Method for simultaneously separating and detecting potassium ions, sodium ions, nitrate radicals and nitrite radicals in molten salt

Abstract

The invention relates to a method for simultaneously separating and detecting potassium ions, sodium ions, nitrate radicals and nitrite radicals in solar fused salt. According to the method disclosed by the invention, the contents of potassium ions, sodium ions, nitrate radicals and nitrite radicals in the solar fused salt can be simultaneously separated and quantitatively detected in single sample injection, and the method is high in separation degree, good in stability, high in accuracy, simple to operate, time-saving and efficient.

Description

Technical Field

[0001] The present invention relates to the technical field of molten salt detection, and in particular to a method for simultaneously separating and detecting potassium ions, sodium ions, nitrates and nitrites in molten salt. Background Art

[0002] The existing testing standard for solar molten salt (nitro type) is GB / T 36376-2018. The main component potassium nitrate is calculated by titrating potassium ions with sodium tetraphenylborate, and sodium nitrite is calculated by titrating nitrite with potassium permanganate, and the content of sodium nitrate is indirectly calculated by deducting other known impurities. This standard does not directly determine the main component, and the sodium tetraphenylborate precipitation titration method has cumbersome steps and is easily interfered by other impurity ions such as ammonium; the potassium permanganate method for determining nitrite is also easily interfered by other reducing substances, which will cause the results to deviate from the true value and have large errors.

[0003] At present, inductively coupled plasma emission spectrometry (ICP) is widely used for the test of cations (sodium ions, potassium ions), and ion chromatography (IC) is widely used for the test of anions (nitrate, nitrite). However, for the test of the main components in molten salt, it is necessary to dilute it by about 10,000 times. The dilution factor is too large, and it cannot be detected at the same time, resulting in large systematic errors, which makes the ratio of nitrate to potassium ions and the ratio of nitrite to sodium ions deviate greatly from the theoretical ratio of 1:1.

[0004] Currently, there is no reliable method that can achieve rapid separation and accurate detection of the main components of molten salt, namely potassium ions, sodium ions, nitrate and nitrite.

[0005] Therefore, the present invention develops a method for simultaneously separating and quantitatively detecting the main components of solar molten salt, potassium ions, sodium ions, nitrate and nitrite, in a single sample injection by high performance liquid chromatography. The method has strong specificity and low interference, simple pretreatment, and a small dilution multiple. Only one step of water dilution is required to complete the sample injection and detection. In addition, the standard sample of the salt to be tested is of high purity and easy to obtain, and the calibration calculation is accurate, thereby avoiding the error caused by separate detection. Summary of the invention

[0006] The present invention provides a method for simultaneously separating and quantitatively detecting potassium ions, sodium ions, nitrates and nitrites in solar molten salt in a single sample injection, the method comprising the following steps:

[0007] preparing an aqueous solution of solar molten salt comprising potassium nitrate and sodium nitrite;

[0008] The solution is injected into a high performance liquid chromatograph for separation and detection, wherein the stationary phase used for separation is a porous silica gel particle filler coated with sulfonated nano polymer beads, the inner pore region of the porous silica gel particles is modified with a covalently bonded hydrophilic layer, and the outer pore region is modified with sulfonated nano polymer beads; the mobile phase is a 10-100 mM acetate buffer solution with a pH of 4-5 as mobile phase A, acetonitrile as mobile phase B, and formic acid solution as mobile phase C, wherein based on the total volume of the entire mobile phase, the volume ratio of the mobile phase A to the mobile phase B is controlled to be 40:45 to 40:50,

[0009] The high performance liquid chromatograph is sequentially connected in series with an ultraviolet detector and a charged aerosol detector (CAD), wherein the ultraviolet detector is used for detecting nitrate and nitrite, and the charged aerosol detector is used for detecting sodium and potassium ions.

[0010] In the method of the present invention, the step of preparing an aqueous solution of solar molten salt containing potassium nitrate and sodium nitrite, that is, preparing a sample solution, generally comprises weighing a certain amount, generally about 0.1 g, of solar molten salt, and diluting it about 1000 times with water to obtain a sample solution.

