A method for determining boron in aquatic sediments and soil using acid dissolution-inductively coupled plasma atomic emission spectrometry

Abstract

The present invention relates to the technical field of analytical chemistry, and discloses a method for determining boron in aquatic sediments and soil using acid-soluble inductively coupled plasma atomic emission spectrometry. The sample is sealed and heated to decompose after adding hydrochloric acid, hydrofluoric acid and nitric acid. After complete decomposition, an internal standard solution containing ammonium chloride and mannitol protective agent is added, evaporated to remove a large amount of hydrofluoric acid, added to dissolve in tartaric acid solution, and then added with a cation exchange resin to remove most of the salts, shaken well, and measured on an inductively coupled plasma emission spectrum. The detection method detection limit used in the present invention is much lower than that of existing methods, and the minimum requirement for boron detection in soil and aquatic sediments can be achieved. By using the joint protection of ammonium chloride and mannitol, the volatilization loss of boron is avoided, and the rapid and accurate determination of boron in soil and aquatic sediments can be achieved, and the determination results of boron in each content section meet the specification requirements, and the method is easier to master and batch production.

Description

Technical Field

[0001] The present invention relates to the technical field of analytical chemistry, and more particularly to a method for determining boron in aquatic sediments and soil by utilizing acid dissolution-inductively coupled plasma atomic emission spectrometry. Background Art

[0002] Currently, the main methods used in China to determine boron in soil and aquatic sediments are colorimetry, emission spectroscopy, and inductively coupled plasma emission spectroscopy. Colorimetry generally suffers from high detection limits and a cumbersome process. Emission spectroscopy, due to its use of arc-excited powder samples, introduces a low reagent blank, making it highly advantageous for detecting low-content samples; however, its linear range is narrow. Furthermore, detection of organic matter, sulfide, and carbonate samples is less than ideal due to their proneness to splashing. Furthermore, inductively coupled plasma emission spectroscopy, affected by interference from elements such as iron and cobalt, struggles to meet the detection requirements of low-content samples using mathematical correction. Conventional methods have a detection limit exceeding 5 μg / g, which falls short of the minimum requirement for boron detection in soil and aquatic sediments.

[0003] To determine boron in soil and stream sediments, sample digestion can be performed using either acid dissolution or alkaline fusion. Alkaline fusion introduces a significant amount of salt, leading to significant matrix interference and high detection limits in inductively coupled plasma optical emission spectrometry. Acid dissolution, to prevent boron volatilization during evaporation, typically requires the addition of phosphoric acid or direct injection of the sample into a hydrofluoric acid medium during dissolution. Both methods have drawbacks: phosphoric acid introduces a high blanking rate, while hydrofluoric acid is highly corrosive, creating a challenging working environment for personnel protection and requiring a specialized sample injection system. This approach is rarely used for batch testing. To ensure complete sample dissolution and reduce the method's detection limit, a dedicated sample injection system is often employed.

[0004] The present invention employs acid dissolution. After the introduction of hydrofluoric acid, the removal of the hydrofluoric acid and the prevention of boron volatilization loss are key aspects of the method. Therefore, a method for determining boron in aquatic sediments and soil using acid dissolution-inductively coupled plasma atomic emission spectrometry that is simple and easy to use, while also preventing boron volatilization loss and further effectively reducing the detection limit, is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides a method for determining boron in aquatic sediments and soil by acid dissolution-inductively coupled plasma atomic emission spectrometry. The method adopts the joint protection of ammonium chloride and mannitol to avoid the volatilization loss of boron and the addition of phosphoric acid, effectively reducing the detection limit. The method is simple and easy to master, and is more suitable for mass production.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for determining boron in aquatic sediments and soil using acid dissolution-inductively coupled plasma atomic emission spectrometry, the method comprising the following steps:

[0008] (1) Weigh a certain amount of the same type of water sediment or soil sample for future use;

[0009] (2) Add the mixed acid to the above sample, shake well, then add an appropriate amount of nitric acid, and heat in a sealed container to decompose;

[0010] (3) After decomposition is complete, add internal standard solution and heat and evaporate to dryness;

[0011] (4) adding tartaric acid solution to dissolve soluble salts, adding cation exchange resin to remove most of the salts, shaking, and adding water to prepare a test solution;

[0012] (5) The solution to be tested is measured using inductively coupled plasma emission spectroscopy.

[0013] Furthermore, the amount of nitric acid added in step (2) can be appropriately increased or decreased according to the content of organic matter in the sample; the purity specification of the nitric acid is analytical grade.

[0014] Furthermore, the mixed acid in step (2) is an equal volume mixture of hydrochloric acid and hydrofluoric acid.

[0015] Furthermore, the purity specifications of the hydrochloric acid and hydrofluoric acid are both analytically pure.

[0016] Furthermore, the sealed heating decomposition in step (2) uses a polytetrafluoroethylene sealed crucible, the heating temperature is 120-160° C., and the insulation time is more than 3 hours.

