Method for detecting effective molybdenum in soil by oscillation extraction inductively coupled plasma emission spectrometry

Abstract

The invention discloses a method for detecting the content of effective molybdenum in soil by oscillation extraction inductively coupled plasma emission spectrometry, which comprises the following steps: weighing 5.00 g of soil sample (particle size of 60-100 meshes) in a polyethylene plastic bottle, adding 50.00 mL of oxalic acid-ammonium oxalate extracting agent for dilution, tightly covering the bottle stopper, oscillating for 20 minutes in a reciprocating manner at the temperature of 25 + / -3 DEG C at the frequency of 180 times / min, standing for 8 hours for extraction, and filtering to obtain the effective molybdenum content in the soil. And centrifugally separating. Sequentially adding nitric acid and perchloric acid into the extract to decompose organic matters, then adding nitric acid to make the solution clear, and determining the content of effective molybdenum by inductively coupled plasma emission spectrometry. According to the method, the detection limit is 0.002 mg / kg, the detection lower limit is 0.008 mg / kg, the relative standard deviation RSD is 3.79%-8.40% (n is equal to 8), the relative error RE is 6.55%-8.75% (n is equal to 8), and detection values are all in the uncertainty range. The method is low in detection limit, high in precision and accuracy, high in operability, particularly low in detection cost and suitable for detecting effective molybdenum in batch soil samples.

Description

Technical Field

[0001] The invention relates to the technical field of determination of effective molybdenum content in soil, and in particular to a method for detecting effective molybdenum in soil by oscillation leaching inductively coupled plasma emission spectrometry. Background Art

[0002] Available molybdenum in soil refers to the molybdenum element that can be absorbed and utilized by plants. Molybdenum is one of the trace elements necessary for plant growth and development. It is involved in the synthesis and activity regulation of various enzymes in plants and has an important influence on physiological processes such as nitrogen metabolism, photosynthesis, and respiration of plants. Therefore, the available molybdenum content in soil has an important influence on the growth, development, and yield quality of plants.

[0003] Molybdenum in soil can be divided into four parts: water-soluble molybdenum, exchangeable molybdenum, mineral molybdenum and organically bound molybdenum. The effective molybdenum in soil is mainly water-soluble molybdenum, exchangeable molybdenum and other molybdenum that can be absorbed by plants. The determination of effective molybdenum in soil can be carried out by colorimetry, polarography, atomic absorption spectrophotometry, inductively coupled plasma mass spectrometry, etc.

[0004] Colorimetric method: Potassium thiocyanate method is often used. It has high sensitivity, but has strict requirements on color development conditions. Currently, potassium thiocyanate colorimetric method is widely used. In acidic solution, potassium thiocyanate (KCNS) and pentavalent molybdenum form orange-red complex Mo(CNS)5 or [MoO(CNS)5] in the presence of a reducing agent. 2- , extracted with an organic solvent (isoamyl alcohol, etc.) and then measured colorimetrically.

[0005] Polarography: The polarographic catalytic wave of the molybdenum-phenylacetic acid-chlorate-sulfuric acid system is very effective in determining trace amounts of molybdenum. The results are much more sensitive than the potassium thiocyanate (KCNS) colorimetric method (the minimum detectable molybdenum is 0.06 ng).

[0006] Atomic absorption spectrophotometry: Weigh 5 grams of soil sample (air-dried, 100 mesh) into a 125 ml conical flask, add 25 ml of 0.275 mol / L ammonium oxalate-oxalic acid solution, shake for 1 hour and filter. Use a micropipette to draw 10 microliters and measure according to the standard curve determination method. According to the absorbance, check the molybdenum content on the standard curve. This method is compared with the thiocyanate colorimetric method of molybdenum, and the results are similar.

[0007] Inductively coupled plasma mass spectrometry (ICP-MS) method: After the soil sample is extracted and filtered with oxalic acid-ammonium oxalate buffer solution, the filtrate is directly detected by an inductively coupled plasma mass spectrometer (ICP-MS). After the sample is brought into the atomization system by the carrier gas for atomization, the target element enters the axial channel of the plasma in the form of an aerosol, is fully evaporated, dissociated, atomized and ionized in high temperature and inert gas, and is converted into charged positive ions that enter the mass spectrometer through the ion collection system. The mass spectrometer separates and qualitatively and quantitatively analyzes the ions according to their mass-to-charge ratio. Within a certain concentration range, the response value corresponding to the mass-to-charge ratio of the ion is proportional to its concentration. However, the market price of the inductively coupled plasma mass spectrometer (ICP-MS) instrument is significantly too high (more than one million). This high cost constitutes a great economic pressure for ordinary laboratories. Therefore, its popularization and adoption in practical applications are subject to certain restrictions.

[0008] Inductively coupled plasma optical emission spectrometry (ICP-OES) is a method of atomic emission spectrometry analysis using an efficient plasma as an excitation light source, which can simultaneously determine multiple elements. It is suitable for elemental analysis from trace to constant in various samples. In terms of market price, the price of such instruments (ICP-OES) is usually half that of inductively coupled plasma mass spectrometry (ICP-MS), which makes it more popular in ordinary laboratories and shows greater affordability in terms of capital procurement.