[0011] Before or after the step of preparing the sample solution, the method of the present invention further comprises the step of preparing a standard solution. The step comprises dissolving a potassium nitrate standard and a sodium nitrite standard in water to obtain a mixed standard solution of potassium nitrate and sodium nitrite. The concentration range of the potassium nitrate and sodium nitrite standard solutions is generally 10 μg / mL to 1000 μg / mL, and those skilled in the art can determine the appropriate concentration of the standard solution according to the specific circumstances.

[0012] In the method of the present invention, the prepared sample solution is separated and detected by high performance liquid chromatography. Specifically, the prepared sample solution is injected into a high performance liquid chromatograph, and the chromatographic column stationary phase of the liquid chromatograph used is a porous silica gel particle filler coated with sulfonated nano polymer beads, the inner pore region of the porous silica gel particles is modified with a covalently bonded hydrophilic layer, and the outer pore region is modified with sulfonated nano polymer beads.

[0013] The filler is based on high-purity spherical porous silica particles with a particle size of usually 3 μm. The inner pore region is modified with an organic layer providing reverse phase and anion exchange performance using nano-polymer silica hybrid technology, and the outer pore region is modified with a sulfonated nano-polymer with cation exchange function, ensuring the spatial separation of the anion exchange region (inner pore region) and the cation exchange region (outer pore region), so that the two retention mechanisms work simultaneously and allow them to be independently controlled. Therefore, the stationary phase filler has three retention mechanisms: anion exchange, cation exchange and reverse phase.

[0014] The mobile phase used includes acetate buffer solution as mobile phase A, acetonitrile as mobile phase B, and formic acid solution as mobile phase C. The acetate buffer solution is usually adjusted to pH 4-5 with acetic acid and mobile phase C formic acid, and its concentration is usually 10-100mM, preferably 15-50mM, and more preferably 20-30mM. Based on the total volume of the mobile phase, the volume ratio of mobile phase A to mobile phase B is controlled to be 40:45 to 40:50, preferably 40:45.

[0015] In a specific embodiment, the chromatographic column used is an Acclaim Trinity P1 liquid chromatography column. In a high performance liquid chromatograph, isocratic elution is preferably used. The flow rate of the mobile phase is 0.7-0.9 mL / min, preferably 0.8 mL / min. The column temperature is 30-40° C., preferably 40° C.

[0016] In the method of the present invention, the detector used by the high performance liquid chromatograph comprises an ultraviolet detector and an electric aerosol detector connected in series successively. The sample separated after eluting from the chromatographic column first enters the ultraviolet detector to detect nitrate and nitrite, and then enters the electric aerosol detector to detect sodium ion and potassium ion. The ultraviolet detector is usually preferably a diode array detector (DAD). In the ultraviolet detector, the detection wavelength for detecting nitrate and nitrite is usually 205nm-230nm (scope), preferably 210nm.

[0017] The content of sodium ion, potassium ion, nitrate and nitrite in the sample solution can be calculated by external standard method. Specifically, using the chromatographic conditions described above, the mixed standard solution prepared above is injected into a high performance liquid chromatograph to obtain a chromatogram of each concentration standard solution, and the corresponding peak area is measured. The standard curve of nitrate and nitrite ions is drawn with the mass concentration of sodium ion, potassium ion, nitrate and nitrite ions as the horizontal coordinate and the peak area as the vertical coordinate. The content of sodium ion, potassium ion, nitrate and nitrite in the sample solution to be tested is calculated by external standard method according to the standard curve.

