Method for detecting heavy metals in agricultural products

Abstract

The invention discloses an agricultural product heavy metal detection method which comprises the following steps: S1, adjusting the humidity of a room temperature environment, weighing a dried agricultural product sample, and putting the dried agricultural product sample into a special digestion tank; s2, adding a proper amount of digestion reagent into the digestion tank, and mixing by using stirring equipment; s3, performing microwave digestion by adopting stepped temperature control, including three stages of low-temperature preheating, medium-temperature digestion and high-temperature strengthening, and digesting the sample; s4, after digestion is completed, a digestion solution is transferred into a clean container and diluted; a stepped control microwave digestion technology is adopted, the temperature and microwave power in the digestion process are accurately controlled, heavy metal evaporation loss is effectively avoided, the detection accuracy is improved, and the method comprises four steps of sample preparation, reagent mixing, stepped microwave digestion and digestion solution analysis. By combining the optimized reagent ratio and mixing time, efficient extraction and purification of heavy metal elements are ensured.

Description

Technical Field

[0001] The invention relates to the field of sampling, in particular to the field of preparing samples for testing, and specifically to a method for detecting heavy metals in agricultural products. Background Art

[0002] As an indispensable part of human daily diet, the quality and safety of agricultural products are not only related to everyone's health and well-being. With the rapid development and widespread application of modern agricultural technology, such as excessive use of fertilizers and pesticides and cross-border migration of industrial pollutants, agricultural products may be attacked by various pollution sources in various links such as production, processing, storage and transportation, among which heavy metal pollution is particularly concerned.

[0003] Heavy metals, such as lead (Pb), cadmium (Cd), and mercury (Hg), are difficult to degrade and easily accumulate in organisms. Once these heavy metals enter agricultural products through soil, water or air, they will accumulate step by step along the food chain, eventually posing a serious threat to human health. Long-term intake of agricultural products containing heavy metals may lead to serious diseases such as nervous system dysfunction, liver and kidney damage, decreased immunity, and even cancer, bringing heavy medical burdens and public health challenges to society.

[0004] Faced with this grim situation, although the traditional heavy metal detection methods have guaranteed the bottom line of food safety to a certain extent, their limitations are becoming increasingly prominent. First of all, the ashing method is a commonly used sample pretreatment method. Its high-temperature ashing process not only consumes a lot of energy, but also easily causes high evaporation losses of heavy metal elements, resulting in low test results and unable to truly reflect the heavy metal content in agricultural products.

[0005] Therefore, it is necessary to improve a method for detecting heavy metals in agricultural products in the prior art to solve the above problems. Summary of the invention

[0006] The invention overcomes the shortcomings of the prior art and provides a method for detecting heavy metals in agricultural products.

[0007] To achieve the above object, the technical solution adopted by the present invention is: a method for detecting heavy metals in agricultural products, comprising the following steps:

[0008] S1: Adjust the room temperature and humidity, weigh the dried agricultural product samples, and place them in a special digestion tank;

[0009] S2: Add an appropriate amount of digestion reagent into the digestion tank and mix using a stirring device;

[0010] S3: Microwave digestion is performed using stepped temperature control, including three stages: low-temperature preheating, medium-temperature digestion, and high-temperature intensification, to digest the sample;

[0011] S4: After digestion is completed, open the digestion tank after natural cooling, transfer the digestion solution to a clean container, and dilute it for subsequent analysis.

[0012] In a preferred embodiment of the present invention, in S1, the adjustment range of the room temperature and ambient humidity is set to 60-80% RH to ensure that the agricultural product sample is under suitable humidity conditions before the digestion reagent is added.

[0013] In a preferred embodiment of the present invention, in said S1, the digestion tank is a microwave digestion tank.

[0014] In a preferred embodiment of the present invention, in S2, the mass ratio of the digestion reagent to the agricultural product sample is in the range of 1-3:2-4, and the stirring device is a stirrer for promoting sufficient mixing of the agricultural product sample and the digestion reagent.

