CN111879904A - Method for determining organic selenium in tea - Google Patents
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- CN111879904A CN111879904A CN202010644988.0A CN202010644988A CN111879904A CN 111879904 A CN111879904 A CN 111879904A CN 202010644988 A CN202010644988 A CN 202010644988A CN 111879904 A CN111879904 A CN 111879904A
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Abstract
The invention discloses a method for determining organic selenium in tea, which comprises the following steps: the method comprises the steps of measuring the total selenium content and the inorganic selenium content in the tea, calculating the content of organic selenium in the tea by using a subtraction method, and measuring the total selenium content by adopting a wet digestion process, wherein the wet digestion process comprises the steps of adding mixed acid into the tea, dispelling acid, carrying out first reduction, and adding 0.5-2.5 mL of hydrochloric acid to enable the constant volume acidity to be 15-35%. The method avoids the use of potassium ferricyanide and has the advantage of improving the accuracy of the detection result.
Description
Technical Field
The invention relates to a method for measuring organic selenium in tea, in particular to a method for measuring the organic selenium content in the tea by subtracting the total selenium content and the inorganic selenium content in the tea, belonging to the field of analytical chemistry.
Background
Selenium is one of essential trace elements, and has effects of resisting oxidation, resisting aging, improving immunity, and protecting cardiovascular and cerebrovascular. The nutrient and toxicity threshold of selenium is narrow, and inorganic selenium has accumulative toxicity and mutagenic effect, and high content of selenium easily causes food poisoning. The organic selenium has the advantages of low toxicity, high utilization rate of human bodies and the like. The tea tree is a plant with strong selenium collecting capability, and can convert inorganic selenium into organic selenium which is easy to absorb by a human body. The content of the organic selenium is one of evaluation bases of the quality of the tea, so that the method for researching the organic selenium in the tea has practical value.
At present, the method for determining selenium in food by national standard adopts GB5009.93, the method can determine the total selenium content in food, the content of inorganic selenium and organic selenium cannot be distinguished, and the national standard for determining organic selenium is not available up to now. The organic selenium in tea exists in various forms such as selenoprotein, seleno amino acid, selenium polysaccharide, selenium nucleic acid, etc., and the inorganic selenium exists in the form of selenate and selenite anions, and is easily soluble in water. Therefore, the method for determining the content of the organic selenium in China mainly comprises the subtraction method, firstly, the total selenium content in food is determined by referring to GB5009.93-2017, organic selenium and inorganic selenium in a sample to be determined are separated by using a reagent, the organic selenium is extracted by using an organic solvent, then, the content of the inorganic selenium is determined by using a water phase extracting solution, and the organic selenium content is obtained by subtraction. However, the total selenium content and the inorganic selenium content measured by the method have large errors along with the lapse of the standing time, and the detection accuracy is not high.
Disclosure of Invention
An object of the present invention is to solve at least the above problems and to provide at least the advantages described later.
The invention also aims to provide a method for measuring the organic selenium in the tea, the content of the organic selenium in the tea is obtained by subtracting the total selenium content and the inorganic selenium content in the tea, and the hydrochloric acid is adopted to replace potassium ferricyanide, so that the detection result of the organic selenium is more accurate.
To achieve these objects and other advantages in accordance with the present invention, there is provided a method for measuring organic selenium in tea leaves, comprising: the method comprises the steps of calculating the content of organic selenium in the tea by utilizing a differential subtraction method by measuring the content of total selenium and the content of inorganic selenium in the tea, and performing wet digestion on the tea in the measurement of the content of the total selenium;
the wet digestion step of GB5009.93-2017 is as follows:
weighing 0.5-3 g of tea leaf sample, adding 10mL of mixed acid formed by nitric acid-perchloric acid and a plurality of glass beads, and placing for the next day;
acid removal: heating on an electric heating plate the next day, adding nitric acid in time, and continuing heating until the residual volume is 2mL when the solution becomes clear and colorless with generation of white smoke;
reduction: cooling, adding 5mL of hydrochloric acid (6mol/L), and continuing heating until the solution becomes clear and colorless with generation of white smoke;
after cooling, the mixture was transferred to a 10mL volumetric flask, and 2.5mL of potassium ferricyanide (100g/L) was added thereto, to thereby obtain a constant volume with water.
