Rapid detection method for heavy metals in agricultural soil

Abstract

The invention provides an agricultural soil heavy metal rapid detection method, and belongs to the technical field of heavy metal detection.The method comprises the steps that a sample is pretreated, a soil sample is air-dried and then ground, and the ground soil sample is sieved through a 100-mesh sieve; digesting graphite, weighing a sample, adding aqua regia, and digesting in a graphite digestion instrument; iCP-MS detection parameter optimization is carried out, and optimal working parameters of an instrument are determined; quantitative analysis is performed, and a standard curve is drawn; result analysis: calculating the content of heavy metal elements in the soil according to a calculation formula; high-flux detection of mercury and arsenic pollution is realized through combination of an integrated pretreatment process and an instrument, a corrosion-resistant centrifugal tube is taken as an integrated reaction container, a dynamic digestion system of a graphite digestion instrument is combined, and the addition amount and extraction time of aqua regia are optimized, so that the reagent consumption is remarkably reduced on the premise of ensuring full-amount extraction of a target object, and the detection efficiency is improved. Meanwhile, the pollution risk and element loss caused by sample transfer in a traditional method are eliminated.

Description

Technical Field

[0001] The present invention belongs to the technical field of heavy metal detection, and particularly relates to a rapid detection method for heavy metals in agricultural soil. Background Art

[0002] Heavy metal pollution in agricultural soil usually comes from industrial emissions, the use of pesticides and fertilizers, sewage irrigation, etc. Common heavy metals include cadmium, lead, arsenic, mercury, chromium, etc. Mercury and arsenic show strong biotoxicity and migration activity in the soil, seriously threatening the ecosystem and public health. Mercury is easily converted into fat-soluble methylmercury under flooded conditions, which can cause nervous system damage after being enriched and amplified by rice. Arsenic destroys plant cell metabolism in the form of trivalent arsenic, leading to crop yield reduction or even crop failure, and inducing diseases such as skin cancer and bladder cancer through drinking water or agricultural products. Detecting heavy metals in agricultural soil is a core measure to ensure food security and ecological balance. By accurately identifying the spatial distribution and concentration levels of pollution elements such as cadmium, lead, arsenic, and mercury, it is possible to effectively block the entry of pollutants into the food chain through crop absorption, reducing the risk of chronic poisoning in the population. At the same time, it provides a scientific basis for the selection of remediation technologies for polluted farmland, contributing to the sustainable development of agriculture.

[0003] Currently, the detection of mercury and arsenic in soil and sediment mainly relies on atomic fluorescence spectrometry. However, due to its support for only single-element detection mode, it is difficult to achieve multi-element synchronous analysis, and there are significant technical bottlenecks in the detection scenario of batch samples. Its operation process involves complex pretreatment steps (such as aliquoting, digestion, reduction, etc.), resulting in high reagent consumption, rising detection costs, and generating a large amount of heavy metal-containing waste liquid, increasing the risk of environmental secondary pollution. In addition, the long sample processing link makes the single-batch detection cycle usually up to several hours, seriously restricting the detection throughput and making it difficult to meet the actual needs of large-scale soil pollution screening and rapid response. In view of the above problems, the present invention proposes a rapid detection method for heavy metals in agricultural soil, mainly for conventional agricultural soil (such as cultivated land, orchards, etc.), and is particularly suitable for soils with low organic matter content. Summary of the Invention

[0004] The object of the present invention is to address the above problems existing in the prior art and propose a rapid detection method for heavy metals in agricultural soil.

[0005] The object of the present invention can be achieved by the following technical solutions: A rapid detection method for heavy metals in agricultural soil, characterized by comprising: S1. Sample pretreatment: Air-dry the soil sample, grind it, pass it through a 100-mesh sieve, mix it evenly, and then seal and store it; S2. Graphite digestion: Weigh 0 - 1 g of the sample and place it in a digestion tube. Add 5 - 10 mL of aqua regia and 0.2 - 0.5 g of ammonium persulfate powder. After stirring and dissolving, tighten the lid and rotate it once. Place it in a graphite digestion instrument and maintain at 80 - 120 °C for 1 - 4 h. After opening the lid, continue heating to drive off the acid. When the solution remains 2 - 3 mL, add 0.1 g of thiourea and 0.05 g of ascorbic acid. Take it out and cool to room temperature. Add 2 mL of ultrapure water, then add 0.2 mL of electrolyte, vortex and mix evenly, make up the volume and shake well for measurement; Aqua regia, also known as nitrohydrochloric acid, is a highly corrosive liquid that emits yellow fumes. It is a mixture composed of concentrated hydrochloric acid (HCl) and concentrated nitric acid (HNO 3 ) in a volume ratio of 3:1. It is one of the few liquids that can dissolve gold and has strong corrosiveness; at low temperatures (80 - 120 °C), ammonium persulfate ((NH 4 ) 2 S 2 O 8 ) decomposes under acidic conditions to generate sulfate radicals (SO 4 - ), effectively oxidizing As 3+ to As 5+ and significantly reducing the volatilization risk of AsCl 3 . This conforms to the low-temperature oxidation theory. In addition, thiourea ((NH 2 ) 2 CS) forms a stable complex with As 3+ in an acidic medium, which can directly inhibit the formation of AsCl 3 . Ascorbic acid (C 6 H 8 O 6 ) is used as a reducing agent to eliminate the interference of oxidizing ions such as Fe 3+ on the ICP-MS signal.