[0017] Furthermore, the internal standard solution in step (3) contains 10 μg / mL of selenium, 10% ammonium chloride, 5% mannitol, and 1% HCl medium; and the heating evaporation temperature is 110° C.-150° C.

[0018] Furthermore, the concentration of the tartaric acid solution in step (4) is 0.3%; and the water is deionized water.

[0019] Furthermore, the specific preparation steps of the test solution described in step (4) are:

[0020] (1) Weigh 0.15 g of sample into a 30 mL polytetrafluoroethylene sealed crucible;

[0021] (2) After adding 4 mL of mixed acid, shake well, add 0.3 mL of nitric acid, cover, and heat to 150°C on a perforated electric hot plate, keep warm for 3 hours, and leave overnight;

[0022] (3) Open the lid, add 1 mL of internal standard solution, and heat to 150°C and evaporate to dryness;

[0023] (4) Add 5 mL of 0.3% tartaric acid solution, wait for the soluble salt to dissolve, cool, then add 2.5 g of cation exchange resin, shake for 15 minutes, add 10 mL of water and shake well to prepare the test solution.

[0024] It can be seen from the above technical solution that, compared with the prior art, the present invention discloses a method for determining boron in aquatic sediments and soil using acid dissolution-inductively coupled plasma atomic emission spectrometry, which has the following beneficial effects:

[0025] (1) After the sample is decomposed by acid, boron exists in the form of metaborate. After adding mannitol, the two combine to transform into a coordination acid with a large dissociation degree and a ring structure, which can avoid the loss of boron during the evaporation process.

[0026] (2) The presence of a certain amount of ammonium chloride can keep the sample at a certain basicity, making it easier to extract.

[0027] (3) The detection limit of the above method is lower than that of existing methods and can meet the minimum requirements for boron detection in soil and aquatic sediments.

[0028] (4) The method of the present invention is simpler and easier to master than the prior art and is suitable for mass production. DETAILED DESCRIPTION

[0029] The following is a clear and complete description of the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of the present invention.

[0030] The present invention utilizes ammonium chloride and mannitol for joint protection during acid dissolution, thereby avoiding the volatilization loss of boron and the addition of phosphoric acid, thereby effectively reducing the detection limit. The details of the method for determining boron in aquatic sediments and soil using acid dissolution-inductively coupled plasma atomic emission spectrometry implemented in this application are as follows:

[0031] 1. Reagents

[0032] Unless otherwise specified, only reagents and deionized water of confirmed analytical grade shall be used in the analysis. If, in the blank test (3.2), the analytical grade reagents used are detected to contain a content greater than the detection limit of the above elements and it is confirmed that this has affected the determination of low amounts of the above elements in the sample, the reagents shall be purified.

[0033] 1.1 Hydrochloric acid analytical grade

[0034] 1.2 Analytical grade nitric acid

[0035] 1.3 Hydrofluoric acid analytical grade

[0036] 1.4 Internal standard solution: containing 10 μg / mL selenium, 10% ammonium chloride, 5% mannitol, and 1% HCl medium.

[0037] 2. Instruments and Materials

[0038] 2.1 Agilent 5110 ICP-OES

[0039] 2.2 Argon [φ(Ar)=99.9%]

[0040] 2.3 Polytetrafluoroethylene crucible: 30mL

[0041] 2.4 Instrument operating parameters

[0042] Working parameters Technical Parameters Working parameters Technical Parameters RF power 1.2KW Atomizer flow rate (Ar) 0.7L / min Observation direction Radial observation Plasma flow 12L / min Observation altitude 8mm Auxiliary gas flow 1.0L / min Background correction Fitting Pump speed 12rpm Boron measurement wavelength 249.678nm Internal standard selenium wavelength 196.026nm

[0043] 3. Analysis steps

[0044] 3.1 Test material

[0045] The particle size of the sample should be less than 0.097 mm. After drying at 105°C for 2 hours, it should be cooled and placed in a small ground-mouth glass bottle for later use.

[0046] 3.2 Blank test

[0047] Perform duplicate blank tests throughout the entire sample analysis process.

[0048] 3.3 Quality Control

[0049] Select 2 to 4 samples of the same type of stream sediment or soil primary standard material and analyze them simultaneously with the test material.

[0050] 3.4 Preparation of test solution

[0051] Weigh 0.15 g of sample into a 30 mL polytetrafluoroethylene sealed crucible, add 4 mL of mixed acid (equal volumes of hydrochloric acid and hydrofluoric acid), shake well, then add 0.3 mL of nitric acid, cover, heat to 150 ° C on a perforated hot plate, keep warm for 3 h, leave overnight, open the lid, add 1.00 mL of internal standard solution, heat to 150 ° C and evaporate to dryness, add 5 mL of 0.3% tartaric acid solution for extraction, wait until the soluble salt is dissolved and cool, add 2.5 g of cation exchange resin, remove and shake for 15 minutes, add 10 mL of water and shake well for testing.

