Analysis method for measuring content of impurity elements in high-purity cesium

Abstract

The invention discloses an analysis method for determining the content of impurity elements in high-purity cesium, and belongs to the technical field of high-purity metal material detection. The method specifically comprises the following steps: sampling and weighing a sample in a glove box in an inert gas environment, then moving out the glove box, spontaneously decomposing the sample in the air, adding nitric acid to acidify the sample after the sample is converted into an aqueous solution, fixing the volume, determining the sample by using an inductively coupled plasma emission spectrometry, and determining aluminum, iron and lead by using a standard curve method in a horizontal observation mode. Lithium, calcium, sodium and magnesium are measured in a vertical observation mode, potassium and rubidium are measured through a standard addition method, and finally the content of all impurity elements is obtained through calculation. According to the method, oxygen-isolated sampling, spontaneous heating and decomposition are realized, accurate and total analysis of impurity elements is realized through combination of a standard curve method and a standard addition method, the problem that a matrix is difficult to match is avoided, and technical support is provided for production control and market transaction of high-purity cesium.

Description

Technical Field

[0001] The present invention relates to the technical field of high-purity metal material detection, and specifically to an analytical method for determining the content of impurity elements in high-purity cesium. Background Art

[0002] High-purity cesium refers to metallic cesium with a purity of more than 99.9%. It has the characteristics of high activity, strong positive electricity, good electrical conductivity, and excellent photoelectric effect, and is widely used in traditional fields such as electronics, catalysis, biochemistry, and medicine, as well as high-tech fields such as magnetohydrodynamic power generation, ion propulsion engines, photovoltaic cell materials, laser manufacturing, optical fiber communication, and satellite navigation. With the development of technology, the application prospects of high-purity cesium are even broader.

[0003] Impurity elements in high-purity cesium will significantly affect the physical and chemical properties of cesium (such as electrical, optical, and thermal properties), and thus have an adverse impact on its application performance. Therefore, it is necessary to accurately determine and strictly control their content. The state issued the product standard of cesium, "YS / T 1245—2018 Cesium" in 2018, which stipulates the types of impurity elements (i.e., lithium, sodium, potassium, rubidium, calcium, magnesium, iron, aluminum, lead) and the limit requirements, but does not provide an analytical method for the content. The detection methods reported in relevant literature include spectrophotometry, photodynamic method, flame emission spectrometry, and flame atomic absorption spectrometry. These are all single-element analysis methods, with cumbersome operations and low efficiency, and it is difficult to meet the current requirements for rapid analysis. Before using instrument detection, it is necessary to sample and decompose the hermetically stored high-purity cesium to convert it into an aqueous solution. Cesium is the most reactive metal, which will quickly oxidize when exposed to air, making it difficult to sample in air, and it is prone to explosion reactions when encountering liquid solvents. In view of these characteristics, the traditional method is to directly place a whole bottle of sample in a splash-proof closed container, break the bottle, and then slowly add liquid reagents (such as sulfuric acid, water, anhydrous ethanol) for decomposition. This treatment method reduces the severity of decomposition to a certain extent, but it still fails to solve the problem of explosion due to too fast reaction rate, and the whole-bottle reaction method also fails to solve the sampling problem. Therefore, it is of great practical significance and necessity to establish an analytical method with oxygen isolation sampling, mild decomposition, and high detection efficiency. Summary of the Invention

[0004] In view of the above problems, the present invention provides an analytical method for determining the content of impurity elements in high-purity cesium, realizing oxygen isolation sampling, mild decomposition, and rapid determination.

[0005] The technical solution adopted by the present invention includes the following steps:

[0006] (1) Number the centrifuge tubes, and then place the high-purity cesium samples sealed and packaged in ampoules or vials, centrifuge tubes with lids, scissors, and pipettes inside the glove box, where the inside of the glove box is an inert gas; calibrate the one-ten-thousandth electronic balance previously placed inside the glove box with standard weights, then weigh and tare the centrifuge tubes, open the bottle containing the sample with scissors, and use a pipette to transfer 0.05 - 0.25 g of the sample into the centrifuge tube, and weigh the mass of the sample.

[0007] (2) Tighten the centrifuge tubes, take them out of the glove box, and enter the air atmosphere.

[0008] (3) Place the centrifuge tube obliquely in a 100 mL glass beaker, open and remove the lid of the centrifuge tube, and let the sample decompose spontaneously until it decomposes into an aqueous solution.

[0009] (4) Add 5 - 8 mL of water into the centrifuge tube, then add 1.25 - 2.5 mL of analytical reagent grade nitric acid with a mass fraction of 65% - 68%. Add 50 - 70 mL of hot water at 60 - 70 °C into the glass beaker outside the centrifuge tube, immerse the centrifuge tube in the hot water for 15 - 20 min, then take it out and cool it to room temperature, and make the volume up to 25 or 50 mL with water, and shake well to obtain the sample solution.