[0015] In a preferred embodiment of the present invention, in S2, the mixing time ranges from 1 to 5 minutes to ensure that the sample and the reagent are uniformly mixed in a short time.

[0016] In a preferred embodiment of the present invention, in S3, the low-temperature preheating temperature ranges from 80 to 120° C., the microwave power ranges from 200 to 500 W, and the duration ranges from 10 to 30 min.

[0017] In a preferred embodiment of the present invention, in S3, the temperature of the medium-temperature digestion stage is in the range of 150-200° C., the microwave power is in the range of 500-800 W, and the duration is in the range of 30-60 min.

[0018] In a preferred embodiment of the present invention, in S3, the high temperature strengthening temperature ranges from 200 to 250°C, the microwave power ranges from 800 to 1000W, and the duration ranges from 60 to 100min.

[0019] In a preferred embodiment of the present invention, in S4, the natural cooling time ranges from 30 to 60 minutes to ensure that the internal pressure of the digestion tank is safely released and the temperature of the digestion solution is reduced to a processing range, and the processing range of the digestion solution temperature is 20-30°C.

[0020] In a preferred embodiment of the present invention, in said S4, the diluted digestion solution is subjected to heavy metal element detection using an analytical method such as ICP-MS or AAS atomic absorption spectroscopy.

[0021] The present invention solves the defects existing in the background technology and has the following beneficial effects:

[0022] (1) The present invention provides a method for detecting heavy metals in agricultural products. The method uses a step-controlled microwave digestion method, especially in the high-temperature intensification stage, by controlling the temperature range between 200-250°C and supplemented with an appropriate microwave power range of 800-1000W, thereby effectively avoiding the evaporation loss of heavy metal elements caused by the excessively high ashing temperature in the traditional dry digestion, which often reaches 500°C. The step-type temperature control ensures the smooth progress of the digestion process, which not only ensures the full decomposition of organic matter, but also reduces the volatility of heavy metals at high temperatures, thereby significantly improving the accuracy and reliability of the detection results.

[0023] (2) In the present invention, in step S2, the present invention sets a strict mass ratio of 2:3 between the digestion reagent and the agricultural product sample to ensure that the reagent can fully and evenly act on the sample during the digestion process, promote the effective release of heavy metal elements, and at the same time, through sufficient mixing of the stirring equipment, further improve the contact area and reaction efficiency between the sample and the reagent, which helps to completely extract the heavy metal elements from the sample matrix, reduce impurity interference, and improve the purity of the heavy metal elements in subsequent analysis.

[0024] (3) In the present invention, by combining microwave digestion with digestion process control, not only the evaporation loss of heavy metal elements in the digestion process is effectively reduced, but also the extraction purity and detection accuracy of heavy metal elements are significantly improved. The rapid heating and uniform heating characteristics of microwave digestion, combined with step-type temperature control, make the entire digestion process more efficient, stable and easy to control; in addition, by accurately controlling the ratio and mixing time of the digestion reagents, the efficient extraction and purification of heavy metal elements are further ensured. This method not only overcomes many shortcomings of traditional dry digestion, but also significantly improves the efficiency and accuracy of heavy metal detection in agricultural products, providing strong technical support for food safety and quality control. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art are briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative work.

[0026] Figure 1 It is a flow chart of a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited to the specific embodiments disclosed below.

[0029] like Figure 1 As shown, a method for detecting heavy metals in agricultural products comprises the following steps:

[0030] S1: Adjust the room temperature and ambient humidity to 60-80% RH. The humidity range of 60-80% RH ensures that the agricultural product samples are in the best condition before adding the digestion reagent, avoiding the problem of sample moisture absorption due to excessively high humidity or static electricity due to too low humidity, thereby ensuring the stability and efficiency of the subsequent digestion process. Subsequently, weigh the dried agricultural product samples and place them in a dedicated microwave digestion tank to prepare for the subsequent digestion process;

[0031] It should be noted that by using a constant temperature and humidity chamber to control the ambient humidity, the sample pre-treatment error caused by environmental factors is reduced, and the accuracy and repeatability of the test are improved. At the same time, the use of a microwave digestion tank as a container, taking advantage of its excellent heating uniformity and sealing, lays the foundation for subsequent efficient digestion. Agricultural product samples include rice, wheat, etc.