[0009] The inductively coupled plasma spectrometer (ICP-OES) also has the following features:

[0010] ① Fast analysis speed, capable of completing multi-element analysis in samples within one minute;

[0011] ②The detection limit of most elements is at ppb level;

[0012] ③The linear range is as wide as 5 to 6 orders of magnitude;

[0013] ④The precision is quite good;

[0014] ⑤ Low sample consumption, only about 2 ml of test solution;

[0015] ⑥With automatic sample injector, large-scale overnight unmanned analysis can be completed

[0016] Most of the current methods for determining the effective molybdenum content in soil are relatively cumbersome. The inductively coupled plasma mass spectrometry (ICP-MS) method is efficient, accurate and fast. However, due to the high price of the instrument, the popularization and promotion of this detection method are subject to certain restrictions; while the inductively coupled plasma optical emission spectroscopy (ICP-OES) method is also efficient, accurate and fast, but the detection cost is lower, and it is more suitable for promotion and popularization. The present invention is designed, verified and implemented based on the combination of the inductively coupled plasma optical emission spectroscopy (ICP-OES) method and the oscillation extraction theory. Summary of the invention

[0017] In view of the problems existing in the above-mentioned prior art, the present invention provides a method for detecting effective molybdenum in soil by oscillating extraction inductively coupled plasma emission spectrometry. The method can realize batch pre-treatment of soil samples by oscillating extraction, and has the advantages of simple operation, high sensitivity and accuracy, good repeatability test stability, high efficiency, and accurate measurement results.

[0018] In order to achieve the above object, the present invention is implemented by the following technical scheme: a method for detecting effective molybdenum in soil by oscillating leaching inductively coupled plasma emission spectrometry, comprising a sample oscillating leaching pretreatment step and an inductively coupled plasma emission spectrometry detection step of effective molybdenum, wherein:

[0019] In the pre-treatment step of sample oscillation extraction, 5.00 g of soil sample with a particle size of 60-100 mesh was weighed and placed in a polyethylene plastic bottle, 50.00 mL of oxalic acid-ammonium oxalate extractant was added for dilution, the bottle stopper was tightly closed, and the sample was reciprocated and oscillated for 20 min at a frequency of 180 times / min at a temperature of 25°C±3°C, then allowed to stand for 8 h for extraction and centrifuged;

[0020] Accurately transfer 25.00 mL of the filtrate into a 50 mL borosilicate beaker, heat it on a hot plate at about 150 ° C until about 5 mL remains, add 3.0 mL of nitric acid and 1.0 mL of perchloric acid with a plastic pipette, gradually increase the temperature to 180 ° C in a fume hood, continue to heat until nearly dry, and after the organic matter is completely decomposed, add 5.0 mL of nitric acid solution while hot to rinse the cup wall, slightly heat until the solution is clear, transfer the solution to a 10.0 mL colorimetric tube without damage, make up to volume with water, shake well, dry filter, and the filtrate is tested. Use an inductively coupled plasma optical emission spectrometer (ICP-OES) to determine the effective molybdenum content;

[0021] Determination steps of effective molybdenum: a certain volume of molybdenum standard solution is respectively aspirated into a 100mL volumetric flask, and a series of standard solutions with standard curve concentrations of 0μg / L, 5.00μg / L, 10.0μg / L, 20.0μg / L, 50.0μg / L, and 100.0μg / L are prepared. The mass concentration of molybdenum is used as the horizontal axis, and the ratio of the response value to the response value of the internal standard is used as the vertical axis. A calibration curve is established using an inductively coupled plasma emission spectrometer.

[0022] Preferably, the effective molybdenum in the method refers to water-soluble effective molybdenum.

[0023] Preferably, the sample can be various types of soil, including cultivated soil, garden soil, forest and grassland soil, etc.; it can be an air-dried sample or a fresh sample.

[0024] Preferably, in the above method, the soil sample must be prepared according to the laboratory soil preparation requirements and be an air-dried sample that passes through a 2 mm aperture sieve, and this sample is the soil sample to be tested.

[0025] Before the determination and analysis of effective molybdenum, flush the system with nitric acid solution, and the blank intensity value of the instrument decreases until it reaches the lowest value. At this time, the analytical signal of the instrument is stable, and the sample is analyzed under the same conditions as those for establishing the calibration curve. During the sample detection process, if the molybdenum concentration in the test solution exceeds the maximum value of the calibration curve, it can be diluted with primary water, and an equal amount of magnesium sulfate solution is added according to the dilution multiple, and then re-detected.

