitative manner as given in GB/T7378 and was calculated as follows:

in the formula: v is the volume of 0.1mol/L hydrochloric acid titration solution consumed by titration, mL;

c, the accurate concentration of the hydrochloric acid titration solution (the concentration of the hydrochloric acid titration solution used in the experiment is calibrated to be 0.0983mol/L), and mol/L;

m is sample mass, g.

Because the national standard titration method judges the titration end point by distinguishing the color change of the indicator through human eyes, different people have different color sensitivity degrees and are influenced by the current light source of the experiment, and the results obtained by the same experimenter in different time and different environments can still have differences, thereby causing errors to the results.

Comparative example two:

adopting a photometric titration method:

weighing 0.5g of sample, adding the sample into 100mL of water, placing the sample on a high-precision photothermal potential analyzer, adding two drops of bromophenol blue indicator, adding a magnetic rotor, and uniformly stirring. The titration method selects equivalent titration, and the volume of single-step liquid collapsing is 0.1 mL; a Switzerland universal photometric electrode is used, the wavelength is selected to be 571nm, after the electrode and a liquid feed pipe are immersed into the liquid level, a prepared hydrochloric acid titration solution with the concentration of 0.1mol/L is used for titration until the end point, and the titration volume is read;

the alkalinity of the samples was expressed in terms of the mass percent X (%) of sodium oxide (Na2O) in a quantitative manner as given in GB/T7378 and was calculated as follows:

in the formula: v is the volume of 0.1mol/L hydrochloric acid titration solution consumed by titration, mL;

c, the accurate concentration of the hydrochloric acid titration solution (the concentration of the hydrochloric acid titration solution used in the experiment is calibrated to be 0.0983mol/L), and mol/L;

m is sample mass, g.

Detecting the change of the absorbance of the indicator by adopting a photometric electrode to judge the titration end point; measuring the alkalinity of three surfactant samples of fatty alcohol-polyoxyethylene ether sodium sulfate, lauryl sodium sulfate and coconut acid methyl monoethanolamide by a photometric titration method; because the high-concentration coconut acid methyl monoethanolamide can cause the turbidity and light-tightness of a sample solution and influence the judgment of a photometric electrode on a titration end point, 0.5g of the sample is weighed and used for a titration experiment; as shown in FIGS. 1(a), (b) and (c), the photometric titration curves of all three surfactants have a distinct jump, which can be used as the basis for determining the endpoint of titration.

And (3) evaluating the consistency of the results of the first example and the second example according to the alkalinity result obtained by a national standard titration method:

three replicates of each surfactant sample were made and the average alkalinity measurements are shown in table 1:

TABLE 1 comparison of measured mean values of surfactant alkalinity

The results show that: for sodium fatty alcohol polyoxyethylene ether sulfate and sodium dodecyl sulfate, the alkalinity measurement results of the photometric titration method and the potentiometric titration method are higher than those of the national standard titration method, while for coconut oil acid methyl monoethanolamide, the alkalinity measurement results of the national standard titration method and the potentiometric titration method are higher than those of the photometric titration method; the reason is that the sample is in a turbid state after being dissolved, the judgment of the titration end point by the photometric electrode can be interfered, and the titration end point can be more accurately judged by the sample potentiometric titration method. Therefore, compared with the photometric titration method, the potentiometric titration method has wider application range of the sample.

The results of the first example, the first comparative example, and the second comparative example were evaluated for consistency:

for the alkalinity measurements of three samples, namely sodium fatty alcohol polyoxyethylene ether sulfate, sodium lauryl sulfate and cocoate methyl monoethanolamide, each sample was subjected to three repeated experiments, and the repeatability (RSD%) results are shown in table 2:

TABLE 2 repeatability comparison of three methods for surfactant alkalinity determination

The results show that: the repeatability of both the photometric titration method and the potentiometric titration method is superior to that of the national standard titration method; the national standard titration method adopts a burette for manual titration, the titration accuracy can only reach 0.05mL, while the improved method of the application adopts an automatic titrator, the liquid feeding accuracy can reach 0.0001mL, and the titration accuracy is higher; the national standard titration method adopts human eyes to observe the color change of the indicator to judge the titration end point, and the improved method in the application adopts a potential electrode to detect the jump point of a titration curve to judge the titration end point, so that the titration end point is judged more accurately.

The method for measuring the alkalinity of the surfactant based on the potentiometric titration method has the advantages that the accuracy, the titration precision, the automation degree and the repeatability of the titration end point judgment are superior to those of the national standard method; the titration end point is judged through potential jump, the application range is wider, meanwhile, an indicator is not required to be added into a titration system, the operation is simpler, the method can be used as an optimal improvement method of a national standard method, is applied to the determination of the alkalinity of the actual surfactant, and has good application prospect.

In the description herein, references to the description of "one embodiment," "an example," "a specific example" or the like are intended to mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

The preferred embodiments of the invention disclosed above are intended to be illustrative only. The preferred embodiments are not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Obviously, many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, to thereby enable others skilled in the art to best utilize the invention. The invention is limited only by the claims and their full scope and equivalents.