Method for rapidly and accurately determining calcium and phosphorus contents in tricalcium phosphate by using X-ray fluorescence method

Abstract

The invention discloses a method for rapidly and accurately determining the content of calcium and phosphorus in tricalcium phosphate by using an X-ray fluorescence method. Compared with a traditional chemical analysis method, the method is easy and convenient to operate and short in service time, and does not need a complex pretreatment process. The content of calcium and phosphorus in the sample can be rapidly and accurately determined only by dissolving the sample in dilute nitric acid and adopting an XRF (X-Ray Fluorescence) sample pool solution method. Researches show that the impurities in tricalcium phosphate, such as hydroxyapatite and calcium pyrophosphate, do not affect the XRF determination result, so that the problem of low calcium content caused by impurity interference in the traditional EDTA titration method is avoided.

Description

Technical Field

[0001] The present invention relates to the field of analytical chemistry, and particularly to a method for rapidly determining the calcium and phosphorus contents in tricalcium phosphate using X-ray fluorescence spectrometry (XRF). This method can be widely applied in fields such as the manufacture of inorganic chemical products, material analysis, and medical research, and is particularly significant in the analysis of the calcium and phosphorus element contents of materials. Background Art

[0002] Tricalcium phosphate is one of the main inorganic components of bone tissue and is widely used in fields such as biomedical materials and the manufacture of inorganic chemical products. Due to its chemical composition being similar to the inorganic components of the human skeleton, tricalcium phosphate has good biocompatibility and thus has received much attention in the research of bone substitute materials. In addition, the high hardness and wear resistance of tricalcium phosphate also make it perform excellently in the industrial field. However, traditional chemical analysis methods, such as the EDTA titration method for determining calcium content and the quinoline molybdate gravimetric method for determining phosphorus content, usually take a long time and have complex operation steps, and are easily interfered by impurities in the sample.

[0003] When using the traditional EDTA titration method to determine the calcium content in tricalcium phosphate, impurities in the sample such as hydroxyapatite and calcium pyrophosphate will compete with EDTA for binding, resulting in a lower determination result. In the traditional chemical titration process, it is necessary to add a masking agent and adjust the pH value to 12 - 13 to reduce the interference of other metal ions, but it is difficult to completely eliminate the influence on the determination result. In contrast, X-ray fluorescence spectrometry (XRF) does not require cumbersome pretreatment steps, can rapidly and accurately determine the calcium and phosphorus contents in tricalcium phosphate, and effectively avoids the influence of impurities in the sample on the measurement result, so it has become a more ideal analysis method.

[0004] Technical Difficulties of Conventional Chemical Detection 1. The sample pretreatment is complex. Impurities in the sample may interfere with the detection, and additional purification steps are required.

[0005] 2. The detection steps are cumbersome: The EDTA titration method used for determining calcium and the quinoline molybdate gravimetric method used for determining phosphorus in chemical detection involve multiple steps. Among them, in the gravimetric method for determining phosphorus, strong acids and high temperatures are used to dissolve the sample, with complex operations and long time consumption, requiring a large amount of chemical reagents, increasing the cost and the difficulty of waste liquid treatment.

[0006] 3. The accuracy and sensitivity are not high: With many operation steps, errors are easily introduced, affecting the accuracy of the results. It is necessary to strictly control the determination conditions, such as pH, and a masking agent also needs to be added to eliminate the metal effect of the sample.

[0007] Technical Difficulties of XRF Detection 1. Matrix effect and spectral interference: The matrix of tricalcium phosphate can affect the detection of XRF, resulting in deviation of results, which needs to be corrected by standard samples and establishing a mathematical model. The X-ray spectra of some elements may overlap, affecting the detection accuracy, and a method of complex data processing needs to be established.

[0008] 2. Requirements for uniformity of sample preparation: XRF detection requires the sample to be uniform to ensure the reproducibility of results. Summary of the Invention

[0009] The present invention aims to provide a method for rapidly and accurately determining the calcium and phosphorus contents in tricalcium phosphate using X-ray fluorescence spectrometry (XRF). This method overcomes the problems of complex operation, long time consumption, and impurity interference in traditional chemical analysis methods by optimizing the sample pretreatment process. X-ray fluorescence spectrometry can complete the determination of calcium and phosphorus contents in a short time by detecting the net intensities of calcium and phosphorus elements in the sample and combining with a standard curve, and has the advantages of simple operation and rapid analysis.