[0026] In summary, the present invention adopts an oscillation extraction-inductively coupled plasma optical emission spectrometry (ICP-OES) method to detect effective molybdenum in soil. After the soil sample to be tested is mixed with an oxalic acid-ammonium oxalate extractant, it is heated in an oscillating device for pre-leaching treatment. Multiple samples can be processed at the same time, so that large-scale pre-treatment can be performed, and the operation is simple. Combined with a subsequent inductively coupled plasma optical emission spectrometry (ICP-OES) instrument with an automatic sampling device, sampling and testing can be performed without supervision to improve the fluency and practicality of the work, thereby further improving the detection efficiency; on the other hand, combined with the subsequent inductively coupled plasma optical emission spectrometry (ICP-OES) method, the method has a low detection cost, a low detection limit, and high precision and accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a working curve diagram of detecting effective molybdenum content in soil by using the oscillation leaching-inductively coupled plasma optical emission spectroscopy (ICP-OES) method of the present invention. DETAILED DESCRIPTION

[0028] The accuracy and precision of the method of the present invention are further described below.

[0029] Experimental method: Place the soil sample to be tested in a 100mL polyethylene plastic bottle, add (oxalic acid-ammonium oxalate extractant), and gently shake the polyethylene plastic bottle to disperse the soil. After heating and oscillating extraction, centrifuge, collect the upper clear liquid, and use an inductively coupled plasma optical emission spectrometer (ICP-OES) to determine the effective molybdenum content. The specific method verification includes experimental conditions such as instruments and reagents, soil sample pretreatment, standard curve drawing, detection limit, precision and accuracy. Among them:

[0030] (1) Experimental conditions

[0031] ①Instrument conditions

[0032] Inductively coupled plasma spectrometer (ICP-OES) instrument (iCAP-PRO-X, vertical torch, two-way observation, full spectrum test, minimum exposure time 15 seconds, Thermo Fisher Scientific). Intelligent large-capacity full-temperature oscillator (TS-211B, rotation frequency: 60-300 rpm, oscillation accuracy: ±1 rpm, swing amplitude: ￠26 mm, timing range: 1-999 hours, maximum capacity: 250 mL × 36 tubes, Changzhou Jintan Jingda Instrument Manufacturing Co., Ltd.). Desktop low-speed multi-tube rack centrifuge (TD-5Z, maximum speed 4000 r / min, Sichuan Shuke Instrument Co., Ltd.). Electronic balance (FA2004N, weighing range 0-200 g, reading accuracy 0.0001 g, Shanghai Precision Instrument Technology Co., Ltd.).

[0033] Table 1 Inductively coupled plasma spectroscopy (ICP-OES) instrument operating parameters

[0034]

[0035] ② Reagents used in the experiment

[0036] Standard samples for analysis of effective soil components: Huadu gray tidal soil in Guangdong, Yingtan red soil in Jiangxi, Qing'an black soil in Heilongjiang, Luochuan loess soil in Shaanxi, Tonghua brown soil in Jilin, Anyang tidal soil in Henan, and Jianyang purple soil in Sichuan, numbered ASA-6b-CZ, ASA-5b-CZ, ASA-7a-CZ, ASA-9a-CZ, ASA-1b-CZ, ASA-2b-CZ, and ASA-3b-CZ, all of which were developed by the Institute of Geophysical and Geochemical Exploration, Chinese Academy of Geological Sciences. Among them, ASA-6b-CZ, ASA-5b-CZ, and ASA-1b-CZ are acidic soils, and ASA-7a-CZ, ASA-9a-CZ, ASA-2b-CZ, and ASA-3b-CZ are alkaline soils. At the same time, three actual soil samples were selected, numbered TR1, TR2, and TR3.

[0037] Molybdenum standard stock solution, 1000 mg / L, number GSB04-1737-2004, National Nonferrous Metals and Electronic Materials Analysis and Testing Center.

[0038] Magnesium sulfate and anhydrous sodium carbonate, analytical grade, were purchased from Sinopharm Chemical Reagent Co., Ltd.

[0039] Sulfuric acid and nitric acid, high purity, Sinopharm Chemical Reagent Co., Ltd.

[0040] ③Soil sample pretreatment

[0041] Weigh 5.00g of soil sample (particle size 60-100 mesh) into a polyethylene plastic bottle, add 50.00mL of oxalic acid-ammonium oxalate extractant to dilute, cover the bottle cap tightly, and at a temperature of 25℃±3℃, reciprocate at a frequency of 180 times / min for 20min, then stand for 8h for extraction and centrifugation. Accurately transfer 25.00mL of filtrate into a 50mL borosilicate beaker, heat on a hot plate at about 150℃ until about 5mL remains, add 3.0mL of nitric acid and 1.0mL of perchloric acid with a plastic pipette, gradually increase the temperature to 180℃ in a fume hood, continue to heat until nearly dry, and after the organic matter is completely decomposed, add 5.0mL of nitric acid solution while hot to rinse the cup wall, slightly heat until the solution is clear, transfer the solution into a 10.0mL colorimetric tube without damage, make up to volume with water, shake well, dry filter, and the filtrate is tested. The instrument conditions of the inductively coupled plasma optical spectrometer (ICP-OES) are shown in Table 1.

