Method for inhibiting coffee ring effect and correcting LIBS matrix effect

Abstract

The invention belongs to the related technical field of laser-induced plasma emission spectroscopy, and discloses a method for inhibiting coffee ring effect and correcting LIBS (laser-induced breakdown spectroscopy) matrix effect, which comprises the following steps: respectively introducing a first element and a second element which have similar characteristics with precipitated and non-precipitated elements in to-be-detected chlorate, and respectively preparing into a solution A and a solution B; mixing and oscillating to form a uniform suspension, and heating and drying the uniform suspension to obtain a sample; ablating the sample based on an LIBS technology, collecting original spectral data, and obtaining a distribution area of each element to be detected; dividing the distribution area into a settling area and a non-settling area, respectively selecting a first element and a second element as internal standard elements for the two areas, selecting an internal standard spectral line according to spectral line information of the internal standard elements, and finally performing quantitative analysis by using an internal standard method. According to the method, the coffee ring effect and the matrix effect can be effectively inhibited while the advantages of high efficiency and convenience of LIBS are reserved, so that the stability and quantitative performance of an LIBS detection spectrum are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field related to laser-induced plasma emission spectroscopy, and more specifically, relates to a method for suppressing the coffee ring effect and correcting the LIBS matrix effect. Background Art

[0002] Currently, quantitative analysis of elements in chloride salt samples using laser-induced breakdown spectroscopy (LIBS) typically requires cooling the sample first. However, cooled molten chloride salts, primarily composed of magnesium chloride, calcium chloride, and sodium chloride, are highly deliquescent at room temperature, increasing the sample's surface water content and causing the spectral signal to decrease and become unstable. Therefore, precipitation is used during testing to convert the deliquescent salts into less deliquescent salts, which are then dried and deposited.

[0003] However, since non-precipitated elements (such as Na) are unevenly distributed due to the coffee ring effect, this leads to their uneven distribution on the surface and thus exhibits obvious matrix effects, which not only significantly interferes with the spectral intensity but also further reduces the accuracy of element quantitative detection.

[0004] To suppress the coffee ring effect, researchers have tried a variety of methods, including rapid drying, adding surfactants or adhesives, controlling droplet volume, spin coating or spray coating instead of drop sheets, using microstructured substrates, and applying external fields. However, these methods generally have certain limitations, such as changing solution composition, introducing spectral interference, complex sample preparation, high equipment requirements, or poor reproducibility. Furthermore, it is often difficult to fundamentally eliminate the problems of particle migration and uneven deposition during the droplet drying process.

[0005] Methods for suppressing matrix effects primarily include internal standardization, standard addition, matrix-matching calibration, multivariate correction algorithms, optimization of excitation parameters (such as delay time), and the use of auxiliary techniques such as dual-pulse excitation or spatial confinement. While these methods can improve quantitative accuracy to a certain extent, they each have significant limitations. For example, the traditional internal standardization method cannot simultaneously internally standardize all elements to be analyzed when elements are distributed in different regions. The standard addition method is cumbersome and inefficient. Matrix matching is limited by the availability of standard samples. Multivariate models rely heavily on sample size and representativeness. Adjustment of excitation conditions and field assistance often require complex equipment or precise control.

[0006] Accordingly, this field urgently needs to make further research and improvement in order to better meet the comprehensive needs of quantitative analysis of elements in deliquescent chloride salts. Summary of the Invention

[0007] To address one or more of the above-mentioned deficiencies or needs in the prior art, the present invention provides a method for suppressing the coffee ring effect and correcting for matrix effects in LIBS. The method introduces an exogenous precipitable element to suppress the coffee ring effect in the distribution of non-precipitable elements in the analyte. Simultaneously, improvements are made to the internal standard method. Consequently, the method can more effectively suppress the coffee ring effect and correct for matrix effects while retaining the advantages of LIBS's efficiency and convenience, thereby improving the stability and quantitative performance of LIBS detection spectra. Furthermore, the method offers advantages such as ease of operation, high efficiency and precision, and good adaptability, making it particularly suitable for the quantitative analysis of elements in various deliquescent chloride salts.