[0010] (5) Take another centrifuge tube the same as in step (4), add analytical reagent grade nitric acid with the same volume and mass fraction as in step (4), make the volume up to the same volume as in step (4) with water, and shake well to obtain the blank solution.

[0011] (6) Prepare a series of standard working solutions containing aluminum, iron, lead, lithium, calcium, sodium, and magnesium with a multi-element mixed standard stock solution.

[0012] (7) Set the analysis conditions of the inductively coupled plasma optical emission spectrometer, and then in the horizontal observation mode, in the order of increasing mass concentrations of aluminum, iron, and lead in the series of standard working solutions, measure their signal intensities in turn. Respectively, take the mass concentrations of aluminum, iron, and lead as the abscissa and the corresponding signal intensities as the ordinate to draw the standard curve. Then, measure the blank solution and the sample solution in turn, and the instrument automatically calculates the mass concentrations of aluminum, iron, and lead in the blank solution and the sample solution according to the standard curve. Then, in the vertical observation mode, in the order of increasing mass concentrations of lithium, calcium, sodium, and magnesium in the series of standard working solutions, measure their signal intensities in turn. Respectively, take the mass concentrations of lithium, calcium, sodium, and magnesium as the abscissa and the corresponding signal intensities as the ordinate to draw the standard curve. Then, measure the blank solution and the sample solution in turn, and the instrument automatically calculates the mass concentrations of lithium, calcium, sodium, and magnesium in the blank solution and the sample solution according to the standard curve.

[0013] (8) Remove 4 - 5 portions of 5.00 mL solutions from the sample solution. For one portion, no potassium standard solution is added. For the remaining portions, potassium standard solutions with proportional volumes are added respectively. After shaking well, measure the signal intensities of potassium in these solutions in sequence. Using the mass concentration of the added potassium standard solution as the abscissa and the corresponding potassium signal intensity as the ordinate, plot the standard curve. The instrument automatically extends the curve in the reverse direction to intersect with the abscissa, and the absolute value of the intersection point is the mass concentration of potassium in the sample solution. Similarly, rubidium is also determined using the same standard addition method.

[0014] (9) According to the measured mass concentrations of each impurity element, calculate the content of each impurity element in the sample according to formula (1). If an impurity element is not detected, measure the blank solution continuously for 11 times to obtain 11 mass concentration values, calculate its standard deviation, use 3 times the standard deviation as the detection concentration, and then calculate the method detection limit according to formula (2). Then, the content of the undetected impurity element is expressed as "< method detection limit".

[0015] Formula (1) w x represents the mass fraction of the impurity element to be measured in the sample, with the unit of %;

[0016] ρ x represents the mass concentration of the impurity element to be measured in the sample solution, with the unit of mg / L;

[0017] ρ 0 represents the mass concentration of the impurity element to be measured in the blank solution, with the unit of mg / L;

[0018] V represents the fixed volume of the sample solution, with the unit of mL;

[0019] m represents the sample amount, with the unit of g;

[0020] Formula (2) w represents the method detection limit, with the unit of %;

[0021] ρ represents the detection concentration, with the unit of mg / L;

[0022] V represents the fixed volume of the sample solution, with the unit of mL;

[0023] m represents the sample amount, with the unit of g.

[0024] Preferably, in step (1), the centrifuge tube with a lid must be dry. Otherwise, when the sample is put in, it will immediately react explosively with the water in the centrifuge tube. Select a volume of 50 mL for convenience of subsequent decomposition and fixed volume. The material is polypropylene.

[0025] Preferably, in step (1), the inert gas in the glove box is selected as argon.

[0026] Preferably, in the step (1), the sample is generally in a liquid state. When the room temperature is relatively low, especially in winter, cesium will solidify (the melting point of cesium is 28.4 °C). At this time, the sample can be slightly heated to melt it, and then the bottle containing the sample can be opened for sampling.

[0027] Preferably, in the step (1), the measuring range of the pipette is selected as 0.2 mL. According to the density of cesium, 1.879 g / cm 3 , the volume corresponding to a sampling amount of 0.2 g can be calculated as 0.10 mL. Therefore, the sampling volume of the pipette is adjusted in advance to facilitate accurate sampling. The sampling amount will be affected by the sample delivery amount (generally about 1 g of analytical sample is equipped for each batch of products), and it can be adjusted according to the actual situation.

[0028] Preferably, in the step (1), it is best to take 4 sub-samples for each sample, with 2 sub-samples used for the standard curve method determination and the remaining 2 sub-samples used for the standard addition method determination.

