CN111007197A - Method for rapidly determining thioglycollic acid content - Google Patents
Method for rapidly determining thioglycollic acid content Download PDFInfo
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- CN111007197A CN111007197A CN201911351039.7A CN201911351039A CN111007197A CN 111007197 A CN111007197 A CN 111007197A CN 201911351039 A CN201911351039 A CN 201911351039A CN 111007197 A CN111007197 A CN 111007197A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N31/00—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods
- G01N31/16—Investigating or analysing non-biological materials by the use of the chemical methods specified in the subgroup; Apparatus specially adapted for such methods using titration
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
- G01N21/75—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated
- G01N21/77—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator
- G01N21/78—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator producing a change of colour
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N30/00—Investigating or analysing materials by separation into components using adsorption, absorption or similar phenomena or using ion-exchange, e.g. chromatography or field flow fractionation
- G01N30/02—Column chromatography
- G01N30/88—Integrated analysis systems specially adapted therefor, not covered by a single one of the groups G01N30/04 - G01N30/86
Abstract
The invention provides a rapid determination method of thioglycollic acid content, which adopts iodine to oxidize sulfydryl under alkaline condition and generates IO through reaction3 ‑Limiting the reaction speed, and determining the titration end point to obtain the thioglycollic acid content. The rapid determination method for the thioglycollic acid content realizes that the recovery rate of the thioglycollic acid by a titration method reaches 98 percent, and meanwhile, the method is stable.
Description
Technical Field
The invention belongs to the field of cosmetics, and particularly relates to a rapid determination method for thioglycollic acid content.
Background
Thioglycolic acid is the main raw material of daily cosmetic cold perm essence and depilatory. The content determination method under 3.9 thioglycolic acid in the technical specification of cosmetics (2015 edition) is high performance liquid chromatography, ion chromatography and titration method. Thioglycolic acid has strong acidity, and a very low pH value is required to realize good chromatographic behavior under the condition of reverse phase chromatography. Too low a pH can reduce the lifetime of the chromatographic column and increase the detection cost. Ion chromatography requires support from ion chromatographs with low prevalence. The third analysis method is titration with iodometric solution under acidic environment. In comparison, the third method is economical, simple and convenient and is very suitable for measuring the content of the thioglycolic acid raw material. The method has the problems that thioglycolic acid and iodine react under an acidic environment as follows:
2HSCH2COOH+I2→HOOCH2C-S-S-CH2COOH+2HI
the reaction is characterized by limited sensitivity and the recovery rate of the method is 91-93%. For example, the standards of thioglycollic acid raw material medicines in European standards are required to be more than 98%, and the acidic condition iodometry measurement method does not meet the European Union export requirements. Under the alkaline environment, the mercapto compound can perform a redox reaction with iodine quantitatively, and the titration sensitivity theoretically meets the requirement. However, this method has problems in operability, recovery rate of the method is less than 80%, and reproducibility is not satisfactory. The titration method relates to the use of a pre-feed liquid, the volume of the pre-feed liquid, the reaction time after the pre-feed is used, the titration speed and other test factors. The possible reason for the problems of iodometry with thioglycolic acid in alkaline environment is the contradiction between influencing factors and reaction mechanism in titration.
Disclosure of Invention
In view of the above, the present invention aims to provide a rapid determination method for thioglycolic acid content, which realizes a thioglycolic acid titration method recovery rate of 98%, and is stable.
In order to achieve the purpose, the technical scheme of the invention is realized as follows:
a method for quickly measuring the content of mercaptoacetic acid under alkaline conditionBy oxidation of mercapto groups with iodine, by reaction of the produced IO3 -Limiting the reaction speed, and determining the titration end point to obtain the thioglycollic acid content.
Further, the method comprises the following steps: adding thioglycolic acid into a sodium hydroxide solution, stirring for the first time, then adding a pre-collapsing liquid, stirring for the second time, titrating by using an iodine standard titration solution after stirring is finished, measuring the potential of the solution, stopping titration after a sudden change of the potential occurs, drawing a potential change curve, and determining a titration end point to obtain the thioglycolic acid content.
