Method for determining aluminum content by graphite furnace atomic absorption spectrometry

Abstract

The application provides a method for determining the content of aluminum by graphite furnace atomic absorption spectrometry. The method comprises the following steps: preparing an aluminum series calibration solution added with an alkali metal nitrate, determining the absorbance of the solution by using a graphite furnace atomic absorption spectrometer, and then drawing a standard curve with the determined absorbance as the ordinate and the content of aluminum in the aluminum series calibration solution added with the alkali metal nitrate as the abscissa; adding the alkali metal nitrate into a sample to be determined, determining the absorbance of the sample by using the graphite furnace atomic absorption spectrometer, and then calculating the content of aluminum in the sample to be determined according to the standard curve. The method can fully atomize the aluminum element, improve the measurement accuracy, and solve the problem of different atomization rates of sample water and calibration solution, and mask the interference of other metal oxides.

Description

Technical Field

[0001] This invention relates to a method for determining aluminum content using graphite furnace atomic absorption spectrometry, belonging to the field of metal content detection technology. Background Technology

[0002] The method of determining aluminum by electrothermal atomization of samples using a high-temperature graphite furnace is widely used in water quality testing and monitoring. In existing technologies, graphite furnace atomic absorption spectrometry (GFAAS) for aluminum content determination utilizes an atomizer made of graphite material in the shape of a tube or cup. The sample is heated to 2500°C using an electric current, and the absorbance is measured at a wavelength of 309.3 nm to calculate the aluminum content. However, when measuring aluminum, an amphoteric substance, unstable results occur, and this instability becomes more pronounced as the aluminum content in the sample decreases.

[0003] The method for measuring aluminum by electrothermal atomization of samples using a high-temperature graphite furnace includes calibration solution treatment and sample water treatment steps. Generally, the calibration solution treatment process includes: dissolving pure aluminum in hydrochloric acid and then diluting it to a certain volume; adding nitric acid to the diluted solution for digestion to form the calibration solution, adding a matrix modifier (usually magnesium nitrate), and then plotting a standard curve. The final product generated after thorough ashing of the calibration solution and matrix modifier is a mixture of Al₂O₃ and magnesium oxide, and atomic excitation is performed using this Al₂O₃ and magnesium oxide mixture as the final state. The sample water is filtered and then digested; during the detection process, it is ashed to form a solid mixture. Even if the sample water contains small amounts of other metal ions, the solid mixture formed after ashing will contain a relatively high proportion of other metal oxides. Therefore, the final state of aluminum atom excitation is in the form of the Al₂O₃ mixture or other aluminum mixtures.

[0004] Based on the principle of melting and boiling points of solid mixtures, mixtures containing other metal oxide impurities have lower melting and boiling points than pure Al2O3, and these points vary considerably depending on the type of impurity. Pure Al2O3 has a melting point of 2050℃ and a boiling point of 2980℃. Currently, graphite furnace atomic absorption spectrometry (GFAAS) needs to consider the temperature resistance and stability of the graphite tube, and excessively high testing temperatures are not advisable; the testing temperature for aluminum is generally 2500℃. Magnesium oxide has a boiling point of 3600℃, and its effect on lowering the boiling point of Al2O3 is minimal. The higher the atomization rate of a substance, the closer the GFA reading is to the true value, and reaching the boiling point is the most significant excitation factor for atomization. In current technology, on the one hand, the calibration solution cannot reach the boiling point of aluminum during testing, resulting in a very low atomization rate and a low slope in the standard curve. Under the same aluminum ion concentration, the absorbance of the standard curve deviates significantly from the absorbance of the sample, causing substantial measurement errors. On the other hand, the presence of other ions causes uncertainty in the atomization rate of the tested sample. Therefore, current methods for determining aluminum content using graphite furnace atomic absorption spectrometry have at least two problems: first, they cannot excite the maximum atomization rate of aluminum; and second, the calibration solution and the test sample exhibit different atomization rates. These two points are the main reasons why the industry cannot accurately determine aluminum content.