[0032] S2: Add an appropriate amount of digestion reagent to the microwave digestion tank, with the mass ratio of digestion reagent to agricultural product sample being 2:3, to ensure that the reagent can fully and not excessively act on the sample. Then, use a blender to mix, with the mixing time controlled within the range of 1-5 minutes, to achieve a rapid and uniform mixing state of the sample and reagent;

[0033] It should be noted that by controlling the amount of digestion reagent and mixing time, efficient mixing of samples and reagents is achieved, and the extraction efficiency of heavy metal elements is improved. At the same time, waste and pollution caused by excessive reagents are avoided, and the detection cost is reduced. The digestion reagent is a mixture of nitric acid and hydrogen peroxide, and the mass ratio of nitric acid to hydrogen peroxide is 2:3.

[0034] S3: Microwave digestion is performed using stepped temperature control, including three stages: low-temperature preheating, medium-temperature digestion, and high-temperature intensification, to digest the sample;

[0035] It should be noted that:

[0036] Low-temperature preheating stage: This stage is the beginning of the entire digestion process. The temperature is set in a relatively low range (80-120°C), and the microwave power is also kept at a moderate level (200-500W). Through gentle heating, the sample begins to gradually heat up, and the internal moisture and volatile components begin to slowly release. At the same time, the digestion reagent begins to contact the sample surface and react initially. The preheating time is between 10-30 minutes;

[0037] Medium-temperature digestion stage: After low-temperature preheating, the temperature gradually rises to the medium temperature range (150-200℃), and the microwave power is also increased to 500-800W accordingly. This stage is the core part of the entire digestion process. The organic matter in the sample begins to decompose in large quantities, and the heavy metal elements are gradually released from the sample matrix and form soluble compounds with the digestion reagent. The medium-temperature digestion lasts for a long time, generally between 30-60 minutes, to ensure that the organic matter can be fully decomposed;

[0038] High temperature intensification stage: After medium temperature digestion, the temperature is further increased to the high temperature range (200-250℃), and the microwave power also reaches the maximum value (800-1000W); this stage is the intensification stage of the digestion process, which aims to completely decompose the remaining organic matter in the sample and ensure that all heavy metal elements are effectively extracted; the high temperature intensification stage lasts for a long time, generally between 60-100 minutes, to ensure the thoroughness of the digestion process.

[0039] Low-temperature preheating effectively avoids violent reactions of samples caused by sudden high temperatures, reduces the risk of sample splashing and container rupture, and promotes the initial mixing and reaction of samples and digestion reagents, laying a good foundation for the subsequent medium-temperature and high-temperature digestion stages; the medium-temperature digestion stage accelerates the decomposition process of organic matter and improves the extraction efficiency of heavy metal elements by increasing temperature and power, while avoiding direct evaporation losses of heavy metal elements at high temperatures, ensuring the accuracy of the test results. In addition, medium-temperature conditions also help reduce side reactions between samples and digestion reagents, improve the purity of the digestion solution and the reliability of subsequent analysis; the high-temperature intensification stage achieves a thorough decomposition of organic matter in the sample and efficient extraction of heavy metal elements through heating and microwave radiation under extreme conditions, which not only improves the digestion efficiency, but also ensures the comprehensiveness and accuracy of the test results, and helps to destroy the complex structures that may exist in the sample, reducing interference factors for the detection of heavy metal elements.

[0040] S4: After digestion is completed, let the digestion tank cool naturally for 30-60 minutes to ensure that the internal pressure is safely released and the digestion solution temperature drops to 20-30°C. Open the digestion tank, transfer the digestion solution to a clean container, and dilute it appropriately for subsequent analysis. The diluted digestion solution is tested for heavy metal elements using high-precision analytical methods such as ICP-MS or AAS atomic absorption spectroscopy.

