Method for analyzing available boron in soil

Abstract

The invention discloses a soil available boron analysis method, which comprises: weighing a soil air-dried sample, placing in a PP round-bottom centrifuge tube, adding a magnesium sulfate solution, screwing the cover, placing in a boiling water bath, and accurately timing for 20 min when the water bath reaches 100 DEG C again; and taking out the centrifugal tube, cooling, centrifuging, carrying out dry filtration, testing filtrate on a machine through ICP-MS, and analyzing to obtain the content of available boron in the air-dried soil sample. The boiling water bath is adopted, so that the problem of poor parallelism caused by undefined external source heating temperature is effectively solved, and the result parallelism is ensured. A quartz vessel is replaced by the PP round-bottom centrifugal tube, so that the problem that boron backgrounds in glassware are inconsistent is solved to the greatest extent. ICP-MS is adopted for testing the effective boron leaching liquor, and the problem that a colorimetric method is prone to being interfered is solved; concentration is needed for measuring a low-content sample, the steps are multiple, and the operation is tedious. And meanwhile, the problem of low sensitivity in ICP test of low-content samples is also solved.

Description

Technical Field

[0001] The invention relates to the technical field of soil testing and analysis, and in particular to an analysis method for effective boron in soil. Background Art

[0002] Boron is an essential trace element for plant growth. Boron can promote the conversion and movement of carbohydrates, accelerate plant growth and development, and promote early maturity; Boron plays an important role in the formation and development of plant reproductive organs, promotes pollen germination, stimulates pollen tube elongation, has a special effect on plant fertilization, is conducive to seed formation, and reduces flower and fruit drop; Boron can also increase the stress resistance of plants, enhance the drought and disease resistance of crops, and prevent terminal bud brown rot, heart rot, etc. Boron in the soil is divided into water-soluble boron, acid-soluble boron and insoluble boron. Water-soluble boron is effective boron, which is the part that can be directly absorbed and utilized by plant roots. The current method for testing effective boron is NY / T 1121.8 and the second edition of the "Soil Analysis Technical Specifications". The operation is as follows:

[0003] Extraction: Weigh 10g of air-dried sample with a particle size of 2mm into a 250mL quartz conical flask, add 20mL of water, and install a quartz condenser reflux device. Boil over low heat and keep it at a slight boil for 5min (accurate timing), remove the heat source, continue reflux condensation for 5min (accurate timing), remove the conical flask, and cool. Add 2d100g / L magnesium sulfate solution to the boiled solution to accelerate clarification, centrifuge, and dry filter.

[0004] Colorimetric: Pipette 4 mL of filtrate into a 10 mL colorimetric tube, add 0.5 mL of acidic potassium permanganate solution, shake well, let stand for 2-3 min, add 0.5 mL of 100 g / L ascorbic acid solution, shake well, wait until the purple-red color fades and the faded manganese dioxide precipitate is completely dissolved, add 5 mL of mixed color developer, shake well and let stand for 1 h, and then perform colorimetric determination at a wavelength of 415 nm using a 2 cm optical path cuvette.

[0005] In addition: The second edition of the "Soil Analysis Technical Specifications" mentions that ICP can be used to directly test the effective boron in the above-mentioned extract.

[0006] The prior art has the following disadvantages:

[0007] 1. The existing method only states that the solution should be brought to a slightly boiling state, but the heating temperature of the electric furnace is uncertain, the temperature of the slightly boiling state is difficult to control, the degree of extraction is inconsistent, and the results have poor reproducibility.

[0008] 2. All hard glasses contain boron, even quartz glass. Since the content of boron in glass products is uneven, it is difficult to solve the problem of poor sample repeatability even by deducting blanks.

[0009] 3. The colorimetric method is easily interfered by nitrate. Calcium hydroxide needs to be added to make an alkaline reaction, then evaporated in a water bath, slowly burned to destroy the nitrate, and finally add an appropriate amount of nitric acid to dissolve the residue and compare the color. The operation process is cumbersome and time-consuming, and the parallelism of the results is difficult to guarantee.

