CN111024665A - Method for measuring content of organic selenium in selenium-enriched rice or product prepared from selenium-enriched rice - Google Patents
Method for measuring content of organic selenium in selenium-enriched rice or product prepared from selenium-enriched rice Download PDFInfo
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- CN111024665A CN111024665A CN201911347754.3A CN201911347754A CN111024665A CN 111024665 A CN111024665 A CN 111024665A CN 201911347754 A CN201911347754 A CN 201911347754A CN 111024665 A CN111024665 A CN 111024665A
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- G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
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Abstract
The invention belongs to the field of food quality analysis methods, and relates to a method for determining the content of organic selenium in selenium-enriched rice or products prepared from the selenium-enriched rice. The method comprises the following steps: pretreating raw materials, drawing a standard curve and measuring a sample. The method explores the influence of different pretreatment on the extraction rate of the organic selenium, determines the method for measuring the organic selenium of the rice, and realizes the determination of the content of the organic selenium in the selenium-enriched rice raw material.
Description
Technical Field
The invention belongs to the field of food quality analysis methods, and particularly relates to a method for determining the content of organic selenium in selenium-enriched rice or products prepared from the selenium-enriched rice.
Background
Selenium (selenium) is one of essential trace elements for human body, has various biological effects, especially has physiological functions of enhancing immunity, preventing chronic diseases and resisting cancer, and is receiving attention. Selenium nutrition is taken by the body through diet. Due to the limitation of environmental selenium resources (for example, 72% of China are regions with different selenium deficiency), the selenium content in natural foods in most regions is low. The selenium content of crops is improved through agricultural measure improvement, and biological selenium enrichment of agricultural products can be realized. Nowadays, the selenium-rich industry is developed under the support of government, and selenium-rich products already occupy certain markets. However, in the current selenium-rich industrial chain, most selenium-rich products only have the limitation or identification of the total selenium content, and the content of organic selenium is only explained. Therefore, some products added with inorganic selenium (sodium selenite, sodium selenate and the like) are mixed with the fish eyes, and the healthy development of the industry is restricted.
The national standard basically belongs to a chemical detection method for detecting selenium in grains, and needs to carry out acid treatment on a sample, the treatment method generally adopts an ashing method, a microwave digestion method, a wet digestion method and the like, the operation is complex, strong acid is used, a large amount of acid gas is generated, the treatment time of the whole sample is long, at least 2 hours is long, and time and labor are wasted.
In addition, selenium can be measured by various methods such as atomic fluorescence spectrometry, ultraviolet-visible spectrophotometry, atomic absorption spectrometry, inductively coupled plasma mass spectrometry, and the like.
The rice is a bulk grain crop, and the determination of organic selenium in the selenium-rich rice needs to be carried out by a grease removal process, but the loss of processing selenium is inevitably introduced in the process. The existing organic selenium detection method usually uses the chemical combination of selenium monomers as a standard sample, and adopts a method of adding standard recovery rate to evaluate the extraction rate of selenium, and the method can only realize the evaluation of the detection of free organic selenium in a sample, but can not quantify selenium compounds existing in a combined state form in the sample, thereby influencing the objective reflection of the total organic selenium content in the sample.
Disclosure of Invention
In order to overcome the problems, the invention aims to provide a method for measuring the content of organic selenium in selenium-enriched rice or products prepared from the selenium-enriched rice.
The invention provides a method for measuring the content of organic selenium in selenium-enriched rice or products prepared from the selenium-enriched rice, which comprises the following steps: pretreating raw materials, drawing a standard curve and measuring a sample;
the raw material pretreatment comprises the following steps:
(1) accurately weighing 4-8 parts of 2-10g sample, placing the sample in a polytetrafluoroethylene solution digestion tank, respectively adding 3-15mL of nitric acid and 1-3mL of hydrogen peroxide, shaking up, covering, placing for a period of time for pre-digestion, placing in a microwave digestion instrument, and sequentially digesting according to the following procedures: the temperature is 110-; the temperature is 140-; the temperature is 170-; meanwhile, making a reagent blank;
(2) and (3) cooling at room temperature, transferring the digestive juice into a triangular flask, heating on an electric heating plate until the residual volume is about 2-10mL, cooling, adding 5-15mL of 6-12mol/L hydrochloric acid, continuously heating until the solution becomes clear and colorless and is accompanied by white smoke, reducing hexavalent selenium into tetravalent selenium, cooling, transferring the sample digestive juice, and fixing the volume in a 25-50mL volumetric flask to obtain a sample solution.