[0008] To achieve the above objectives, according to the present invention, a method for suppressing the coffee ring effect and correcting the LIBS matrix effect is provided, characterized in that the method comprises the following steps: S1. Select a first element or its compound having similar precipitation properties to the precipitating element in the chloride salt to be tested, dissolve it in distilled water to form a solution; then dissolve the chloride salt to be tested in the solution to prepare solution A; S2. Weigh the dispersant NNO (sodium salt of 2-naphthalenesulfonic acid formaldehyde polymer) and dissolve it in deionized water to form a dispersant solution. Then, select a carbonate or sulfate of a second element with similar solubility characteristics to the non-precipitated element in the chloride salt to be tested, and add it to the dispersant solution to prepare Solution B. S3, mixing the liquid A and the liquid B and ultrasonically shaking them to form a uniform suspension; S4, adding dropwise the uniform suspension obtained in step S3 and storing the suspension, heating the suspension, and completely drying the suspension to obtain a sample that is no longer deliquescent and has suppressed coffee ring effect; S5. ablating the samples based on LIBS technology, and collecting LIBS raw spectrum data of each sample; S6. Obtaining the distribution area of ​​each element to be measured in the sample based on the LIBS original spectrum data; S7, dividing the distribution area into a precipitation area corresponding to the precipitating element and a non-precipitating area corresponding to the non-precipitating element; S8. Select the first element as the internal standard element of the element to be measured for the precipitation area, and select the second element as the internal standard element of the element to be measured for the non-precipitation area, then select the internal standard spectral line according to the spectral line information of these internal standard elements, and finally use the internal standard method to perform quantitative analysis of all the elements to be measured.

[0009] As a further preferred embodiment of the present invention, in step S1, the precipitating elements in the chloride salt to be tested are preferably Ca and Mg, and the first element having similar precipitation characteristics is preferably Ba, an element of the same group.

[0010] As a further preferred embodiment of the present invention, in step S1, during the preparation of solution A, while introducing a first element having similar precipitation characteristics to the precipitating element in the chloride salt to be measured, it is ensured that the content of all elements to be measured in solution A remains unchanged.

[0011] As a further preferred embodiment of the present invention, in step S2, the non-precipitable element in the chloride salt to be measured is preferably Na, and the second element having similar solubility characteristics to Na is preferably K.

[0012] As a further preferred embodiment of the present invention, in step S2, when the chloride salt to be measured contains Na element, the dispersant solution needs to be subjected to a sodium removal treatment.

[0013] As a further preference of the present invention, the sodium removal treatment is preferably performed by ion exchange chromatography: first, an H-type cation exchange resin is added to the chromatography column, and a sodium-containing dispersant solution is poured from the top of the chromatography column, and the treated solution is collected below the chromatography column; after each chromatography, the H-type cation exchange resin is continuously rinsed with deionized water to ensure that no dispersant remains, and then a new H-type cation exchange resin is replaced; the above operation is repeated three or more times to obtain a dispersant solution free of sodium.

[0014] As a further preferred embodiment of the present invention, in step S3, the uniform suspension is preferably prepared by the following process: S31, adding the solution B to multiple clean containers in batches and in a quantitative manner until all the solution B is packaged; S32, mixing the liquid A with the liquid B in each clean container by shaking in a mass ratio of 1 to 5, and obtaining the desired multiple uniform suspensions after mixing.

[0015] As a further preferred embodiment of the present invention, in step S4, the sample is preferably generated by the following process: S41. Use a circular hole puncher to punch holes with a diameter of 8 mm to 10 mm in the tape, and then stick the tape on a pure quartz glass slide. S42. Use a pipette to drop 50 μL to 100 μL of the uniform suspension into the circular holes on the pure quartz glass slide. The added suspension is confined in the circular holes. Then, place the pure quartz glass slide on a heating table and dry it at a temperature of about 60° C. for 1 to 5 minutes to obtain the desired sample.

[0016] As a further preference of the present invention, in step S8, the internal standard spectrum line is preferably selected in the following manner: compare the spectrum line information of the internal standard element, and select the spectrum line whose energy level on the spectrum line of the internal element is closest to the energy level on the analysis line of the element to be measured, and use it as the internal standard spectrum line.

