A sample treatment method and impurity detection method for white carbon black

Abstract

This invention provides a sample preparation method and impurity detection method for silica, belonging to the field of elemental analysis technology. The sample preparation method for silica includes the following steps: (1) mixing silica with concentrated hydrochloric acid and stirring, then evaporating to dryness to obtain sample one; (2) cooling sample one and adding acetic anhydride, mixing and stirring, then evaporating to dryness to obtain sample two; (3) repeating the acetic anhydride treatment and cooling to obtain sample three; (4) adding sample three to hydrochloric acid solution, filtering the filtrate, and making up to volume to obtain the test solution. The impurity detection method for silica includes: S1, preparing the test solution according to the sample preparation method for silica; S2, establishing a standard working curve; S3, sending the test solution obtained in S1 into an inductively coupled plasma atomic emission spectrometer, with the sample introduction system being a quartz sample introduction system; S4, calculating the proportions of total iron, manganese, and copper content in silica. This invention avoids the use of hydrofluoric acid to treat samples and can be detected using a common quartz sample introduction system.

Description

Technical Field

[0001] This invention belongs to the field of elemental analysis technology, specifically relating to a sample processing method and impurity detection method for silica. Background Technology

[0002] Precipitated hydrated silica, also known as white carbon black, appears as a white powder or granules. It is an amorphous silica hydrate, generally expressed as SiO2·nH2O, and is an important basic inorganic chemical raw material with an amorphous microstructure. Its applications are extensive, found in tires, silicone rubber, shoe soles, animal feed, toothpaste, PE separators, coatings, and many other products. Methods for determining impurities such as copper (Cu), manganese (Mn), and iron (Fe) in precipitated hydrated silica include atomic absorption spectrometry and ultraviolet-visible spectrophotometry. However, atomic absorption spectrometry has low detection limits, difficulties in simultaneous determination of multiple elements, and unsatisfactory sensitivity for some elements.

[0003] In GB / T 36764-2018, "Determination of Heavy Metal Content in Rubber Compounding Agents by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP)," the content of impurity elements copper (Cu), manganese (Mn), and iron (Fe) is determined using ICP, enabling simultaneous multi-element sampling and detection. However, since silica is mainly composed of silicon dioxide, the sample needs to be treated with hydrofluoric acid. Under the action of hydrofluoric acid, the silicon dioxide is converted into silicon tetrafluoride and volatilizes, leaving the impurity elements to be measured in the treated sample. However, when the treated sample is prepared into a solution of a certain volume, the hydrofluoric acid in the solution will corrode glass products. Furthermore, the sample introduction system of ICP generally contains silicon dioxide (such as the plasma rectangular tube that maintains the continuous discharge of the inductively coupled plasma, which is generally a device composed of three concentric quartz tubes). Therefore, treatment with hydrofluoric acid will damage the sample introduction system of the equipment. GB / T 36764-2018 recommends using a hydrofluoric acid-resistant injection system for detection. This requires ICP to prepare a separate injection system, which undoubtedly increases costs, and the introduction system is inconvenient to change and cumbersome to operate. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a sample preparation method and impurity detection method for silica, which eliminates the need for hydrofluoric acid in the sample preparation process and removes the restriction that a hydrofluoric acid-resistant sample introduction system must be used in the detection process.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] In a first aspect, a method for treating silica samples includes the following steps:

[0007] (1) The precipitated hydrated silica was mixed with concentrated hydrochloric acid and stirred, then evaporated to dryness to obtain sample one;

[0008] (2) After cooling sample one, add acetic anhydride, mix and stir, then evaporate to dryness to obtain sample two;

[0009] (3) After cooling sample 2, add acetic anhydride, mix and stir, then evaporate to dryness and cool to obtain sample 3;

[0010] (4) Add sample 3 to hydrochloric acid solution, stir and filter the filtrate, dilute with water to obtain the test solution.

