Method for measuring selenium in farmland soil by atomic fluorescence spectrometry
Through atomic fluorescence spectrometry combined with the use of potassium borohydride reducing agent, digestion and reduction conditions are optimized, and the problems of low detection limit and insufficient sensitivity of soil selenium detection in the prior art are solved, achieving efficient and accurate selenium detection effect.
Patent Information
- Application Number
- CN202510446994.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-04-10
- Publication Date
- 2025-07-04
AI Technical Summary
The detection limit of the method of detecting selenium in soil in the prior art is low, has low sensitivity, is complex in operation, is high in cost, and is difficult to achieve accurate detection.
The method of determining selenium in soil was used by atomic fluorescence spectrometry. The soil sample was mixed with mixed acid and then digested with heat, concentrated hydrochloric acid was added to reduce and extract, and the selenium content was measured using an atomic fluorescence photometer, and potassium borohydride was used as a reducing agent to optimize the digestion and reduction conditions.
The selenium detection with low detection limit and high sensitivity is achieved. The method is simple, economical and accurate, eliminating the problem of low selenium results and is suitable for the detection of selenium in farmland soil.
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Figure CN120253787A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of chemical detection, and particularly relates to a method for determining selenium in farmland soil by atomic fluorescence spectrometry. Background Art
[0002] Selenium is a trace element required by the human body, which can play roles in antioxidant, anti-aging, protecting the cardiovascular and cerebrovascular, and inhibiting tumors. However, excessive intake of selenium can be harmful to the human body. With people paying more and more attention to physical health and strengthening the awareness of environmental protection for survival, it is imperative to determine selenium in soil. Selenium is a rare and dispersed element with a crustal abundance of 0.05×10 -6 , and it is also a chalcophile element, mainly distributed in volcanic and volcanogenic sedimentary deposits. There is also selenium distribution in farmland soil in China. Selenium is an important trace element essential for the human body and also an essential life element for the metabolism of other animals and plants. The selenium content in soil directly affects the selenium content in crops. Selenium is widely used in glass, metallurgy, electronics, national defense, chemical industry, medicine, and agriculture, etc.
[0003] In the prior art, the methods for detecting selenium mainly include 2,3-diaminonaphthalene fluorescence photometry, diaminonaphthalene fluorescence photometry, colorimetry, electrochemistry method, gas chromatography, atomic absorption spectrophotometry, etc. However, for the above methods, the detection limit of ICP-MS for selenium is low, the pipe diameter is easily blocked, the interference is large, the cost is high, and the detection accuracy is relatively low, which cannot achieve the purpose of high accuracy. While the atomic fluorescence method has simple and rapid pretreatment, the instrument is inexpensive, and the accurate method is the development trend of inspection work.
[0004] Therefore, how to provide a selenium detection method with low detection limit, high sensitivity, simple and rapid operation is a technical problem that those skilled in the art need to solve urgently. Summary of the Invention
[0005] To solve the above technical problems, the present invention proposes a method for determining selenium in farmland soil by atomic fluorescence spectrometry.
[0006] To achieve the above object, the present invention provides the following technical solutions:
[0007] A method for determining selenium in farmland soil by atomic fluorescence spectrometry, comprising the following steps:
[0008] Mix the soil sample with a mixed acid and heat for digestion, then add concentrated hydrochloric acid to reduce and extract while it is hot. After the extraction is completed, add ferric chloride solution, and use an atomic fluorescence photometer to determine the selenium content.
[0009] Preferably, during the process of using the atomic fluorescence photometer to determine the selenium content, potassium borohydride is used as the reducing agent;
[0010] More preferably, the reducing agent is specifically obtained by adding potassium borohydride with a mass fraction of 2% to a potassium hydroxide solution with a mass fraction of 0.5%.
[0011] Beneficial effects: In the present invention, an intelligent temperature-controlled (180 °C) hot plate is used to digest selenium in farmland soil. Concentrated hydrochloric acid is used to reduce hexavalent selenium to tetravalent selenium. The tetravalent selenium reacts with potassium borohydride to form a hydride, and the atomic fluorescence spectrometry is used to measure its fluorescence intensity. The fluorescence intensity is proportional to the concentration of selenium. Moreover, the method provided by the present invention has low cost, less interference, is economical and practical, and has high accuracy.
[0012] Preferably, the ratio of the addition amount of the soil sample to the mixed acid is 0.5 g : (10 - 12) mL.
