CN109709049B - Rapid molybdenum digestion method - Google Patents
Rapid molybdenum digestion method Download PDFInfo
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- CN109709049B CN109709049B CN201811435520.XA CN201811435520A CN109709049B CN 109709049 B CN109709049 B CN 109709049B CN 201811435520 A CN201811435520 A CN 201811435520A CN 109709049 B CN109709049 B CN 109709049B
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Abstract
The invention relates to a digestion method of metal elements, in particular to a rapid digestion solution of molybdenum, which comprises the following raw materials in parts by weight: 8-12 parts of nitric acid aqueous solution, 3-6 parts of sodium ferrate aqueous solution, 1-2.5 parts of sodium persulfate aqueous solution and 0.2-0.4 part of modified rubidium chloride; the digestion method provided by the invention has the advantages that the digestion time is greatly shortened, and the sample accuracy is also improved; in addition, the method is simple and stable to operate, can effectively improve the working efficiency, and has a good application prospect.
Description
Technical Field
The invention relates to a digestion method of metal elements, belongs to the technical field of chemical component detection, and particularly relates to a rapid digestion method of molybdenum.
Background
Because the environmental sample has a plurality of pollution types and complex components, and most of the components to be measured have low concentration and different forms, and a large amount of interfering substances exist in the sample. More importantly, with the development of environmental science and technology, most organic pollutants still can be quantitatively described by comprehensive indexes (such as COD, BOD, TOC and the like) and cannot meet the requirements of environmental monitoring work. Many organic matters belong to persistent and biologically-accumulable toxic pollutants and have a 'three-cause' effect, and the organic matters have extremely low concentration in an environmental medium, contribute extremely little to the comprehensive indexes or cannot be reflected at all. This means that prior to analytical determination, different sample pretreatments are required to obtain a morphology and concentration of the component to be determined which is suitable for the analytical method requirements and which maximizes separation from interfering substances. When inorganic elements in an environmental sample (a water sample, a soil sample, solid waste, particles trapped during atmospheric sampling, and the like) are measured, the environmental sample needs to be digested, organic matters are destroyed, the particles are dissolved, and elements to be measured in various valence states are oxidized into a single high valence state or converted into an inorganic compound which is easy to decompose.
Molybdenum is a necessary trace element for human bodies, and the content of molybdenum in the human bodies is very small and only accounts for one million of the weight of the human bodies. Although the content of molybdenum is extremely small, it has a considerable importance for human life. However, the method for detecting molybdenum in China is not complete up to now. In the prior art, a traditional wet digestion manual method is used for detection, and a mixed solution of sulfuric acid and nitric acid is used as a digestion solution, so that the sulfuric acid has high density, is difficult to volatilize, has long digestion time, wastes time and labor, and has low accuracy; in addition, because the boiling point of the sulfuric acid is high, the volatilization is difficult, the residual liquid after digestion is basically sulfuric acid, the acidity in the sample is larger than the curve acidity, the sensitivity is reduced, and the data is low.
Disclosure of Invention
The invention aims to provide a rapid molybdenum digestion method, which has a good molybdenum digestion effect, can greatly shorten the digestion time, improves the accuracy of a sample, and can meet the requirements of actual detection.
The invention provides a rapid molybdenum digestion method, which is realized by the following technical scheme:
a rapid digestion method of molybdenum adopts a digestion solution, and the digestion solution comprises the following raw materials in parts by weight: 8-12 parts of nitric acid aqueous solution, 3-6 parts of sodium ferrate aqueous solution, 1-2.5 parts of sodium persulfate aqueous solution and 0.2-0.4 part of modified rubidium chloride.
As a preferable scheme, the digestion solution comprises the following raw materials in parts by weight: 9-11 parts of nitric acid aqueous solution, 4-5 parts of sodium ferrate aqueous solution, 1.5-2 parts of sodium persulfate aqueous solution and 0.25-0.35 part of modified rubidium chloride.
As an optimal scheme, the digestion solution comprises the following raw materials in parts by weight: 10 parts of nitric acid aqueous solution, 4.5 parts of sodium ferrate aqueous solution, 1.8 parts of sodium persulfate aqueous solution and 0.3 part of modified rubidium chloride.
As a preferable embodiment, the method for preparing modified rubidium chloride comprises the following steps:
(1) adding rubidium chloride powder and benzene sulfinic acid into absolute ethyl alcohol, heating to 55-65 ℃, stirring for 40-70 min, cooling to room temperature, and standing for 2.5-4 hours; the mass ratio of the benzene sulfinic acid to the rubidium chloride powder is 1: 10-13, wherein the mass ratio of the absolute ethyl alcohol to the rubidium chloride powder is 3-5.5: 1;
(2) adding fatty alcohol-polyoxyethylene ether into the mixture obtained in the step (1), heating and stirring at 55-75 ℃ for 80-95 min, filtering, and drying to obtain the modified rubidium chloride powder; the fatty alcohol-polyoxyethylene ether and rubidium chloride powder is 1: 12 to 16.
