Method for detecting effective molybdenum in soil through ultrasonic extraction and inductively coupled plasma emission spectroscopy

Abstract

The invention discloses a method for detecting effective molybdenum in soil through ultrasonic extraction and inductively coupled plasma emission spectrometry. The method comprises a pretreatment step of ultrasonic extraction of a sample and a determination step through the inductively coupled plasma emission spectrometry. The method comprises the following steps: weighing 10.00 g of a soil sample (air dry basis, particle size of 60-100 meshes), putting the soil sample into a polyethylene centrifuge tube, adding 100.00 mL of an oxalic acid-ammonium oxalate extracting agent for dilution, and slightly shaking the polyethylene centrifuge tube to disperse the soil; performing ultrasonic extraction and centrifugation, collecting supernate in a colorimetric tube, sequentially adding nitric acid and perchloric acid into the supernate to decompose organic matters, adding nitric acid to make the solution clear, preparing a to-be-detected solution, and determining the content of effective molybdenum by using inductively coupled plasma emission spectrometry; the method disclosed by the invention is low in operation detection limit, high in precision and accuracy, simple, convenient and feasible, and relatively high in practicability; particularly, the detection cost is low, the economic benefit is fully reflected, and the method becomes a preferable scheme for detecting the content of effective molybdenum in batch soil samples.

Description

Technical Field

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

[0002] Ultrasonic extraction (also known as ultrasonic extraction) is used by innovative people to extract effective content from soil and various animals and plants due to its unique advantages of low extraction temperature, high extraction rate and short extraction time. It is a modern technical means to replace the infiltration extraction method to achieve efficient, energy-saving and environmentally friendly extraction.

[0003] The effective molybdenum in the soil is mainly water-soluble molybdenum, exchangeable molybdenum and other molybdenum that can be absorbed by plants. Molybdenum is one of the trace elements necessary for plant growth and development, and has an important impact on plant growth, development and yield quality.

[0004] The determination of available molybdenum in soil can be done by colorimetry, polarography, atomic absorption spectrophotometry, inductively coupled plasma mass spectrometry, inductively coupled plasma emission spectrometry, etc.

[0005] Inductively coupled plasma emission spectrometry is a method of atomic emission spectrometry using a highly efficient plasma as an excitation light source, which can simultaneously determine multiple elements and is suitable for elemental analysis from trace to constant amounts in various samples.

[0006] The inductively coupled plasma spectrometer also has the following features:

[0007] ① Fast analysis speed, capable of completing multi-element analysis in samples within one minute;

[0008] ②The detection limit of most elements is at ppb level;

[0009] ③The linear range is as wide as 5 to 6 orders of magnitude;

[0010] ④The precision is quite good;

[0011] ⑤ Low sample consumption, only about 2 ml of test solution;

[0012] ⑥With automatic sample injector, large-scale overnight unmanned analysis can be completed

[0013] The present invention is designed, verified and realized based on the combination of inductively coupled plasma emission spectroscopy and ultrasonic extraction theory. Summary of the invention

[0014] 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 ultrasonic extraction of inductively coupled plasma emission spectroscopy, with the aim of improving the efficiency of draw-rope length calibration and improving the calibration accuracy of the product, thereby avoiding inaccurate product length measurement parameters.

[0015] 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 ultrasonic extraction and inductively coupled plasma emission spectrometry, the method comprising a sample ultrasonic extraction pretreatment step and an inductively coupled plasma emission spectrometry determination step;

[0016] The pre-treatment steps for ultrasonic extraction of samples are:

[0017] Weigh 10.00 g of soil sample into a polyethylene centrifuge tube. The soil sample used is: air-dried basis, particle size 60-100 mesh;

[0018] Add 100.00 mL of oxalic acid-ammonium oxalate extractant to dilute, shake the polyethylene centrifuge tube slightly to disperse the soil, perform ultrasonic extraction, collect the clear solution, add nitric acid and perchloric acid to the clear solution to decompose the organic matter, and then add nitric acid to make the solution clear. This clear solution is prepared as the test solution;

[0019] Inductively coupled plasma optical emission spectrometry determination steps:

[0020] Taking the test solution prepared in the pre-treatment step of ultrasonic extraction of the sample, and determining the content of effective molybdenum by inductively coupled plasma emission spectrometry;

[0021] A series of standard solutions were prepared using a certified molybdenum standard stock solution, and a calibration curve was established with the mass concentration of molybdenum as the abscissa and the ratio of the response value to the response value of the internal standard as the ordinate.