The wet digestion adopted by the invention comprises the processes of adding mixed acid into a tea sample, dispelling acid, carrying out first reduction, and adding 0.5-2.5 mL of hydrochloric acid to enable the constant volume acidity to be 15-35%.
Preferably, the mixed acid is added and then placed for 2-4 hours.
Preferably, the first reduction is carried out by adding 4-8 mL1+1 hydrochloric acid solution after the acid removing treatment.
Preferably, the inorganic selenium content determination process comprises: adding ultrapure water into tea leaves, performing ultrasonic treatment, filtering to obtain filtrate, extracting the filtrate to obtain a water phase, concentrating, removing acid, performing secondary reduction, and adding 0.5-2.5 mL of hydrochloric acid to ensure that the constant volume acidity is 15-35% to obtain a solution to be detected.
Preferably, when ultrapure water is added to tea leaves, the ratio of the amount of tea leaves to the amount of ultrapure water is 1 g: 10-15 mL.
Preferably, the ultra-pure water is added into the tea leaves for ultrasonic treatment for 20-30 min.
Preferably, the filter residue is washed for 3-5 times in the filtering process.
Preferably, the extraction is performed by using an organic mixed solution, and the organic mixed solution comprises ethyl acetate, petroleum ether and cyclohexane; the volume ratio of the ethyl acetate to the petroleum ether to the cyclohexane to the organic mixed solution is 1-3: 4-8: 10.
Preferably, the ratio of the tea leaves to the organic mixed solution in the inorganic selenium content measuring process is 1 g: 3-5 mL.
Preferably, the first reduction is carried out by adding 4-8 mL of 1+1 hydrochloric acid solution.
The invention at least comprises the following beneficial effects: the method adopts ultrasonic separation and extraction separation to remove organic selenium in the sample, and detects inorganic selenium. The organic selenium in the tea is extracted by adopting ultrasonic extraction and mixed organic solvent of ethyl acetate, petroleum ether and cyclohexane, so that the separation effect is more complete. In the detection process, potassium ferricyanide is decomposed into cyanide under the high-temperature acidic environment, so that the body health of an operator is influenced. Meanwhile, in the acid solution in the detection process, ferric ions in potassium ferricyanide can be reduced by tetravalent selenium in the solution to be detected to generate ferrous ions, and the ferrous ions react with the ferric ions in the solution to generate Turnbull's blue, so that the detection result is low, and the measurement is influenced. The use of potassium ferricyanide is reduced in the detection process, so that the detection result is more accurate.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention.
Detailed Description
The present invention is further described in detail below with reference to examples so that those skilled in the art can practice the invention with reference to the description.
It is to be noted that the experimental methods described in the following embodiments are all conventional methods unless otherwise specified, and the reagents and materials are commercially available unless otherwise specified.
Example one
Total selenium content determination sample treatment: weighing 0.5g of tea A sample, adding 9mL of nitric acid and 1mL of perchloric acid, adding glass beads, and uniformly mixing. Standing for 4h, heating to 2mL, cooling, adding 8mL1+1 hydrochloric acid solution, continuing heating and volatilizing to 2mL, taking down and cooling, adding 0.5mL concentrated hydrochloric acid, transferring into a 10mL volumetric flask, and performing constant volume mixing by using ultrapure water to obtain the total selenium solution to be detected.
Treating an inorganic selenium content determination sample: weighing 1g of tea A sample, adding 15mL of ultrapure water, carrying out ultrasonic extraction for 20min, filtering with filter paper, repeatedly washing filter residues for 4 times, and combining filtrates. Extracting with 3mL of organic mixture of ethyl acetate, petroleum ether and cyclohexane at a volume ratio of 1:1:8 for 4 times, separating out the water phase, heating in water bath to 5mL, pouring into a conical flask, adding 4mL of nitric acid, adding glass beads, and mixing. Heating to 2mL, cooling, adding 8mL1+1 hydrochloric acid solution, continuing heating and volatilizing to 2mL, taking down and cooling, adding 0.5mL concentrated hydrochloric acid, transferring into a 10mL volumetric flask, and diluting with ultrapure water to a constant volume and mixing uniformly to obtain the inorganic selenium solution to be detected.