[0017] In general, the above technical solutions conceived by the present invention have the following technical advantages compared with the existing technology: 1. The present invention can effectively suppress the coffee ring effect of the distribution of non-precipitable elements in the elements to be measured by introducing exogenous precipitable elements; 2. The present invention further divides the distribution characteristics of different elements to be measured into precipitated and non-precipitated types, and then selects elements with the same characteristics as the target element as internal standard elements. In this way, matrix effects are corrected separately. Compared with the existing technology, the stability and quantitative performance of LIBS detection spectra can be better improved, thereby obtaining more accurate and reliable detection results. 3. The entire operation process of the present invention does not require changing the properties of the solution or substrate. It can suppress the coffee ring effect while correcting the LIBS matrix effect while maintaining the advantages of LIBS efficiency and convenience. It also has the advantages of easy control, high efficiency and precision, and good adaptability. Therefore, it is particularly suitable for application scenarios of quantitative analysis of elements in various deliquescent chloride salts. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a flow chart of the overall process of coffee ring suppression and classification matrix effect correction based on LIBS according to the present invention; Figure 2 is a pseudo-color diagram of the distribution of the Na element in a sample without the introduction of the Ba element according to one embodiment of the present invention; Figure 3 is a pseudo-color diagram of the distribution of the Na element in the sample after the Ba element is introduced according to one embodiment of the present invention; Figure 4 This is a pseudo-color image of the distribution of Na and K elements in a sample after K element is introduced according to one embodiment of the present invention; Figure 5 is a pseudo-color image of the distribution of Ca, Mg, and Ba elements in a sample after the introduction of Ba element according to one embodiment of the present invention; Figure 6 This is a calibration curve diagram of Ca, Mg, and Na elements in a sample obtained according to an embodiment of the present invention. DETAILED DESCRIPTION

[0019] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0020] As analyzed in the "Background Art," the major drawback or shortcoming of the prior art is that the coffee ring effect is suppressed solely by changing the properties of the solution or substrate, without subsequently correcting for the matrix effect. Therefore, in the present invention, the elements to be measured are divided into precipitating types (such as Ca and Mg) and non-precipitating types (such as Na) based on their precipitation characteristics. Additional precipitation is introduced to increase the precipitation amount, thereby suppressing the coffee ring effect. Furthermore, different internal standard elements are used, depending on the distribution regions of the precipitating and non-precipitating elements, to further correct for the matrix effect, thereby achieving rapid and high-precision detection of elements in deliquescent salts. Accordingly, the present application achieves more effective suppression of the coffee ring effect while retaining the high efficiency and convenience advantages of LIBS, without requiring changes to the solution or substrate properties, while simultaneously achieving LIBS matrix effect classification correction.

[0021] Figure 1 This is the overall process flow chart of the method for suppressing the coffee ring effect and correcting the LIBS matrix effect according to the present invention, which will be referred to below. Figure 1 , to explain the present invention in more detail.

[0022] Step 1: Preparation of Liquid A.

[0023] In this step, a first element or its compound having similar precipitation properties to the precipitating element in the chloride salt to be tested is selected and dissolved in distilled water to form a solution; the chloride salt to be tested is then dissolved in the solution to prepare Solution A; More specifically, for the first element introduced above, in order to avoid spectral interference of the precipitated substance on the element to be measured, the introduced element should mainly meet the following requirements: (1) The element has similar precipitation characteristics to the precipitating element in the original test solution, that is, it easily forms precipitation with the same anion; In addition, the following other requirements may also be met: (2) The element does not affect the original chemical reaction process in other precipitates. When adding other salts containing the element, the introduced anions must also meet this requirement; (3) The salt containing the introduced element should have a large solubility at room temperature to meet the requirement of a large addition amount; (4) The atomic emission lines of the introduced elements do not interfere with the analytical lines of the elements to be measured.

[0024] Step 2: Preparation of Liquid B.

[0025] In this step, a dispersant, NNO (sodium salt of 2-naphthalenesulfonic acid formaldehyde polymer), is weighed and dissolved in deionized water to form a dispersant solution. A carbonate or sulfate of a second element having similar solubility characteristics to the non-precipitated element in the chloride salt to be tested is then added to the dispersant solution to form Solution B. More specifically, this step can be divided into the following two cases: (1) If the element to be measured does not contain sodium, directly weigh the dispersant NNO and dissolve it in water to prepare a dispersant solution with a mass concentration of, for example, 5%; (2) If the element to be measured contains sodium, it is necessary to remove the sodium. In this case, dispersant NNO is weighed and dissolved in water, and the dispersant solution is preferably desodiumized using ion exchange chromatography, as follows: Add H-type cation exchange resin to the chromatography column, pour the sodium dispersant solution from the top of the chromatography column, and use a beaker to collect the treated solution at the bottom of the chromatography column. After each chromatography, use deionized water to continuously rinse the resin to ensure that no dispersant remains. Then replace the new resin. This step can be repeated three times to obtain a 2-naphthalenesulfonic acid formaldehyde polymer (C 21 H 16 O6S2) solution, inductively coupled plasma optical emission spectrometry (ICP-OES) can be used to confirm that there is no sodium in the dispersant solution.