[0006] S3. Optimization of ICP-MS detection parameters: Use a 1.00 μg / L ICP-MS tuning solution to optimize the instrument's indicators and determine the best working parameters of the instrument; S4. Quantitative analysis: Prepare a standard series of mixed concentration points containing 0 - 10.0 μg / L of mercury and 0 - 100.0 μg / L of arsenic. Add the internal standard working solution online and mix it with the sample. Use ICP-MS to measure and plot the standard curve; Among them, the concentration ranges of mercury (0 - 10 μg / L) and arsenic (0 - 100 μg / L) cover the common heavy metal pollution levels in agricultural soils.

[0007] S5. Result analysis: Calculate the content of heavy metal elements in the soil according to the calculation formula.

[0008] Preferably, in step S1, the soil sample is conventional agricultural soil, including cultivated land or orchards; After the soil sample is air-dried and ground according to the standard requirements, it is first passed through a 10-mesh nylon sieve, and then a part of the sample passing through the 10-mesh nylon sieve is taken out by the quartering method and ground continuously until it all passes through a 100-mesh nylon sieve.

[0009] Among them, the quartering method for sample division is convenient for reducing the error caused by particle size differences, ensuring the uniformity of the test sample. By sieving in stages from 10 meshes to 100 meshes, it effectively avoids the time-consuming of directly grinding to a fine sieve, facilitates optimizing the efficiency, improves the sample pretreatment efficiency. In addition, using nylon sieve material is convenient for avoiding metal contamination. If a stainless steel sieve is used, Fe and Cr interference may be introduced.

[0010] Preferably, in step S2, when weighing the sample, the mass of the sample is accurate to 0.1 mg, with high-precision weighing. Especially for trace mercury or arsenic, it is convenient for reducing the concentration deviation caused by weighing error, improving the reliability of the detection data, and meeting the matrix matching requirements for low-concentration detection by ICP-MS.

[0011] Preferably, in step S2, when the sample is digested in a graphite digester, first pre-react at 80 °C for 30 min, then raise the temperature to 110 °C and maintain for 1 - 2 h, and finally raise the temperature to 120 °C and maintain for 1 - 2 h to ensure complete digestion; Among them, the 30-min pre-reaction at 80 °C is used to activate ammonium persulfate and preliminarily oxidize easily decomposable organic matter; the 1 - 2 h maintenance at 110 °C is the main digestion stage, and most of the organic matter decomposition is completed at a low temperature; the 1 - 2 h acid expulsion at 120 °C, slowly evaporating to 2 - 3 mL, can avoid the loss of As. The overall process temperature is always ≤120 °C, avoiding the AsCl 3 volatilization threshold (130 °C) and meeting the digestion requirements at the same time.

[0012] The electrolyte includes tris(hexafluoroisopropyl) phosphite and tris(2,2,2-trifluoroethyl) borate; Among them, the ratio of tris(hexafluoroisopropyl) phosphite to tris(2,2,2-trifluoroethyl) borate is 1:1.

[0013] Tris(hexafluoroisopropyl) phosphite and tris(2,2,2-trifluoroethyl) borate (1:1) as fluorinated organic esters may inhibit the corrosion of the ICP-MS cone by Cl - residue in the digestion solution and complex trace metal ions, reducing matrix interference, thereby improving the detection stability.

[0014] Preferably, in step S2, in addition to all the samples, a blank sample is prepared separately; Among them, for the blank sample, no soil sample is added, and the remaining steps are the same as those for the sample with soil added.

[0015] By setting the blank, background subtraction is achieved to eliminate the background values introduced by reagent, environmental, and vessel contamination. The contamination risk during the experiment is monitored through the blank value, such as insufficient purity of aqua regia or environmental Hg contamination, thereby improving the detection accuracy.

[0016] Preferably, in step S3, the optimal parameters are: nebulizer flow rate 0.95 L / min; auxiliary gas flow rate 1.2 L / min; plasma gas flow rate 15 L / min; inductively coupled plasma radio frequency power 1400 W; peristaltic pump rotation speed 35 r / min; oxide (CeO / Ce) ≤ 0.025; double charge (Ce++ / Ce) ≤ 0.03.

[0017] A low nebulizer flow rate (0.95 L / min) is conducive to increasing the atomization efficiency, improving the signal intensity, and enhancing the sensitivity; the matching of the auxiliary gas and plasma gas flow rates (1.2 / 15 L / min) is conducive to maintaining the plasma stability, reducing signal fluctuations, and enhancing the stability; strictly restricting CeO / Ce (≤ 0.025) and Ce++ / Ce (≤ 0.03) ensures low oxide and double charge interferences, which is applicable to the precise determination of As and Hg.

[0018] Preferably, in step S4, when preparing the standard series solution of mercury, according to the principle of stepwise dilution, standard series mixed concentration points containing 1.00 μg / L, 2.00 μg / L, 4.00 μg / L, 6.00 μg / L, 8.00 μg / L, and 10.0 μg / L of mercury are prepared respectively.

[0019] Preferably, in step S4, when preparing the standard series solution of arsenic, according to the principle of stepwise dilution, standard series mixed concentration points containing 10.00 μg / L, 20.00 μg / L, 40.00 μg / L, 60.00 μg / L, 80.00 μg / L, and 100.0 μg / L of arsenic are prepared respectively.