[0010] The X-ray fluorescence method of the present invention is applicable to various calcium and phosphorus compound samples, especially tricalcium phosphate samples. This method can avoid the errors caused by impurities such as hydroxyapatite and calcium pyrophosphate in the sample during the determination of calcium content, thereby ensuring the accuracy of the measurement results. Compared with the traditional EDTA titration method and quinoline molybdate gravimetric method, the X-ray fluorescence method provided by the present invention has higher precision and repeatability.

[0011] The present invention provides a method for rapidly determining the calcium and phosphorus contents in tricalcium phosphate using X-ray fluorescence spectrometry, and the method comprises the following steps: (1) Add dilute nitric acid solution to the tricalcium phosphate sample, heat and stir to completely dissolve it, dilute to the scale, then add it to an XRF sample container, and perform film sealing; (2) Add dilute nitric acid solution to the tricalcium phosphate standard, heat and stir to completely dissolve it, dilute to the scale, then add it to an XRF sample container, and perform film sealing; (3) Use an X-ray fluorescence spectrometer to scan and measure the calcium and phosphorus contents of the dissolved tricalcium phosphate sample and tricalcium phosphate standard respectively.

[0012] In step (1), the volume concentration of the dilute nitric acid is 5 - 20%; in some cases, the dilute nitric acid can be prepared in a 1+5 configuration.

[0013] After adding the dilute nitric acid, the concentration of the tricalcium phosphate sample is controlled to be 1 - 60 g / L, preferably 4 - 40 g / L.

[0014] In step (1), after adding the dilute nitric acid, heat to 25 - 35°C and stir to dissolve.

[0015] In the technical solution of the present invention, the pretreatment of the sample solution includes dissolving the tricalcium phosphate sample with dilute nitric acid to ensure that the sample is evenly dispersed and avoid the interference of accidental errors caused by unevenness on the measurement results. The sample solution is placed in a dedicated XRF sample cell and scanned and analyzed by an S8 Tiger XRF instrument. Using the sample cell solution method can improve the accuracy and repeatability of the measurement and effectively avoid the interference of the uneven distribution of impurities such as hydroxyapatite and calcium pyrophosphate in the sample on the measurement results.

[0016] In step (3), the measurement parameters for Ca detected by the X-ray fluorescence spectrometer are as follows: the spectral line is selected as CaKA1-HR-Min, the mask is selected as 34 mm, the mode is normal pressure helium, the voltage is 40 - 60 kV, the current is 70 - 90 mA, the crystal 2d = 4.026 Ao, the collimator = 0.23 degrees, the detector flow gas counter LLD = 50%, ULD = 150%, the peak position 2θ = 113.039 degrees, and the wavelength = 3.3584 Ao.

[0017] In some preferred cases, in step (3), among the measurement parameters for Ca detected by the X-ray fluorescence spectrometer, the voltage is 50 - 60 kV and the current is 70 - 80 mA.

[0018] The measurement parameters for P detected by the X-ray fluorescence spectrometer are as follows: the spectral line is selected as PKA1-HR-Min, the mask is selected as 34 mm, the mode is normal pressure helium, the voltage is 20 - 30 kV, the current is 120 - 150 mA, the crystal 2d = 8.752 Ao, the collimator = 0.23 degrees, the detector flow gas counter LLD = 50%, ULD = 150%, the peak position 2θ = 89.433 degrees, and the wavelength = 6.1570 Ao.

[0019] In some preferred cases, among the measurement parameters for P detected by the X-ray fluorescence spectrometer, the voltage is 25 - 30 kV and the current is 140 - 150 mA.

[0020] During the measurement process, the net intensities of calcium and phosphorus elements in the sample are detected by X-ray fluorescence method, which specifically includes: (1) Before measurement, a working curve is drawn using a standard tricalcium phosphate sample. (2) During measurement, according to the fitting of the net intensity values of calcium and phosphorus elements with the working curve, the calcium and phosphorus contents are automatically calculated to avoid the influence of sample impurities such as hydroxyapatite and calcium pyrophosphate on the results. (3) Multiple measurements are carried out using standard samples of different masses to ensure a good linear relationship of the working curve, thereby improving the accuracy of the measurement results.