[0018] The present invention adopts a liquid chromatography method, uses a chromatographic column containing the above-mentioned specific stationary phase filler, especially an Acclaim Trinity P1 liquid chromatography column combined with an acetate buffer / acetonitrile mobile phase, generates multiple retention mechanisms such as reverse phase, anion exchange and cation exchange based on the mixed effect of the hydrophobic effect and electrostatic effect of the stationary phase, strictly controls the proportion of mobile phase components to adjust the hydrophobicity of nitrate and nitrite, sets reasonable elution conditions and sequentially connects an ultraviolet detector and an electric aerosol detector in series, can achieve simultaneous separation and quantitative detection of the contents of potassium ions, sodium ions, nitrate and nitrite in solar molten salt in a single sample injection, the method has high separation degree, good stability, high accuracy, simple operation, time saving and high efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 :Standard curves of sodium ion, potassium ion, nitrate and nitrite of standard solution

[0020] Figure 2 :According to Example 1, the solar molten salt sample was subjected to liquid chromatography separation and the chromatogram obtained by the DAD detector

[0021] Figure 3 : The chromatogram obtained by liquid chromatography separation of the solar molten salt sample according to Example 1 through the CAD detector

[0022] Figure 4 : Chromatogram obtained by liquid chromatography separation of solar molten salt sample according to Comparative Example 1

[0023] Figure 5 : Chromatogram obtained by liquid chromatography separation of solar molten salt sample according to Comparative Example 2

[0024] Figure 6 : Chromatogram obtained by liquid chromatography separation of solar molten salt sample according to Comparative Example 3 DETAILED DESCRIPTION

[0025] The technical solution of the present invention will be described more clearly and completely below in conjunction with embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments, and do not limit the protection scope of the present invention in any way.

[0026] Experimental Materials:

[0027] Potassium nitrate standard and sodium nitrite standard: purchased from Sinopharm Chemical Reagent Co., Ltd.

[0028] Solar molten salt sample: purchased from Weifang Changsheng Nitrate Co., Ltd.

[0029] Instruments and equipment:

[0030] Liquid chromatograph: Vanquish high performance liquid chromatograph, purchased from Thermo Fisher, USA

[0031] DAD detector: Model Vanquish Diode Array Detector HL, purchased from Thermo Fisher

[0032] CAD detector: Model Vanquish Charged Aerosol Detector F, purchased from Thermo Fisher

[0033] Embodiment 1:

[0034] The Vanquish high performance liquid chromatograph from Thermo Fisher, USA, was used, and the chromatographic conditions were set as follows:

[0035] Chromatographic column: Thermo Acclaim Trinity P1 (specification: 3.0 mm*150 mm*3 μm);

[0036] Elution mode: isocratic elution;

[0037] Mobile phase: Mobile phase A was 20 mM NH4OAc / 0.1% HOAc buffered saline solution (pH 5), mobile phase B was acetonitrile, mobile phase C was 0.1% formic acid, and the volume ratio of mobile phases A, B, and C was 40:45:15;

[0038] Flow rate: 0.8 mL / min;

[0039] Column temperature: 40°C;

[0040] Injection volume: 1.0 μL;

[0041] Detector: A DAD detector (detection wavelength: 210 nm) and a CAD detector were connected in series.

[0042] Preparation of standard solution:

[0043] Weigh 250 mg of potassium nitrate standard and sodium nitrite standard respectively, dissolve them quantitatively in water, and prepare a series of concentrations of KNO3 and NaNO2 mixed standard solutions.

[0044] Preparation of sample solution:

[0045] Weigh 100 mg of sample and dilute to 100 mL with water.

[0046] According to the above chromatographic conditions, take 1.0 μL of sample solution and inject it into the high performance liquid chromatograph to record the chromatogram. The sample chromatogram is shown in Figure 2 and Figure 3 .

[0047] The chromatogram shows that the retention times of sodium ion, potassium ion, nitrite and nitrate are approximately 3.8 min, 4.5 min, 12.6 min and 15.2 min, respectively. Their peak times differ greatly and the separation is good.

[0048] The inventors found that nitrite could not be detected by connecting a liquid chromatograph to a CAD detector. Based on this finding, the inventors connected a DAD detector and a CAD detector to the liquid chromatograph in series, first detecting nitrate and nitrite by the DAD detector, and then detecting sodium ions and potassium ions by the CAD detector, thereby successfully separating and detecting sodium ions, potassium ions, nitrate and nitrite. Figure 2 and Figure 3 shown.