[0010] 4. Red soil accounts for a large proportion of the total soil area in Hainan, while the effective boron content in red soil is only less than 1% of the total boron. The water-soluble boron content in the soil is too low, which will cause colorimetry difficulties and require concentrated solutions. Concentration steps: Accurately absorb more solution onto an evaporating dish, add saturated calcium hydroxide to make an alkaline reaction, then evaporate to dryness in a water bath, add an appropriate amount of hydrochloric acid to dissolve, and finally compare colors. Since acidity has a great influence on color development, the standard solution needs to be processed synchronously. The entire operation process is very cumbersome, the results are poorly reproducible, and the efficiency is extremely low, which cannot meet the accuracy and efficiency requirements of batch sample testing.

[0011] 5. If the second edition of the "Technical Specifications for Soil Analysis" recommends that the extract be tested with ICP instead of colorimetry, the work efficiency will be greatly improved, the parallelism of the results will also be greatly improved, and the test results for samples with medium and high content will be relatively ideal. However, due to the sensitivity of ICP, it is difficult to accurately determine the low content of effective boron. As mentioned in Article 4 above, the soil in Hainan is mainly low in effective boron.

[0012] Based on the above shortcomings of the existing methods and the current situation of large soil flux, a more efficient and stable extraction technology and a highly sensitive detection technology are needed to effectively improve work efficiency. Summary of the invention

[0013] Aiming at the demand for large-scale soil testing, the present invention develops a method for extracting effective boron by heating in a boiling water bath and detecting effective boron by ICP-MS, which can achieve the purpose of high-throughput extraction and accurate analysis of effective boron.

[0014] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0015] A method for analyzing available boron in soil is provided, comprising the following steps:

[0016] Weigh the air-dried soil sample into a PP round-bottom centrifuge tube, add magnesium sulfate solution, tighten the lid, and place it in a boiling water bath. When the water bath reaches 100 degrees again, accurately time 20 minutes; take out the centrifuge tube, cool, centrifuge, dry filter, and test the filtrate on an ICP-MS machine to analyze the content of effective boron in the air-dried soil sample.

[0017] Furthermore, the particle size of the air-dried soil sample was 2 mm.

[0018] Furthermore, the mass ratio of the air-dried soil sample to the magnesium sulfate solution was 500:1.

[0019] The beneficial effects of the present invention are:

[0020] 1. The present invention changes the heating method from an electric furnace to a boiling water bath. The heating time is optimized, which effectively solves the problem of parallelism caused by unclear exogenous heating temperature (difficult to define the micro-boiling degree), and ensures the parallelism of the results.

[0021] 2. The present invention replaces the quartz container with a PP round-bottom centrifuge tube, thereby eliminating the problem of inconsistent boron background in the glass (quartz) container to the greatest extent.

[0022] 3. The present invention adopts ICP-MS to test the effective boron extract, which solves the problem that the colorimetric method is easily interfered with; the problem that the low-content sample needs to be concentrated, has many steps and is cumbersome to operate. At the same time, it also solves the problem that the sensitivity of ICP testing low-content samples is not high. DETAILED DESCRIPTION

[0023] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0024] Embodiment (boiling water bath heating extraction)

[0025] Weigh 10g of 2mm particle size air-dried sample into a 100mL PP round-bottom centrifuge tube, add 20mL 1g / L magnesium sulfate solution, tighten the lid, put it into a boiling water bath, and when the water bath reaches 100 degrees again, accurately time 20 minutes. Take out the centrifuge tube, cool, centrifuge, and dry filter. The filtrate is tested on an ICP-MS machine.

[0026] Comparative Example 1 (Graphite Digestion Instrument Heating Extraction)

[0027] Extraction: Weigh 10g of 2mm particle size air-dried sample into a 50mL PP round-bottom centrifuge tube, add 20mL water, tighten the lid, and place in a graphite furnace heated to 120°C, boil the solution and keep it slightly boiling for 5min (accurate timing), turn off the graphite furnace, continue heating at residual temperature for 5min (accurate timing), take out the centrifuge tube, and cool it. Add 2d100g / L magnesium sulfate solution to the boiled solution to accelerate clarification, centrifuge, and dry filter.