[0021] The X-ray fluorescence spectrometer used in the measurement process is S8 Tiger XRF. When measuring the calcium and phosphorus contents, appropriate spectral lines and measurement parameters are selected to ensure the accuracy and repeatability of the results. At the same time, the measurement results are calculated by fitting through a standard curve.

[0022] After each standard sample is measured, the measurement result is compared with the standard value, and a standard curve is automatically generated by software fitting. If a new standard sample is added, its data needs to be imported into the existing standard curve, and the accuracy and stability of the curve are ensured through multi-point data fitting.

[0023] The determination of calcium and phosphorus contents in tricalcium phosphate by X-ray fluorescence method is not only simple in operation, but also can effectively avoid the interference of impurities in the sample on the results. Impurities such as hydroxyapatite and calcium pyrophosphate do not affect the accurate determination of calcium and phosphorus contents. Compared with the traditional EDTA titration method, this method significantly improves the accuracy of calcium and phosphorus content determination.

[0024] The X-ray fluorescence method of the present invention can be widely applied to the determination of calcium and phosphorus contents in inorganic chemical industry, medical materials, and other materials containing calcium and phosphorus elements, solves the measurement error problem in the traditional method, and greatly improves the work efficiency.

[0025] The technical solution of the present invention places calibration tablets with known components into the instrument to complete the drift correction of the instrument (here, SQ1N, SQ2N, SQ3N, and STG5 are used).

[0026] Select an X-ray source with appropriate energy according to the sample (Kα1 line is selected for both Ca and P).

[0027] A series of standard samples after dissolution treatment with a mass gradient are used to set the sample elements and corresponding contents and then measured to obtain the net intensity of the elements at each corresponding content. Through software analysis, the establishment of the standard curve of calcium and phosphorus element contents and the element net intensity is completed.

[0028] The significance of detection parameters for accurate detection: It can improve accuracy, sensitivity, efficiency, and reduce background and interference between elements. Description of the Drawings

[0029] Figure 1 : Calcium standard curve of tricalcium phosphate.

[0030] Figure 2 : Phosphorus standard curve of tricalcium phosphate.

[0031] Figure 3 : Working curve of calcium obtained by fitting multiple material reference substances.

[0032] Figure 4 : Working curve of phosphorus obtained by fitting multiple material reference substances. Detailed implementation mode

[0033] Example 1: Drawing of the working curve of calcium and phosphorus contents First, select a standard tricalcium phosphate sample (β-TCP). Weigh a series of samples with different masses (from 0.100 g to 1.100 g) (specifically: 0.100 g, 0.200 g, 0.400 g, 0.800 g, 1.100 g). Put them into a beaker, add 25 mL of 1+5 dilute nitric acid solution, heat and stir to completely dissolve the samples. Then transfer the dissolved solution to a 50 mL volumetric flask and dilute to the mark. Pour 15 mL of the diluted solution into a special sample container for XRF. The bottom of this container is sealed with a polypropylene film to ensure that the sample liquid does not leak.

[0034] Put the standard sample container into the sample pool of the X-ray fluorescence spectrometer. Edit the measurement method in the XRF analysis software and input the calcium and phosphorus content values in the standard sample. Based on 1 g of the standard sample (calcium content 38.76%, phosphorus content 19.97%), multiply the weighed sample mass by the corresponding coefficient to obtain the calcium and phosphorus contents of the standard sample. For example, in this example, for the sample weighed 0.200 g, the calcium content and phosphorus content are multiplied by 0.2 respectively.

[0035] In the measurement software of the S8 Tiger X-ray fluorescence spectrometer, select the "Application" toolbar and open the "Method" module. First, input the calcium and phosphorus contents of the standard sample, create a new method file, and import a series of tricalcium phosphate standard samples as the reference. Then select to measure the standard sample, put the standard sample slice into the sample pool of the XRF instrument, and click "Start" to start the measurement.