[0052] 3.5 Drawing of working curve

[0053] Into a series of polytetrafluoroethylene crucibles, accurately pipette boron standard solutions containing 0μg, 4μg, 8μg, 16μg, 32μg, 60μg, 80μg, and 150μg of boron, respectively. Prepare the corresponding standard solutions according to step (3.4), shake them well, and dilute them simultaneously with the sample solution. Measure according to the instrument operating conditions specified in 2.4, and draw the working curve using a computer.

[0054] 4. Calculation of analysis results

[0055] Calculate the content of each element according to the following formula:

[0056]

[0057] Where: m1—the content of the element to be measured in the sample solution found from the working curve, μg;

[0058] m0—the content of the element to be measured in the blank test solution found from the working curve, μg;

[0059] m S —Sample mass, g.

[0060] 5. Sample analysis

[0061] 5.1 Method detection limit

[0062] The detection limit of the method was calculated using three times the standard deviation of the results of 11 blank determinations.

[0063]

[0064] The detection limit of the above method is much lower than the actual detection limit of existing methods (greater than 5μg / g), which can meet the minimum requirement for boron detection in soil and aquatic sediments (<1μg / g).

[0065] 5.2 Protective effects of mannitol and ammonium chloride

[0066] Prepare the sample solution according to 3.4 in the following medium using 35 μg boron standard. The results are shown in the table below.

[0067]

[0068]

[0069] Note: Ammonium chloride is 1, mannitol is 2

[0070] From the above recovery results, it can be seen that mannitol has a very significant effect on reducing boron loss. In the presence of appropriate amounts of ammonium chloride and mannitol, boron loss is basically non-existent under the above experimental conditions.

[0071] 5.3 Method precision

[0072] In order to evaluate the precision of this method, the following five soil and stream sediment standard materials with different contents were selected for determination (8 samples for each).

[0073]

[0074] The above results show that the determination results of boron in each content range meet the specification requirements.

[0075] 5.4 Method Accuracy

[0076] In order to evaluate the accuracy of this method and its applicability to samples, 10 soil and 8 stream sediment national primary reference materials were tested. The results are shown in the following table:

[0077] Accuracy of soil determination for national primary standard material

[0078] Standard substances GSS-2 GSS-3 GSS-5 GSS-7 GSS-8 GSS-17 GSS-36 GSS-38 GSS-39 GSS-43 Standard value Cs 36 23 53 10 54 24 39 85 131 46 Measured value C 35.9 20.6 57.8 9.90 57.6 23.2 36.0 78.1 128.8 50.4 △lgc 0.001 0.048 0.038 0.004 0.028 0.015 0.035 0.037 0.008 0.039

[0079] Determination of the accuracy of national first-level standard material stream sediment

[0080] Standard substances GSD-2a GSD-9 GSD-10 GSD-11 GSD-12 GSD-15 GSD-18 GSD-19 Standard value Cs 9.7 54 26 68 24 53 5.5 14 Measured value C 8.1 52.27 24.1 70.88 22.8 51.6 5.54 14.5 △lgc 0.078 0.014 0.033 0.018 0.022 0.012 0.003 0.015

[0081] The above results of the determination of boron in various content ranges in soil and aquatic sediments show that the accuracy ΔlgC of all results is less than 0.1, which meets the specification requirements, indicating that this method can be used for the rapid and accurate determination of boron in soil and aquatic sediments.

[0082] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for determining boron in aquatic sediments and soil using acid dissolution-inductively coupled plasma atomic emission spectrometry, characterized in that: The method comprises the following steps: (1) Weigh 0.15 g of sample into a 30 mL polytetrafluoroethylene sealed crucible; (2) Add 4 mL of a mixture of hydrochloric acid and hydrofluoric acid, shake well, then add 0.3 mL of nitric acid, cover, and heat to 150°C on a perforated electric hot plate, keep warm for 3 hours, and leave overnight; (3) Open the lid, add 1 mL of internal standard solution, and heat to 150°C and evaporate to dryness; (4) Add 5 mL of 0.3% tartaric acid solution, wait for the soluble salt to dissolve, cool, then add 2.5 g of cation exchange resin, shake for 15 min, add 10 mL of water and shake well to prepare the test solution; (5) measuring the solution to be tested by inductively coupled plasma emission spectroscopy; The internal standard solution in step (3) contains 10 μg / mL of selenium, 10% ammonium chloride, 5% mannitol, and 1% HCl medium.

2. The method for determining boron in aquatic sediments and soil using acid dissolution-inductively coupled plasma atomic emission spectrometry according to claim 1, characterized in that: The purity specification of the nitric acid in step (2) is analytical grade.

3. The method for determining boron in aquatic sediments and soil using acid dissolution-inductively coupled plasma atomic emission spectrometry according to claim 1, characterized in that: The mixed acid in step (2) is an equal volume mixture of hydrochloric acid and hydrofluoric acid.

4. The method for determining boron in aquatic sediments and soil using acid dissolution-inductively coupled plasma atomic emission spectrometry according to claim 3, characterized in that: The hydrochloric acid and hydrofluoric acid are both analytically pure.

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