Meanwhile, a comparison test is carried out, the preparation method of the total selenium solution to be tested is the same as that of the inorganic selenium solution to be tested, except that after the total selenium solution to be tested is transferred into a 10mL volumetric flask, 0.5mL of concentrated hydrochloric acid is added instead of 2.5mL of potassium ferricyanide solution (100 g/L).
After 1h, respectively detecting the total selenium content in the total selenium solution to be detected and the inorganic selenium content in the inorganic selenium solution to be detected, repeating the detection for 6 times, calculating the average value, wherein the organic selenium content is the total selenium content-the inorganic selenium content, and the detection results are shown in table 1;
after 4h, respectively detecting the total selenium content in the total selenium solution to be detected and the inorganic selenium content in the inorganic selenium solution to be detected, repeating the detection for 6 times, calculating the average value, wherein the organic selenium content is the total selenium content-the inorganic selenium content, and the detection results are shown in table 2;
TABLE 11 h test results (n ═ 6)
Table 24 h test results (n ═ 6)
| Name (R) | Total selenium (mg/kg) | Inorganic selenium (mg/kg) | Organic selenium (mg/kg) |
| Hydrochloric acid | 1.62 | 0.30 | 1.32 |
| Potassium ferricyanide | 1.35 | 0.28 | 1.07 |
As can be seen from the measurement results in tables 1 and 2, the relative deviation of the total selenium content, the inorganic selenium content and the organic selenium content of the solution to be measured in which the potassium ferricyanide solution is added is more than 20% as the standing time is increased. Adding hydrochloric acid, and detecting to obtain solution containing total selenium, inorganic selenium and organic selenium with relative difference less than 5%. When the GB5009.93-2017 is adopted to detect the selenium content in the tea, hydrochloric acid is used to replace potassium ferricyanide in the detection process, so that the potassium ferricyanide is prevented from being decomposed into cyanide in a high-temperature acidic environment in the detection process, and the potassium ferricyanide reacts with ferrous ions in an acidic solution to generate Turnbull's blue in the detection process, so that the influence on the determination is avoided. Finally, the purpose of accurately measuring the organic selenium in the tea is achieved, and the detection problems of the selenium content and the selenium form in the tea are solved.
Example two
And (3) total selenium content determination: weighing 1g of tea B sample, adding 9mL of nitric acid and 1mL of perchloric acid, adding glass beads, and uniformly mixing. Standing for 2h, heating to 2mL, cooling, adding 4mL1+1 hydrochloric acid solution, continuing heating to volatilize to 2mL, taking off and cooling. Adding 2.5mL of concentrated hydrochloric acid, transferring into a 10mL volumetric flask, adding water to a constant volume, uniformly mixing, and measuring the total selenium content.
And (3) measuring the content of inorganic selenium: weighing 2g of tea B sample, adding 30mL of ultrapure water, carrying out ultrasonic extraction for 30 minutes, filtering with filter paper, repeating the filter residue for 2 times, and combining the filtrates. Extracting with 10mL of organic mixture of ethyl acetate, petroleum ether and cyclohexane at a volume ratio of 3:2:5 for 2 times, separating out the water phase, heating in water bath to 10mL, pouring into a conical flask, adding 4mL of nitric acid, adding glass beads, and mixing. Heating to 2mL, cooling, adding 4mL1+1 hydrochloric acid solution, continuing heating to volatilize to 2mL, taking off and cooling. Adding 2.5mL concentrated hydrochloric acid, transferring into a 10mL volumetric flask, diluting with ultrapure water to constant volume, mixing, and measuring inorganic selenium content.
3 replicates were made and the results are shown in Table 3.