[0042] (2) Standard curve drawing

[0043] Before analysis, flush the system with nitric acid solution, and the blank intensity value of the instrument decreases until the value is the lowest. At this time, the analytical signal of the instrument is stable, and the sample is analyzed under the same conditions as the calibration curve. During the sample detection process, if the molybdenum concentration in the test solution exceeds the maximum value of the calibration curve, it can be diluted with primary water (in accordance with GB / T6682 regulations), and an equal amount of magnesium sulfate solution is added according to the dilution multiple, and then re-tested.

[0044] A certain volume of molybdenum standard solution was drawn into a 100mL volumetric flask. The standard curve concentrations were configured as: 0μg / L, 5.00μg / L, 10.0μg / L, 20.0μg / L, 50.0μg / L, and 100.0μg / L. The standard solutions with different mass concentrations were sequentially injected into the inductively coupled plasma emission spectrometer. The mass concentration of the element to be measured was used as the horizontal axis, and the signal value of the element to be measured was used as the vertical axis to draw the standard curve.

[0045] (3) Method detection limit

[0046] According to the requirements for detection limit calculation in the Technical Guidelines for the Formulation and Revision of Environmental Monitoring Analysis Methods (HJ 168-2020), the detection limit calculation formula is determined as follows:

[0047] MDL=t(n-1,0.99)×S, t(n-1,0.99)=3.143

[0048] Without weighing the sample, perform eight consecutive tests under the conditions specified in the above optimal analysis method, calculate the standard deviation (S) of the eight tests, calculate the detection limit as (3S), and the lower limit of detection is the detection limit*4.

[0049] Table 2 Method detection limit, detection lower limit data table

[0050]

[0051]

[0052] As shown in Table 2, after experimental testing, the method's sample measurement detection limit was 0.002 mg / kg, and the lower detection limit was 0.008 mg / kg, which is consistent with the requirements of the "Sample Testing and Quality Control Guidelines" of the Soil Survey: when the sample weight is 5.00 g and the extractant is 50 mL of oxalic acid-ammonium oxalate extractant, the method detection limit is: 0.002 mg / kg, and the lower detection limit is: 0.008 mg / kg.

[0053] (4) Method precision and method accuracy

[0054] As shown in Table 3, standard substances with low, medium and high contents (ASA-1b-CZ, ASA-2b-CZ, ASA-3b-CZ) were selected. With reference to the provisions of HJ 168-2020 "Technical Guidelines for the Development of Environmental Monitoring Analytical Method Standards", the mean value, standard deviation (S) and relative standard deviation (RSD) of the test results were calculated respectively.

[0055] Table 3 Method precision data table

[0056]

[0057] (5) Accuracy

[0058] Certified reference materials ASA-1b-CZ, ASA-2b-CZ, and ASA-3b-CZ with low, medium, and high concentrations were selected to detect their effective molybdenum contents respectively. The relative errors were calculated by comparing with the standard values. The results are shown in Table 4-11.

[0059] Table 4 Test data of certified reference materials / standard samples

[0060]

[0061] (II) Optimization of temperature and time

[0062] (1) Optimization of extraction temperature

[0063] Soil available molybdenum is a typical conditional selectivity test. Any change in pretreatment conditions will cause a large change in the results. The extraction temperature has a significant effect on the determination of available molybdenum. This test selected certified soil standard substances: ASA-1b-CZ (standard value: 0.46±0.07mg / kg), ASA-2b-CZ (standard value: 0.21±0.03mg / kg), ASA-3b-CZ (standard value: 0.10±0.02mg / kg) and ASA-9a-CZ (standard value: 0.08±0.01mg / kg). The test investigated the effects of extraction temperatures of 15℃, 20℃, 22℃, 25℃, 28℃ and 30℃ on the determination results. When the extraction time was fixed at 30min and the oscillator frequency was fixed at 180r / min, a constant temperature shaker was used to carry out conditional selection tests at different temperatures. The determination results are shown in Table 5 (the conditional selection tests are the average results of 3 measurements).

[0064] Table 5 Effect of different extraction temperatures on the determination results

[0065]

[0066] As shown in Table 5, the determination results of effective molybdenum increase with the increase of extraction temperature. When the extraction temperature is less than 22℃, the determination results are small and the extraction is incomplete; when the extraction temperature is 22℃~28℃, the determination results are stable, and the results of different soils are within the standard value range; when the extraction temperature is greater than 28℃, the determination results are large, indicating that there are many interference factors in the soil extract and the determination results are drifting. Therefore, 22℃~28℃ is selected as the extraction temperature.

[0067] (2) Optimization of oscillation time

[0068] With the above experimental conditions unchanged, the influence of oscillation time on the test results was investigated. The experiment was carried out under the conditions of oscillation frequency of 180r / min and extraction temperature of 22-28℃. The oscillation time was changed and the time range was 15-40min. The specific test results are shown in Table 6.