[0013] Preferably, the mixed acid is obtained by uniformly mixing a nitric acid solution, a hydrofluoric acid solution, and a perchloric acid solution in a volume ratio of 5:5:1.
[0014] Preferably, the density of the hydrochloric acid solution is 1.19 g / ml, the density of the nitric acid solution is 1.42 g / ml, the density of the hydrofluoric acid solution is 1.13 g / ml, and the density of the perchloric acid solution is 1.67 g / ml.
[0015] Preferably, the temperature of the heating digestion is 120 - 180 °C, more preferably 180 °C, and the time is 4 h.
[0016] Beneficial effects: When the temperature is lower than 120 °C, the digestion time of the sample is very long, and the digestion effect on the sample is not good. When the temperature is between 120 - 180 °C, the digestion time of the sample is 4 h, and the digestion effect on the sample is better. When the temperature is higher than 180 °C, Se will volatilize in the form of hydride or chloride, and the selenium content will escape and be lost, resulting in a low final test result. At the heating digestion temperature in the present invention, the sample digestion time can be shortened, and the selenium content can be ensured not to be lost.
[0017] Preferably, the ratio of the addition amount of the soil sample to the concentrated hydrochloric acid is 0.5 g : 5 mL.
[0018] Preferably, the temperature of the reduction extraction is 150 - 170 °C, and the time is 3 - 7 min.
[0019] Beneficial effects: If hydrochloric acid reduction is carried out at 180 °C or higher than 180 °C, the test sample will overflow from the crucible due to excessive temperature, and at the same time, selenium will volatilize and be lost in the form of chloride, which is not convenient for operation.
[0020] Preferably, the ratio of the addition amount of the soil sample to the concentrated hydrochloric acid is 0.5 g : 2 mL.
[0021] Preferably, the ferric chloride solution is obtained by adding 265 g of FeCl3·6H2O to 40 ml of concentrated hydrochloric acid for dissolution and then making up the volume to 500 ml.
[0022] Advantageous effects: The ferric chloride in the present invention can mask interfering ions (such as copper, lead, etc.) and reduce the matrix effect in subsequent detections.
[0023] Preferably, the determination conditions of the atomic fluorescence spectrometer are as follows: photomultiplier tube voltage 280 V, reading delay time 2 s, reading time 18 s, carrier flow interval time 10 s, lamp current 45 mA, atomizer height 8.0 mm, temperature 200 °C, reading mode peak area, carrier gas flow rate 400 ml / min, shielding gas flow rate 800 ml / min, injection volume 0.5 ml.
[0024] Compared with the prior art, the present invention has the following advantages and technical effects:
[0025] The present invention uses temperature control (180 °C) to digest farmland soil and then uses the hydride generation-atomic fluorescence method to determine selenium, eliminating the problem of low results in the determination of selenium by the atomic fluorescence method. The present invention adopts a nitric acid, hydrofluoric acid, perchloric acid system, potassium borohydride as a reducing agent, and uses the atomic fluorescence method to determine selenium in soil. It has a low detection limit, high sensitivity, and the method is simple, economical, accurate, efficient, and environmentally friendly, and is the best choice for determining the selenium element content in soil. BRIEF DESCRIPTION OF THE DRAWINGS
[0026] The drawings constituting a part of this application are used to provide a further understanding of this application. The schematic embodiments and descriptions thereof of this application are used to explain this application and do not constitute an improper limitation to this application. In the drawings:
[0027] Figure 1 is the selection of curves under different acidity conditions in the present invention;
[0028] Figure 2 is the working curve of the atomic fluorescence spectrometry in the present invention;
[0029] Figure 3 is the selenium content results of Examples 1-3 and Comparative Example 1. DETAILED DESCRIPTION OF THE EMBODIMENTS
[0032] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.
[0033] To make the above objects, features, and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.
[0034] An embodiment of the present invention discloses a method for determining selenium in farmland soil by atomic fluorescence spectrometry, which includes the following steps:
[0035] Mix the soil sample with a mixed acid and heat for digestion, then add concentrated hydrochloric acid to reduce and extract while it is hot. After the extraction is completed, add ferric chloride solution, and then use an atomic fluorescence spectrometer to determine the selenium content.
[0036] In a preferred embodiment, during the process of determining the selenium content by the atomic fluorescence spectrometer, potassium borohydride is used as the reducing agent;
[0037] In a more preferred embodiment, the reducing agent is specifically obtained by adding 2% potassium borohydride to a 0.5% potassium hydroxide solution by mass fraction.