Table 3 test results (n ═ 3)
The total selenium content of the tea B sample is 0.51mg/kg, and the relative standard deviation RSD is 5.0%. The content of inorganic selenium is 0.15mg/kg, and the RSD is 7.5 percent. The content of organic selenium is 0.35mg/kg, and RSD is 4.3%. Indicating that the method has better precision.
EXAMPLE III
Total selenium content determination sample treatment: weighing 2g of tea C sample, adding 9mL of nitric acid and 1mL of perchloric acid, adding glass beads, and uniformly mixing. Standing for 4h, heating to 2mL, cooling, adding 5mL1+1 hydrochloric acid solution, continuing heating to volatilize to 2mL, taking off and cooling. Adding 1mL of concentrated hydrochloric acid, transferring into a 10mL volumetric flask, performing constant volume mixing by using ultrapure water, and measuring the total selenium content.
Treating an inorganic selenium content determination sample: weighing 2g of tea C sample, adding 20mL of ultrapure water, carrying out ultrasonic extraction for 25min, filtering with filter paper, repeatedly washing filter residues for 3 times, and combining filtrates. Extracting with 5mL ethyl acetate, petroleum ether and cyclohexane at volume ratio of 2:2:6 for 3 times, separating water phase, heating in water bath to 10mL, pouring into a conical flask, adding 4mL nitric acid, adding glass beads, and mixing. Heating to 2mL, cooling, adding 5mL1+1 hydrochloric acid solution, continuing heating to volatilize to 2mL, taking off and cooling. Adding 1mL of concentrated hydrochloric acid, transferring into a 10mL volumetric flask, performing constant volume mixing by using ultrapure water, and measuring the content of inorganic selenium.
The pretreatment of the tea sample C was as above to form a total selenium content test solution and an inorganic selenium content test solution, 3 concentration levels were added thereto, 3 parallel samples were prepared, and the recovery rates were calculated, and the results are shown in Table 4.
Table 4 results of recovery test with standard addition (n ═ 3)
As can be seen from the results in Table 4, the recovery rate of the detection results is 89.7% -112.7%, indicating that the detection method has high accuracy.
Comparative example 1
The procedure of the tea B sample was the same as in example two except that 0.2mL of hydrochloric acid was added to the solution during the measurement of the total selenium content and the inorganic selenium content, and the solution was transferred to a volumetric flask to maintain the acidity at 5%. 3 replicates were made and the results are shown in Table 5.
The procedure of the tea B sample was the same as in example two except that 4mL of hydrochloric acid was added to the tea B sample during the measurement of the total selenium content and during the measurement of the inorganic selenium content, and the tea B sample was transferred to a volumetric flask to maintain the acidity at 50%. 3 replicates were made and the results are shown in Table 5.
Table 5 comparative example one test result (n ═ 3)
As can be seen from Table 5, the tea B sample had a total selenium of 0.37mg/kg and a relative standard deviation RSD of 16.2% at 5% acidity. The content of inorganic selenium is 0.09mg/kg, and the RSD is 22.2 percent. The organic selenium content was found to be 0.28mg/kg, and the RSD was 14.3%.
Under the condition of 50% acidity, the total selenium of the tea B sample is measured to be 0.30mg/kg, and the relative standard deviation RSD is 13.3%. The content of inorganic selenium is 0.06mg/kg, and the RSD is 44.1 percent. The organic selenium content is 0.24mg/kg, and the RSD is 8.6%.
As can be seen from tables 5 and 3, the measurement result of comparative example one was inferior in precision.
Comparative example No. two
The tea B sample was processed in the same manner as in example two except that 10mL of cyclohexane was used for 3 times of extraction and the organic selenium was separated and removed. 3 replicates were made and the results are shown in Table 6.
Table 6 test results of comparative example two (n ═ 3)
| Number of measurements | Total selenium (mg/kg) | Inorganic selenium (mg/kg) | Organic selenium (mg/kg) |
| 1 | 0.49 | 0.34 | 0.15 |
| 2 | 0.55 | 0.30 | 0.25 |
| 3 | 0.52 | 0.37 | 0.15 |
| Mean value of | 0.52 | 0.34 | 0.18 |
The total selenium of the tea B sample was measured to be 0.52mg/kg with a relative standard deviation RSD of 5.8%. The content of inorganic selenium is 0.34mg/kg, and the RSD is 10.4 percent. The organic selenium content is 0.18mg/kg, and the RSD is 31.5%.