[0069] Table 6 Effect of different oscillation time on the measurement results

[0070]

[0071] It can be seen from Table 6 that the results are better when the oscillation time is more than 20 minutes. When the oscillation time is more than 25 minutes, all test results are within the guaranteed value range given by the certified material. When the time is less than 20 minutes, the extraction will not be complete, resulting in a low result, indicating that the oscillation time is too short and the effective molybdenum in the soil standard cannot be fully extracted; when the time is too long, more than 40 minutes, it has little effect on the extraction results, but considering that the later oscillation needs to be left to stand for a long time and there is sufficient extraction time, in order to improve work efficiency, the oscillation time is 20 minutes. Considering the efficiency of the pretreatment work, 20 minutes is selected as the optimal oscillation time.

[0072] (3) Oscillation frequency optimization

[0073] Oscillation frequency is a very important step for the effective extraction of various elements in the soil. If the oscillation frequency is slow, the extraction time needs to be increased accordingly. If the oscillation frequency is too fast, the requirements for the extraction device will be greatly increased.

[0074] This section uses national standard substances ASA-1b-CZ (standard value: 0.46±0.07mg / kg), ASA-2b-CZ (standard value: 0.21±0.03mg / kg), and ASA-3b-CZ (standard value: 0.10±0.02mg / kg). The intelligent large-capacity full-temperature oscillator is set to oscillate five times at frequencies of 100 times / min, 120 times / min, 150 times / min, 180 times / min, and 200 times / min, respectively.

[0075] Table 7 Effect of oscillation frequency on effective molybdenum mass concentration in the leaching solution

[0076]

[0077] As shown in Table 7, when the oscillation frequency is controlled at 180 times / min, the leaching efficiency is optimal, and the results measured for different soils are all within the standard value range. This shows that the stability of the measurement results is better at an oscillation frequency of 180 times / min, so the oscillation frequency is selected to be controlled at 180 times / min.

[0078] (4) Oscillation mode optimization

[0079] There are two commonly used oscillation modes at present, one is cyclotron oscillation and the other is reciprocating oscillation. This experiment conducts two experiments to compare the two oscillation modes.

[0080] This section uses national standard substances ASA-1b-CZ (standard value: 0.46±0.07mg / kg), ASA-2b-CZ (standard value: 0.21±0.03mg / kg), ASA-3b-CZ (standard value: 0.10±0.02mg / kg), ASA-9a-CZ (standard value: 0.08±0.01mg / kg) for testing. Each oscillation method is tested 5 times in parallel and the average value of 5 measurements is taken. The extraction results are shown in Table 8.

[0081] Table 8 Effect of oscillation mode on determination results of effective molybdenum in leaching solution

[0082]

[0083] From Table 8, it can be seen that the effective extraction method is reciprocating oscillation, which is the best extraction method. The measured value is closest to the standard value. The reciprocating oscillation amplitude is large, the soil sample and the extract are in sufficient contact, and the extraction effect is better. The cyclotron soil sample gathers in the center of the extraction bottle, the contact is insufficient, and it is not conducive to extraction. Therefore, this method selects reciprocating oscillation extraction.

[0084] (5) Optimization of the standing time of the extract

[0085] The standing time of the leaching solution is one of the key factors affecting the accuracy of the determination of effective molybdenum content. In order to optimize the leaching process and determine the optimal standing time of the leaching solution, this section intends to analyze the effect of different standing times of the leaching solution on the change of effective molybdenum content.

[0086] The standard substances ASA-1b-CZ (standard value: 0.46±0.07mg / kg), ASA-2b-CZ (standard value: 0.21±0.03mg / kg), ASA-3b-CZ (standard value: 0.10±0.02mg / kg) and ASA-9a-CZ (standard value: 0.08±0.01mg / kg) for soil effective component analysis were selected, and 50mL of oxalic acid-ammonium oxalate buffer determined in the previous section was added respectively. The mixture was shaken at a speed of 150r / min for 1h, and then the supernatant was removed after standing for 2h, 4h, 6h, 8h, 10h, 12h, 14h, 16h, 18h and 20h, respectively, and diluted with oxalic acid-ammonium oxalate buffer for determination. The effect of different standing time on the determination results of molybdenum content was investigated. The results are shown in Table 9.

[0087] Table 9 Measurement results of filtrate at different standing times

[0088]

[0089] As shown in Table 9, when the effective molybdenum content in the soil is low (ASA-3b-CZ, ASA-9a-CZ), the standing time has no significant effect on the determination results; when the effective molybdenum content is high (ASA-1b-CZ, ASA-2b-CZ), the standing time has a greater impact on the determination results. When the standing time is less than 10h, the mass concentration of effective molybdenum in the extract is generally low, and with the extension of the standing time, the measured value gradually increases. This is because the extraction time is short, the chelation of the extractant and the molybdenum ions in the soil is incomplete, resulting in low determination results; when the standing time is 10-14h, the curve tends to be flat, and the determination results are relatively stable; when the standing time is greater than 14h, with the dissolution of various ions such as Ca, Na, K, Mg, Al, Ti, Fe, and Mn in the soil, the matrix in the soil sample solution changes, and the interference factors caused by the matrix effect are enhanced, resulting in high determination results. Considering comprehensively, the standing time is selected to be 10-14h. When the standing time is 8 to 11 hours, the measurement results are consistent with the standard value with a small error. Considering saving experimental cycles and improving detection efficiency, the extraction time of effective molybdenum is 8 hours.