[0038] In a preferred embodiment, the ratio of the addition amount of the soil sample to the mixed acid is 0.5 g : (10 - 12) mL.
[0039] In a preferred embodiment, the mixed acid is obtained by uniformly mixing nitric acid solution, hydrofluoric acid solution, and perchloric acid solution in a volume ratio of 5:5:1.
[0040] In a preferred embodiment, the density of the hydrochloric acid solution is 1.19 g / ml, the density of the nitric acid solution is 1.42 g / ml, the density of the hydrofluoric acid solution is 1.13 g / ml, and the density of the perchloric acid solution is 1.67 g / ml.
[0041] In a preferred embodiment, the temperature for heating digestion is 120 - 180 °C, and the time is 4 h.
[0042] In a preferred embodiment, the ratio of the addition amount of the soil sample to concentrated hydrochloric acid is 0.5 g : 5 mL.
[0043] In a preferred embodiment, the temperature for reduction extraction is 150 - 170 °C, and the time is 3 - 7 min.
[0044] In a preferred embodiment, the ratio of the addition amount of the soil sample to concentrated hydrochloric acid is 0.5 g : 2 mL.
[0045] In a preferred embodiment, the ferric chloride solution is obtained by dissolving 265 g of FeCl3·6H2O in 40 ml of concentrated hydrochloric acid and then diluting to 500 ml.
[0046] In a preferred embodiment, the determination conditions of the atomic fluorescence photometer are as follows: the voltage of the photomultiplier tube is 280 V, the reading delay time is 2 s, the reading time is 18 s, the carrier gas interval time is 10 s, the lamp current is 45 mA, the height of the atomizer is 8.0 mm, the temperature is 200 °C, the reading mode is peak area, the carrier gas flow rate is 400 ml / min, the shielding gas flow rate is 800 ml / min, and the injection volume is 0.5 ml.
[0047] Unless otherwise specified, the raw materials in the embodiments of the present invention are all obtained through commercial channels;
[0048] Among them, the soil samples were taken from Ledu District, Haidong City, Qinghai Province, during the third national soil census.
[0049] The density of the hydrochloric acid solution is 1.19 g / ml;
[0050] The density of the nitric acid solution is 1.42 g / ml;
[0051] The density of the hydrofluoric acid solution is 1.13 g / ml;
[0052] The density of the perchloric acid solution is 1.67 g / ml;
[0053] Selenium standard stock solution: 100 mg·L -1 , and it is diluted step by step to 0.1 mg·L during use -1 .
[0054] Ferric chloride solution: Weigh 265 g of FeCl3·6H2O, add 40 ml of concentrated hydrochloric acid to dissolve it, and make up the volume to 500 ml.
[0055] Potassium borohydride solution: Add potassium borohydride with a mass fraction of 2% to a potassium hydroxide solution with a mass fraction of 0.5% to obtain a potassium borohydride solution.
[0056] Carrier: Measure 40 ml of ferric chloride solution, add 80 ml of concentrated hydrochloric acid, and make up the volume to 500 ml.
[0057] All the reagents used are of analytical grade (99.9%), and the water is secondary deionized water. All the glassware used is soaked in a dilute nitric acid (5 + 95) solution for more than 24 h.
[0058] The equipment used in the embodiments of the present invention includes:
[0059] BAF-2000 double-channel atomic fluorescence photometer;
[0060] SD series intelligent hotplate (Tianjin Tuozhiming Experimental Instrument Equipment Co., Ltd., Sino-German cooperation).
[0061] Example 1
[0062] A method for determining selenium in farmland soil by atomic fluorescence spectrometry, comprising the following steps:
[0063] Accurately weigh 0.5000 g of soil sample into a 30 ml polytetrafluoroethylene crucible, moisten it with a little water, add 10 ml of mixed acid (obtained by mixing nitric acid solution, hydrofluoric acid solution and perchloric acid solution in a volume ratio of 5:5:1 evenly), heat and digest at 180 °C on an intelligent electric hot plate for 4 h until the volume is 0.5 ml, then add 5 ml of concentrated hydrochloric acid and reduce and extract while it is hot for 5 min. After the extraction is completed, rinse the inner wall of the crucible with pure water, add 2 ml of ferric chloride solution, then transfer it to a 25 ml plastic colorimetric tube, make up the volume to the mark with pure water and shake well, and then use a BAF-2000 double-channel atomic fluorescence photometer for determination. Among them, the detection conditions are: the reducing agent is potassium borohydride solution, the photomultiplier tube voltage is 280 V, the reading delay time is 2 s, the reading time is 18 s, the carrier gas interval time is 10 s, the lamp current is 45 mA, the height of the atomizer is 8.0 mm, the temperature is 200 °C, the reading mode is peak area, the carrier gas flow rate is 400 ml / min, the shielding gas flow rate is 800 ml / min, and the injection volume is 0.5 ml.