[0020] Preferably, in step S4, the internal standard working solution 72 Ge, 185 Re is added online through a tee and mixed with the sample, and ICP-MS in the collision cell mode is used for determination; Among them, when drawing the standard curve, the mass concentration is used as the abscissa, and the ratio of the corresponding response value to the internal standard response value is used as the ordinate to draw the calibration curves of mercury and arsenic.

[0021] Ge and Re respectively compensate for Hg (volatile) and As (affected by ArCl +Signal drift (interference) is corrected, and matrix effects are compensated; polyatomic ion interference is eliminated in the collision cell mode; the internal standard ratio method (response value / internal standard value) reduces the impact of injection fluctuations on the results, facilitating the improvement of precision.

[0022] Preferably, in step S5, the calculation formula for the contents C (mg / kg) of mercury and arsenic elements in the soil is: C (mg / kg) = (C 1 - C 0 )·V·K / m·1000 where C 1 is the concentration of the substance to be measured, with the unit of μg / L; where C 0 is the concentration of the analyte in the blank solution, with the unit of μg / L; where V is the volume of constant volume, with the unit of mL; where m is the sample weighing amount, with the unit of g; where K is the dilution factor of the sample.

[0023] Compared with the prior art, the rapid detection method for heavy metals in agricultural soil of the present invention has the following beneficial effects: 1. A rapid detection method for heavy metals in agricultural soil provided by the present invention uses a centrifuge tube as a reaction vessel, combines a gradient temperature control system of a graphite digestion instrument to achieve dynamic digestion, synchronously couples an inductively coupled plasma mass spectrometry (ICP-MS) detection technology, and establishes a quantitative analysis system for mercury (Hg) and arsenic (As), shortening the overall detection time.

[0024] 2. A rapid detection method for heavy metals in agricultural soil provided by the present invention uses a sealed centrifuge tube as a processing container, which is convenient and fast, has few pollution factors, high sample extraction efficiency, reduces the transfer steps in the pretreatment process, and minimizes the risk of introducing pollution and losing analytes.

[0025] 3. A rapid detection method for heavy metals in agricultural soil provided by the present invention optimizes the digestion system through a gradient digestion experimental system, determines the optimal addition amount of aqua regia, so that it can not only achieve the full extraction of the target substance, ensure data accuracy, but also reduce the waste of reagents.

[0026] 4. A rapid detection method for heavy metals in agricultural soil provided by the present invention determines the optimal sample extraction time by establishing different sample extraction times and exploring the influence of sample extraction time on the detection results, so as to not only break through the dissolution threshold of heavy metals, ensure detection accuracy, but also avoid the ineffective loss of reagents and the reduction of equipment life caused by over-digestion.

[0027] 5. A rapid detection method for heavy metals in agricultural soil provided by the present invention. By verifying the detection limit, precision, and accuracy of the method, it is proved that the method has a low detection limit, and both the precision and accuracy meet the analysis requirements, and it can be accurately used for the determination of mercury and arsenic in soil and sediment.

[0028] In summary, the present invention provides a rapid detection method for heavy metals in agricultural soil. Through an integrated pretreatment process combined with instrument coupling, high-throughput detection of mercury and arsenic pollution is achieved. Using corrosion-resistant centrifuge tubes as integrated reaction vessels, combined with a dynamic digestion system of a graphite digestion instrument, by optimizing the addition amount of aqua regia and extraction time, reagent consumption is significantly reduced on the premise of ensuring the complete extraction of target substances, and at the same time, the pollution risk and element loss caused by sample transfer in traditional methods are eliminated. Description of the Drawings

[0029] Figure 1 It is the standard curve graph of mercury element in Specific Example Two.

[0030] Figure 2 It is the standard curve graph of arsenic element in Specific Example Two. Detailed Embodiments

[0031] The following are specific examples of the present invention in combination with the drawings, and the technical solutions of the present invention will be further described, but the present invention is not limited to these examples. Specific Example One:

[0032] A rapid detection method for heavy metals in agricultural soil includes: S1. Sample pretreatment: Air-dry the soil sample, grind it, pass it through a 100-mesh sieve, mix it evenly, and store it sealed. S2. Graphite digestion: Weigh 0 - 1 g of the sample and place it in a digestion tube, add 5 - 10 mL of aqua regia, add 0.2 - 0.5 g of ammonium persulfate powder, stir to dissolve, tighten the lid and turn it around once, place it in a graphite digestion instrument, maintain at 80 - 120 °C for 1 - 4 h, continue to heat and drive off the acid after opening the lid. When the solution remains 2 - 3 mL, add 0.1 g of thiourea and 0.05 g of ascorbic acid, take it out and cool to room temperature, add 2 mL of ultrapure water, then add 0.2 mL of electrolyte, vortex and mix evenly, and make up the volume and shake well for measurement. Aqua regia, also known as nitrohydrochloric acid, is a very corrosive liquid that emits yellow fumes. It is a mixture composed of concentrated hydrochloric acid (HCl) and concentrated nitric acid (HNO 3 ) in a volume ratio of 3:1. It is one of the few liquids that can dissolve gold and has strong corrosiveness. At low temperatures (80 - 120 °C), ammonium persulfate ((NH 4 ) 2 S 2 O 8 ) decomposes under acidic conditions to generate sulfate radicals (SO4 - ), effectively oxidizes As 3+ to As 5+ , significantly reducing the volatilization risk of AsCl 3 , in line with the low-temperature oxidation theory. Additionally, thiourea ((NH 2 )) 2 CS) forms a stable complex with As 3+ in an acidic medium, capable of directly inhibiting the formation of AsCl 3 . Ascorbic acid (C 6 H 8 O 6 ), as a reducing agent, is used to eliminate the interference of oxidizing ions such as Fe 3+ on the ICP-MS signal.