According to the present invention, preferably, the plotting of the standard curve includes: preparing a series of concentration gradient standard solutions, measuring the fluorescence intensity by using a hydride atomic fluorescence spectrometry, drawing a standard curve by using the concentration as an abscissa and the fluorescence value as an ordinate, and measuring a curve equation.
According to the present invention, preferably, the method of preparing a series of concentration gradient standard solutions comprises: accurately sucking 1-5mL of selenium standard use solution into a 100-500mL volumetric flask, performing constant volume to obtain 5-20 mu g/mL of selenium standard solution, and automatically diluting the solution into a series of standard solutions with concentration gradients by an instrument.
According to the invention, preferably, the concentration of the standard solution of the series of concentration gradients is 1.0. mu.g/mL, 2.0. mu.g/mL, 4.0. mu.g/mL, 8.0. mu.g/mL, 10.0. mu.g/mL.
According to the present invention, preferably, the sample assay comprises: and sequentially measuring the fluorescence values of the blank solution and the sample solution, obtaining the selenium content in the sample solution to be measured according to the standard curve, and calculating the selenium content in the sample.
The reliability and the accuracy of the method are verified through a recovery rate test and a precision test.
According to the present invention, preferably, the recovery test comprises: accurately weighing 4-8 parts of 2-10g sample, adding 2-5mL of 40-80 mu g/mL selenium standard solution, processing according to a sample pretreatment method, measuring a fluorescence value, and calculating a standard recovery rate.
According to the invention, preferably, the precision test comprises: the fluorescence intensity of the selenium standard solutions was measured and the RSD thereof was calculated, respectively.
The invention has the beneficial effects that:
1. the invention has the advantages that a method for analyzing the content of organic selenium in selenium-enriched rice and products is established aiming at the current situation that the data information of the organic selenium of the products in the selenium-enriched industrial chain is lack. The influence of different pretreatment on the extraction rate of the organic selenium is explored, the method for measuring the organic selenium of the rice is determined, and the determination of the content of the organic selenium in the selenium-rich rice raw material is realized.
2. The invention compares the pretreatment method of the rice sample, and adopts the atomic fluorescence spectrometry to determine and analyze the selenium content in the rice, thereby finally determining the optimal test conditions: compared with the two pretreatment methods, the microwave digestion sample is complete and rapid and is superior to the wet digestion; the hydride generation-atomic fluorescence spectrometry is used for measuring the selenium content in the sample liquid, and has the advantages of high sensitivity, high precision, simple operation and low cost.
Additional features and advantages of the invention will be set forth in the detailed description which follows.
Detailed Description
Preferred embodiments of the present invention will be described in more detail below. While the following describes preferred embodiments of the present invention, it should be understood that the present invention may be embodied in various forms and should not be limited by the embodiments set forth herein.
Example 1
The invention provides a method for measuring the content of organic selenium in selenium-enriched rice or products prepared from the selenium-enriched rice, which comprises the following steps:
1.1 instruments and reagents
AFS-9330 model double-channel six-lamp atomic fluorescence photometer, selenium hollow cathode lamp, and temperature-adjustable electric lamp from Beijing Jitian instruments LtdHot plate, high speed pulverizer. Selenium single element solution standard substance: 100 μ g/mL, purchased from the national institute of metrology science. Selenium standard use solution (1. mu.g/mL): accurately transferring 1.0mL of selenium standard solution into a 100mL volumetric flask, fixing the volume to a scale, and preparing when the solution is used on the day. Potassium borohydride and sodium hydroxide are both superior pure. Acid used for experiments (HNO)3、HClO4、HCl、H2SO4) All are super pure, and water is first-grade water.