[0064] Examples 2 - 3
[0065] A method for determining selenium in farmland soil by atomic fluorescence spectrometry, which is different from Example 1 only in that the heating and digestion temperatures are 120 °C and 150 °C respectively. The remaining process steps and parameters are the same as those in Example 1.
[0066] Comparative Examples 1 - 7
[0067] A method for determining selenium in farmland soil by atomic fluorescence spectrometry, which is different from Example 1 only in that the heating and digestion temperatures are 80 °C, 90 °C, 100 °C, 190 °C, 200 °C, 210 °C and 220 °C respectively. The remaining process steps and parameters are the same as those in Example 1.
[0068] Examples 4 - 5
[0069] A method for determining selenium in farmland soil by atomic fluorescence spectrometry, which is different from Example 1 only in that the reduction and extraction temperatures are 150 °C and 160 °C respectively. The remaining process steps and parameters are the same as those in Example 1.
[0070] Comparative Example 8
[0071] A method for determining selenium in farmland soil by atomic fluorescence spectrometry, which is different from Example 1 only in that the reduction and extraction temperature is 180 °C. The remaining process steps and parameters are the same as those in Example 1.
[0072] Under these conditions, the sample overflows and dries due to excessive temperature, and selenium volatilizes and is lost in the form of chloride, which is not convenient for operation and the selenium content cannot be accurately measured.
[0073] Examples 6 - 9
[0074] A method for determining selenium in farmland soil by atomic fluorescence spectrometry, which is different from Example 1 only in that the addition amounts of the mixed acid are 11 mL, 12 mL, 13 mL, and 14 mL respectively. The remaining process steps and parameters are the same as those in Example 1.
[0075] Comparative Examples 9 - 12
[0076] A method for determining selenium in farmland soil by atomic fluorescence spectrometry, which is different from Example 1 only in that the addition amounts of the mixed acid are 4 mL, 6 mL, 8 mL, and 9 mL respectively. The remaining process steps and parameters are the same as those in Example 1.
[0077] Technical effects
[0078] 1. Detection limit and linear regression equation
[0079] In 100 - mL volumetric flasks, different amounts of selenium standard solution were added, 8 mL of ferric chloride solution was added, and they were diluted to the mark with 10% mixed acid, 10% hydrochloric acid, and 10% nitric acid respectively, and mixed well to measure the working curves. The results are as Figure 1 shown. It can be seen that with the mixed acid and nitric acid as the acidity media, the linearity of selenium and the accuracy of the standard samples are not ideal. With 10% hydrochloric acid as the medium condition, the linearity of selenium and the accuracy of the standard samples meet the test requirements. Therefore, in this invention, a working curve of selenium standard solution is drawn using 10% hydrochloric acid medium.
[0080] In 100 - mL volumetric flasks, different amounts of selenium standard solution were added, 8 mL of ferric chloride solution was added, and they were diluted to the mark with 10% hydrochloric acid and mixed well. According to the instrument working conditions, the standard solution series of selenium was measured. Finally, it was found that selenium showed a linear relationship in the range of 0.001 - 0.008 mg·L -1 IF = 258.746*C - 3.817, the correlation coefficient was 0.9999, and the method detection limit (LD, 3σ) was 0.001 μg·ml -1 . The working curve is as Figure 2 shown. The standard series points of 0.002 mg·L -1 were continuously measured 11 times, and the relative standard deviation was 0.63%.
[0081] Two samples of the soil in Ledu District, Haidong City, Qinghai Province, from the third national soil census were taken, and the selenium element content in them was determined by the method of Example 1. The measurement results and spike recovery rates are shown in Table 1 below.
[0082] Table 1
[0083]
[0084] As can be seen from Table 1, the method of Example 1 for determining the selenium content in the Sanpu soil sample is accurate and reliable and can be applied to actual detection.