[0029] In the step (3), the principle of the spontaneous decomposition method is as follows: High-purity cesium rapidly oxidizes in the air to form oxides such as cesium peroxide, cesium superoxide, and cesium ozonide. The oxides absorb water vapor in the air and gradually turn into white cesium hydroxide solid. Since cesium hydroxide has strong deliquescence, it will then absorb water vapor and gradually turn into an aqueous solution of cesium hydroxide. The principle is shown in Figure 2 , and the main chemical reaction equations are as follows:

[0030] Cs(s or l) + O 2 (g) → 2Cs x O y (s) (Cs 2 O 2 、CsO 2 、CsO 3 etc.)

[0031] Cs x O y (s) + H 2 O(g) → CsOH(s) + O 2 (g)

[0032] CsOH(s) + H 2 O(g) → CsOH(l) + H 2 O(l)

[0033] Preferably, in the step (3), the spontaneous decomposition is achieved by relying on oxygen and water vapor in the air. The oxidation rate in this step is extremely fast, but the water absorption rate is relatively slow. Especially when the air is dry and the humidity is low, the water absorption rate will become slower. At this time, it can be placed on the porcelain plate of a desiccator with water at the bottom. And in order to make the spontaneous decomposition proceed sufficiently, it needs to be placed for more than 12 h or overnight.

[0034] Preferably, in the steps (4) and (5), the water in the centrifuge tube is primary water meeting the requirements of GB / T 6682—2008, and the water outside the tube is tap water.

[0035] Preferably, in the step (4), the fixed volume depends on the sampling amount. When the sampling amount is 0.1 - 0.25 g, the fixed volume is selected as 50 mL; when the sample amount is within 0.1 g, the fixed volume is selected as 25 mL.

[0036] Preferably, in the step (6), the multi - element mixed standard stock solution contains lithium, sodium, calcium, magnesium, iron, aluminum, lead, etc., and the concentration of each element is 100 μg / mL.

[0037] Preferably, in the step (6), the preparation method of the series of standard working solutions is as follows: respectively pipette 0 mL, 0.10 mL, 0.30 mL, 0.50 mL, 1.00 mL, 2.00 mL of the multi - element mixed standard stock solution into 6 100 - mL volumetric flasks, add 5 mL of analytical - reagent - grade nitric acid with a mass fraction of 65% - 68%, make up the volume to the mark with primary water, and shake well. The mass concentrations of each impurity element in this series of standard working solutions are 0.00 mg / L, 0.10 mg / L, 0.30 mg / L, 0.50 mg / L, 1.00 mg / L, 2.00 mg / L respectively. In addition, the mass concentration of the series of standard working solutions can be appropriately adjusted according to the content of the elements to be measured in the sample solution.

[0038] Preferably, in the step (7), for the standard curve drawn based on the series of standard working solutions, the correlation coefficient needs to be above 0.999. Otherwise, find out the standard working solution with a large deviation, re - prepare it until the correlation coefficient reaches above 0.999.

[0039] Preferably, in the step (7), the impurity elements are determined by two observation methods. Among them, aluminum, iron, and lead are determined by the horizontal method because the content of these three impurity elements is often below 0.0002%, and the horizontal method can maintain a low detection ability; lithium, calcium, sodium, and magnesium are determined by the vertical method because these four impurity elements are alkali metals and alkaline earth metals and are easily ionized and interfered by cesium. The interference can be reduced or eliminated by the vertical method.

[0040] Preferably, in the step (7), it is measured by an inductively coupled plasma emission spectrometer manufactured by Thermo Fisher Scientific, and its working conditions are as follows: the peristaltic pump speed is 50 r / min; the RF generator power is 1.15 kW; the nebulizer gas flow rate is 0.6 L / min; the auxiliary gas flow rate is 0.5 L / min; the nebulizer pressure is 0.23 MPa; the flushing time is 30 s; the integration time is 15 s; the number of integrations is 3 times; the working gas is high-purity argon with a purity greater than 99.99%; the analysis spectral lines are: lithium 607.7 nm, sodium 589.5 nm, calcium 393.3 nm, magnesium 280.2 nm, iron 259.9 nm, aluminum 396.1 nm, lead 220.3 nm.

[0041] Preferably, in the step (8), potassium and rubidium are determined by the standard addition method, aiming to eliminate the strong interference of cesium to improve the accuracy.

[0042] Preferably, in the step (8), the volume of the potassium (or rubidium) standard solution added to each sample solution should be controlled within 1% of the volume of the sample solution. Since the volume increment is extremely small, the total volume is still regarded as 5.00 mL and remains unchanged.

[0043] Preferably, in the step (8), the analysis spectral line of potassium is 766.4 nm, and the analysis spectral line of rubidium is 780.0 nm.