[0033] S3. Optimization of ICP-MS detection parameters: Use a 1.00 μg / L ICP-MS tuning solution to optimize the instrument's indicators and determine the best working parameters of the instrument; S4. Quantitative analysis: Prepare a standard series of mixed concentration points containing 0 - 10.0 μg / L of mercury and 0 - 100.0 μg / L of arsenic. Add the internal standard working solution online, mix it with the sample, and use ICP-MS for determination to plot the standard curve; Among them, the concentration ranges of mercury (0 - 10 μg / L) and arsenic (0 - 100 μg / L) cover the common heavy metal pollution levels in agricultural soils.

[0034] S5. Result analysis: Calculate the content of heavy metal elements in the soil according to the calculation formula.

[0035] In step S1, the soil sample is conventional agricultural soil, including cultivated land or orchards; Among them, after the soil sample is air-dried and ground according to the standard requirements, it is first passed through a 10-mesh nylon sieve, and then a part of the sample passing through the 10-mesh nylon sieve is taken out by the quartering method and ground continuously until it all passes through a 100-mesh nylon sieve.

[0036] Among them, using the quartering method for sub-sampling is convenient for reducing the error caused by particle size differences, ensuring the uniformity of the test sample. By sieving in stages, from 10 mesh to 100 mesh, it effectively avoids the time-consuming of directly grinding to a fine sieve, is convenient for optimizing efficiency, and improves the pre-treatment efficiency of the sample. Additionally, using nylon sieve material is convenient for avoiding metal contamination. If a stainless steel sieve is used, it may introduce Fe and Cr interference.

[0037] In step S2, when weighing the sample, the mass of the sample is accurate to 0.1 mg, with high-precision weighing. Especially for trace mercury or arsenic, it is convenient for reducing the concentration deviation caused by weighing error, improving the reliability of the detection data, and meeting the matrix matching requirements of ICP-MS for low-concentration detection.

[0038] In step S2, when the sample is digested in a graphite digester, it is first pre-reacted at 80 °C for 30 min, heated to 110 °C and maintained for 1 - 2 h, and finally raised to 120 °C and maintained for 1 - 2 h to ensure complete digestion; Among them, the pre-reaction at 80 °C for 30 min is used to activate ammonium persulfate and initially oxidize easily decomposable organic matter; the maintenance at 110 °C for 1 - 2 h is the main digestion stage, and most of the organic matter is decomposed at low temperature; the acid expulsion at 120 °C for 1 - 2 h, slowly evaporating to 2 - 3 mL, can avoid the loss of As, and the temperature throughout the whole process is always ≤120 °C, avoiding the AsCl 3 volatilization threshold (130 °C), while meeting the digestion requirements.

[0039] The electrolyte includes tris(hexafluoroisopropyl) phosphite and tris(2,2,2-trifluoroethyl) borate; Among them, the ratio of tris(hexafluoroisopropyl) phosphite to tris(2,2,2-trifluoroethyl) borate is 1:1.

[0040] Tris(hexafluoroisopropyl) phosphite and tris(2,2,2-trifluoroethyl) borate (1:1) as fluorinated organic esters may inhibit the corrosion of the ICP-MS cone by Cl - residue and complex trace metal ions, reducing matrix interference, thereby improving the detection stability.

[0041] In step S2, in addition to all the samples, blank samples are prepared separately; Among them, the blank samples do not add soil samples, and the remaining steps are the same as those of the samples with soil samples added.

[0042] By setting the blank, background subtraction is achieved, eliminating the background value introduced by reagent, environment and vessel contamination, and monitoring the pollution risk of the experimental process through the blank value, such as insufficient purity of aqua regia or environmental Hg pollution, thereby improving the detection accuracy.

[0043] In step S3, the optimal parameters are: nebulizer flow rate 0.95 L / min; auxiliary gas flow rate 1.2 L / min; plasma gas flow rate 15 L / min; inductively coupled plasma radio frequency power 1400 W; peristaltic pump rotation speed 35 r / min; oxide (CeO / Ce) ≤0.025; double charge (Ce++ / Ce) ≤0.03.

[0044] A low nebulizer flow rate (0.95 L / min) facilitates increasing the atomization efficiency, enhancing the signal intensity, and improving the sensitivity; the matching of the auxiliary gas and plasma gas flow rates (1.2 / 15 L / min) facilitates maintaining the plasma stability, reducing the signal fluctuations, and enhancing the stability; strictly limiting CeO / Ce (≤0.025) and Ce++ / Ce (≤0.03) ensures low oxide and double-charge interferences and is applicable to the accurate determination of As and Hg.