[0022] Preferably, the preparation method of the oxalic acid-ammonium oxalate extractant is: weigh 24.9 g of ammonium oxalate and 12.6 g of oxalic acid, dissolve them in water and make up to 1 L, and the pH value is 3.3.

[0023] Preferably, the ultrasonic extraction conditions are set to: ultrasonic frequency 40 kHz, ultrasonic temperature 25° C. and ultrasonic extraction time 10 min.

[0024] Preferably, the supernatant is collected by centrifugation at a speed of 4000 r / min for 5 min, and the supernatant is collected in a colorimetric tube.

[0025] Preferably, the effective molybdenum measured is water-soluble effective molybdenum.

[0026] Preferably, the soil sample is an air-dried sample or a fresh sample, such as cultivated land soil, garden soil, forest and grassland soil, etc.

[0027] In summary, the present invention provides a method for detecting effective molybdenum in soil by ultrasonic extraction and inductively coupled plasma emission spectroscopy. Compared with the prior art, the present invention has the following beneficial effects: the present invention adopts ultrasonic extraction-inductively coupled plasma emission spectroscopy to detect effective molybdenum in soil, and after the soil sample to be tested is mixed with oxalic acid-ammonium oxalate leaching agent, it is heated in an oscillating device for pre-leaching treatment, and multiple samples can be processed at the same time, thereby large-scale pre-treatment is possible, and the operation is simple. Combined with the subsequent inductively coupled plasma emission spectrometer with an automatic sampling device, the sampling test can be carried out without supervision, so as 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 emission spectroscopy, the method has a low detection cost, a low detection limit, and high precision and accuracy.

[0028] The detection limit of the method is 0.002 mg / kg, the lower detection limit is 0.008 mg / kg, the relative standard deviation RSD is 3.79%-8.40% (n=8), the relative error RE is 6.55%-8.75% (n=8), and the detection values ​​are all within the uncertainty range.

[0029] The method of the present invention has a low detection limit, high precision and accuracy, and is suitable for the detection of effective molybdenum in batch soil samples. At the same time, the method of the present invention is simple and easy to implement, and has high practicality; in particular, the detection cost is low, which fully reflects the economic benefits, making it a preferred solution for the detection of effective molybdenum content in batch soil samples. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a working curve diagram for determining the effective molybdenum content in soil according to the present invention. DETAILED DESCRIPTION The accuracy and precision of the method of the present invention are specifically tested in the following experiments in combination with experimental conditions and methods.

[0031] Experimental method: Place the soil sample to be tested in a 100mL polyethylene centrifuge tube, add oxalic acid-ammonium oxalate extractant, and gently shake the polyethylene centrifuge tube to disperse the soil. After ultrasonic extraction, centrifuge, collect the supernatant, and use an inductively coupled plasma emission spectrometer to determine the content of effective molybdenum. 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:

[0032] (1) Experimental conditions

[0033] ①Instrument conditions

[0034] Inductively coupled plasma spectrometer (iCAP-PRO-X, vertical torch, two-way observation, full spectrum test, minimum exposure time 15 seconds, Thermo Fisher Scientific). Ultrasonic cleaner (KQ-500B, operating frequency: 40kHz, CNC temperature setting: room temperature to 80℃, CNC timing: 1 to 480min, Zhengzhou Baojing Electronic Technology Co., Ltd.). Desktop low-speed multi-tube rack centrifuge (TD-5Z, maximum speed 4000r / min, Sichuan Shuke Instrument Co., Ltd.). Electronic balance (FA2004N, weighing range 0 to 200g, reading accuracy 0.0001g, Shanghai Precision Instrument Technology Co., Ltd.).

[0035] Table 1 Inductively coupled plasma spectrometer operating parameters

[0036]

[0037] ② Reagents used in the experiment

[0038] Standard samples for soil effective component analysis: brown soil in Tonghua, Jilin, tidal soil in Anyang, Henan, and purple soil in Jianyang, Sichuan, numbered ASA-1b-CZ, ASA-2b-CZ, and ASA-3b-CZ, respectively, all developed by the Institute of Geophysical and Geochemical Exploration, Chinese Academy of Geological Sciences. ASA-1b-CZ is acidic soil, and ASA-2b-CZ and ASA-3b-CZ are alkaline soils. Actual soil samples from the three regions were taken to verify the method.

[0039] Molybdenum standard stock solution, 1000 mg / L, number GSB04-1737-2004, National Nonferrous Metals and Electronic Materials Analysis and Testing Center.