[0044] The present invention has the following beneficial effects compared with the prior art:

[0045] (1) Aiming at the situation that high-purity cesium is extremely easy to oxidize and it is very difficult to take samples in the air, the present invention uses the inert gas in the glove box to exhaust oxygen to create an anaerobic environment and realizes oxygen-isolated sampling.

[0046] (2) Aiming at the problem that the traditional decomposition method explodes due to too fast reaction rate, in order to slow down the reaction rate, the present invention proposes the idea of introducing reaction gas to decompose the sample. Utilizing the physical and chemical properties of cesium and its compounds (cesium is easy to oxidize, cesium oxide is easy to absorb water vapor, and cesium hydroxide is easy to deliquesce), the air spontaneous decomposition method is proposed, realizing mild decomposition, and no reagents are added during the decomposition process, reflecting green environmental protection.

[0047] (3) The matrix in this sample solution is cesium nitrate, which will interfere with the accurate determination of impurity elements and it is necessary to eliminate the interference. However, according to the "Regulations on the Safety Management of Hazardous Chemicals", cesium nitrate belongs to an explosive precursor substance and is under the control of the public security department. Therefore, the matrix interference is not eliminated by the matrix matching method, but by the combination of the standard curve method and the standard addition method, realizing the accurate and comprehensive analysis of impurity elements, thus avoiding the problem of difficult matrix matching. At the same time, compared with the traditional single-element analysis method, the detection efficiency is also significantly improved.

[0048] The present invention realizes oxygen-isolated sampling, spontaneous mild decomposition, and rapid and accurate determination, which has important guiding significance for the production, trading, and application of high-purity cesium. Description of the Drawings

[0049] Figure 1 It is a schematic flow chart of the determination method of the present invention;

[0050] Figure 2 It is a schematic diagram of the principle of the spontaneous decomposition method of high-purity cesium. Detailed Embodiments

[0051] The following specifically describes the implementation manner of the present invention through embodiments. The following embodiments are intended to illustrate the present invention rather than further limit the protection scope of the present invention.

[0052] Example 1:

[0053] I. Reagents and Instruments

[0054] Primary water meeting the requirements of GB / T 6682—2008 (for volume fixation in centrifuge tubes and preparation of series of standard working solutions).

[0055] Guaranteed reagent nitric acid with a mass fraction of 65% - 68%.

[0056] Potassium single-element standard solution: with a mass concentration of 20 mg / L, diluted from a potassium standard stock solution with a mass concentration of 1000 mg / L.

[0057] Rubidium single-element standard solution: with a mass concentration of 100 mg / L, diluted from a rubidium standard stock solution with a mass concentration of 1000 mg / L.

[0058] Multi-element mixed standard stock solution: containing Al, Ca, Fe, Li, Mg, Na, Pb, etc., and the mass concentration of each element is 100 μg / mL.

[0059] Centrifuge tube (with a volume of 50 mL and a polypropylene material).

[0060] Glove box (inside the box is high-purity argon with a purity greater than 99.999%, an oxygen content lower than 0.5 ppm, and a water vapor content lower than 0.5 ppm).

[0061] One-ten-thousandth electronic balance.

[0062] Pipette (range 0.2 mL).

[0063] Icap 6300 Inductively Coupled Plasma Emission Spectrometer (produced by Thermo Fisher Scientific), with the following analysis conditions: RF generator power is 1.15 kW; peristaltic pump speed is 50 r / min; nebulizer gas flow rate is 0.6 L / min; auxiliary gas flow rate is 0.5 L / min; nebulizer pressure is 0.23 MPa; flushing time is 30 s; integration time is 15 s; number of integrations is 3 times; the working gas is high-purity argon with a purity greater than 99.99%.

[0064] II. Sample Preparation

[0065] (1) Sampling and weighing. Take 4 dry 50-mL centrifuge tubes, numbered 4, 6, 7, and 8 (where tubes 4 and 6 are used for parallel determination of potassium and rubidium, and tubes 7 and 8 are used for parallel determination of lithium, sodium, calcium, magnesium, iron, aluminum, and lead). Then place the capped centrifuge tubes, the samples sealed in vials (the implementation time is in November, the room temperature is low, and hold them in the palm beforehand to melt them), scissors, and pipettes in the glove box. Calibrate the one-ten-thousandth electronic balance placed in the glove box beforehand with standard weights, and then weigh and tare the centrifuge tubes. Open the vial with scissors, and then use a pipette to aspirate the samples and place them into the 4 centrifuge tubes respectively, and weigh them. The sample amounts are 0.1649 g, 0.1616 g, 0.2176 g, and 0.2153 g in sequence. Tighten the lids of the centrifuge tubes and take them out of the glove box.