[0011] Optionally, the proportions of each raw material are as follows: 20g of precipitated hydrated silica is used as raw material. In step (1), 50mL of concentrated hydrochloric acid is added; in step (2), 40mL of acetic anhydride is added; in step (3), 40mL of acetic anhydride is added; in step (4), 100mL of hydrochloric acid solution is added, 10mL of filtrate is transferred, and water is added to make up to 100mL.

[0012] Optionally, the drying temperature is 80℃; the drying method is a sand bath or a water bath.

[0013] Optionally, the hydrochloric acid solution is prepared by mixing equal volumes of water and concentrated hydrochloric acid.

[0014] Secondly, a method for detecting impurities in silica.

[0015] S1. According to the above sample preparation method for silica, precipitated hydrated silica, concentrated hydrochloric acid and acetic anhydride are used to prepare the test solution.

[0016] S2. Prepare a mixed standard sample using standard stock solutions of copper, manganese, and iron, and simultaneously prepare a blank solution to establish a standard working curve.

[0017] S3. The test solution obtained in S1 is sent into an inductively coupled plasma atomic emission spectrometer to obtain the test concentration. The sample introduction system is a quartz sample introduction system.

[0018] S4. Calculate the percentage of total iron, manganese, and copper content in precipitated hydrated silica.

[0019] Optionally, in S2, the standard working curve is established by a blank solution and a mixed standard sample of each element, and is automatically generated by the device's built-in workstation.

[0020] Optionally, in S3, the prepared test solution is placed into the injection tube, and the ICP device automatically injects the sample.

[0021] Optionally, in S4, the conversion formula for the percentage of total iron, manganese, and copper content in precipitated hydrated silica is as follows:

[0022] The content of each element (ppm) = (k × C × V) / W;

[0023] C: The concentration of the metal element in the test solution, in mg / L;

[0024] V: The volume of the solution to which the test solution is diluted, in ml;

[0025] W: Mass of silica weighed, in g;

[0026] k: Mass conversion factor (the volume ratio of the filtrate taken to the volume of the test solution after dilution).

[0027] The beneficial effects of this invention are as follows:

[0028] 1. The method of the present invention uses concentrated hydrochloric acid to acidify fumed silica, adds acetic anhydride multiple times, heats it in a sand bath to evaporate it to dryness, and finally dissolves and filters it with hydrochloric acid (1+1) solution. A certain volume of filtrate is then diluted to a certain volume volume flask for testing, thus avoiding damage to the equipment system caused by the use of hydrofluoric acid.

[0029] 2. The method of this invention uses a mixed standard solution to determine the content of each element, achieving simultaneous determination of three elements. Results show that the linear range and peak elution of these three elements are good, with no mutual interference. Furthermore, a blank subtraction method is used to check for interference (signal, peaks, etc.) in the regions where the target analyte appears, thus eliminating chemical interference. Attached Figure Description

[0030] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0031] Figure 1 The diagram shows the calibration curves in Example 1, where (a) is a linear graph of the calibration curve for Fe element; (b) is a linear graph of the calibration curve for Mn element; and (c) is a linear graph of the calibration curve for Cu element.

[0032] Figure 2 The following are peak shape diagrams from Example 1, where (a) is a peak shape diagram of standard solutions of Fe element at different concentrations; (b) is a peak shape diagram of standard solutions of Mn element at different concentrations; and (c) is a peak shape diagram of standard solutions of Cu element at different concentrations. Detailed Implementation

[0033] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of skill in the art. The reagents and raw materials used in this invention are readily available through conventional means, and unless otherwise specified, they shall be used in accordance with conventional methods or product instructions. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to the methods of this invention. The preferred embodiments and materials described herein are for illustrative purposes only.

[0035] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0036] A method for determining the total iron, manganese, and copper content in precipitated hydrated silica, comprising the following steps:

[0037] S1. Prepare the test solution by precipitating hydrated silica, concentrated hydrochloric acid and acetic anhydride;

[0038] S2. Prepare a mixed standard sample using standard stock solutions of copper, manganese, and iron, and simultaneously prepare a blank solution to establish a standard working curve.