[0040] ③Soil sample pretreatment

[0041] Weigh 10.00 g of soil sample (air dried basis, particle size 60-100 mesh) into a polyethylene centrifuge tube, add 100.00 mL of oxalic acid-ammonium oxalate extractant to dilute, and gently shake the polyethylene centrifuge tube to disperse the soil. Further, ultrasonic extraction is preferably carried out at 40 kHz and 25 ° C for 15 min, and more preferably centrifuged at 4000 r / min for 5 min after the end of the extraction, and the supernatant is collected in a colorimetric tube. This clear solution is the test solution, and the content of effective molybdenum is determined by inductively coupled plasma emission spectrometry. The instrument conditions of the inductively coupled plasma emission spectrometer are shown in Table 1.

[0042] (2) Drawing of standard curve

[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 taken 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, 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. The standard curve was drawn, such as the working curve for determining the effective molybdenum content in soil, as shown in the figure. Figure 1 shown.

[0047] (3) Method detection limit

[0048] According to the requirements for detection limit calculation in the relevant standard "Technical Guidelines for the Formulation and Revision of Environmental Monitoring Analysis Methods" (HJ 168-2020), the detection limit calculation formula is determined as follows:

[0049] MDL=t(n-1,0.99)×S, t(n-1,0.99)=3.143

[0050] 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.

[0051] Table 2 Method detection limit, detection lower limit data table

[0052]

[0053] 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 10.00 g and the extractant is 100 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.

[0054] (4) Method precision and method accuracy

[0055] As shown in Table 3, standard substances (ASA-1b-CZ, ASA-2b-CZ, ASA-3b-CZ) with low, medium and high contents were selected. According to the relevant standard reference 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.

[0056] Table 3 Method precision data table

[0057]

[0058] (5) Accuracy

[0059] Certified reference materials ASA-1b-CZ, ASA-2b-CZ and ASA-3b-CZ with low, medium and high concentrations were selected. The effective molybdenum contents were detected according to the above-mentioned inventive method, and the relative errors were calculated by comparing with the standard values. The results are shown in Table 4.

[0060] Table 4 Test data of certified reference materials / standard samples

[0061]

[0062] (II) Optimization of ultrasound time

[0063] The standard substances (ASA-1b-CZ, ASA-2b-CZ, ASA-3b-CZ) were extracted by ultrasonic cleaning at 40kHz and 25°C for 2, 5, 10, 15, 20, and 30 minutes, respectively. The results are shown in Table 5.

[0064] Table 5 Effect of ultrasonic time on test results

[0065]

[0066] As shown in Table 5, when the extraction time is 5-10 minutes, the test result is too small, and the effective molybdenum component in the soil sample has not been completely extracted; when the extraction time is 10 minutes, it is close to the certificate value; when the extraction time is greater than 10 minutes, the measured value does not change much. In view of this, in order to ensure the accuracy and time efficiency of the effective molybdenum determination data, we can set the ultrasonic extraction time to 10 minutes. Specific embodiments

[0068] The present invention will be further described in detail below in conjunction with specific embodiments to provide a better understanding of the present invention, but the present invention is not limited to the following embodiments.

[0069] Example 1

[0070] 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.

[0071] Weigh 10.00g of soil sample (air dried basis, particle size 60-100 mesh) in a polyethylene centrifuge tube, add 100.00mL of oxalic acid-ammonium oxalate extractant to dilute, and gently shake the polyethylene centrifuge tube to disperse the soil. Further, ultrasonic extraction is preferably carried out at 40kHz and 25°C for 10min, more preferably centrifuged at 4000r / min for 5min after the extraction, collect the supernatant in a colorimetric tube, add nitric acid and perchloric acid to the clear liquid to decompose the organic matter, and then add nitric acid to make the solution clear. This solution is the solution to be tested, and then the content of effective molybdenum is determined by inductively coupled plasma emission spectrometry. The instrument conditions of the analytical instrument inductively coupled plasma spectrometer are shown in Table 1. The measured values ​​are 0.19mg / kg and 0.29mg / kg respectively.

[0072] 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.

[0073] 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.

[0074] Example 2

[0075] 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.

[0076] Weigh 10.00g of soil sample (air dried basis, particle size 60-100 mesh) in a polyethylene centrifuge tube, add 100.00mL of oxalic acid-ammonium oxalate extractant to dilute, and gently shake the polyethylene centrifuge tube to disperse the soil. Further, ultrasonic extraction is preferably carried out at 40kHz and 25°C for 10min, more preferably centrifuged at 4000r / min for 5min after the extraction, collect the supernatant in a colorimetric tube, add nitric acid and perchloric acid to the clear liquid to decompose the organic matter, and then add nitric acid to make the solution clear. This solution is the solution to be tested, and then the content of effective molybdenum is determined by inductively coupled plasma emission spectrometry. The instrument conditions of the analytical instrument inductively coupled plasma spectrometer are shown in Table 1. The measured values ​​are 0.24mg / kg and 0.33mg / kg respectively.