[0041] It should be noted that the natural cooling process ensures the safety of the digestate during transfer and avoids dangers and errors caused by high temperature. The diluted digestate is tested by high-precision analysis methods, which can accurately and quickly determine the content of heavy metal elements in agricultural products, providing reliable data support for food safety and quality control. At the same time, this step also reflects the standardization and normalization of the testing process, and improves the credibility and comparability of the test results.

[0042] Embodiment 1:

[0043] Heavy metal testing of wheat was performed using the above method;

[0044] S1: Use a constant temperature and humidity chamber to adjust the room temperature and humidity of the laboratory to 65% RH to ensure a stable environment; weigh 0.5 g of dried wheat and place it in a microwave digestion tank.

[0045] S2: According to the mass of wheat, calculate and measure 1.0g of a mixture of nitric acid and hydrogen peroxide in a mass ratio of 2:3, slowly add it to the digestion tank, and use a blender to mix the wheat and the mixture of nitric acid and hydrogen peroxide in the microwave digestion tank for 3 minutes until the wheat and the mixture of nitric acid and hydrogen peroxide are evenly mixed.

[0046] S3: Place the microwave digestion tank in the microwave digestion instrument, set the temperature to 100℃, the microwave power to 300W, and preheat for 20 minutes; after the preheating is completed, it automatically rises to 180℃, and the microwave power increases to 600W, and medium-temperature digestion is carried out for 45 minutes; after the medium-temperature digestion is completed, the temperature is further raised to 220℃, the microwave power reaches the maximum value of 900W, and high-temperature enhanced digestion is carried out for 80 minutes.

[0047] S4: After digestion is completed, let the digestion tank cool naturally to room temperature for 50 minutes to ensure that the internal pressure is safely released and the temperature of the digestion solution drops to 25°C. Open the microwave digestion tank, carefully transfer the digestion solution to a clean container, and dilute it to 10mL with high-purity water to ensure the sensitivity of ICP-MS analysis. Use the ICP-MS instrument to perform quantitative analysis of the lead element on the diluted digestion solution.

[0048] Embodiment 2: This embodiment is basically the same as Embodiment 1, except that: in S3, the microwave digestion tank is placed in a microwave digestion instrument, the temperature is set to 100°C, the microwave power is 200W, and preheating is performed for 20min; after the preheating is completed, it is automatically raised to 180°C, the microwave power is increased to 600W, and medium-temperature digestion is performed for 45min; after the medium-temperature digestion is completed, the temperature is further raised to 220°C, the microwave power reaches a maximum value of 900W, and high-temperature enhanced digestion is performed for 80min.

[0049] Embodiment 3: This embodiment is basically the same as Embodiment 1, except that: in S3, the microwave digestion tank is placed in a microwave digestion instrument, the temperature is set to 100°C, the microwave power is 500W, and preheating is performed for 20min; after the preheating is completed, it is automatically raised to 180°C, the microwave power is increased to 600W, and medium-temperature digestion is performed for 45min; after the medium-temperature digestion is completed, the temperature is further raised to 220°C, the microwave power reaches a maximum value of 900W, and high-temperature enhanced digestion is performed for 80min.

[0050] Embodiment 4: This embodiment is basically the same as Embodiment 1, except that: in S3, the microwave digestion tank is placed in a microwave digestion instrument, the temperature is set to 100°C, the microwave power is 300W, and preheating is performed for 20min; after the preheating is completed, it is automatically raised to 180°C, the microwave power is increased to 500W, and medium-temperature digestion is performed for 45min; after the medium-temperature digestion is completed, the temperature is further raised to 220°C, the microwave power reaches a maximum value of 900W, and high-temperature enhanced digestion is performed for 80min.