[0036] During the measurement, the determination parameters of Ca detected by the X-ray fluorescence spectrometer: the spectral line selects CaKA1-HR-Min, the mask selects 34 mm, the mode is normal pressure helium, the voltage is 50 kV, the current is 72 mA, the crystal 2d = 4.026 Å, the collimator = 0.23 degrees, the detector flow gas counter LLD = 50%, ULD = 150%, the peak position 2θ = 113.039 degrees, the wavelength = 3.3584 Å The determination parameters of P detected by the X-ray fluorescence spectrometer: the spectral line selects PKA1-HR-Min, the mask selects 34 mm, the mode is normal pressure helium, the voltage is 30 kV, the current is 120 mA, the crystal 2d = 8.752 Å, the collimator = 0.23 degrees, the detector flow gas counter LLD = 50%, ULD = 150%, the peak position 2θ = 89.433 degrees, the wavelength = 6.1570 Å Perform a scanning measurement using an X-ray fluorescence spectrometer and record the net intensity values of calcium and phosphorus elements for each sample. Using the measured net intensity values as the vertical axis and the calcium and phosphorus contents of the standard samples as the horizontal axis, automatically generate a working curve using software and fit a linear relationship curve between the calcium and phosphorus contents and the net intensity.

[0037] Example 2: Determination of Samples During the actual sample determination process, weigh 1.000 g ± 0.001 g of tricalcium phosphate sample. According to the steps in Example 1, dissolve the sample in 25 mL of 1+5 dilute nitric acid solution and dilute to the 50 mL mark. Pour 15 mL of the solution into an XRF sample container and place it in the sample cell of the X-ray fluorescence spectrometer.

[0038] In this example, the XRF sample cell solution method is selected for parallel measurement of tricalcium phosphate samples. Using the same sample, perform 5 measurements respectively, record the net intensity value of each measurement, and obtain the average value and standard deviation of the calcium and phosphorus contents.

[0039] Start the X-ray fluorescence spectrometer, select the preset working curve method for calcium and phosphorus contents, enter the sample name and perform the measurement. The measurement result is the net intensity values of calcium and phosphorus elements. The software substitutes the net intensity values into the working curve and automatically calculates the calcium and phosphorus contents in the sample.

[0040] Table 1 shows the corresponding relationship between the calcium content and the net intensity of the tricalcium phosphate sample, and Table 2 shows the corresponding relationship between the phosphorus content and the net intensity. Through linear regression analysis of the measurement data, obtain the fitting graph of the working curve, Figure 1 and Figure 2 are the standard curves for calcium and phosphorus respectively.

[0041] Table 1 Corresponding Relationship between Calcium Content and Calcium Net Intensity in XRF

[0042] Table 2 Corresponding Relationship between Phosphorus Content and Phosphorus Net Intensity in XRF

[0043] The above experimental data shows that this method has good reproducibility and will not have a large impact on the experimental results due to different measurement times or slight changes in the environment.

[0044] Finally, the selected standard curve is jointly drawn from the above five groups of corresponding points, and the obtained standard curve and the standard curves obtained from the 5 groups of measurement values respectively have an R 2 above 0.999.

[0045] Example 2: Verification of the Accuracy and Precision of XRF Determination To verify the accuracy and precision of X-ray fluorescence method, the standard samples were measured using the sample cell powder method and the sample cell solution method respectively. By comparing the three groups of measurement results with the theoretical values, it was found that the relative error and relative deviation of the sample cell solution method were both less than 1%, while those of the sample cell powder method were larger and the accuracy was poorer.

[0046] The steps of the sample cell powder method are as follows: 1. Grind the sample into a uniform fine powder with a particle size less than 50um and dry it thoroughly to avoid moisture interference.

[0047] 2. Prepare a sample cell with a diameter of 40mm based on a polypropylene film, ensuring it is clean and not contaminated.

[0048] 3. Uniformly load the powder sample into the sample cell to about one-third of the total height of the sample cell, avoiding voids or layering. Gently compact the sample if necessary to ensure a flat surface.

[0049] 4. After sealing with the corresponding sample cell lid, place it in the instrument for measurement.