[0049] According to the above chromatographic conditions, 1.0 μL of the mixed standard solution of KNO3 and NaNO2 was injected into the high performance liquid chromatograph for liquid chromatography separation and detection to obtain the quadratic linear fitting curves of sodium ions and potassium ions and the linear equation curves of nitrate and nitrite, as shown in Figure 2. Figure 1 As shown, the linear equation of nitrite is: y = 0.0901x + 0.0947, and the correlation coefficient R 2 =0.9992; nitrate linear equation: y = 0.1016x-0.0778, correlation coefficient R 2 =0.9991; Sodium ion quadratic fitting linear equation: y = -0.000019x 2 +0.0319x+0.1420, correlation coefficient R 2 =0.9987; Potassium ion quadratic fitting linear equation: y = -0.000014x 2 +0.0250x+0.0096, correlation coefficient R 2 =0.9991, wherein x represents the concentration of each ion; y represents the response peak area of ​​the corresponding ion in the detection spectrum. The linear relationship of each linear equation is good, so it can be well used for the determination of sodium ion, potassium ion, nitrate and nitrite.

[0050] The contents of sodium ion, potassium ion, nitrate and nitrite in the above samples were calculated by external standard method using the above linear relationship equation. Three batches of samples were measured in parallel 3 times, and the average value of each batch of samples was calculated. The results are shown in Table 1 below:

[0051] Table 1: Contents of sodium, potassium, nitrate and nitrite in solar molten salt samples

[0052]

[0053] It can be seen from the above results that the method of the present invention can simultaneously separate and detect the contents of sodium ions, potassium ions, nitrate and nitrite, and the results obtained have good repeatability and high accuracy. In addition, the ratio of nitrate to potassium ions and the ratio of nitrite to sodium ions have a small deviation from the theoretical ratio of 1:1, all within 3%.

[0054] Accuracy test:

[0055] The recovery of the method of the present invention was determined as follows. The results are shown in Table 2 below:

[0056] 1. Preparation of calibration curve series solutions: Weigh 500 mg of potassium nitrate and sodium nitrite standards into a 50 mL volumetric flask, record the mass to an accuracy of 0.1 mg, and dissolve in water to make up the volume. This solution is the mother solution of the standard, and the concentration is about 10000 mg / L. Prepare the calibration curve series solutions by diluting them step by step and test them.

[0057] 2. Sample preparation: Considering that the surface of solar molten salt is very easy to absorb water, and it is large granular, and there is also the situation of uneven distribution, even if the same sampling method will have deviation in concentration, but from its own chemical composition, it is potassium nitrate and sodium nitrite, so potassium nitrate and sodium nitrite standard products are used to prepare simulated samples of similar concentrations and then test. This eliminates the problem of uneven sample itself, and the accuracy of the method can still be tested. The specific steps are as follows: weigh about 0.05g potassium nitrate and 0.045g sodium nitrite to 100mL volumetric flask, record the mass and be accurate to 0.1mg, prepare 5 parts in parallel with the same steps, two of which are directly dissolved in water and tested, and the results are averaged to obtain the concentration of each ion in the simulated sample; the other three parts are dissolved in water and tested after adding 2.5mL10000mg / L standard mother solution, and the recovery rate is calculated according to the average value of each ion concentration value of the spiked sample solution and each ion concentration of the simulated sample.

[0058] Table 2: Spike recovery

[0059]

[0060] As can be seen from the above table, the recovery rates of the four ions of the molten salt sample are all between 95% and 100%, indicating that the method of the present invention has a high recovery rate and good accuracy. Therefore, the detection method of the present invention has accurate and reliable measurement results.

[0061] Comparative Example 1:

[0062] The same high performance liquid chromatograph and the same chromatographic conditions as in Example 1 were used, except that the volume ratio of mobile phase A to B was 40:60, and there was no mobile phase C. The sample solution was separated and tested, and the resulting chromatogram was as shown in FIG. Figure 4 shown.