[0039] S3. The test solution obtained in S1 is sent into an inductively coupled plasma atomic emission spectrometer to obtain the test concentration;

[0040] S4. Calculate the percentage of total iron, manganese, and copper content in precipitated hydrated silica.

[0041] The specific steps for S1 are as follows:

[0042] (1) The precipitated hydrated silica was mixed with concentrated hydrochloric acid and then evaporated to dryness to obtain sample one;

[0043] The process of change of each raw material is as follows: concentrated hydrochloric acid reacts with precipitated water and silica under sand bath heating conditions to acid hydrolyze the precipitated water and silica, and the reaction produces silicates.

[0044] (2) After cooling sample one, add acetic anhydride, mix and stir, then evaporate to dryness to obtain sample two;

[0045] The process of change of each raw material is as follows: Acetic anhydride is added to the silicate formed by acidification of precipitated water and silicon dioxide, and an acylation reaction occurs. Acetic anhydride has the characteristics of easy bond breaking and easy water absorption, which accelerates the reaction.

[0046] (3) After cooling sample 2, add acetic anhydride, mix and stir, evaporate to dryness, and cool (acetic anhydride is treated twice in total) to obtain sample 3;

[0047] The process of changing each raw material is as follows: The second addition of acetic anhydride is to further induce an acylation reaction, ensuring that the silicate reacts completely with the acetic anhydride and releases free metal ions.

[0048] (4) Add sample three to hydrochloric acid solution, stir and filter the filtrate, dilute with water to obtain the test solution;

[0049] The process of change of each raw material is as follows: hydrochloric acid solution is added to combine with free metal ions to obtain the acid solution to be tested.

[0050] The proportions of each raw material are as follows: 20g of precipitated hydrated silica is used as raw material. In step (1), 50mL of concentrated hydrochloric acid is added; in step (2), 40mL of acetic anhydride is added; in step (3), 40mL of acetic anhydride is added; in step (4), 100mL of hydrochloric acid solution is added, 10mL of filtrate is transferred, and water is added to make up to 100mL.

[0051] In S1, the evaporation temperature is 80℃; the evaporation method is a sand bath or a water bath.

[0052] In S2, the standard working curve is established by combining a blank solution and mixed standard samples of each element, automatically generated by the equipment's built-in workstation. In this scheme, the standard curve is established by preparing six standard solutions of proportional mass concentrations at gradients based on the content of each element in the product.

[0053] A linear correlation coefficient of 0.999 or higher is sufficient to meet the usage requirements.

[0054] In S3, the sample tube is placed into the prepared test solution, and the ICP device automatically injects the sample.

[0055] The sample introduction system is a quartz sample introduction system.

[0056] In S4, the conversion formula for the percentage of total iron, manganese, and copper content in precipitated hydrated silica is:

[0057] The content of each element (ppm) = (k × C × V) / W;

[0058] C: The concentration of the metal element in the test solution, in mg / L;

[0059] V: The volume of the solution to which the test solution is diluted, in ml;

[0060] W: Mass of silica weighed, in g;

[0061] k: Mass conversion factor (10 ml of filtrate, diluted to 100 mL of test solution, then k = 10).

[0062] Example 1:

[0063] The method for determining the total iron, manganese, and copper content in precipitated hydrated silica includes the following steps:

[0064] S1. Prepare the test solution by precipitating hydrated silica, concentrated hydrochloric acid and acetic anhydride. The specific steps are as follows.

[0065] (a) Weigh 20g of silica (i.e., precipitated hydrated silica) sample accurately to 0.0001g using a balance and record the sample weight. If the sample is in block or large particle form, grind it in a mortar until there are no particles. To ensure that there are no large particles, the ground sample needs to be filtered through a 300-micron test sieve. Place the accurately weighed silica in a 250ml evaporating dish and slowly add 50mL of concentrated hydrochloric acid to the porcelain evaporating dish containing the sample.

[0066] Note: The addition of concentrated hydrochloric acid should be done slowly, with constant stirring, to avoid splashing of the sample after a large amount of concentrated hydrochloric acid is added. After the concentrated hydrochloric acid has been completely added, stir evenly with a glass rod and evaporate to dryness in an 80°C sand bath or water bath until the sample is a white powder, thus obtaining the evaporated silica sample.