[0051] Embodiment 5: This embodiment is basically the same as Embodiment 1, except that: in S3, the microwave digestion tank is placed in a microwave digestion instrument, the temperature is set to 100°C, the microwave power is 300W, and preheating is performed for 20min; after the preheating is completed, it is automatically raised to 180°C, the microwave power is increased to 800W, and medium-temperature digestion is performed for 45min; after the medium-temperature digestion is completed, the temperature is further raised to 220°C, the microwave power reaches a maximum value of 900W, and high-temperature enhanced digestion is performed for 80min.

[0052] Embodiment 6: This embodiment is basically the same as Embodiment 1, except that: in S3, the microwave digestion tank is placed in a microwave digestion instrument, the temperature is set to 100°C, the microwave power is 300W, and preheating is performed for 20min; after the preheating is completed, it is automatically raised to 180°C, the microwave power is increased to 600W, and medium-temperature digestion is performed for 45min; after the medium-temperature digestion is completed, the temperature is further raised to 220°C, the microwave power reaches a maximum value of 800W, and high-temperature enhanced digestion is performed for 80min.

[0053] Embodiment 7: This embodiment is basically the same as Embodiment 1, except that: in S3, the microwave digestion tank is placed in a microwave digestion instrument, the temperature is set to 100°C, the microwave power is 300W, and preheating is performed for 20min; after the preheating is completed, it is automatically raised to 180°C, the microwave power is increased to 600W, and medium-temperature digestion is performed for 45min; after the medium-temperature digestion is completed, the temperature is further raised to 220°C, the microwave power reaches a maximum value of 1000W, and high-temperature enhanced digestion is performed for 80min.

[0054] Observe the change in solution volume: During the digestion process, regularly observe and record the change in solution volume. (If the solution volume decreases significantly, then the evaporation loss is large; if the solution volume decreases slightly, then the evaporation loss is small).

[0055] Table 1:

[0056]

[0057]

[0058] It can be seen from Table 1 that Example 1, Example 2 and Example 3 used microwave powers of 300 W, 200 W and 500 W for preheating respectively.

[0059] Heavy metal detection results: The lead (Pb) concentration is relatively stable at different powers, with a small difference of 0.138 mg / kg for Example 1 (300 W), 0.137 mg / kg for Example 2 (200 W), and 0.140 mg / kg for Example 3 (500 W). The cadmium (Cd) concentration decreases slightly with decreasing power, with a small difference of 0.015 mg / kg for Example 1 (300 W), 0.013 mg / kg for Example 2 (200 W), and 0.011 mg / kg for Example 3 (500 W).

[0060] Summary: It can be seen that the 300W microwave power provides relatively stable heavy metal detection results while maintaining low evaporation losses.

[0061] Table 2:

[0062]

[0063] It can be seen from Table 2 that Example 1, Example 4 and Example 5 used microwave powers of 600 W, 500 W and 800 W respectively for medium-temperature digestion.

[0064] Heavy metal detection results: the lead (Pb) concentration is the lowest (0.131 mg / kg) in Example 4 (500 W), 0.137 mg / kg in Example 1 (600 W), and the highest (0.149 mg / kg) in Example 5 (800 W); the cadmium (Cd) concentration is also the lowest (0.012 mg / kg) in Example 4, 0.014 mg / kg in Example 1, and 0.010 mg / kg in Example 5.

[0065] Summary: In the medium-temperature digestion stage, a microwave power of 500 W can provide lower heavy metal detection results, but both high power (800 W) and low power (500 W) may lead to higher evaporation losses. A microwave power of 600 W provides relatively stable heavy metal detection results while maintaining low evaporation losses.

[0066] Table 3:

[0067]

[0068] It can be seen from Table 3 that the lead (Pb) detection result in Example 1 (0.137 mg / kg) is between Example 6 (0.131 mg / kg) and Example 7 (0.133 mg / kg), indicating that at a power of 900 W, the lead release and detection results are relatively stable and not easily affected by power fluctuations; the evaporation loss in Example 1 is estimated to be "trace", which is significantly lower than the "significant" evaporation loss in Examples 6 and 7, meaning that at a power of 900 W, the effective ingredients in the sample can be better retained, reducing errors and losses caused by evaporation, thereby improving the accuracy and reliability of the detection results.