[0026] Next, based on the solubility characteristics or distribution patterns of the non-precipitated elements in the elements to be measured after adding the precipitant, a carbonate or sulfate of the appropriate element is selected so that after adding the carbonate or sulfate to the dispersant solution, the element has the same solubility characteristics or distribution patterns as the non-precipitated elements to be measured.

[0027] Step 3: Preparation of uniform suspension.

[0028] In this step, the liquid A and the liquid B are mixed and ultrasonically shaken to form a uniform suspension; More specifically, the above step 3 can be further completed according to the following sub-steps: S31, adding a quantitative amount (e.g., 5 ml) of Solution B dropwise in batches into multiple clean containers (e.g., glass bottles) until all Solution B is dispensed; S32, mixing the liquid A with the liquid B in each clean container by shaking in a mass ratio of 1 to 5, and obtaining a plurality of desired light yellow uniform suspensions after mixing.

[0029] Step 4: Sample preparation.

[0030] In this step, the uniform suspension obtained in step S3 is added dropwise and stored, and then heated and completely dried to obtain a sample that is no longer deliquescent and has suppressed coffee ring effect; More specifically, the above step 4 can be further completed according to the following sub-steps: S41. Use a circular hole puncher to punch holes with a diameter of 8 mm to 10 mm in the tape, and then stick the tape on a pure quartz glass slide. S42. Use a pipette to drop 50 μL to 100 μL of the uniform suspension into the circular holes on the pure quartz glass slide. The added suspension is confined in the circular holes. Then, place the pure quartz glass slide on a heating table and dry it at a temperature of about 60° C. for 1 to 5 minutes to obtain the desired sample.

[0031] Step 5: LIBS detection.

[0032] In this step, the samples are ablated based on the LIBS technology, and the LIBS raw spectrum data of each sample is collected. This process is common knowledge in the field and will not be described in detail here.

[0033] Step 6: Obtain the distribution area of ​​the element to be measured.

[0034] In this step, the distribution area of ​​each element to be measured in the sample is obtained based on the LIBS original spectrum data.

[0035] Step 7: Division of precipitation area and non-precipitation area.

[0036] In this step, the distribution area obtained above is further divided into a precipitation area corresponding to the precipitating elements and a non-precipitating area corresponding to the non-precipitating elements; Step 8: Quantitative analysis by internal standard method, during which matrix correction is also achieved.

[0037] In this step, the first element is selected as the internal standard element of the element to be measured in the precipitation area, and the second element is selected as the internal standard element of the element to be measured in the non-precipitation area. Then, the internal standard spectral line is selected according to the spectral line information of these internal standard elements, and finally the internal standard method is used to perform quantitative analysis of all the elements to be measured.

[0038] More specifically, for example, after LIBS mapping imaging of the element to be measured using a microscopic LIBS imaging analyzer, the area can be divided into precipitation and non-precipitation areas according to the distribution of precipitated elements and non-precipitated elements. Based on the distribution of the element to be measured in these two areas, the element with the same distribution area as the element to be measured is selected as the internal standard element of the element to be measured. Based on the spectral line information of the internal standard element, the spectral line with the upper energy level of the spectral line of the internal standard element closest to the upper energy level of the analytical line of the element to be measured is selected as the internal standard spectral line. Finally, quantitative analysis is performed using the internal standard method.

[0039] A specific embodiment will be given below to explain the present invention in more detail.