[0085] 2. Use the above working curve to determine the selenium element content in the soils of Examples 1-7. The selenium content results of Examples 1-3 and Comparative Example 1 are as Figure 3 shown. It can be seen that when the temperature is lower than 120 °C, the digestion time of the sample is very long and the digestion effect on the sample is not good. When the temperature is between 120-180 °C, the digestion time of the sample is 4 h and the digestion effect on the sample is better. When the temperature is higher than 180 °C, Se will volatilize in the form of hydride or chloride, and the selenium content will escape and be lost, resulting in a lower final test result. Therefore, the best digestion temperature point of 180 °C is selected, which can not only shorten the sample digestion time but also ensure that the selenium content is not lost. 180 °C is the best choice.
[0086] 3. Selection of the amount of mixed acid added
[0087] The experiment used mixed acid to control the temperature and digest selenium in farmland soil, and optimized the amount of mixed acid used. The results are shown in Table 2. It can be seen that when the amount of mixed acid is greater than 10 ml, it has no effect on the digestion of the sample, while when it is less than 10 ml, the sample digestion is incomplete. Especially the use of HF acid can completely digest the sample and eliminate the influence of silica on the encapsulation of selenium. Therefore, the present invention selects 10-12 ml, which can not only have a good digestion effect but also reduce the cost.
[0088] Table 2
[0089] Recommended value of Se / mg / kg Measured value of Se / mg / kg Comparative Example 9 0.197 0.036 Comparative Example 10 0.197 0.086 Comparative Example 11 0.197 0.151 Comparative Example 12 0.197 0.172 Example 1 0.197 0.195 Example 6 0.197 0.194 Example 7 0.197 0.195 Example 8 0.197 0.194 Example 9 0.197 0.195
[0090] The above is only a preferred specific embodiment of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed in the present application should be covered by the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.
Claims
1. A method for determining selenium in farmland soil by atomic fluorescence spectrometry, characterized in that, It includes the following steps: Mix the soil sample with mixed acid and heat for digestion, then add concentrated hydrochloric acid to reduce and extract while it is hot. After the extraction is completed, add ferric chloride solution, and determine the selenium content using an atomic fluorescence photometer.
2. The method for determining selenium in farmland soil by atomic fluorescence spectrometry according to claim 1, characterized in that, The ratio of the addition amount of the soil sample to the mixed acid is 0.5 g : (10 - 12) mL.
3. The method for determining selenium in farmland soil by atomic fluorescence spectrometry according to claim 1, characterized in that, The mixed acid is obtained by uniformly mixing nitric acid solution, hydrofluoric acid solution and perchloric acid solution in a volume ratio of 5:5:
1.
4. A method for determining selenium in farmland soil by atomic fluorescence spectrometry according to claim 3, characterized in that, The density of the concentrated hydrochloric acid solution is 1.19 g / ml, the density of the nitric acid solution is 1.42 g / ml, the density of the hydrofluoric acid solution is 1.13 g / ml, and the density of the perchloric acid solution is 1.67 g / ml.
5. A method for determining selenium in farmland soil by atomic fluorescence spectrometry according to claim 1, characterized in that, The temperature for the heating digestion is 120 - 180 °C, and the time is 4 h.
6. The method for determining selenium in farmland soil by atomic fluorescence spectrometry according to claim 1, wherein, The ratio of the addition amount of the soil sample to the concentrated hydrochloric acid is 0.5 g : 5 mL.
7. A method for determining selenium in farmland soil by atomic fluorescence spectrometry according to claim 1, characterized in that, The temperature for the reduction extraction is 150 - 170 °C, and the time is 3 - 7 min.
8. A method for determining selenium in farmland soil by atomic fluorescence spectrometry according to claim 1, characterized in that, The ratio of the addition amount of the soil sample to the concentrated hydrochloric acid is 0.5 g : 2 mL.
9. The method for determining selenium in farmland soil by atomic fluorescence spectrometry according to claim 1, characterized in that, The ferric chloride solution is obtained by adding 265 g of FeCl3·6H2O to 40 ml of concentrated hydrochloric acid for dissolution, and then making up the volume to 500 ml.
10. A method for determining selenium in farmland soil by atomic fluorescence spectrometry according to claim 1, characterized in that, The determination conditions of the atomic fluorescence photometer are as follows: photomultiplier tube voltage 280 V, reading delay time 2 s, reading time 18 s, carrier flow interval time 10 s, lamp current 45 mA, atomizer height 8.0 mm, temperature 200 °C, reading mode peak area, carrier gas flow rate 400 ml / min, shielding gas flow rate 800 ml / min, injection volume 0.5 ml.