Furthermore, the concentration of the sodium hydroxide solution is 0.8-1.2mol/L, and the volume is 45-55 mL.
Furthermore, the addition amount of the pre-crushing liquid is 45-75% of the theoretical dosage. The theoretical dosage is calculated according to the addition amount of thioglycollic acid to obtain the theoretical dosage of the pre-feed liquid.
Further, the time of the first stirring step is 50-70s, and the speed is 800-.
Further, the time of the second stirring step is 15-25min, and the speed is 800-.
Further, the titration step is that after 1 drop of iodine standard titration solution is added, the solution is retained for 20s, and then the next drop is added.
The method controls the speed of the iodine titration liquid and the alkali to fully react and IO3 -The quantitative titration of the thioglycolic acid under the alkaline environment is realized. The dosage of the pre-feeding liquid is strictly controlled, and the titration end point is reached in advance due to too little use.
The titration process equation of thioglycolic acid iodine in alkaline environment is as follows:
in alkaline environment, iodine is subjected to disproportionation reaction and oxidation-reduction reaction to generate IO3Is the actual oxidant for the subsequent oxidation reaction, the reaction formula is as follows:
the disproportionation reaction speed of iodine is the rate-limiting step of oxidation reaction in the alkaline environment of thioglycollic acid, so that the reaction is titrated on the basis of using a pre-fed liquid, the reaction speed is increased, and the rapid stirring is carried out at the same time, so that IO (input/output) is reduced3Local over-concentration causing decomposition, causing a positive error in the titration results. IO (input/output)3Unstable in alkaline environments, decomposable failure, the following decomposition reactions taking place:
IO3 -+5I2+3H2O→3I2+6OH
compared with the prior art, the rapid determination method for the thioglycollic acid content has the following advantages:
(1) the rapid determination method for the thioglycollic acid content realizes that the recovery rate of the thioglycollic acid by a titration method reaches 98 percent, and meanwhile, the method is stable.
(2) The rapid determination method for the thioglycollic acid content provided by the invention can realize economic, rapid and accurate detection of the thioglycollic acid, and provides a new method for detecting the purity of the thioglycollic acid, especially raw materials. No HPLC or ion chromatography equipment and consumable support is required.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:
FIG. 1 is a graph of the titration curve as described in example 1 of the present invention.
Detailed Description
Unless defined otherwise, technical terms used in the following examples have the same meanings as commonly understood by one of ordinary skill in the art to which the present invention belongs. The test reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the experimental methods are conventional methods unless otherwise specified.
The invention is described in detail below with reference to embodiments and the accompanying drawings.
Example 1
A rapid determination method for thioglycollic acid content comprises the following steps: adding 0.0221g of thioglycolic acid into 50mL of 1mol/L sodium hydroxide solution, stirring at 1000rpm for 60s, then adding 8.5mL of pre-feed solution, stirring at 1000rpm for reaction for 20min, after stirring, titrating by using an iodine standard titration solution, retaining for 20s after 1 drop, measuring the solution potential by using a composite electrode, stopping titration after the obtained potential is greater than 20% of a theoretical value, drawing a potential change curve, determining the titration end point to be 14.302mL as shown in figure 1, and substituting into a stoichiometric equation to obtain the thioglycolic acid content of 99.337%.
Comparative example 1
A method for measuring the content of thioglycollic acid comprises the following steps: weighing 0.215g of thioglycolic acid of a sample, putting the thioglycolic acid in an iodine flask, adding 20mL of 10% hydrochloric acid solution (10 mL of concentrated hydrochloric acid is taken and added into 90mL of water for uniform mixing) and 50mL of water, slowly heating the mixture to boiling, adding 5mL of water after cooling, and stirring the mixture by using an electromagnetic stirrer until the mixture is dissolved. 2mL of starch solution is added, and the solution is titrated with 0.05M iodine standard solution until the color mutation or the blue color does not disappear within 1min, and 21.63mL of the titrated solution is consumed. The thioglycolic acid content was calculated to be 92.67%.