[0069] Comparative Example:

[0070] The embodiments are basically the same, except that: in S3, the wheat is ashed by an ashing method, the heating temperature is 500° C., and the ashing time is 5 h.

[0071] Table 2:

[0072]

[0073] It can be seen from Table 1 that the evaporation loss of heavy metals in the embodiment is estimated to be trace, indicating that the evaporation loss of heavy metals is effectively controlled; the evaporation loss of the comparative example is estimated to be significant, indicating that the high temperature and open environment during the ashing process lead to the loss of some volatile heavy metals, indicating that the embodiment shows higher accuracy in extracting heavy metals from wheat.

[0074] The above is based on the ideal embodiment of the present invention. Through the above description, relevant personnel can make various changes and modifications without departing from the technical concept of the present invention. The technical scope of the present invention is not limited to the content in the specification, and the technical scope must be determined according to the scope of the claims.

Claims

1. A method for detecting heavy metals in agricultural products, characterized in that: The following steps are involved: S1: Adjust the room temperature and humidity, weigh the dried agricultural product samples, and place them in a special digestion tank; S2: Add an appropriate amount of digestion reagent into the digestion tank and mix using a stirring device; S3: Microwave digestion is performed using stepped temperature control, including three stages: low-temperature preheating, medium-temperature digestion, and high-temperature intensification, to digest the sample; S4: After digestion is completed, open the digestion tank after natural cooling, transfer the digestion solution to a clean container, and dilute it for subsequent analysis.

2. A method for detecting heavy metals in agricultural products according to claim 1, characterized in that: In the step S1, the adjustment range of the room temperature humidity is set to 60-80% RH to ensure that the agricultural product sample is under suitable humidity conditions before the digestion reagent is added.

3. A method for detecting heavy metals in agricultural products according to claim 1, characterized in that: In S1, the digestion tank is a microwave digestion tank.

4. A method for detecting heavy metals in agricultural products according to claim 1, characterized in that: In S2, the mass ratio of the digestion reagent to the agricultural product sample is in the range of 1-3:2-4, and the stirring device is a stirrer, which is used to promote the full mixing of the agricultural product sample and the digestion reagent.

5. A method for detecting heavy metals in agricultural products according to claim 4, characterized in that: In the step S2, the mixing time ranges from 1 to 5 minutes to ensure that the sample and the reagent are uniformly mixed in a short time.

6. A method for detecting heavy metals in agricultural products according to claim 1, characterized in that: In S3, the low-temperature preheating temperature ranges from 80 to 120° C., the microwave power ranges from 200 to 500 W, and the duration ranges from 10 to 30 min.

7. A method for detecting heavy metals in agricultural products according to claim 1, characterized in that: In S3, the temperature of the medium-temperature digestion stage ranges from 150 to 200°C, the microwave power ranges from 500 to 800W, and the duration ranges from 30 to 60 minutes.

8. A method for detecting heavy metals in agricultural products according to claim 1, characterized in that: In S3, the high temperature strengthening temperature ranges from 200 to 250°C, the microwave power ranges from 800 to 1000W, and the duration ranges from 60 to 100 minutes.

9. A method for detecting heavy metals in agricultural products according to claim 1, characterized in that: In the S4, the natural cooling time ranges from 30 to 60 minutes, ensuring that the internal pressure of the digestion tank is safely released and the temperature of the digestion solution is reduced to a processing range, and the processing range of the digestion solution temperature is 20-30°C.

10. A method for detecting heavy metals in agricultural products according to claim 1, characterized in that: In S4, the diluted digestion solution is subjected to heavy metal element detection using an analytical method such as ICP-MS or AAS atomic absorption spectroscopy.

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