[0066] (2) Spontaneous decomposition. Place the centrifuge tubes obliquely in a 100-mL glass beaker, open and remove the lids of the centrifuge tubes. At this time, the samples will immediately decompose spontaneously in the air and all turn into aqueous solutions after being placed for 21 h.

[0067] (3) Acidification and volume fixation. Add 5 mL of water and 2.5 mL of GR nitric acid with a mass fraction of 65% - 68% to the centrifuge tubes. Add 55 mL of hot water at 60 °C to the glass beaker outside the centrifuge tubes, and immerse the centrifuge tubes in the hot water for 15 min. Take out the centrifuge tubes, cool to room temperature, and fix the volume to 50 mL with water, and shake well to obtain the sample solution.

[0068] III. Blank Test

[0069] Take another 50-mL centrifuge tube, add 2.5 mL of GR nitric acid with a mass fraction of 65% - 68%, fix the volume to 50 mL with water, and shake well to obtain the blank solution to eliminate the reagent errors brought by nitric acid and water.

[0070] IV. Preparation of Series of Standard Working Solutions

[0071] Transfer 0 mL, 0.10 mL, 0.30 mL, 0.50 mL, 1.00 mL, and 2.00 mL of the multi-element mixed standard stock solution into six 100 mL volumetric flasks respectively. Add 5 mL of high-purity nitric acid with a mass fraction of 65% - 68%, make up the volume with water, and shake well. The mass concentrations of each impurity element in this series of standard working solutions are 0.00 mg / L, 0.10 mg / L, 0.30 mg / L, 0.50 mg / L, 1.00 mg / L, and 2.00 mg / L respectively.

[0072] V. Determination of Impurities

[0073] (1) Determination of lithium, sodium, calcium, magnesium, iron, aluminum, and lead. Under the set analysis conditions of the inductively coupled plasma optical emission spectrometer, in the order of increasing mass concentrations of aluminum, iron, and lead in the series of standard working solutions, measure their signal intensities in turn. Respectively, take the mass concentrations of aluminum, iron, and lead as the abscissa and the corresponding signal intensities as the ordinate to plot the standard curves, and check the correlation coefficients of the standard curves, all of which are above 0.999 (see Table 1). Then, measure the blank solution and the sample solution in turn, and the instrument automatically calculates the mass concentrations of aluminum, iron, and lead in the blank solution and the sample solution according to the standard curves.

[0074] Then, under the vertical observation mode, in the order of increasing mass concentrations of lithium, sodium, calcium, and magnesium in the series of standard working solutions, measure their signal intensities in turn. Respectively, take the mass concentrations of lithium, sodium, calcium, and magnesium as the abscissa and the corresponding signal intensities as the ordinate to plot the standard curves, and check the correlation coefficients of the standard curves, all of which are above 0.999 (see Table 1). Then, measure the blank solution and the sample solution in turn, and the instrument automatically calculates the mass concentrations of lithium, sodium, calcium, and magnesium in the blank solution and the sample solution according to the standard curves.

[0075] (2) Determination of potassium and rubidium. Take out five 5.00 mL solutions from sample solution No. 6, and add 0, 0.01 mL, 0.025 mL, 0.0375 mL, and 0.05 mL of the potassium single-element standard solution with a mass concentration of 20 mg / L respectively, and shake well. Then the mass concentrations of the added potassium standard solutions are 0, 0.04 mg / L, 0.10 mg / L, 0.15 mg / L, and 0.20 mg / L respectively. Then, use the standard addition method mode of the inductively coupled plasma optical emission spectrometer to measure the signal intensities of potassium in these five solutions in turn. Take the mass concentrations of the added potassium standard solutions as the abscissa and the corresponding signal intensities as the ordinate to plot the standard curve, and check the correlation coefficient of the standard curve, which is above 0.999. Then click calculate, and the instrument automatically extends the standard curve backward to intersect with the abscissa. The absolute value of the intersection point is the mass concentration of potassium in sample solution No. 6. Then measure the mass concentration of potassium in sample solution No. 4.

[0076] From the test sample solution No. 4, take out 4 portions of 5.00 mL solutions, and add 0, 0.01 mL, 0.02 mL, and 0.04 mL of rubidium single-element standard solution with a mass concentration of 100 mg / L respectively. Shake well. Then the mass concentrations of the added rubidium standard solutions are 0, 0.20 mg / L, 0.40 mg / L, and 0.80 mg / L. Then use the standard addition method of inductively coupled plasma emission spectrometer to measure the signal intensities of rubidium in these 4 solutions in turn. Take the mass concentration of the added rubidium standard solution as the abscissa and the corresponding signal intensity as the ordinate to draw a standard curve, and check the correlation coefficient, which is above 0.999. Then click to calculate, and the instrument automatically extends the standard curve backward to intersect with the abscissa. The absolute value of the intersection point is the mass concentration of rubidium in the sample solution No. 4. Then measure the mass concentration of rubidium in the sample solution No. 6.