1.2 working conditions of the apparatus
The lamp has 80mA of main current, 40mA of auxiliary cathode current, 270V of negative high voltage, 400mL/min of carrier gas flow, 800mL/min of shielding gas flow and 8mm of atomizer height. Measurement mode standard curve method, peak area in reading form, reading time 9s and delay time 1.0 s.
1.3 Experimental methods
(1) Accurately weighing 6 parts of 2-10g rice sample, placing the rice sample in a polytetrafluoroethylene solution digestion tank, respectively adding 7mL nitric acid and 2mL hydrogen peroxide, shaking up, covering, placing for a period of time to pre-digest the rice sample, placing the rice sample in a microwave digestion instrument, and sequentially digesting the rice sample according to the following procedures: the temperature is 120 ℃, the power is 1600W and 100 percent, and the holding time is 2 min; the temperature is 150 ℃, the power is 1600W and 100 percent, and the holding time is 5 min; the temperature is 180 ℃, the power is 1600W and 100 percent, and the holding time is 10 min; meanwhile, reagent blanks are made.
(2) And (3) cooling at room temperature, transferring the digestive juice into a triangular flask, heating on an electric heating plate until the residual volume is about 2mL, cooling, adding 5mL of 6mol/L hydrochloric acid, continuously heating until the solution becomes clear and colorless with the appearance of white smoke, and reducing the hexavalent selenium into the tetravalent selenium. And cooling, transferring the sample digestive juice to a 25mL volumetric flask for constant volume and standby application to serve as a sample solution.
(3) Drawing a standard curve: accurately sucking 1mL of selenium standard use solution (1 mu g/mL) into a 100mL volumetric flask, and carrying out constant volume to obtain 10 mu g/mL of selenium standard solution. The instrument automatically dilutes the solution into standard solutions with the concentrations of 1.0 mug/mL, 2.0 mug/mL, 4.0 mug/mL, 8.0 mug/mL and 10.0 mug/mL, the fluorescence intensity of the standard solutions is measured, a standard curve is drawn by taking the concentration as an abscissa and the fluorescence value as an ordinate, and the curve equation I is 106.0831C +0.7562, R is measured2＝0.9999。
(4) Recovery rate test: accurately weighing 6 parts of 3g rice sample, adding 0.5mL of 50 mu g/mL selenium standard solution, carrying out sample pretreatment according to the microwave digestion method, measuring the fluorescence value, and calculating the recovery rate of the added standard, wherein the result is shown in Table 1.
(5) And (3) precision test: the fluorescence intensities of the selenium standard solutions of 2. mu.g/mL, 4. mu.g/mL, and 6. mu.g/mL were measured, respectively, and the RSD was calculated (n-10). The RSD of the method is 4.79%, 3.62% and 1.45%, which shows that the method has good reproducibility and high precision.
(6) And (3) sample determination: and sequentially measuring the fluorescence values of the blank solution and the sample solution, obtaining the selenium content in the sample solution to be measured according to the standard curve, and calculating to obtain the selenium content in the sample.
1.4 Wet digestion comparative test
Crushing rice with a high-speed pulverizer, and storing the sample in a self-sealing bag at 0-4 deg.C. Accurately weighing 3g of 6 parts of the crushed sample into a 100mL triangular flask, adding 10mL of mixed acid and a few glass beads, covering a watch glass, and carrying out cold digestion and standing overnight. Heating on the electric heating plate the next day, and adding acid liquor in time. When the solution became clear and colorless with a large amount of white smoke, the solution was further heated to a residual volume of about 2mL and cut into pieces which could not be evaporated to dryness. Cooling, adding 5mL of 6mol/L hydrochloric acid, and continuously heating until the solution becomes clear and colorless with the appearance of white smoke to completely reduce the hexavalent selenium into the tetravalent selenium. After cooling, the flask was transferred to a 25mL volumetric flask to make a constant volume while making a reagent blank, and the results are shown in Table 1.