[0050] The sample cell solution method, compared with the powder method, is to replace the powder with a solution. Weigh 1.000g of the sample, after the same dissolution treatment as the standard sample, load it into the sample cell to about one-third of the total height of the sample cell, and then place it in the instrument for determination. Then the reading of the instrument is the final determination value. If it is other mass, the element content obtained on the instrument finally needs to be divided by this mass to obtain the determination value.

[0051] Table 3 shows the results of the standard samples measured by the powder method and the solution method. It can be seen that the deviation between the measured value of the sample cell solution method and the theoretical value is extremely small, indicating that the X-ray fluorescence method of the present invention has excellent precision and accuracy.

[0052] Table 3 Results of calcium and phosphorus contents of standard samples measured by XRF sample cell powder method and solution method

[0053] Example 3: Verification of the universality of XRF determination To verify this, different materials were used for analysis here. Five different masses of standard samples of hydroxyapatite and calcium hydrogen phosphate were taken to obtain the standard curves of calcium and phosphorus (0.100g, 0.300g, 0.500g, 0.700g, 1.000g were selected for hydroxyapatite; 0.200g, 0.500g, 0.800g, 1.000g, 1.200g were selected for corresponding calcium hydrogen phosphate), and then these standard sample points were added to the original standard curve of tricalcium phosphate.

[0054] The detection was carried out under the detection conditions of Example 1.

[0055] By performing linear regression analysis on the measurement data, a fitting graph of the working curve is obtained. Figure 3 and Figure 4 are the standard curves of calcium and phosphorus respectively. It is found that all points can still be connected into a curve with good linearity (R 2 > 0.999). Thus, it can be seen that using X-ray fluorescence method to determine the calcium and phosphorus content in tricalcium phosphate not only has high accuracy, but also can be widely applied to different types of materials containing calcium and phosphorus elements, without worrying about the huge impact of impurity interference in the materials on the measurement results. The method of the present invention is simple to operate and has a fast measurement speed, providing a more efficient tool for inorganic material analysis.

[0056] Example 4: Influence of different acid concentrations on the dissolution of tricalcium phosphate To verify the influence of the concentration of dilute nitric acid solution on the dissolution effect of tricalcium phosphate, three different concentrations of nitric acid solutions, 1+1, 1+5, and 1+10, were selected to treat 1.000 g of tricalcium phosphate samples respectively, using the same operation steps as in Example 1. The experiments show that when using the 1+5 dilute nitric acid solution, the sample dissolves most completely and evenly, while too low a concentration (1+10) will lead to incomplete dissolution of the sample, and too high a concentration (1+1), the sample is also difficult to dissolve in it (the reaction of high-concentration nitric acid is intense, and a passivation layer may be formed on the surface of tricalcium phosphate, hindering further dissolution. And high-concentration nitric acid may trigger side reactions to generate insoluble compounds, such as calcium nitrate precipitating when locally supersaturated). Therefore, in actual operation, it is recommended to use the 1+5 dilute nitric acid solution to improve the sample dissolution effect and the reliability of XRF measurement results.

[0057] Example 5: Influence of increased impurity content on measurement stability To verify the influence of increased impurity content on the XRF measurement results, different amounts of hydroxyapatite (1%, 5%, 10%) were artificially added to the same tricalcium phosphate samples. Under each impurity content condition, 1.000 g of the sample was dissolved in dilute nitric acid and the calcium and phosphorus content determination was completed according to the measurement steps of Example 1. The experimental results are shown in Table 4 and Table 5 below. When the impurity content reaches 10%, there are slight deviations in the measurement results, but under the impurity content conditions of 1% and 5%, the XRF measurement results are relatively stable, indicating that this method has strong measurement stability when the impurities are less and is suitable for the detection of high-purity samples in practical applications.

[0058] Table 4 Relative deviation of XRF determination results of calcium element under different impurity content conditions

[0059] Table 5 Relative deviation of XRF determination results of phosphorus element under different impurity content conditions

[0060] 。

Claims

1. A method for rapidly determining the calcium and phosphorus content in tricalcium phosphate using X-ray fluorescence, characterized in that: The method comprises the following steps: (1) Add dilute nitric acid solution to the tricalcium phosphate sample, heat and stir to completely dissolve it, dilute to scale, add it to the XRF sample container, and seal it with a film; (2) Add dilute nitric acid solution to tricalcium phosphate standard, heat and stir to completely dissolve it, dilute to scale, add to the XRF sample container, and seal with a film; (3) The dissolved tricalcium phosphate sample and the tricalcium phosphate standard were scanned and measured for the calcium and phosphorus content of the samples using an X-ray fluorescence spectrometer.