[0028] Test: The filtrate was tested on ICP-MS.

[0029] Comparative Example 2 (Oven Heating Extraction)

[0030] Extraction: Weigh 10g of 2mm particle size air-dried sample into a 100mL PP round-bottom centrifuge tube, add 20mL 1g / L magnesium sulfate solution, tighten the lid, put the centrifuge tube into an oven heated to 130℃, and accurately time for 1h. Take out the centrifuge tube, cool, centrifuge, and dry filter.

[0031] Test: The filtrate was tested on ICP-MS.

[0032] The feasibility of this method was verified using national certified soil standard materials GBW07413a, GBW07414a, GBW07415a, GBW07416a, GBW07417a, GBW07459, GBW07460; soil reference materials ASA-1b-CZ, ASA-2b-CZ, ASA-3b-CZ, ASA-4b-CZ, ASA-5b-CZ, ASA-6b-CZ, ASA-7a-CZ, ASA-10a-CZ, NSA-1, NSA-4, and the results were within the recommended range with good precision and accuracy. The results are shown in Tables 1-4 below.

[0033] Table 1 NY / T 1121.8-2006 standard method test results

[0034]

[0035]

[0036] Table 2 Comparative Example 1 Graphite Digestion Apparatus Heating Extraction Method Test Results

[0037]

[0038] Table 3 Comparative Example 2 Oven Heating Extraction Method Test Results

[0039]

[0040]

[0041] Table 4 Test results of the boiling water bath heating extraction method according to the present invention

[0042]

[0043] As shown in Table 2 above, the precision of the parallel samples of the graphite digestion heating extraction method in Comparative Example 1 is poor, and the results are higher or lower than the effective boron standard value. It is speculated that due to the difference in temperature between the peripheral and middle holes of the porous graphite digestion instrument, and the small pore size (for placing a 50mL centrifuge tube), the soil is easily accumulated, and the permeability of the extract is poor, resulting in inconsistent extraction levels.

[0044] As shown in Table 3 above, the precision of the parallel samples of the oven heating extraction method in Comparative Example 2 is poor, and the results are higher or lower than the recommended values ​​in the certificate. The reason is speculated that the oven is heated by circulating air, which leads to differences in local temperature and inconsistent solution extraction rates.

[0045] 1. The exogenous heating solution is slightly boiled, but the degree of slightly boiled is difficult to define; the improved graphite furnace heating and oven heating temperatures are uneven, resulting in poor parallelism. The present invention changes the heating method to a boiling water bath, and by optimizing the heating time, effectively solves the problem of inconsistent temperature and time control, ensuring the parallelism of the results.

[0046] 2. Aiming at the problem of inconsistent boron background caused by quartz glass and quartz condenser reflux device, the present invention replaces the quartz container with a PP round-bottom centrifuge tube, thus eliminating the interference of boron background in the container to the greatest extent.

[0047] 3. The colorimetric method is susceptible to interference, low-content samples require concentrated solutions, and the steps are many and the operation is cumbersome; the ICP test of low-content sample solutions has low sensitivity. The present invention uses the high sensitivity of ICP-MS to test the effective boron extract in soil. Soil standard substances or reference substances from different regions, different contents, and different textures are used to verify the feasibility of the method. The precision and accuracy of the results are greatly improved compared with the standard method, and can basically achieve the recommended value range (Table 4).

[0048] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

[0049] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A method for analyzing available boron in soil, characterized in that: The following steps are involved: Weigh the air-dried soil sample into a PP round-bottom centrifuge tube, add magnesium sulfate solution, tighten the lid, and place it in a boiling water bath. When the water bath reaches 100 degrees again, accurately time 20 minutes; take out the centrifuge tube, cool, centrifuge, dry filter, and test the filtrate on an ICP-MS machine to analyze the content of effective boron in the air-dried soil sample.

2. The method for analyzing soil available boron according to claim 1, characterized in that: The particle size of the air-dried soil sample is 2 mm.

3. The method for analyzing soil available boron according to claim 1, characterized in that: The mass ratio of the air-dried soil sample to the magnesium sulfate solution is 500:1.

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