[0045] In step S4, when preparing the standard series solution of mercury, according to the principle of stepwise dilution, standard series mixed concentration points containing 1.00 μg / L, 2.00 μg / L, 4.00 μg / L, 6.00 μg / L, 8.00 μg / L, and 10.0 μg / L of mercury are prepared respectively.

[0046] In step S4, when preparing the standard series solution of arsenic, according to the principle of stepwise dilution, standard series mixed concentration points containing 10.00 μg / L, 20.00 μg / L, 40.00 μg / L, 60.00 μg / L, 80.00 μg / L, and 100.0 μg / L of arsenic are prepared respectively.

[0047] In step S4, the internal standard use solution 72 Ge, 185 Re is added online through a tee to be mixed with the sample, and ICP-MS in the collision cell mode is used for determination; Among them, when drawing the standard curve, the mass concentration is used as the abscissa, and the ratio of the corresponding response value to the internal standard response value is used as the ordinate to draw the calibration curves of mercury and arsenic.

[0048] Ge and Re respectively compensate for the signal drifts of Hg (volatile) and As (affected by ArCl + interference), correct the matrix effect; the collision cell mode eliminates the polyatomic ion interference; the internal standard ratio method (response value / internal standard value) reduces the influence of the injection fluctuation on the result and is convenient for improving the precision.

[0049] In step S5, the calculation formula for the contents C (mg / kg) of mercury and arsenic elements in the soil is: C (mg / kg) = (C 1 - C 0 ) · V · K / m · 1000 Among them, C 1 is the concentration of the substance to be measured, with the unit of μg / L; Among them, C 0 is the concentration of the analyte in the blank solution, with the unit of μg / L; Among them, V is the fixed volume, with the unit of mL; Among them, m is the sample weighing amount, with the unit of g; Among them, K is the dilution factor of the sample. Specific Example 2:

[0050] Specific Example 2 is for the preparation of the standard curves of mercury and arsenic mentioned in Specific Example 1. The content of Specific Example 2 is as follows: According to the principle of stepwise dilution, standard series mixed concentration points containing mercury at 1.00 μg / L, 2.00 μg / L, 4.00 μg / L, 6.00 μg / L, 8.00 μg / L, 10.0 μg / L and standard series mixed concentration points containing arsenic at 10.00 μg / L, 20.00 μg / L, 40.00 μg / L, 60.00 μg / L, 80.00 μg / L, 100.0 μg / L are prepared respectively. The internal standard use solution 72 Ge, 185 Re is added online through a three-way tube, mixed with the sample, and determined by ICP-MS in the collision cell mode; Among them, when drawing the standard curve, the mass concentration is used as the abscissa, and the ratio of the corresponding response value to the internal standard response value is used as the ordinate to draw the calibration curves of mercury and arsenic.

[0051] Ge and Re respectively compensate for the signal drift of Hg (volatile) and As (affected by ArCl + interference), correct the matrix effect; the collision cell mode eliminates polyatomic ion interference; the internal standard ratio method (response value / internal standard value) reduces the influence of injection fluctuation on the result and is convenient for improving the precision.

[0052] The standard curve of mercury is as Figure 1 shown, and the standard curve of arsenic is as Figure 2 shown. Specific Example 3:

[0053] Specific Example 3 is an optimization test for the addition amount of aqua regia mentioned in Specific Example 1. Aqua regia is a mixture composed of concentrated hydrochloric acid (HCl) and concentrated nitric acid (HNO 3 ) in a volume ratio of 3:1. The content of Specific Example 2 is as follows: 1. Prepare the sample Air-dry the soil sample according to the standard requirements, grind it, first pass it through a 10-mesh nylon sieve, then take a part of the sample that has passed through the 10-mesh nylon sieve by the quartering method and continue to grind it until it all passes through a 100-mesh nylon sieve. After mixing evenly, seal and store it. Weigh 0.2 g of the sample into a 50-mL centrifuge tube (accurate to 0.1 mg). Use soil reference materials GSS-23 and GSS-34, and measure five portions of each reference material respectively. Add 5 - 10 mL of aqua regia (volume ratio of hydrochloric acid / nitric acid is 3:1), add 0.2 - 0.5 g of ammonium persulfate powder, stir to dissolve, then tighten the lid and rotate it once. Among them, the addition amounts of aqua regia are 5.0, 6.0, 7.0, 8.0, 9.0, and 10.0 mL respectively. According to the above steps, prepare blank samples without adding soil samples.

[0054] 2. Digestion test Place the sample in a graphite digestion instrument. First, pre-react at 80 °C for 30 min, then raise the temperature to 110 °C and maintain it for 1 - 2 h, and finally raise it to 120 °C and maintain it for 1 - 2 h to ensure complete digestion. Open the lid and continue heating to drive off the acid. When the solution remains 2 - 3 mL, add 0.1 g of thiourea and 0.05 g of ascorbic acid, take it out and cool it to room temperature, add 2 mL of ultrapure water, then add 0.2 mL of electrolyte (tris(hexafluoroisopropyl) phosphite and tris(2,2,2-trifluoroethyl) borate = 1:1), vortex and mix evenly, make up the volume and shake well, and take the supernatant for ICP-MS determination.