2. The method for rapidly determining the calcium and phosphorus content in tricalcium phosphate using X-ray fluorescence method according to claim 1, characterized in that: The volume concentration of the dilute nitric acid in step (1) is 5-20%; after adding the dilute nitric acid, the concentration of the tricalcium phosphate sample is controlled to be 1-60 g / L.

3. The method for rapidly determining the calcium and phosphorus content in tricalcium phosphate using X-ray fluorescence method according to claim 1, characterized in that: In step (1), the concentration of the tricalcium phosphate sample is controlled to be 4-40 g / L.

4. The method for rapidly determining the calcium and phosphorus content in tricalcium phosphate using X-ray fluorescence method according to claim 1, characterized in that: After adding dilute nitric acid in step (1), heat to 25-35°C and stir to dissolve.

5. The method for rapidly determining the calcium and phosphorus content in tricalcium phosphate using X-ray fluorescence method according to claim 1, characterized in that: In step (3), the measurement parameters of the X-ray fluorescence spectrometer for detecting Ca are: the spectral line is CaKA1-HR-Min, the mask is 34 mm, the mode is atmospheric pressure helium, the voltage is 40-60 kV, the current is 70-90 mA, the crystal 2d = 4.026 Ao, the collimator = 0.23 degrees, the detector flow counter LLD = 50%, ULD = 150%, the peak position 2θ = 113.039 degrees, and the wavelength = 3.3584 Ao.

6. The method for rapidly determining the calcium and phosphorus content in tricalcium phosphate using X-ray fluorescence method according to claim 5, characterized in that: In step (3), the measurement parameters of Ca detected by X-ray fluorescence spectrometer are voltage 50-60 kV and current 70-80 mA.

7. The method for rapidly determining the calcium and phosphorus content in tricalcium phosphate using X-ray fluorescence method according to claim 1, characterized in that: The measurement parameters of X-ray fluorescence spectrometer for detecting P are as follows: PKA1-HR-Min is selected for the spectral line, 34mm is selected for the mask, the mode is atmospheric pressure helium, the voltage is 20-30kV, the current is 120-150mA, the crystal 2d=8.752Ao, the collimator=0.23 degrees, the detector flow counter LLD=50%, ULD=150%, the peak position 2θ=89.433 degrees, and the wavelength=6.1570Ao.

8. The method for rapidly determining the calcium and phosphorus content in tricalcium phosphate using X-ray fluorescence method according to claim 7, characterized in that: The measurement parameters of X-ray fluorescence spectrometer for detecting P are voltage 25-30kV and current 140-150mA.

9. The method for rapidly determining the calcium and phosphorus content in tricalcium phosphate using X-ray fluorescence method according to any one of claims 5 to 8, characterized in that: The measuring process uses X-ray fluorescence to detect the net intensity of calcium and phosphorus elements in the sample, specifically including: (1) Before measuring the sample, a working curve was drawn using a standard tricalcium phosphate sample; (2) During measurement, the calcium and phosphorus content is automatically calculated based on the net intensity value of the calcium and phosphorus elements and the working curve fitting, avoiding the influence of sample impurities such as hydroxyapatite and calcium pyrophosphate on the results; (3) Use standard samples of different masses to perform multiple measurements to ensure that the linear relationship of the working curve is good, thereby improving the accuracy of the measurement results.

10. The method for rapidly determining the calcium and phosphorus content in tricalcium phosphate using X-ray fluorescence method according to claim 9, characterized in that: The X-ray fluorescence instrument used in the determination process is S8 Tiger XRF. When measuring the calcium and phosphorus content, appropriate spectral lines and measurement parameters are selected to ensure the accuracy and repeatability of the results; at the same time, the measurement results are fitted and calculated through the standard curve.

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