[0077] 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.

[0078] Example 3

[0079] 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.

[0080] Weigh 10.00g of soil sample (air dried basis, particle size 60-100 mesh) in a polyethylene centrifuge tube, add 100.00mL of oxalic acid-ammonium oxalate extractant to dilute, and gently shake the polyethylene centrifuge tube to disperse the soil. Further, ultrasonic extraction is preferably carried out at 40kHz and 25°C for 10min, more preferably centrifuged at 4000r / min for 5min after the extraction, collect the supernatant in a colorimetric tube, add nitric acid and perchloric acid to the clear liquid to decompose the organic matter, and then add nitric acid to make the solution clear. This solution is the solution to be tested, and then the content of effective molybdenum is determined by inductively coupled plasma emission spectrometry. The instrument conditions of the analytical instrument inductively coupled plasma spectrometer are shown in Table 1. The measured values ​​are 0.11mg / kg and 0.21mg / kg respectively.

[0081] 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 0.11 mg / kg and 0.22 mg / kg respectively.

[0082] Refer to the specification of the determination of effective 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:

[0083] Table 6 Permissible deviation of the results of determination of effective molybdenum by oxalic acid-ammonium oxalate extraction-potassium thiocyanate colorimetry

[0084]

[0085] The results of Examples 1 to 3 above show that the results of the ultrasonic extraction-inductively coupled plasma emission spectrometry 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 6. It can be seen that the ultrasonic extraction-inductively coupled plasma emission spectrometry method has the advantages of high accuracy and good repeatability when determining the effective molybdenum content in soil.

[0086] 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 ultrasonic extraction and inductively coupled plasma emission spectroscopy, characterized in that: The method comprises a sample ultrasonic extraction pre-treatment step and an inductively coupled plasma emission spectrometry determination step; The pre-treatment steps for ultrasonic extraction of samples are: Weigh 10.00 g of soil sample into a polyethylene centrifuge tube. The soil sample used is: air-dried basis, particle size 60-100 mesh; Add 100.00 mL of oxalic acid-ammonium oxalate extractant to dilute, shake the polyethylene centrifuge tube slightly to disperse the soil, perform ultrasonic extraction, collect the clear solution, add nitric acid and perchloric acid to the clear solution to decompose the organic matter, and then add nitric acid to make the solution clear. This clear solution is prepared as the test solution; Inductively coupled plasma optical emission spectrometry determination steps: Taking the test solution prepared in the pre-treatment step of ultrasonic extraction of the sample, and determining the content of effective molybdenum by inductively coupled plasma emission spectrometry; A series of standard solutions were prepared using a certified molybdenum standard stock solution, and a calibration curve was established with the mass concentration of molybdenum as the abscissa and the ratio of the response value to the response value of the internal standard as the ordinate.

2. The method for detecting effective molybdenum in soil by ultrasonic extraction and inductively coupled plasma emission spectroscopy according to claim 1, characterized in that: The preparation method of oxalic acid-ammonium oxalate extractant is as follows: weigh 24.9 g of ammonium oxalate and 12.6 g of oxalic acid, dissolve them in water to make up to 1 L, and take the pH value to 3.

3.

3. The method for detecting effective molybdenum in soil by ultrasonic extraction and inductively coupled plasma emission spectroscopy according to claim 1, characterized in that: The ultrasonic extraction conditions were set as follows: ultrasonic frequency of 40 kHz, ultrasonic temperature of 25°C and ultrasonic extraction time of 10 min.

4. The method for detecting effective molybdenum in soil by ultrasonic extraction and inductively coupled plasma emission spectroscopy according to claim 1, characterized in that: The supernatant was collected by centrifugation at a speed of 4000 r / min and a centrifugation time of 5 min, and the supernatant was collected in a colorimetric tube.

5. The method for detecting effective molybdenum in soil by ultrasonic extraction and inductively coupled plasma emission spectroscopy according to claim 1, characterized in that: The effective molybdenum measured is the water-soluble effective molybdenum.

6. The method for detecting effective molybdenum in soil by ultrasonic extraction and inductively coupled plasma emission spectroscopy according to claim 1, characterized in that: Soil samples were either air-dried or fresh.

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