As a preferable scheme, the digestion solution is prepared by the following steps: adding the nitric acid aqueous solution, the sodium ferrate aqueous solution, the sodium persulfate aqueous solution and the modified rubidium chloride into a container in sequence, and uniformly mixing to obtain the modified rubidium chloride.
Preferably, the concentration of the nitric acid aqueous solution is 1.43-1.52 g/ml.
Preferably, the mass fraction of the sodium ferrate aqueous solution is 8-15%.
Preferably, the mass fraction of the sodium persulfate aqueous solution is 10-18%.
As a preferable scheme, the total digestion time is 20-30 min.
As a preferable scheme, the rapid digestion method of molybdenum comprises the following steps:
(1) sampling: collecting an air sample by using a small plastic sampling clamp provided with a microporous filter membrane at a sampling point of a workplace, folding the dust-collecting surface of the filter membrane inwards after sampling, and putting the filter membrane into a clean container for transportation and storage;
(2) preparing a reagent: deionized water, digestion liquid and sulfuric acid solution;
(3) digestion: first digestion: putting the sampled microporous filter membrane into a container, adding 5-8 mL of digestion solution, shaking uniformly at normal temperature, then putting into a microwave digestion device for digestion, and taking out a sample after the first digestion is finished; and (4) second digestion: continuing heating and digesting, evaporating the digestion solution, repeating the operation until the color of the liquid is bright, and stopping digesting; dissolving with sulfuric acid, quantitatively transferring into 50ml volumetric flask, metering to a certain volume, shaking to , and taking 5ml in a colorimetric tube with a plug for determination.
As a preferable scheme, the flow rate of the collected air sample in the step (1) is 1-1.5L/min, the collection time is 1-5 h, and the number of folding the dust-collecting surface of the filter membrane inwards is 2-3.
Preferably, the volume fraction of the sulfuric acid in the step (2) is 10-15%.
As a preferable scheme, the microwave digestion in the step (3) is carried out under the conditions of power of 1400-1600W, temperature rise time of 4-6 min, temperature control of 90-110 ℃ and microwave digestion time of 2-3 min.
As a preferable scheme, the heating condition for the second digestion in the step (3) is to heat up to 180-200 ℃ within 4-5 min.
As a preferable scheme, the molybdenum element is measured by adopting a standard curve method, and the preparation method of the standard curve is as follows:
taking 6 colorimetric tubes with plugs, adding 0.0, 0.5, 1.0, 2.0, 3.0 and 5.0ml of molybdenum standard solution respectively, adding sulfuric acid solution to 5.0ml respectively to prepare 0.0, 1.0, 2.0, 4.0, 6.0 and 10.0ug /ml of molybdenum standard series, adding 6ml of developing solution into each standard tube, shaking uniformly, standing for 10min, measuring absorbance at 470nm wavelength, repeatedly measuring each concentration for 3 times, and drawing a standard curve according to the absorbance average value to the molybdenum content (mug).
As a preferred scheme, the preparation method of the molybdenum standard solution comprises the following steps: 0.2522g of sodium molybdate is dissolved in sulfuric acid, and quantitatively transferred to a 100ml volumetric flask, the volume is constant, and the solution is 1.0mg/ml standard stock solution; immediately before use, the solution was diluted with sulfuric acid to a molybdenum standard solution of 10.0. mu.g/ml.
As a preferred embodiment, the preparation method of the color developing solution comprises the following steps: 100mL of 250 g/L potassium thiocyanate solution, 50 g/L ascorbic acid solution and 50% (volume fraction) sulfuric acid solution are mixed with 5mL of 0.4 g/L cuprous chloride solution, and the mixture is prepared on the same day.