As can be seen from tables 3 and 6, the results of measurement of inorganic selenium and organic selenium were inferior in accuracy, and the effect of extracting organic selenium from cyclohexane was inferior to that of the mixed organic reagent.
While embodiments of the invention have been described above, it is not limited to the applications set forth in the description and the embodiments, which are fully applicable to various fields of endeavor for which the invention may be embodied with additional modifications as would be readily apparent to those skilled in the art, and the invention is therefore not limited to the details given herein and to the embodiments shown and described without departing from the generic concept as defined by the claims and their equivalents.
Claims (10)
1. A method for measuring organic selenium in tea comprises the following steps: the method is characterized in that the wet digestion comprises the processes of adding mixed acid into the tea, dispelling acid, performing first reduction, and adding 0.5-2.5 mL of hydrochloric acid to enable the constant volume acidity to be 15-35%.
2. The method for measuring organic selenium in tea leaves as claimed in claim 1, wherein the mixed acid is added to the tea leaves and then the mixture is left for 2-4 hours.
3. The method for measuring organic selenium in tea leaves according to claim 1, wherein the first reduction is performed by adding 4 to 8mL of 1+1 hydrochloric acid solution after the acid removing treatment.
4. The method for measuring organic selenium in tea leaves as claimed in claim 1, wherein the inorganic selenium content measuring process comprises: adding ultrapure water into tea leaves, performing ultrasonic treatment, filtering to obtain filtrate, extracting the filtrate to obtain a water phase, concentrating, removing acid, performing secondary reduction, and adding 0.5-2.5 mL of hydrochloric acid to ensure that the constant volume acidity is 15-35% to obtain a solution to be detected.
5. The method for measuring organoselenium in tea leaves as claimed in claim 4, wherein the ratio of the amount of tea leaves to ultrapure water when ultrapure water is added to tea leaves is 1 g: 10-15 mL.
6. The method for measuring organic selenium in tea leaves as claimed in claim 4, wherein the ultra pure water is added to the tea leaves and the ultrasound is performed for 20 to 30 min.
7. The method for determining organic selenium in tea leaves as claimed in claim 4, wherein the filter residue is washed 3-5 times in the filtering process.
8. The method for detecting organoselenium in tea of claim 4, wherein the extraction is performed using an organic mixture comprising ethyl acetate, petroleum ether, and cyclohexane; the volume ratio of the ethyl acetate to the petroleum ether to the cyclohexane to the organic mixed solution is 1-3: 4-8: 10.
9. The method for measuring organic selenium in tea leaves as claimed in claim 4, wherein the ratio of the amount of the tea leaves to the amount of the organic mixed solution in the process of measuring the content of inorganic selenium is 1 g: 3-5 mL.
10. The method for determining organic selenium in tea leaves as claimed in claim 4, wherein the first reduction is performed by adding 4-8 mL1+1 hydrochloric acid solution.
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Citations (3)
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| CN107084953A (en) * | 2017-04-21 | 2017-08-22 | 恩施硒德生物工程有限公司 | Method for detecting content of plant-derived organic selenium |
| CN108341761A (en) * | 2018-01-30 | 2018-07-31 | 广西师范学院 | The preparation method of Organic Selenium cyano compound |
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| CN106770116A (en) * | 2016-12-26 | 2017-05-31 | 安徽出入境检验检疫局检验检疫技术中心 | The method of Se form in SPE AFS DETERMINATION honey and fruit juice |
| CN107084953A (en) * | 2017-04-21 | 2017-08-22 | 恩施硒德生物工程有限公司 | Method for detecting content of plant-derived organic selenium |
| CN108341761A (en) * | 2018-01-30 | 2018-07-31 | 广西师范学院 | The preparation method of Organic Selenium cyano compound |
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Application publication date: 20201103 |