[0077] VI. Result Calculation and Representation

[0078] According to the measured mass concentrations of each impurity element, calculate the content of each impurity element in the sample according to formula (1), and the results are shown in Table 2. Since lithium, magnesium, aluminum, and lead are not detected, measure the blank solution continuously for 11 times to obtain 11 mass concentration values, calculate their standard deviation, and take 3 times of the standard deviation as the detection concentration. Then calculate the method detection limit according to formula (2) (see Table 3). Then the content of the undetected impurity element is expressed as "< method detection limit".

[0079] The calculation results are in units of %, and are retained to the 4th decimal place; when not detected, report lower than the method detection limit, and the method detection limit is retained to 1 significant figure.

[0080] Formula (1) w x represents the mass fraction of the measured impurity element in the sample, in units of %;

[0081] ρ x represents the mass concentration of the measured impurity element in the sample solution, in units of mg / L;

[0082] ρ 0 represents the mass concentration of the measured impurity element in the blank solution, in units of mg / L;

[0083] V represents the constant volume of the sample solution, in units of mL;

[0084] m represents the sample amount, in units of g.

[0085] Formula (2) w represents the method detection limit, in units of %;

[0086] ρ represents the detection concentration, in units of mg / L;

[0087] V represents the fixed volume of the sample solution, with the unit of mL;

[0088] m represents the sample amount, with the unit of g.

[0089] Table 1 Standard curve of impurity elements

[0090] element <![CDATA[Linear range / mg·L -1 > linear equation correlation coefficient aluminum 0.10～2.00 Y = 9073.59*X + 27.80 0.999947 iron 0.10～2.00 Y = 13090.37*X + 61.77 0.999495 lead 0.10～2.00 Y = 1191.72*X + 10.14 0.999906 lithium 0.10～2.00 Y = 10604.29*X + 333.23 0.999834 sodium 0.10～2.00 Y = 1441.33*X + 27.59 0.999760 calcium 0.10～2.00 Y = 15752.25*X + 411.51 0.999415 magnesium 0.10～2.00 Y = 2641.17*X + 6.61 0.999863 potassium 0.04～0.20 Y = 193717.46*X + 8113.98 0.999663 rubidium 0.20～0.80 Y = 45542.84*X + 18352.08 0.999905

[0091] Table 2 Content of impurity elements in high-purity cesium measured in Example 1

[0092] sodium potassium calcium lithium magnesium 0.0015％ 0.0013％ 0.0003％ <0.00007％ <0.00003％ aluminum lead rubidium iron <0.00008％ <0.0002％ 0.0091％ 0.0001％

[0093] Table 3 Determination of method detection limit

[0094]

[0095] VII. Standard addition recovery test

[0096] Furthermore, to verify the accuracy of the method, a standard addition recovery test was conducted. Pipette 2 portions of 5.00 mL sample solution, and add 0.02 mL and 0.005 mL of multi-element mixed standard stock solution with a mass concentration of 100 mg / L respectively. After shaking well, measure the results, as shown in Table 4. It can be seen from Table 4 that the standard addition recovery rate of sodium is 103.0% and that of calcium is 107.8%, which is relatively good; the standard addition recovery rates of the remaining impurities (magnesium, lithium, aluminum, iron, lead) are between 68.3% and 120.0%. Since their contents are all lower than 0.0002%, the influence is not significant; in addition, potassium and rubidium are determined by the standard addition method, eliminating the matrix interference of cesium. Therefore, this method has good accuracy.

[0097] Table 4 Standard addition recovery test of Example 1

[0098]

[0099]

[0100] Example 2:

[0101] Take 4 dry 50 mL centrifuge tubes, numbered 1, 2, 3, and 4. Then place the capped centrifuge tubes, the samples sealed in vials, scissors, and pipettes in the glove box. Calibrate the one-ten-thousandth electronic balance that has been previously placed in the glove box with standard weights, and then weigh and tare the centrifuge tubes. Open the vial with scissors, and then use a pipette to aspirate the sample into the centrifuge tube and weigh it to obtain sample amounts of 0.0714 g, 0.0700 g, 0.0724 g, and 0.0720 g. Cover the lids of the centrifuge tubes and take them out of the glove box. Place the centrifuge tubes obliquely in a 100 mL glass beaker, open and remove the lids of the centrifuge tubes, and place them in the fume hood to decompose spontaneously. After 24 h, add 5 mL of water and 1.25 mL of nitric acid with a mass fraction of 65% - 68% to the inclined centrifuge tubes. Add 55 mL of hot water at 60 °C to the glass beaker outside the centrifuge tubes, and immerse the centrifuge tubes in the hot water for 15 min. Take out the centrifuge tubes, cool them to room temperature, make up the volume to 25 mL with water, and shake well to obtain the sample solutions. Take another 50 mL centrifuge tube, add 1.25 mL of analytical reagent grade nitric acid with a mass fraction of 65% - 68%, make up the volume to 25 mL with water, and shake well to obtain the blank solution. Set the analysis conditions of the inductively coupled plasma emission spectrometer, then determine by inductively coupled plasma emission spectrometry, and use the standard curve method to determine the mass concentrations of aluminum, iron, and lead in the sample blank solution and the sample solutions under the horizontal observation mode, and determine the mass concentrations of lithium, calcium, sodium, and magnesium in the sample blank solution and the sample solutions under the vertical observation mode. Use the standard addition method to determine the mass concentrations of potassium and rubidium in the sample solutions (where samples 1 and 2 are used for parallel determination of lithium, sodium, calcium, magnesium, iron, aluminum, lead, and potassium; samples 3 and 4 are used for parallel determination of rubidium), and calculate their contents according to formula (1), and the results are shown in Table 5.