[0055] 3. Results

[0056] The extraction efficiency of the sample has a significant correlation with the amount of aqua regia used. Optimizing its addition amount is a key technical link to ensure the accuracy of detection and economic environmental protection. Insufficient amount of aqua regia will cause incomplete extraction of target substances (such as Hg, As), resulting in systematically low determination results; excessive use will increase reagent consumption, the pressure of experimental waste treatment and detection costs. Select soil reference materials GSS-23 and GSS-34 with matrix representativeness, and systematically explore the influence of the digestion solution volume on the heavy metal extraction efficiency through gradient experiments (amount of aqua regia used is 5.00 - 12.00 mL), aiming to establish the best digestion system that takes into account both detection efficiency and sustainability.

[0057] Experimental data show (Table 1) that when the amount of aqua regia is 5.00 mL, the measured values of Hg and As for all reference materials deviate significantly from the standard range, confirming that low-dose aqua regia cannot effectively destroy the sample matrix. As the amount increases to 7.00 mL, the extraction efficiency of mercury increases significantly, and its measured value enters the standard range, but the extraction of arsenic is still insufficient, and the measured value deviates from the standard limit; when the amount of aqua regia is increased to 8.00 mL, the dissolution reaction of arsenic tends to be complete, and the measured results of Hg and As are consistent with the standard values; when the amount is further increased to 12.00 mL, the measured values remain stable. Based on this, 8.00 mL is determined as the optimal amount of aqua regia. This condition can not only achieve the full extraction of the target substances, ensure data accuracy, but also reduce reagent waste, reducing the consumption by 20% compared with the conventional 10 mL scheme. Specific Example 4:

[0058] Specific Example 4 is an optimization test of the extraction time of the analyte in the sample mentioned in Specific Example 3. The content of Specific Example 4 is as follows: 1. Preparation of samples Air-dry and grind the soil sample according to the standard requirements. First, pass it through a 10-mesh nylon sieve, and then take a part of the sample passing through the 10-mesh nylon sieve with the quartering method and continue to grind it until it all passes through a 100-mesh nylon sieve. After mixing evenly, seal and store it. Weigh 0.2 g of the sample into a 50 mL centrifuge tube (accurate to 0.1 mg). Use soil reference materials GSS-23 and GSS-34, and take five portions of each reference material. Add 8 mL of aqua regia (volume ratio of hydrochloric acid / nitric acid 3:1), add 0.2 - 0.5 g of ammonium persulfate powder, stir to dissolve, tighten the lid and rotate it once. According to the above steps, prepare a blank sample without adding soil sample.

[0059] 2. Digestion test Place the sample in a graphite digestion instrument. First, pre-react at 80 °C for 30 min, raise the temperature to 110 °C and maintain it for 1 - 2 h, and finally raise it to 120 °C and maintain it for 1 - 2 h to ensure complete digestion. Open the lid and continue heating to drive off the acid. When the solution remains 2 - 3 mL, add 0.1 g of thiourea and 0.05 g of ascorbic acid, take it out and cool to room temperature, add 2 mL of ultrapure water, then add 0.2 mL of electrolyte (tris(hexafluoroisopropyl) phosphite and tris(2,2,2-trifluoroethyl) borate = 1:1), vortex and mix evenly, make up the volume and shake well, and take the supernatant for ICP-MS determination.

[0060] Among them, the holding time of the sample at 120 °C is set at 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, and 4.0 h respectively.

[0061] 3. Results

[0062] The extraction time is one of the core parameters affecting the accuracy of heavy metal detection. Its length directly determines the kinetic equilibrium of the target substance transferring from the solid phase matrix to the liquid phase. Insufficient time will result in the incomplete dissolution of bound heavy metals (such as sulfide-bound arsenic and organic matter-chelated mercury), causing a systematic underestimation of the detection value; while excessive prolongation may increase the extraction rate, but it may introduce acidolysis side reactions (such as carbonization of organic matter) or increase energy consumption. Therefore, precisely controlling the extraction duration is a key link in balancing detection efficiency and data reliability.

[0063] Based on soil reference materials GSS-23 and GSS-34, this invention systematically investigated the effect of extraction time (1.0 - 2.0 h) on the dissolution efficiency of heavy metals in a digestion system at 120 °C. As shown in Table 2, when the extraction time was 1.0 - 1.6 h, the measured values of mercury and arsenic deviated significantly from the certified values of the reference materials, indicating that short-time digestion was difficult to break the stable occurrence forms of heavy metals (such as arsenopyrite inclusions); when the time was extended to 1.6 - 2.0 h, the dissolution of the target substances approached kinetic equilibrium, and the measured values of mercury and arsenic were highly consistent with the standard range. Thus, the optimal extraction time was determined to be 1.9 h. This condition could not only break through the dissolution threshold of heavy metals to ensure detection accuracy but also avoid the ineffective consumption of reagents and the reduction of equipment life caused by over-digestion. Specific Example Five:

[0064] Specific Example Five is about the detection limits and lower limits of determination for the heavy metal detection methods in the soil samples mentioned in Specific Examples One, Two, Three, and Four. The content of Specific Example Five is as follows: 1. Sample preparation First, prepare blank samples, strictly following the actual sample pretreatment process (including steps such as acid digestion and volume fixation).