[0090] (6) Optimization of separation method

[0091] There are two commonly used separation methods at present, filtration separation and centrifugal separation. In order to optimize the leaching process and determine the best centrifugal method, this section intends to analyze the changes in effective molybdenum content under different centrifugal methods.

[0092] Under the optimal experimental scheme selected above, the national standard substances ASA-1b-CZ (standard value: 0.46±0.07), ASA-2b-CZ (standard value: 0.21±0.03), ASA-3b-CZ (standard value 0.10±0.02), and ASA-9a-CZ (standard value: 0.08±0.01) were used to conduct the experiment. Each separation method was repeated 5 times, and the average value of 5 measurements was taken. The extraction results are shown in Table 10.

[0093] Table 10 Effect of separation method on effective molybdenum mass concentration in leaching solution

[0094]

[0095] It can be seen from Table 10 that the extraction of effective molybdenum, the measured value of centrifugal separation is basically consistent with the standard value. The result of the determination by filtering with filter paper is smaller. Before filtering, although the filter paper must be treated with dilute hydrochloric acid, the filter paper has adsorption on molybdenum, and dry filtration is easy to block the filter paper, which is time-consuming. Occasionally, the filter paper is damaged, causing filtration, making the filtrate turbid, affecting liquid injection, blocking the mass spectrometer nebulizer and reducing the atomization efficiency, which will cause the result to be low. And by centrifugation, the centrifugal time is short, the solution is clear, and the solution is taken for determination, saving the experimental cycle. Therefore, this method selects centrifugation as the most efficient and convenient method.

[0096] (7) Granularity selection optimization

[0097] Since the standard material is a 60-mesh original sample, a certain mass of the selected standard material is taken, ground manually, and passed through 100-mesh sieves and 200-mesh sieves respectively to investigate the effect of sample particle size on the effective molybdenum test results. The experiment is carried out according to the optimal factors of the above single-factor experiment.

[0098] Table 11 Effect of particle size on extraction effect

[0099]

[0100] As can be seen from Table 11, the experimental results of effective molybdenum show that when the same sample is between 60 mesh and 100 mesh, the analysis results are not much different, and the standard sample error is basically within the standard sample error range, which meets the quality requirements of soil effective molybdenum analysis. However, as the particle size becomes smaller, the test results are high. When the sample particle size is less than 200 mesh, the result deviation is large, because the smaller the particle size during extraction, the larger the solution contact area. In addition to effective molybdenum, other forms of molybdenum may also be extracted from the extract. The extraction is more comprehensive, and part of the total amount of molybdenum is also leached, resulting in a high measured value. Therefore, the effective molybdenum particle size of the test sample should not be less than 60 mesh. Therefore, when preparing the sample, the effective molybdenum is selected to pass through the 60-mesh to 100-mesh sieve for the experiment, and the particle size should not be too fine.

[0101] Example 1

[0102] Weigh two fresh soil samples from a farmland in Xuzhou, Jiangsu (avoiding the fertilization site), with the sampling depth of the effective soil layer being 0 to 20 cm thick. Spread them into a 2 to 3 cm thin layer and air dry them naturally in a well-ventilated air-drying room without direct sunlight.

[0103] Weigh 5.00g of soil sample (particle size 60-100 mesh) into a polyethylene plastic bottle, add 50.00mL of oxalic acid-ammonium oxalate extractant to dilute, cover the bottle cap tightly, and at a temperature of 25℃±3℃, reciprocate at a frequency of 180 times / min for 20min, then stand for 8h for extraction and centrifugation. Accurately transfer 25.00mL of filtrate into a 50mL borosilicate beaker, heat on a hot plate at about 150℃ until about 5mL remains, add 3.0mL of nitric acid and 1.0mL of perchloric acid with a plastic pipette, gradually increase the temperature to 180℃ in a fume hood, continue to heat until nearly dry, and after the organic matter is completely decomposed, add 5.0mL of nitric acid solution while hot to rinse the cup wall, slightly heat until the solution is clear, transfer the solution into a 10.0mL colorimetric tube without damage, make up to volume with water, shake well, dry filter, and the filtrate is tested. The instrument conditions of the analytical instrument inductively coupled plasma spectrometer (ICP-OES) are shown in Table 1. The measured values ​​are 0.18 mg / kg and 0.31 mg / kg respectively.