[0040] Example 1 In Example 1, the elements to be measured are Ca, Mg, and Na, so chlorides of these three elements are also used in the calibration solution. To introduce exogenous precipitable elements, allowing them to co-precipitate with the original precipitating elements, thereby controlling the solid matter content in the system and suppressing the coffee ring effect of Na, and to avoid spectral interference from the introduced precipitates on the elements to be measured, the introduced elements should meet the following requirements: For the sample system of Example 1, according to the above requirements for the introduction of elements, barium (Ba), a congener of Ca and Mg, meets all the conditions for the introduction of elements: First, Ba reacts easily with CO3 as easily as Ca and Mg. 2- A precipitation reaction occurs in CO3 2- Under the condition of constant excess, the addition of Ba element does not affect the reaction of Ca, Mg and Na elements. At the same time, BaCl2 can be selected as the salt for introducing Ba element, in which Cl - It does not affect the reaction of Ca, Mg, and Na elements, nor does it react with CO3 2- reaction. Secondly, BaCl2 has a high solubility. At 20°C, the solubility of BaCl2 is 35.7g, which can meet the needs of different supplementary amounts of precipitates. Finally, by consulting the energy level information of the atomic emission spectrum, it can be seen that the Ba element does not interfere with the elemental analysis lines of Ca, Mg, and Na. In summary, the Ba element meets the requirements of being introduced as an element into the CaCl2, MgCl2, and NaCl molten salt systems. At the same time, the introduced Ba element is consistent with the precipitation characteristics of the Ca and Mg elements. The chemical reactions and particle movement laws of the Ba element during sample preparation should be similar to those of the Ca and Mg elements, that is, first reacting with CO3 2- The reaction generates a precipitate, which combines with the dispersant molecules to form large-mass particles, thus being distributed in the middle area of ​​the sample like Ca and Mg elements.

[0041] The specific preparation steps of this embodiment 1 are as follows: (1) Prepare solution A and solution B: The elements to be measured in Example 1 are calcium, magnesium and sodium, so the chlorides of these three elements are also used in the calibration solution: weigh 11.1 g of anhydrous calcium chloride, 20.3 g of magnesium chloride hexahydrate and 5.85 g of sodium chloride, add water to make the solution dilute to 200 ml, and obtain an ion stock solution with a total concentration of 0.5 mol / L. Further dilute the solution in different proportions to obtain solutions with total concentrations of 0.06 mol / L, 0.08 mol / L, 0.1 mol / L, 0.12 mol / L, 0.14 mol / L, 0.16 mol / L, 0.18 mol / L, 0.20 mol / L, 0.22 mol / L and 0.24 mol / L, respectively, and mark them as 1-9# in sequence; the concentrations of Mg element are 0.14 wt.%, 0.19 wt.%, 0.24 wt.%, 0.29 wt.%, 0.34 wt.%, 0.38 wt.%, 0.43 wt.%, 0.48 wt.%, 0.53 wt.%; the concentrations of Ca element are 0.24 wt.%, 0.32 wt.%, 0.40wt.%, 0.48 wt.%, 0.56 wt.%, 0.64 wt.%, 0.72 wt.%, 0.80 wt.%, 0.88 wt.%; the concentrations of Na element are 0.14 wt.%, 0.18 wt.%, 0.23 wt.%, 0.28 wt.%, 0.32 wt.%, 0.37 wt.%, 0.41 wt.%, 0.46 wt.%, 0.51wt.%.

[0042] Since the elements to be measured contain Na, in this embodiment, the dispersant NNO (2-naphthalenesulfonic acid formaldehyde polymer sodium salt, C 21 H 16 O6S2) is dissolved in water, and the dispersant solution is desodiumized using ion exchange chromatography (if the element to be tested does not contain Na, 2-naphthalenesulfonic acid formaldehyde polymer sodium salt can be used directly). H-type cation exchange resin is added to the chromatography column, and the sodium-containing dispersant solution is poured from the top of the chromatography column. A beaker is used to collect the treated solution at the bottom of the chromatography column. After each chromatography, the resin is continuously rinsed with deionized water to ensure that no dispersant residue is left. Then, a new resin is replaced. This step is repeated three times to obtain 2-naphthalenesulfonic acid formaldehyde polymer (C 21 H 16For a 5% 2-naphthalenesulfonic acid formaldehyde polymer solution, inductively coupled plasma optical emission spectrometry (ICP-OES) can be used to confirm that there is no sodium in the dispersant solution. Since Mg and Ca elements among the elements to be measured can be precipitated, a 1.2 mol / L anhydrous potassium carbonate solution is prepared to ensure that the metal ions can be completely precipitated. This solution is mixed with a 5% 2-naphthalenesulfonic acid formaldehyde polymer solution in a 1:1 ratio to obtain a mixed precipitate containing 2.5 wt.% 2-naphthalenesulfonic acid formaldehyde polymer and 0.6 mol / L potassium carbonate, which is used to precipitate metal ions.