[0065] 2. Digestion experiment Place the sample in a graphite digestion instrument. First, pre-react at 80 °C for 30 min, then raise the temperature to 110 °C and maintain for 1 - 2 h, and finally raise the temperature to 120 °C and maintain for 1 - 2 h to ensure complete digestion. Open the lid and continue heating to drive off the acid. When the solution remains 2 - 3 mL, add 0.1 g of thiourea and 0.05 g of ascorbic acid, take it out and cool to room temperature, add 2 mL of ultrapure water, then add 0.2 mL of electrolyte ((tris(hexafluoroisopropyl) phosphite and tris(2,2,2-trifluoroethyl) borate = 1:1)), vortex and mix evenly, fix the volume and shake well, and take the supernatant for ICP-MS determination.

[0066] 3. Results Based on the instrumental response values of Hg and As in the blank solution, they were converted into the equivalent contents in the sample matrix through the mass - volume conversion factor (m / V = 0.20 g / 50.0 mL); subsequently, the standard deviation (S) of 7 parallel determinations was calculated using the Bessel formula, and according to the EPA 40 CFR Part 136 specification, the MDL was calculated by the t - value method (n = 7, t = 3.143 when the confidence level is 99%) (MDL = 3.143×S); finally, the lower limit of quantification (LOQ) was set as 4×MDL, which conforms to the general definition of the lower limit of quantification in ISO 11843 - 2.

[0067]

[0068] In the detection of heavy metals in agricultural soils, the method detection limit (MDL) and the lower limit of quantification (LOQ) are the core indicators for evaluating the sensitivity and applicability of detection techniques. MDL determines the minimum pollutant concentration that the method can identify, directly affecting the early warning ability of pollution; LOQ defines the reliable concentration range for quantitative analysis, ensuring the accuracy and repeatability of the detection results of low - content heavy metals. Clarifying these two parameters has a fundamental supporting role in scientifically determining the soil pollution level (such as the "Risk Control Standards for Soil Pollution in Agricultural Land"), guiding the setting of remediation thresholds, and ensuring the safety of agricultural products.

[0069] To ensure the sensitivity and reliability of the detection method, the present invention uses the full - process digestion - statistics method of the blank matrix to verify the method detection limit (MDL) and the lower limit of quantification (LOQ). As shown in Table 3, the systematic statistics based on the blank sample standard deviation method (n = 7, confidence level 99%) show that: the method detection limit of mercury (Hg) is 0.001 mg·kg -1 , and the lower limit of quantification is 0.004 mg·kg -1 ; the method detection limit and the lower limit of quantification of arsenic (As) are 0.004 mg·kg -1 and 0.016 mg·kg -1 respectively. This result meets the technical requirements for trace heavy metal analysis (Hg detection limit ≤ 0.005 mg·kg -1 , As ≤ 0.01 mg·kg -1 , referring to HJ680 - 2013), confirming that the method can accurately identify extremely low - concentration Hg and As pollution in farmland soils (such as abnormal fluctuations near the natural background value), providing a reliable technical basis for the refined control of pollution risks. Specific Example Six:

[0070] Specific Example Six is for the precision and accuracy detection of the heavy metal substance detection method in the soil samples mentioned in Specific Examples One, Two, Three, Four, and Five. The content of Specific Example Six is as follows: 1. Select national first-class soil reference materials GSS-23 and GSS-34 to carry out precision and accuracy verification. Accurately weigh 6 portions of 0.2 g (accurate to 0.1 mg) standard samples and place them in 50 mL corrosion-resistant centrifuge tubes. According to the optimized digestion system (6.0 mL HCl + 2.0 mL HNO 3 ), perform acid leaching, program the temperature to 120 °C in a graphite digestion instrument to complete the pretreatment. After acid removal and concentration, make up the volume, and use ICP-MS to determine the content of the target substances.

[0071] 2. Result calculation: Calculate the relative standard deviation (RSD / %) based on the 6 measurement results to judge the precision of the method, and judge the accuracy of the method by whether the average value of the 6 measurement results is within the range of the reference material.

[0072]

[0073] 3. Conclusion As can be seen from Table 4, the precision (RSD ≤ 4.4%) and accuracy meet the technical requirements for heavy metal detection in the "Technical Specifications for Soil Environmental Quality Monitoring" (HJ / T 166-2004), indicating that the method performance meets the standards. In summary, the graphite digestion-ICP-MS method established in the present invention shows high-precision and high-reliability technical advantages in the detection of mercury and arsenic in soil and sediment: the precision (RSD ≤ 4.4%) and accuracy meet the technical requirements for heavy metal detection in the "Technical Specifications for Soil Environmental Quality Monitoring" (HJ / T 166-2004); the method detection limits (Hg: 0.001 mg / kg, As: 0.004 mg / kg) are significantly lower than the risk screening values for agricultural land, and can sensitively identify early pollution. In addition, in the standard addition recovery experiment, standard substances of 5 μg / kg and 20 μg / kg were added for As and Hg, and the recovery rate ≥ 90%. In summary, by optimizing the digestion system (8 mL of aqua regia, 120 °C / 1.9 h) and system parameters, this method effectively avoids the interference of organic matter and the overlap problem of mass spectrometry polyatomic ions, and is applicable to scenarios such as large-scale soil surveys and polluted site assessments, supporting the high-throughput detection requirements of processing more than 50 batches of samples per day. It can be extended to the synchronous detection of other heavy metals (such as Cd, Pb), providing technical support for the comprehensive evaluation of multi-element pollution; in addition, it can combine unmanned aerial vehicle sampling and GIS technology to construct a spatial distribution model of regional heavy metal pollution, helping to make decisions on precision agriculture and ecological restoration.