[0067] In this step, the silica sample reacts with concentrated hydrochloric acid under sand bath heating conditions to form silicates.

[0068] (b) Cool the evaporated silica sample to room temperature in a fume hood, and slowly add 40 mL of acetic anhydride to the cooled sample. Place it in an 80°C sand bath or water bath to evaporate until the sample turns into a light yellow powder. Then add another 40 mL of acetic anhydride and repeat this process two to three times. Finally, cool the sample to room temperature after it has been completely evaporated.

[0069] In this step, silicate undergoes an acylation reaction with acetic anhydride, releasing free metal ions.

[0070] Verification through examples shows that this method compares the results of treatment with acetic anhydride 2 times and 3 times. The relative standard deviation of the test results is less than 5%, which indicates that treatment with acetic anhydride 2 times can ensure that the total iron, manganese and copper can be completely dissolved.

[0071] (c) Accurately add 100 mL of hydrochloric acid (1+1) using a pipette, stirring continuously with a glass rod during the addition process. After standing for about 5 minutes, filter the solution using medium-speed filter paper and a glass funnel. Transfer the filtrate to a dry and clean small beaker. Then, accurately transfer 10 mL of the filtrate into a 100 mL volumetric flask using a pipette, and dilute to the mark with ultrapure water to obtain the test solution.

[0072] S2. Prepare a mixed standard sample using standard stock solutions of copper, manganese, and iron, and simultaneously prepare a blank solution to establish a standard working curve.

[0073] Standard stock solutions of copper (Cu), manganese (Mn), and iron (Fe) were prepared into mixed standard samples, and blank solutions were also prepared. The standard working curves for each element were established using seven points from the blank solutions and mixed standard samples. These curves were automatically generated by the equipment's built-in workstation, and a linear correlation coefficient above 0.999 was considered sufficient for use. The concentrations of the mixed standard samples are shown in Table 1 (Concentrations of Standard Working Curve Solutions (mg / L)).

[0074] Table 1

[0075]

[0076] The standard curve in this scheme is established by preparing six standard solutions of proportional mass concentrations based on the content of each element in the product.

[0077] This step follows the concentration preparation process in the table. In step S3, the sample is injected for testing. This process uses the equipment to obtain the standard curve values, which facilitates subsequent sample testing.

[0078] S3. The test solution obtained in S1 is sent into an inductively coupled plasma atomic emission spectrometer to obtain the test concentration, specifically:

[0079] (a) Turn on the equipment and its software, turn on the gas source, and ignite after the equipment is stable. Then select the preset method and flush the equipment for 5 minutes.

[0080] (b) After the equipment is rinsed, a blank test is performed first, and then samples are injected sequentially from low concentration to high concentration to establish a working standard curve (at least 7 points for each element). The correlation coefficient must be at least 0.999 before sample testing can be carried out.

[0081] (c) Place the injection tube into the prepared test solution, click test, and the device will automatically inject the sample. The injection system is a quartz injection system.

[0082] (d) Wait for the test solution to be tested, and the equipment will automatically display the test concentration (unit: mg / L).

[0083] Among them, the peak shapes of each element in inductively coupled plasma atomic emission spectrometry (ICP) are as follows: Figure 2 As shown in Table 2, the optimal measurement wavelengths are also the corresponding measurement wavelengths for each element in this embodiment. Selecting the optimal measurement wavelength can improve the accuracy of detection.

[0084] Table 2

[0085] Element name Recommended optimal measurement wavelength (nm) Argon (Ar) (as IS) 420.067 Copper (Cu) 324.756 Iron (Fe) 238.204 Manganese (Mn) 257.611

[0086] The optimal measurement parameters for the inductively coupled plasma atomic emission spectrometer (ICP) are shown in Table 3, which are also the operating conditions in this embodiment.