[0104] The effective molybdenum content in the soil was determined by the oxalic acid-ammonium oxalate extraction-potassium thiocyanate colorimetric method in "Determination of Available Molybdenum in Forest Soil" LY / T 1259-1999, and a comparative experiment was conducted with the present invention: 25.00 g of air-dried soil (passing through a 2 mm nylon sieve) was weighed and placed in a plastic bottle, and 250 mL of oxalic acid-ammonium oxalate extractant was added. The bottle stopper was tightly closed, and the mixture was vibrated at a constant temperature (25° C.) for 8 hours on an oscillator (oscillator frequency was 150 to 180 times per minute). Filter (using filter paper treated with 6 mol / L hydrochloric acid), and the initial 10 to 15 mL of turbid filtrate was discarded during filtration.

[0105] Take 200mL of filtrate (containing no more than 6μg of molybdenum) in a beaker, evaporate to a small volume on an electric furnace, transfer to a quartz evaporating dish or a 50mL hard glass beaker, and continue to evaporate to dryness. After strengthening the heat to destroy part of the oxalate, transfer to a high-temperature electric furnace and burn at 450℃ to destroy oxalic acid and organic matter. After cooling, add 10mL of 6.5mol / L hydrochloric acid to dissolve the residue. Transfer to a 125mL separatory funnel and add water to a volume of about 45mL. Add 1g of citric acid and 2-3mL of isoamyl alcohol-carbon tetrachloride mixture. Shake for 2min. After standing and stratifying, discard the isoamyl alcohol-carbon tetranitride layer. Add 3mL of potassium thiocyanate solution and mix well, so that the solution presents the blood red color of Fe(CNS)3. Add 2mL of tin dichloride solution and mix well, and the red color gradually disappears. Accurately add 10.0mL of isoamyl alcohol-carbon tetrachloride mixture, vibrate for 2-3 minutes, let stand for stratification, filter the isoamyl alcohol-carbon tetrachloride layer into a colorimetric tank with dry filter paper, and perform colorimetric determination at a wavelength of 470nm. The measured values ​​are 0.18mg / kg and 0.30mg / kg respectively.

[0106] Example 2

[0107] Weigh two fresh soil samples from a farmland in Jingmen, Hubei (avoiding the fertilization site), with the sampling depth of the effective soil layer being 0 to 20 cm thick. Spread them into a thin layer of 2 to 3 cm and air dry them naturally in a well-ventilated air-drying room without direct sunlight.

[0108] Weigh 5.00g of soil sample (particle size 60-100 mesh) into a polyethylene plastic bottle, add 50.00mL of oxalic acid-ammonium oxalate extractant to dilute, cover the bottle cap tightly, and at a temperature of 25℃±3℃, reciprocate at a frequency of 180 times / min for 20min, then stand for 8h for extraction and centrifugation. Accurately transfer 25.00mL of filtrate into a 50mL borosilicate beaker, heat on a hot plate at about 150℃ until about 5mL remains, add 3.0mL of nitric acid and 1.0mL of perchloric acid with a plastic pipette, gradually increase the temperature to 180℃ in a fume hood, continue to heat until nearly dry, and after the organic matter is completely decomposed, add 5.0mL of nitric acid solution while hot to rinse the cup wall, slightly heat until the solution is clear, transfer the solution into a 10.0mL colorimetric tube without damage, make up to volume with water, shake well, dry filter, and the filtrate is tested. The instrument conditions of the analytical instrument inductively coupled plasma spectrometer (ICP-OES) are shown in Table 1. The measured values ​​are 0.26 mg / kg and 0.34 mg / kg respectively.

[0109] Similarly, a comparative experiment was conducted using the oxalic acid-ammonium oxalate extraction-potassium thiocyanate colorimetric method, and the results of the effective molybdenum content were measured to be 0.25 mg / kg and 0.33 mg / kg respectively.

[0110] Example 3

[0111] Weigh two fresh soil samples from a farmland in Jiaxing, Zhejiang (avoiding the fertilization site), with the sampling depth of the effective soil layer being 0 to 20 cm thick. Spread them into a thin layer of 2 to 3 cm and air dry them naturally in a well-ventilated air-drying room without direct sunlight.

[0112] Weigh 5.00g of soil sample (particle size 60-100 mesh) into a polyethylene plastic bottle, add 50.00mL of oxalic acid-ammonium oxalate extractant to dilute, cover the bottle cap tightly, and at a temperature of 25℃±3℃, reciprocate at a frequency of 180 times / min for 20min, then stand for 8h for extraction and centrifugation. Accurately transfer 25.00mL of filtrate into a 50mL borosilicate beaker, heat on a hot plate at about 150℃ until about 5mL remains, add 3.0mL of nitric acid and 1.0mL of perchloric acid with a plastic pipette, gradually increase the temperature to 180℃ in a fume hood, continue to heat until nearly dry, and after the organic matter is completely decomposed, add 5.0mL of nitric acid solution while hot to rinse the cup wall, slightly heat until the solution is clear, transfer the solution into a 10.0mL colorimetric tube without damage, make up to volume with water, shake well, dry filter, and the filtrate is tested. The instrument conditions of the analytical instrument inductively coupled plasma spectrometer (ICP-OES) are shown in Table 1. The measured values ​​are 0.11 mg / kg and 0.23 mg / kg respectively.