[0043] In addition, during the preparation of the test liquid, an additional set of barium chloride solutions was prepared (the BaCl2 addition amounts were 2 wt.%, 4 wt.%, 6 wt.%, 8 wt.%, and 10 wt.%, respectively). It was only necessary to change the solvent from deionized water to BaCl2 solution. This method not only completed the introduction of the Ba element, but also ensured that the contents of the three elements Ca, Mg, and Na in the test liquid remained unchanged.

[0044] (2) Mix the precipitate and the test solution. Each test solution is mixed with the precipitate at a ratio of 1:2.5.

[0045] (3) Oscillating the suspension: Use an ultrasonic machine to oscillate the mixture, set the temperature to 25°C, and oscillate for 1 min. After mixing, a white suspension is obtained.

[0046] (4) Drying the suspension: Use a pipette to quickly add 70 μL of the suspension onto a pure quartz glass slide. The glass slide is adhered with a tape with a hole. The diameter of the hole is 10 mm. The added suspension is confined in the hole to prevent it from diffusing outward. Finally, place the glass slide on a heating table at a constant temperature of 60°C for drying.

[0047] In order to more intuitively see the inhibitory effect of coffee replacement on the precipitation of the non-precipitable element Na in the element to be measured by replacing deionized water with barium chloride solution, the same micro-LIBS imaging analyzer and parameters were used to scan and image the Ba-containing sample (BaCl2 addition amount is, for example, 8wt.%), and a pseudo-color distribution map of the Na element in the Ba-containing sample was obtained, as shown in Figure 2. Figure 2 、 3 In order to avoid the influence of the intensity range in the image on the contrast of the false color image, the attached Figure 2 The strength range of samples 1# to 9# is similar to that of the attached Figure 3 Samples 1# to 9# correspond to each other and remain consistent. Figure 2 and Figure 3 It is known that Figure 3The rings of samples 1# to 9# disappeared, the colors became more uniform across the entire range, and the spectral intensity differences at each point decreased, indicating that the differences in the Na content between points were significantly reduced, and the Na element was nearly evenly distributed in the sample, meaning that the coffee ring effect was effectively suppressed. Figure 3 and Figure 4 As can be seen from the figure, the distribution pattern of K is close to that of Na, so K can be used as an internal standard element for Na. The distribution pattern of Ba is close to that of Ca and Mg, so Ba can be used as an internal standard element for Ca and Mg.

[0048] (5) Obtain LIBS atomic spectra of each sample The LIBS laser energy was set to 10 mJ. The sample was fixed on a three-dimensional displacement platform and the sample surface was adjusted to 1.5 mm above the focal plane of the lens. The acquisition delay was 0.8 μs, and the acquisition gate width was 3.5 μs.

[0049] (6) Correction of matrix effects For Na, in order to select a suitable internal standard element, its non-precipitability requires that the internal standard element also have this property. When preparing the precipitant, K can be considered as its internal standard element. Moreover, the spectral line of K element does not interfere with the spectral line of Na element. Therefore, K element meets the basic requirements for being an internal standard element for Na.

[0050] The internal standard elements introduced by the above steps were used to select appropriate internal standard lines to perform typing corrections on the precipitated and non-precipitated elements. The results are shown in the attached figure. Figure 5 As shown in the figure, Ba Ⅱ 455.4nm, Ba Ⅱ 413.1nm, K Ⅰ 766.4nm were selected as internal standard elements of Ca, Mg, and Na, respectively, and the fitting coefficient R 2 The values ​​of 0.995, 0.988, and 0.997 were respectively. This indicates that the introduction of an additional precipitation method to suppress the coffee ring effect of Na can effectively improve the quantitative effect of LIBS for Na, and the matrix effect typing correction process based on the internal standard method derived from this can effectively improve the accuracy and stability of the quantitative analysis of Ca, Mg, and Na.

[0051] In summary, the method of the present invention can more effectively suppress the coffee ring effect and matrix effect while maintaining the advantages of LIBS's high efficiency and convenience, thereby improving the stability and quantitative performance of LIBS detection spectra. It also has the advantages of easy control, high efficiency and precision, and good adaptability. Therefore, it is particularly suitable for the application of quantitative analysis of elements in various deliquescent chloride salts and has good practical value and application prospects.