[0087] Table 3

[0088]

[0089] In S4, the conversion formula for the percentage of total iron, manganese, and copper content in precipitated hydrated silica is:

[0090] The content of each element (ppm) = (k × C × V) / W;

[0091] C: The concentration of the metal element in the test solution, in mg / L;

[0092] V: The volume of the solution to which the test solution is diluted, in ml;

[0093] W: Mass of silica weighed, in g;

[0094] k: mass conversion factor, k = 10 (10 ml filtrate, diluted to 100 mL test solution, then k = 10).

[0095] 1. Limit of detection

[0096] In this embodiment, the limit of detection (LOD) and limit of quantitation (LOQ) are evaluated using the blank standard deviation method. This involves determining the LOD by analyzing a large number of sample blanks or by adding a sample blank at the lowest acceptable concentration. The number of independent tests should be no less than 10 (n≥10), and the standard deviation (s) of the LOD is calculated. 3s is the LOD of this method, and three times the LOD is the LOQ. The LOD and LOQ are evaluated according to the blank standard deviation evaluation method in GB / T 27417-2017, and the experimental data are shown in Table 4. In the table, lead has the highest LOD, and manganese has the lowest, reflecting the probability of misdetection for several elements during the testing process. The evaluation tests using the LOD and LOQ accurately reflect the lowest detectable concentration of this method, thus providing accurate detection results.

[0097] Table 4

[0098]

[0099] 2. Precision testing

[0100] Precision determination method is expressed as relative standard deviation. A single sample (commercially available precipitated water and silica) is repeatedly tested 7 times. The results of the 7 tests are recorded, and the mean, standard deviation and relative standard deviation (RSD) are calculated respectively. Precision is expressed as relative standard deviation (RSD). The results are shown in Table 5.

[0101] Table 5

[0102]

[0103]

[0104] The table indicates that the concentrations of the three metallic elements measured were all less than 10 mg / L, and the actual precision of this invention is less than 5%, meeting the requirement of a relative standard deviation of less than 7.5%. (Precision assessment refers to Appendix B of GB / T27417-2017)

[0105] 3. Recovery rate test

[0106] The recovery rate experimental data are shown in Table 6.

[0107] Table 6

[0108] element scalar Spiked values Sample measurement value Recovery rate Iron (Fe) 2.50 mg / L 5.245 mg / L 2.520 mg / L 91.7％ Manganese (Mn) 0.50 mg / L 1.013 mg / L 0.526 mg / L 102.7％ Copper (Cu) 0.50 mg / L 0.965 mg / L 0.496 mg / L 106.7％

[0109] The recovery rate in the table is between 90% and 110%, indicating that the precision of the present invention meets the requirements.

[0110] The calibration curve in step S2 is as follows Figure 1 As shown, where, Figure 1 (a) is a linear graph of the calibration curve of Fe element, indicating that the linear correlation coefficient of Fe element established for different concentrations is 0.999984; Figure 1 (b) shows the calibration curve for Mn element, indicating that the linear correlation coefficient of Mn element established for different concentrations is 0.999996; Figure 1 c) shows the linearity of the Cu element calibration curve, indicating that the linear correlation coefficient for Cu at different concentrations is 0.999994. The correlation coefficients of the calibration curves for all three elements are above 0.999, demonstrating that the standard curves designed in this scheme have good linearity.

[0111] Comparative verification experiment:

[0112] This method is compared with the determination methods of "GB / T 36764-2018 Determination of Heavy Metal Content in Precipitated Hydrated Silica in Rubber Compounds by Inductively Coupled Plasma Atomic Emission Spectrometry" and "Detection of Metal Ion Content in Precipitated Hydrated Silica in Rubber Compounds by Atomic Absorption Spectrophotometer (HG / T 3061-2009)". The results of the comparison of the detection results of copper, manganese and iron show that the deviations of the two methods from this method are not more than 5%.

[0113] This invention can replace the operating procedure in "GB / T 36764-2018 Determination of Heavy Metal Content in Precipitated Hydrated Silica by Inductively Coupled Plasma Atomic Emission Spectrometry" for rubber compounding agents, accurately detecting the total iron, manganese, and copper content in precipitated hydrated silica. It does not use hydrofluoric acid as a treatment agent, nor does it require a hydrofluoric acid-resistant sample introduction system; it can be performed using a common quartz sample introduction system.