Comparative example 2
A method for measuring the content of thioglycollic acid comprises the following steps: a chromatographic column: ZORBAX SB-C18 column (250 mm. times.4.6 mm. times.5 m); mobile phase: acetonitrile +0.01mol/LKH2PO4 (pH adjusted to 2.5 with phosphoric acid) (8+ 92); flow rate: 1.0 mL/min; detection wavelength: 215 nm; column temperature: 30 ℃; sample introduction amount: 10L; taking 25, 50,100,150 and 200 mu L of thioglycolic acid standard solution (1mg/mL), placing the thioglycolic acid standard solution in a 10mL volumetric flask, adding 8 percent of gradient standard solution which is dissolved and diluted to a scale, shaking up to obtain the gradient standard solutions with the concentrations of 2.5,5.0,10.0,15.0 and 20.0 mu g/mL, respectively sucking 10 mu L of the solution, injecting the solution into a liquid chromatographic column, recording the peak area of a chromatogram, and drawing a standard curve by adopting a least square method.
Weighing 2.103g of thioglycolic acid, placing the thioglycolic acid in a 10mL volumetric flask, dissolving and diluting the thioglycolic acid to the scale with 8% acetonitrile, and shaking up. Suck 100 μ L of the above solution, put it in a 10mL volumetric flask, add 8% dissolved and diluted to the mark, shake it up. 50 mu L of the solution is placed in a 10mL volumetric flask, 8 percent of the solution is added and dissolved and diluted to the scale mark, and the sample solution is obtained after shaking up. And (3) sucking 10 mu L of the solution, injecting the solution into a liquid chromatographic column, recording the peak area of a chromatogram, substituting the peak area into a standard curve equation, and calculating the purity of the thioglycolic acid to be 99.18%.
The results obtained in example 1 and comparative examples 1-2 show that the method used in example 1 is simple, easy, rapid and accurate, improves the efficiency and universality of detecting thioglycolic acid in perm and depilatory cosmetics, and provides technical support for export trade detection of thioglycolic acid as a raw material.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (7)
1. A rapid determination method of thioglycollic acid content is characterized in that: the method adopts iodine to oxidize sulfydryl under alkaline condition, and IO generated by reaction3 -Limiting the reaction speed, and determining the titration end point to obtain the thioglycollic acid content.
2. The method for rapidly determining the thioglycollic acid content according to claim 1, wherein: the method comprises the following steps: adding thioglycolic acid into a sodium hydroxide solution, stirring for the first time, then adding a pre-collapsing liquid, stirring for the second time, titrating by using an iodine standard titration solution after stirring is finished, measuring the potential of the solution, stopping titration after a sudden change of the potential occurs, drawing a potential change curve, and determining a titration end point to obtain the thioglycolic acid content.
3. The method for rapidly determining the thioglycollic acid content according to claim 2, wherein: the concentration of the sodium hydroxide solution is 0.8-1.2mol/L, and the volume is 45-55 mL.
4. The method for rapidly determining the thioglycollic acid content according to claim 2, wherein: the addition amount of the pre-crushing liquid is 45-75% of the theoretical dosage.
5. The method for rapidly determining the thioglycollic acid content according to claim 2, wherein: the time of the first stirring step is 50-70s, and the speed is 800-1200 rpm.
6. The method for rapidly determining the thioglycollic acid content according to claim 2, wherein: the time of the second stirring step is 15-25min, and the speed is 800-1200 rpm.
7. The method for rapidly determining the thioglycollic acid content according to claim 2, wherein: the titration step is that after 1 drop of iodine standard titration liquid is dripped, the titration liquid stays for 20s, and then the next drop is dripped.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113008820A (en) * | 2021-03-03 | 2021-06-22 | 南昌航空大学 | Method for measuring content of sulfydryl |
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| CN109932476A (en) * | 2017-12-15 | 2019-06-25 | Tcl集团股份有限公司 | A kind of measuring method of quantum dot surface ligand coverage rate |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113008820A (en) * | 2021-03-03 | 2021-06-22 | 南昌航空大学 | Method for measuring content of sulfydryl |
| CN113008820B (en) * | 2021-03-03 | 2022-10-28 | 南昌航空大学 | Method for measuring content of sulfydryl |
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