Has the advantages that: according to the rapid molybdenum digestion method, the modified rubidium chloride obtained by the preparation method is added, so that compared with the prior art, the digestion time is greatly shortened to 20-30 min from the original 2h, the sample accuracy is improved, the relative standard deviation is small, and a lower detection limit is obtained; in addition, the method is simple, convenient and stable to operate, and can effectively reduce the working strength while improving the working efficiency.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are a part of the embodiments of the present invention, but not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Embodiment 1 quick digestion method of molybdenum
The digestion solution comprises the following raw materials in parts by weight: 10 parts of nitric acid aqueous solution, 4.5 parts of sodium ferrate aqueous solution, 1.8 parts of sodium persulfate aqueous solution and 0.3 part of modified rubidium chloride;
the preparation method of the modified rubidium chloride comprises the following steps:
(1) adding rubidium chloride powder and benzene sulfinic acid into absolute ethyl alcohol, heating to 60 ℃, stirring for 60 min, cooling to room temperature, and standing for 3 hours; the mass ratio of the benzene sulfinic acid to the rubidium chloride powder is 1: 11.5, wherein the mass ratio of the absolute ethyl alcohol to the rubidium chloride powder is 4.5: 1;
(2) adding fatty alcohol-polyoxyethylene ether into the mixture obtained in the step (1), heating and stirring at 65 ℃ for 85 min, filtering, and drying to obtain the modified rubidium chloride powder; the fatty alcohol-polyoxyethylene ether and rubidium chloride powder is 1: 14.
the rapid molybdenum digestion method comprises the following steps:
(1) sampling: collecting an air sample for 1.2h at a sampling point of a workplace by using a small plastic sampling clamp provided with a microporous filter membrane at a flow rate of 1.2L/min, folding the dust-collecting surface of the filter membrane inwards for 3 times after sampling, and putting the filter membrane into a clean container for transportation and storage;
(2) preparing a reagent: deionized water; the digestion solution is prepared from a nitric acid aqueous solution, a sodium ferrate aqueous solution and a sodium persulfate aqueous solution according to a volume ratio of 4: 1:1, wherein the concentration of the nitric acid aqueous solution is 1.45g/ml, the mass fraction of the sodium ferrate aqueous solution is 35 percent, and the concentration of the sodium persulfate aqueous solution is 1.38 g/ml; the volume fraction of the sulfuric acid solution is 13%;
(3) digestion: first digestion: putting the sampled microporous filter membrane into a container, adding 5-8 mL of digestion solution, shaking uniformly at normal temperature, then putting the container into a microwave digestion device for digestion, wherein the power is 1500W, the temperature rise time is 5min, the temperature is controlled to be 100 ℃, the microwave digestion time is 3min, and taking out a sample after the first digestion is finished; and (4) second digestion: heating to 200 deg.C within 5min, continuing digestion, volatilizing digestion solution, repeating the above operations, digesting until the color of the liquid is transparent, stopping digestion, and digesting for a total time of 23 min; dissolving with sulfuric acid, quantitatively transferring into 50ml volumetric flask, metering to a certain volume, shaking to , and taking 5ml in a colorimetric tube with a plug for determination.
(4) Preparation of a standard curve:
taking 6 colorimetric tubes with plugs, adding 0.0, 0.5, 1.0, 2.0, 3.0 and 5.0ml of molybdenum standard solution respectively, adding sulfuric acid solution to 5.0ml respectively to prepare 0.0, 1.0, 2.0, 4.0, 6.0 and 10.0ug /ml of molybdenum standard series, adding 6ml of developing solution into each standard tube, shaking uniformly, standing for 10min, measuring absorbance at 470nm wavelength, repeatedly measuring each concentration for 3 times, drawing a standard curve by using the absorbance average value to the molybdenum content (mug), obtaining a regression equation, wherein the specific results are shown in Table 1.
The preparation method of the molybdenum standard solution comprises the following steps: 0.2522g of sodium molybdate is dissolved in sulfuric acid, and quantitatively transferred to a 100ml volumetric flask, the volume is constant, and the solution is 1.0mg/ml standard stock solution; immediately before use, the solution was diluted with sulfuric acid to a molybdenum standard solution of 10.0. mu.g/ml.
The preparation method of the color developing solution comprises the following steps: 100mL of 250 g/L potassium thiocyanate solution, 50 g/L ascorbic acid solution and 50% (volume fraction) sulfuric acid solution are mixed with 5mL of 0.4 g/L cuprous chloride solution, and the mixture is prepared on the same day.
(5) And (3) accuracy analysis: to verify the accuracy of the method, 20 μ g/ml of molybdenum standard solutions were added to the test samples in volumes of 0.05ml, 0.25ml and 0.5ml, respectively, and the average recovery rate was measured 3 times, with the linear equation of this experiment being y =0.224x +0.0001 and the correlation coefficient r =0.9991, and the specific results are shown in table 2.
(6) Relative standard deviation and detection limit: the same batch of samples was subjected to 20 measurements with the relative standard deviation and detection limit.