[0063] Comparative Example 2:

[0064] The same high performance liquid chromatograph and the same chromatographic conditions as in Example 1 were used, except that the volume ratio of mobile phase A to mobile phase B was 40:20. The sample solution was separated and tested, and the resulting chromatogram was as shown in FIG. Figure 5 shown.

[0065] Depend on Figure 4 and Figure 5 It can be seen that when the proportion of acetonitrile in the mobile phase is increased to 60%, nitrite and nitrate are co-eluted; when the proportion of acetonitrile in the mobile phase is reduced to 20%, nitrite and nitrate can be separated by the baseline, but the nitrate peak becomes broad and tailing, which is not conducive to its quantification. When the proportion of acetonitrile in the mobile phase is set to 45%, nitrite and nitrate can not only be separated by the baseline, but also the peaks of the two ions are sharp and symmetrical. This makes the quantification more accurate and more repeatable. Therefore, nitrite is greatly affected by the proportion of acetonitrile in the mobile phase, and it is particularly important to properly adjust the proportion of acetonitrile for the separation of nitrite.

[0066] Comparative Example 3:

[0067] The same high performance liquid chromatograph and the same chromatographic conditions as in Example 1 were used, except that the chromatographic column used was replaced with a C18 chromatographic column: Acclaim carbonyl C18 (3.0*150 mm, 3 μm), and the sample solution was separated and detected. The obtained chromatogram is shown in FIG. Figure 6 shown.

[0068] Depend on Figure 6 It can be seen that on the C18 reverse phase chromatographic column of the same specifications, according to the response signals of CAD and DAD, the four analytes are not retained and directly co-elute.

Claims

1. A method for simultaneously separating and quantitatively detecting potassium ions, sodium ions, nitrates and nitrites in solar molten salts in a single sample injection, the method comprising the following steps: preparing an aqueous solution of solar molten salt comprising potassium nitrate and sodium nitrite; The solution is injected into a high performance liquid chromatograph for separation and detection, wherein the stationary phase used for separation is a porous silica gel particle filler coated with sulfonated nano polymer beads, the inner pore region of the porous silica gel particles is modified with a covalently bonded hydrophilic layer, and the outer pore region is modified with sulfonated nano polymer beads; the mobile phase comprises a 10-100 mM acetate buffer solution as mobile phase A, acetonitrile as mobile phase B, and formic acid solution as mobile phase C, wherein based on the total volume of the entire mobile phase, the volume ratio of the mobile phase A to the mobile phase B is controlled to be 40:45 to 40:50, The high performance liquid chromatograph is sequentially connected in series with an ultraviolet detector and a charged aerosol detector (CAD), wherein the ultraviolet detector is used for detecting nitrate and nitrite, and the charged aerosol detector is used for detecting sodium and potassium ions.

2. The method according to claim 1, wherein the stationary phase chromatographic column of the high performance liquid chromatograph is an Acclaim Trinity P1 liquid chromatography column.

3. The method of claim 1, wherein the UV detector is a diode array detector (DAD).

4. The method according to any one of claims 1 to 3, wherein isocratic elution is used in the high performance liquid chromatograph.

5. The method according to any one of claims 1 to 3, wherein in the high performance liquid chromatograph, the flow rate of the mobile phase is 0.7-0.9 mL / min.

6. The method according to any one of claims 1 to 3, wherein the column temperature used in the high performance liquid chromatograph is 30-40°C.

7. The method according to any one of claims 1 to 3, wherein the chromatographic conditions of the high performance liquid chromatograph are set as follows: Chromatographic column: Thermo Acclaim Trinity P1, specification 3.0mm*150mm*3μm; Elution mode: isocratic elution; Mobile phase: Mobile phase A was 20 mM pH 5 NH4OAc buffered saline solution, mobile phase B was acetonitrile, and mobile phase C was 0.1% formic acid aqueous solution. The volume ratio of mobile phase A to B was 40:

45. Flow rate: 0.8 mL / min; Column temperature: 40°C; Injection volume: 1.0 μL; Detector: DAD detector, detection wavelength: 210nm and CAD detector connected in series.

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