[0102] In this example, the reagents and instruments, the preparation method of the series of standard working solutions, the determination of impurities, and the determination method of the method detection limit are the same as those in Example 1.

[0103] Table 5 Contents of impurity elements in high-purity cesium measured in Example 2

[0104]

[0105] From the measurement results of the two examples (Table 2 and Table 5), it can be seen that sodium, potassium, and rubidium are the main impurities. These elements are alkali metal elements that are closely adjacent to cesium and have similar chemical properties, making separation difficult; for other impurities, such as calcium, magnesium, iron, lead, aluminum, and lithium, the contents are very low, and most are below 0.0001%.

[0106] In summary, the analytical method for determining the content of impurity elements in high-purity cesium provided by the present invention realizes oxygen-isolated sampling, spontaneous gentle decomposition, and rapid determination. Moreover, through the combination of the standard curve method and the standard addition method, accurate and comprehensive analysis of impurity elements is achieved, avoiding the problem of difficult matrix matching, providing technical support for the detection of trace impurities in high-purity cesium, and being of great significance for improving the product quality of high-purity cesium and promoting application upgrading.

Claims

1. An analytical method for determining the content of impurity elements in high-purity cesium, characterized in that: The following steps are involved: (1) Number the centrifuge tubes, and then place the high-purity cesium samples sealed in ampoules or vials, centrifuge tubes with caps, scissors, and pipettes in a glove box, wherein the glove box is filled with inert gas; calibrate a 1 / 10,000 electronic balance placed in the glove box in advance with a standard weight, and then weigh and peel the centrifuge tubes, open the bottles containing the samples with scissors, and use a pipette to transfer 0.05 to 0.25 g of the samples into the centrifuge tubes, and weigh the mass of the samples; (2) Cover the centrifuge tube tightly, take it out of the glove box, and let it enter the air atmosphere; (3) Place the centrifuge tube at an angle in a 100 mL glass beaker, open and remove the lid of the centrifuge tube, and allow the sample to spontaneously decompose until it decomposes into an aqueous solution; (4) Add 5 to 8 mL of water to the centrifuge tube, then add 1.25 to 2.5 mL of high-grade pure nitric acid with a mass fraction of 65% to 68%, add 50 to 70 mL of hot water at 60 to 70°C to a glass beaker outside the centrifuge tube, soak the centrifuge tube in the hot water for 15 to 20 min, then take it out and cool it to room temperature, dilute it to 25 or 50 mL with water, and shake it well to obtain a sample solution; (5) Take another centrifuge tube that is the same as step (4), add the same volume and mass fraction of high-grade pure nitric acid as step (4), dilute to the same volume as step (4) with water, and shake well to obtain a blank solution; (6) Prepare a series of standard working solutions containing aluminum, iron, lead, lithium, calcium, sodium, and magnesium using a multi-element mixed standard stock solution; (7) Setting the analysis conditions of the inductively coupled plasma emission spectrometer, and then measuring the signal strength in the order of the mass concentration of aluminum, iron, and lead in the series of standard working solutions from low to high in the horizontal observation mode, and drawing a standard curve with the mass concentration of aluminum, iron, and lead as the horizontal coordinate and the corresponding signal strength as the vertical coordinate, and then testing the blank solution and the sample solution in turn, and the instrument automatically calculates the mass concentration of aluminum, iron, and lead in the blank solution and the sample solution according to the standard curve; then, in the vertical observation mode, measuring the signal strength in the order of the mass concentration of lithium, calcium, sodium, and magnesium in the series of standard working solutions from low to high, and drawing a standard curve with the mass concentration of lithium, calcium, sodium, and magnesium as the horizontal coordinate and the corresponding signal strength as the vertical coordinate, and then testing the blank solution and the sample solution in turn, and the instrument automatically calculates the mass concentration of lithium, calcium, sodium, and magnesium in the blank solution and the sample solution according to the standard curve; (8) From the sample solution, remove 4 to 5 5.00 mL portions of solution, of which 1 portion does not contain potassium standard solution, and the remaining portions are added with potassium standard solution in proportion to their volumes. After shaking, the signal intensities of potassium in these solutions are measured in turn. A standard curve is drawn with the mass concentration of the added potassium standard solution as the abscissa and the corresponding potassium signal intensity as the ordinate. The instrument automatically extends the curve in the reverse direction to intersect with the abscissa. The absolute value of the intersection is the mass concentration of potassium in the sample solution. Similarly, rubidium is also measured using the same standard addition method. (9) Based on the measured mass concentration of each impurity element, the content of each impurity element in the sample is calculated according to formula (1); if the impurity element is not detected, the blank solution is measured 11 times continuously to obtain 11 mass concentration values, and the standard deviation is calculated. Three times the standard deviation is taken as the detection concentration, and then the method detection limit is calculated according to formula (2). The content of the undetected impurity element is expressed as "<method detection limit". Formula (1) w x Indicates the mass fraction of the impurity element in the sample, in %; ρ x Indicates the mass concentration of the impurity element being measured in the sample solution, in mg / L; ρ0 represents the mass concentration of the impurity element to be measured in the blank solution, in mg / L; V represents the constant volume of the sample solution, in mL; m represents the sample size in g; Formula (2) w represents the detection limit of the method, in %; ρ represents the detected concentration, in mg / L; V represents the constant volume of the sample solution, in mL; m represents the sample size in g.