[0074] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Those skilled in the art to which the present invention pertains can make various modifications or supplements to the described specific embodiments or use similar methods for substitution, but will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

Claims

1. A method for rapid detection of heavy metals in agricultural soil, characterized in that: include: S1. Sample pretreatment: air-dry the soil sample, grind it, pass it through a 100-mesh sieve, mix it evenly, and seal it for storage; S2, graphite digestion, weigh 0-1g sample and place it in a digestion tube, add 5-10mL aqua regia, add 0.2-0.5g ammonium persulfate powder, stir to dissolve, tighten the lid and rotate it once, place it in a graphite digestion instrument, maintain at 80-120℃ for 1-4h, continue heating to drive out acid after opening the lid, when the solution has 2-3mL left, add 0.1g thiourea and 0.05g ascorbic acid, take it out and cool it to room temperature, add 2mL ultrapure water, then add 0.2mL electrolyte, vortex to mix, and shake to volume for testing; S3, ICP-MS detection parameter optimization, using 1.00μg / L ICP-MS tuning liquid to optimize the instrument indicators and determine the best working parameters of the instrument; S4. Quantitative analysis: prepare a series of standard mixed concentration points containing 0-10.0 μg / L mercury and 0-100.0 μg / L arsenic, add internal standard solution online, mix with the sample, measure by ICP-MS, and draw a standard curve; S5. Analyze the results and calculate the content of heavy metal elements in the soil according to the calculation formula.

2. A method for rapid detection of heavy metals in agricultural soil according to claim 1, characterized in that: In step S1, the soil sample is conventional agricultural soil, including cultivated land or orchard; Among them, the soil samples were air-dried and ground according to the standard requirements, and then passed through a 10-mesh nylon sieve. Then a part of the sample that passed through the 10-mesh nylon sieve was taken out by the quartering method and continued to be ground until all of it passed through a 100-mesh nylon sieve.

3. A method for rapid detection of heavy metals in agricultural soil according to claim 1, characterized in that: In step S2, when weighing the sample, the mass of the sample is accurate to 0.1 mg.

4. A method for rapid detection of heavy metals in agricultural soil as claimed in claim 3, characterized in that: In step S2, when the sample is digested in a graphite digester, it is first pre-reacted at 80°C for 30 min, then heated to 110°C and maintained for 1-2 h, and finally heated to 120°C and maintained for 1-2 h to ensure complete digestion; The electrolyte includes tris(hexafluoroisopropyl)phosphite and tris(2,2,2-trifluoroethyl)borate; The ratio of tris(hexafluoroisopropyl)phosphite to tris(2,2,2-trifluoroethyl)borate is 1:

1.

5. A method for rapid detection of heavy metals in agricultural soil according to claim 4, characterized in that: In step S2, in addition to all samples, a blank sample is prepared; Among them, the blank sample does not have soil samples added, and the remaining steps are the same as those of the sample with soil samples added.

6. A method for rapid detection of heavy metals in agricultural soil according to claim 1, characterized in that: In step S3, the optimal parameters are: atomizer flow rate 0.95 L / min; auxiliary gas flow rate 1.2 L / min; plasma gas flow rate 15 L / min; inductively coupled plasma RF power 1400 W; peristaltic pump speed 35 r / min; oxide (CeO / Ce) ≤ 0.025; double charge (Ce++ / Ce) ≤ 0.

03.

7. A method for rapid detection of heavy metals in agricultural soil according to claim 1, characterized in that: In step S4, when preparing the standard series of mercury solutions, according to the principle of stepwise dilution, a standard series of mixed concentration points containing mercury of 1.00 μg / L, 2.00 μg / L, 4.00 μg / L, 6.00 μg / L, 8.00 μg / L, and 10.0 μg / L are prepared respectively.

8. A method for rapid detection of heavy metals in agricultural soil according to claim 1, characterized in that: In step S4, when preparing the standard series of arsenic solutions, according to the principle of stepwise dilution, a standard series of mixed concentration points containing arsenic at 10.00 μg / L, 20.00 μg / L, 40.00 μg / L, 60.00 μg / L, 80.00 μg / L, and 100.0 μg / L were prepared respectively.

9. A method for rapid detection of heavy metals in agricultural soil according to claim 7 or 8, characterized in that: In step S4, the internal standard liquid 72 Ge, 185 Re was added online through a three-way tube, mixed with the sample, and measured by ICP-MS in collision cell mode; When drawing the standard curve, the mass concentration is used as the horizontal axis, and the ratio of the corresponding response value to the internal standard response value is used as the vertical axis to draw the calibration curves of mercury and arsenic.

10. A method for rapid detection of heavy metals in agricultural soil according to claim 1, characterized in that: In step S5, the calculation formula of the content C (mg / kg) of mercury and arsenic in the soil is: C(mg / kg)=(C1-C0)·V·K / m·1000 Wherein, C1 is the concentration of the substance to be tested, in μg / L; Wherein, C0 is the concentration of the analyte in the blank solution, in μg / L; Wherein, V is the constant volume, in mL; Wherein, m is the sample weight, in g; Where K is the dilution factor of the sample.

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