[0052] It will be easily understood by those skilled in the art that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for suppressing the coffee ring effect and correcting the LIBS matrix effect, characterized in that: The method comprises the following steps: S1. Select a first element or its compound having similar precipitation properties to the precipitating element in the chloride salt to be tested, dissolve it in distilled water to form a solution; then dissolve the chloride salt to be tested in the solution to prepare solution A; S2. Weigh the dispersant NNO (sodium salt of 2-naphthalenesulfonic acid formaldehyde polymer) and dissolve it in deionized water to form a dispersant solution. Then, select a carbonate or sulfate of a second element with similar solubility characteristics to the non-precipitated element in the chloride salt to be tested, and add it to the dispersant solution to prepare Solution B. S3, mixing the liquid A and the liquid B and ultrasonically shaking them to form a uniform suspension; S4, adding dropwise the uniform suspension obtained in step S3 and storing the suspension, heating the suspension, and completely drying the suspension to obtain a sample that is no longer deliquescent and has suppressed coffee ring effect; S5. ablating the samples based on LIBS technology, and collecting LIBS raw spectrum data of each sample; S6. Obtaining the distribution area of ​​each element to be measured in the sample based on the LIBS original spectrum data; S7, dividing the distribution area into a precipitation area corresponding to the precipitating element and a non-precipitating area corresponding to the non-precipitating element; S8. Select the first element as the internal standard element of the element to be measured for the precipitation area, and select the second element as the internal standard element of the element to be measured for the non-precipitation area, then select the internal standard spectral line according to the spectral line information of these internal standard elements, and finally use the internal standard method to perform quantitative analysis of all the elements to be measured.

2. The method according to claim 1, wherein In step S1 , the precipitating elements in the chloride salt to be tested are preferably Ca and Mg, and the first element having similar precipitation characteristics to Ca and Mg is preferably Ba, an element of the same group.

3. The method according to claim 2, wherein In step S1 , during the preparation of solution A, while introducing a first element having similar precipitation characteristics to the precipitating element in the chloride salt to be measured, it is ensured that the content of all elements to be measured in solution A remains unchanged.

4. The method according to any one of claims 1 to 3, wherein: In step S2 , the non-precipitable element in the chloride salt to be tested is preferably Na, and the second element having similar solubility characteristics is preferably K.

5. The method according to any one of claims 1 to 4, characterized in that In step S2, when the chloride salt to be tested contains Na element, the dispersant solution needs to be subjected to a sodium removal treatment.

6. The method according to claim 5, wherein The sodium removal treatment is preferably performed by ion exchange chromatography: first, H-type cation exchange resin is added to the chromatography column, and the sodium-containing dispersant solution is poured from the top of the chromatography column, while the treated solution is collected below the chromatography column; after each chromatography, the H-type cation exchange resin is continuously rinsed with deionized water to ensure that no dispersant remains, and then a new H-type cation exchange resin is replaced; the above operation is repeated three or more times to obtain a sodium-free dispersant solution.

7. The method according to any one of claims 1 to 6, wherein: In step S3, the homogeneous suspension is preferably prepared by the following process: S31, adding the solution B to multiple clean containers in batches and in a quantitative manner until all the solution B is packaged; S32, mixing the liquid A with the liquid B in each clean container by shaking in a mass ratio of 1 to 5, and obtaining the desired multiple uniform suspensions after mixing.

8. The method according to any one of claims 1 to 7, wherein: In step S4, the sample is preferably generated by the following process: S41. Use a circular hole puncher to punch holes with a diameter of 8 mm to 10 mm in the tape, and then stick the tape on a pure quartz glass slide. S42. Use a pipette to drop 50 μL to 100 μL of the uniform suspension into the circular holes on the pure quartz glass slide. The added suspension is confined in the circular holes. Then, place the pure quartz glass slide on a heating table and dry it at a temperature of about 60° C. for 1 to 5 minutes to obtain the desired sample.

9. The method according to any one of claims 1 to 8, wherein: In step S8, the internal standard spectrum line is preferably selected in the following manner: compare the spectrum line information of the internal standard element, and select the spectrum line whose energy level on the spectrum line of the internal element is closest to the energy level on the analysis line of the element to be measured, and use it as the internal standard spectrum line.

Images