2. The method according to claim 1, characterized in that In step (1), the centrifuge tube must be dry, have a volume of 50 mL, and be made of polypropylene.

3. The method according to claim 1, characterized in that: In the step (3), spontaneous decomposition is achieved by relying on oxygen and water vapor in the air. In order to allow the spontaneous reaction to proceed fully, it needs to be left for more than 12 hours or overnight.

4. The method according to claim 1, characterized in that In the step (4), the fixed volume depends on the sampling amount; when the sampling amount is 0.1-0.25 g, the fixed volume is 50 mL; when the sample amount is less than 0.1 g, the fixed volume is 25 mL; in the steps (4) and (5), the water in the centrifuge tube is first-class water that meets the requirements of GB / T 6682-2008, and the water outside the tube is tap water.

5. The method according to claim 1, characterized in that In step (6), the multi-element mixed standard stock solution includes lithium, sodium, calcium, magnesium, iron, aluminum and lead, and the concentration of each element is 100 μg / mL.

6. The method according to claim 1, characterized in that In the step (6), the preparation method of the series of standard working solutions is: respectively transfer 0 mL, 0.10 mL, 0.30 mL, 0.50 mL, 1.00 mL, and 2.00 mL of the multi-element mixed standard stock solution into 6 100 mL volumetric flasks, add 5 mL of high-grade pure nitric acid with a mass fraction of 65% to 68%, make up to volume with first-grade water, and shake well. The mass concentration of each impurity element in this series of standard working solutions is 0.00 mg / L, 0.10 mg / L, 0.30 mg / L, 0.50 mg / L, 1.00 mg / L, and 2.00 mg / L, respectively.

7. The method according to claim 1, characterized in that In the step (7), the correlation coefficient of the standard curve drawn based on the series of standard working solutions must be above 0.

999. Otherwise, a standard working solution with a large deviation is found and re-prepared until the correlation coefficient reaches above 0.

999.

8. The method according to claim 1, characterized in that In the step (7), an inductively coupled plasma emission spectrometer manufactured by Thermo Fisher Scientific is used for measurement, and its working conditions are: peristaltic pump speed is 50r / min; RF generator power is 1.15kW; nebulizer gas flow rate is 0.6L / min; auxiliary gas flow rate is 0.5L / min; nebulizer pressure is 0.23MPa; flushing time is 30s; integration time is 15s; integration times are 3 times; the working gas is high-purity argon with a purity greater than 99.99%; the analysis spectral lines are: lithium 607.7nm, sodium 589.5nm, calcium 393.3nm, magnesium 280.2nm, iron 259.9nm, aluminum 396.1nm, lead 220.3nm.

9. The method according to claim 1, characterized in that: In step (8), the volume of potassium or rubidium standard solution added to each sample solution should be controlled within 1% of the volume of the sample solution. Since the volume increment is very small, the total volume is still regarded as 5.00 mL and remains unchanged.

10. The method according to claim 1, characterized in that In the step (8), the analytical spectrum of potassium is 766.4 nm, and the analytical spectrum of rubidium is 780.0 nm.

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