[0114] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A sample treatment method of white carbon black, characterized by, Includes the following steps: (1) The precipitated hydrated silica was mixed with concentrated hydrochloric acid and stirred, then evaporated to dryness to obtain sample one; The evaporation temperature is 80℃, and the evaporation method is either a sand bath or a water bath. (2) After cooling sample one, add acetic anhydride, mix and stir, then evaporate to dryness to obtain sample two; (3) After cooling sample 2, add acetic anhydride, mix and stir, then evaporate to dryness and cool to obtain sample 3; (4) Add sample three to hydrochloric acid solution, stir and filter the filtrate, dilute with water to obtain the test solution.

2. The sample treatment method of white carbon black according to claim 1, characterized by, The proportions of each raw material are as follows: 20g of precipitated hydrated silica is used as raw material. In step (1), 50mL of concentrated hydrochloric acid is added; in step (2), 40mL of acetic anhydride is added; in step (3), 40mL of acetic anhydride is added; in step (4), 100mL of hydrochloric acid solution is added, 10mL of filtrate is transferred, and water is added to make up to 100mL.

3. A method for detecting impurities of white carbon black, characterized by, The sample processing method for silica according to any one of claims 1-2 includes the following specific steps: S1. According to the sample preparation method of silica, precipitated hydrated silica, concentrated hydrochloric acid and acetic anhydride are used to prepare the test solution. S2. Prepare a mixed standard sample using standard stock solutions of copper, manganese, and iron, and simultaneously prepare a blank solution to establish a standard working curve. S3. The test solution obtained in S1 is sent into an inductively coupled plasma atomic emission spectrometer to obtain the test concentration. The sample introduction system is a quartz sample introduction system. S4. Calculate the percentage of total iron, manganese, and copper content in precipitated hydrated silica.

4. The method for detecting impurities in silica as described in claim 3, characterized in that, In S2, the standard working curve is established by seven points of blank solution and mixed standard samples of each element, and is automatically generated by the equipment's built-in workstation.

5. The method for detecting impurities in silica as described in claim 4, characterized in that, A total of 6 mixed standard samples were prepared, with the following concentrations of each element in the solution: 20 mg / L, 5 mg / L, 1 mg / L, 0.2 mg / L, 0.05 mg / L, and 0.01 mg / L.

6. The method for detecting impurities in silica as described in claim 3, characterized in that, In step S3, the sample tube is placed into the prepared test solution, and the ICP device automatically injects the sample.

7. The method for detecting impurities in silica as described in claim 6, characterized in that, The operating steps are as follows: (a) Turn on the equipment and its software, turn on the gas source, and ignite after the equipment has stabilized. Then select the preset method and flush the equipment for 5 minutes. (b) After the equipment is rinsed, a blank test is performed first, and then samples are injected sequentially from low concentration to high concentration to establish a working standard curve. The correlation coefficient must be at least 0.999 before sample testing can be carried out. (c) Place the sample tube into the prepared test solution, click test, and the device will automatically inject the sample. The injection system is a quartz injection system. (d) Wait for the test solution to be tested, and the equipment will automatically display the test concentration.

8. The method for detecting impurities in silica as described in claim 3, characterized in that, In S4, the conversion formula for the percentage of total iron, manganese, and copper content in precipitated hydrated silica is: The concentration of each element in ppm is calculated as k × C × V / W. C: The concentration of the metal element in the test solution, in mg / L; V: The volume of the solution to which the test solution is diluted, in ml; W: Mass of silica weighed, in g; k: mass conversion factor, which is the volume ratio of the filtrate taken to the volume of the test solution after final volume adjustment.

9. The method for detecting impurities in silica as described in claim 3, characterized in that, The measurement wavelength for copper is 324.756 nm, for iron it is 238.204 nm, and for manganese it is 257.611 nm.

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