Comparative example 1
Comparative example 1 differs from example 1 in that a different digestion solution was used, the digestion solution used in comparative example 1 was prepared by mixing sulfuric acid (ρ 20 ═ 1.84 g/mL) and nitric acid (ρ 20 ═ 1.42 g/mL) in a volume ratio of 1:4, and the rest of the procedure and procedure were the same as in example 1.
Comparative example 2
The difference between the comparative example 2 and the example 1 is that the conventional rubidium chloride is used for replacing the modified rubidium chloride in the formula raw materials of the digestion solution, and the other components and the content are the same; the rest of the operation method and the steps are the same as those of the example 1.
Comparative example 3
The difference between the comparative example 3 and the example 1 is that modified rubidium chloride is not added in the formula raw materials of the digestion solution, and the other components and the content are the same; the rest of the operation method and the steps are the same as those of the example 1.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
TABLE 1 Standard series of concentrations and corresponding absorbances
As can be seen from the data in Table 1, the linear relation r is more than 0.999, and the standard curve and the result manufactured by the method are reliable and meet the actual detection requirements.
TABLE 2 precision, detection limit and accuracy analysis
As can be seen from Table 2, in the embodiment 1 and the comparison 1, the rapid digestion method for molybdenum can greatly shorten the digestion time from 2 hours to 20-30 min, improve the sample accuracy, obtain a lower detection limit with a small relative standard deviation; from example 1 and comparative examples 2 and 3, it can be seen that if conventional rubidium chloride is used instead of or in addition to the modified rubidium chloride according to the present invention, the accuracy, relative standard deviation and detection limit are not as good as those of example 1, and comparative example 2 has the worst effect.
Claims (9)
1. The rapid digestion method of molybdenum is characterized by adopting a digestion solution, wherein the digestion solution comprises the following raw materials in parts by weight: 8-12 parts of nitric acid aqueous solution, 3-6 parts of sodium ferrate aqueous solution, 1-2.5 parts of sodium persulfate aqueous solution and 0.2-0.4 part of modified rubidium chloride;
the preparation method of the modified rubidium chloride comprises the following steps:
adding rubidium chloride powder and benzene sulfinic acid into anhydrous ethanol, and heating to
Stirring for 40-70 min at 55-65 ℃, cooling to room temperature, and standing for 2.5-4 hours; the mass ratio of the benzene sulfinic acid to the rubidium chloride powder is 1: 10-13, wherein the mass ratio of the absolute ethyl alcohol to the rubidium chloride powder is 3-5.5: 1;
(2) and (2) adding fatty alcohol-polyoxyethylene ether into the mixture obtained in the step (1), heating and stirring at 55-75 ℃ for 80-95 min, filtering, and drying to obtain the modified rubidium chloride powder.
2. The molybdenum rapid digestion method as claimed in claim 1, wherein the digestion solution comprises the following raw materials in parts by weight: 9-11 parts of nitric acid aqueous solution, 4-5 parts of sodium ferrate aqueous solution, 1.5-2 parts of sodium persulfate aqueous solution and 0.25-0.35 part of modified rubidium chloride.
3. The molybdenum rapid digestion method as claimed in claim 1, wherein the digestion solution comprises the following raw materials in parts by weight: 10 parts of nitric acid aqueous solution, 4.5 parts of sodium ferrate aqueous solution, 1.8 parts of sodium persulfate aqueous solution and 0.3 part of modified rubidium chloride.
4. The molybdenum rapid digestion method as claimed in claim 1, wherein the digestion solution is prepared by the following steps: adding the nitric acid aqueous solution, the sodium ferrate aqueous solution, the sodium persulfate aqueous solution and the modified rubidium chloride into a container in sequence, and uniformly mixing to obtain the modified rubidium chloride.
5. The molybdenum rapid digestion method according to claim 4, wherein the concentration of the nitric acid aqueous solution is 1.43-1.52 g/ml.
6. The molybdenum rapid digestion method according to claim 4, wherein the mass fraction of the sodium ferrate aqueous solution is 8-15%.
7. The molybdenum rapid digestion method according to claim 4, wherein the mass fraction of the sodium persulfate aqueous solution is 10-18%.
8. The molybdenum rapid digestion method according to claim 1, wherein the total time for digestion is 20-30 min.
9. The rapid molybdenum digestion method according to claim 1, wherein the digestion step comprises: first digestion: putting the sampled microporous filter membrane into a container, adding 5-8 mL of digestion solution, shaking uniformly at normal temperature, then putting into a microwave digestion device for digestion, and taking out a sample after the first digestion is finished; and (4) second digestion: and (4) continuing heating and digesting, evaporating the digestion solution, repeating the operation, digesting until the color of the liquid is bright, and stopping digesting.
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