1.5 test results
(1) Recovery test
As can be seen from Table 1, the recovery rate of wet digestion is 90.28% -95.41%, and the average recovery rate is 93.67%; the recovery rate of microwave digestion is 95.44% -98.12%, and the average recovery rate is 96.51%. The microwave digestion adopted by the invention has higher accuracy.
TABLE 1
(2) Sample concentration determination
The selenium content in the sample is measured by wet digestion and is 0.13mg/kg, and the standard deviation is 8.67 percent; the method of the invention measures the selenium content in the same sample to be 0.18mg/kg, and the standard deviation is 4.62%. The method is shown to have smaller relative standard deviation, and the selenium content in the rice measured by the pretreatment method is higher than that in the wet digestion pretreatment sample, which shows that the microwave digestion sample is more complete and better than the wet digestion. In addition, the method adopts hydride atomic fluorescence spectrometry to measure the selenium content, and has high selectivity and sensitivity.
Having described embodiments of the present invention, the foregoing description is intended to be exemplary, not exhaustive, and not limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments.
Claims (5)
1. A method for measuring the content of organic selenium in selenium-enriched rice or products prepared from the selenium-enriched rice is characterized by comprising the following steps: pretreating raw materials, drawing a standard curve and measuring a sample;
the raw material pretreatment comprises the following steps:
(1) accurately weighing 4-8 parts of 2-10g sample, placing the sample in a polytetrafluoroethylene solution digestion tank, respectively adding 3-15mL of nitric acid and 1-3mL of hydrogen peroxide, shaking up, covering, placing for a period of time for pre-digestion, placing in a microwave digestion instrument, and sequentially digesting according to the following procedures: the temperature is 110-; the temperature is 140-; the temperature is 170-; meanwhile, making a reagent blank;
(2) and (3) cooling at room temperature, transferring the digestive juice into a triangular flask, heating on an electric heating plate until the residual volume is about 2-10mL, cooling, adding 5-15mL of 6-12mol/L hydrochloric acid, continuously heating until the solution becomes clear and colorless and is accompanied by white smoke, reducing hexavalent selenium into tetravalent selenium, cooling, transferring the sample digestive juice, and fixing the volume in a 25-50mL volumetric flask to obtain a sample solution.
2. The method of claim 1, wherein said plotting a standard curve comprises: preparing a series of concentration gradient standard solutions, measuring the fluorescence intensity by using a hydride atomic fluorescence spectrometry, and drawing a standard curve by using the concentration as an abscissa and the fluorescence value as an ordinate.
3. The method of claim 2, wherein the step of preparing a series of concentration gradient standards comprises: accurately sucking 1-5mL of selenium standard use solution into a 100-500mL volumetric flask, performing constant volume to obtain 5-20 mu g/mL of selenium standard solution, and automatically diluting the solution into a series of standard solutions with concentration gradients by an instrument.
4. The method of claim 2, wherein the concentration of the standard solution in the series of concentration gradients is 1.0 μ g/mL, 2.0 μ g/mL, 4.0 μ g/mL, 8.0 μ g/mL, or 10.0 μ g/mL.
5. The method of claim 1, wherein the sample assay comprises: and sequentially measuring the fluorescence values of the blank solution and the sample solution, obtaining the selenium content in the sample solution to be measured according to the standard curve, and calculating the selenium content in the sample.
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| CN113340828A (en) * | 2021-05-31 | 2021-09-03 | 南华大学 | Method for determining influence of selenium fertilizer on heavy metal, nutrient element and quality accumulated in rice |
| CN114365944A (en) * | 2022-01-29 | 2022-04-19 | 南京恒宝田功能农业产业研究院有限公司 | Method and system for evaluating selenium thermal stability of selenium-rich agricultural products |
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| CN111948182A (en) * | 2020-07-22 | 2020-11-17 | 广西壮族自治区农业科学院 | Selenium-enriched peanut and method for measuring content of organic selenium in selenium-enriched peanut product |
| CN113340828A (en) * | 2021-05-31 | 2021-09-03 | 南华大学 | Method for determining influence of selenium fertilizer on heavy metal, nutrient element and quality accumulated in rice |
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