[0113] Similarly, the comparative experiment was conducted using oxalic acid-ammonium oxalate extraction-potassium thiocyanate colorimetry, and the results of the effective molybdenum content were measured to be 0.11 mg / kg and 0.22 mg / kg respectively.

[0114] Refer to the specification of the determination of available molybdenum content in soil by oxalic acid-ammonium oxalate extraction-potassium thiocyanate colorimetric method in "Determination of Available Molybdenum in Forest Soil" LY / T 1259-1999, and the requirements for the absolute deviation of the determination results are as follows:

[0115] Table 12 Permissible deviation of the results of determination of effective molybdenum by oxalic acid-ammonium oxalate extraction-potassium thiocyanate colorimetry

[0116]

[0117]

[0118] The results of Examples 1 to 3 above show that the results of the oscillation extraction-inductively coupled plasma emission spectrometry (ICP-OES) method provided by the present invention for determining the effective molybdenum content in soil are compared with the oxalic acid-ammonium oxalate extraction-potassium thiocyanate colorimetric method, and the allowable relative deviation meets the requirements of Table 12. It can be seen that the oscillation extraction-inductively coupled plasma emission spectrometry (ICP-OES) method not only has the advantages of high accuracy and good repeatability when determining the effective molybdenum content in soil, but also shows strong applicability and consistency when processing complex soil samples. This method uses automated instruments and equipment for determination, which can greatly improve work efficiency and reduce human errors, thereby meeting the needs of rapid determination of a large number of samples.

[0119] The embodiments of the present invention are only used to illustrate the present invention and do not constitute a limitation on the scope of the claims. Other substantially equivalent substitutes that can be thought of by those skilled in the art are all within the protection scope of the present invention.

Claims

1. A method for detecting effective molybdenum in soil by oscillating leaching inductively coupled plasma emission spectrometry, characterized in that: The method comprises a sample oscillation leaching pretreatment step and an effective molybdenum inductively coupled plasma emission spectrometry detection step, wherein: In the pre-treatment step of sample oscillation extraction, 5.00 g of soil sample with a particle size of 60-100 mesh was weighed and placed in a polyethylene plastic bottle, 50.00 mL of oxalic acid-ammonium oxalate extractant was added for dilution, the bottle stopper was tightly closed, and the sample was reciprocated and oscillated for 20 min at a frequency of 180 times / min at a temperature of 25°C±3°C, then allowed to stand for 8 h for extraction and centrifuged; Accurately transfer 25.00 mL of the filtrate into a 50 mL borosilicate beaker, heat it on a hot plate at about 150 ° C until about 5 mL remains, add 3.0 mL of nitric acid and 1.0 mL of perchloric acid with a plastic pipette, gradually increase the temperature to 180 ° C in a fume hood, continue to heat until nearly dry, and after the organic matter is completely decomposed, add 5.0 mL of nitric acid solution while hot to rinse the cup wall, slightly heat until the solution is clear, transfer the solution to a 10.0 mL colorimetric tube without damage, make up to volume with water, shake well, dry filter, and the filtrate is tested. Use an inductively coupled plasma optical emission spectrometer (ICP-OES) to determine the effective molybdenum content; Determination steps of effective molybdenum: a certain volume of molybdenum standard solution is respectively aspirated into a 100mL volumetric flask, and a series of standard solutions with standard curve concentrations of 0μg / L, 5.00μg / L, 10.0μg / L, 20.0μg / L, 50.0μg / L, and 100.0μg / L are prepared. The mass concentration of molybdenum is used as the horizontal axis, and the ratio of the response value to the response value of the internal standard is used as the vertical axis. A calibration curve is established using an inductively coupled plasma emission spectrometer.

2. The method for detecting effective molybdenum in soil by oscillating leaching inductively coupled plasma emission spectrometry according to claim 1, characterized in that: The effective molybdenum in the method refers to water-soluble effective molybdenum.

3. The method for detecting effective molybdenum in soil by oscillating leaching inductively coupled plasma emission spectrometry according to claim 1, characterized in that: The sample can be various types of soil, including air-dried samples and fresh samples.

4. The method for detecting effective molybdenum in soil by oscillating leaching inductively coupled plasma emission spectrometry according to claim 1, characterized in that: The soil sample is prepared into an air-dried sample passing through a 2 mm aperture sieve, and the sample is the soil sample to be tested.

5. The method for detecting effective molybdenum in soil by oscillating leaching inductively coupled plasma emission spectrometry according to claim 1, characterized in that: Before the determination and analysis of effective molybdenum, flush the system with nitric acid solution, and the blank intensity value of the instrument decreases until it reaches the lowest value. At this time, the analytical signal of the instrument is stable, and the sample is analyzed under the same conditions as those for establishing the calibration curve. During the sample detection process, if the molybdenum concentration in the test solution exceeds the maximum value of the calibration curve, it can be diluted with primary water, and an equal amount of magnesium sulfate solution is added according to the dilution multiple, and then re-detected.

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