[0005] Therefore, developing a novel method for determining aluminum content using graphite furnace atomic absorption spectrometry has become one of the urgent problems to be solved in this field. Summary of the Invention

[0006] To address the aforementioned technical problems, the present invention aims to provide a method for determining aluminum content using graphite furnace atomic absorption spectrometry. This method enables the aluminum element to be fully atomized, improving measurement accuracy, and also solves the problem of different atomization rates between sample water and calibration solutions, masking interference from other metal oxides.

[0007] To achieve the above objectives, the present invention provides a method for determining aluminum content using graphite furnace atomic absorption spectrometry, comprising the following steps:

[0008] (1) Prepare an aluminum series calibration solution with added alkali metal nitrates, and measure the absorbance of the aluminum series calibration solution with added alkali metal nitrates using a graphite furnace atomic absorption spectrometer. Then, plot a standard curve with the measured absorbance as the ordinate and the aluminum content in the aluminum series calibration solution with added alkali metal nitrates as the abscissa.

[0009] (2) Add alkali metal nitrate to the sample to be tested, measure its absorbance using a graphite furnace atomic absorption spectrometer, and then calculate the aluminum content in the sample to be tested based on the standard curve obtained in step (1).

[0010] In the above method, preferably, the aluminum series calibration solution with added alkali metal nitrate is prepared by the following steps: taking different amounts of aluminum standard solution, adding appropriate amounts of nitric acid and alkali metal nitrate, and diluting each solution with water to obtain an aluminum series calibration solution with an aluminum content of 1 μg / L-100 μg / L. More preferably, the aluminum content in the aluminum series calibration solution with added alkali metal nitrate is 10 μg / L-60 μg / L. Those skilled in the art should understand that the aluminum content in the aluminum series calibration solution with added alkali metal nitrate is at appropriate concentration intervals. Specifically, the aluminum content in the prepared aluminum series calibration solution with added alkali metal nitrate can be 10 μg / L, 20 μg / L, 30 μg / L, 40 μg / L, or 60 μg / L, respectively.

[0011] In the above method, preferably, the alkali metal nitrate includes sodium nitrate and / or potassium nitrate, etc.

[0012] In the method of this invention, alkali metal nitrates, specifically sodium nitrate and / or potassium nitrate, are added to both the calibration solution and the sample to be tested. During the detection process using graphite furnace atomic absorption spectrometry, alkali metal oxides are formed after ashing. The compound of the alkali metal oxide and aluminum forms aluminate at high temperature, and atomic excitation is performed using this aluminate as the final state. According to a specific embodiment of this invention, taking sodium nitrate as an example, sodium oxide is formed during the ashing period of sodium nitrate, with the chemical equation: 4NaNO3=2Na2O+2N2+5O2. Sodium oxide reacts with the amphoteric substance aluminum hydroxide to form sodium aluminate, with the chemical equation: Na2O+2Al(OH)3=2NaAlO2+3H2O. Atomic excitation is performed using the final state NaAlO2. The boiling point of the aluminate formed by sodium and potassium is approximately 2300℃. Therefore, the method of the present invention can significantly reduce the graphite furnace measurement temperature, enabling aluminum to be fully atomized at 2350℃, stimulating the maximum atomization rate of aluminum, and allowing the slopes of the standard curve and the sample to fully overlap, thereby improving the accuracy of the measurement. Furthermore, the standard curve obtained has a better linear relationship than the prior art. In addition, the method of the present invention solves the problem of different atomization rates between the sample water and the calibration solution, and masks the interference of other metal oxides.

[0013] In the above method, preferably, based on the volume of the aluminum series calibration solution containing the added alkali metal nitrate, the amount of alkali metal nitrate added is 0.005-0.03 mmol / L, more preferably 0.02 mmol / L. Specifically, the alkali metal nitrate can be added in solution form, for example, using a sodium nitrate solution, potassium nitrate solution, or a mixed solution of sodium nitrate and potassium nitrate with a concentration of 0.5-3 mmol / L (preferably 2 mmol / L).

[0014] In some specific embodiments of the present invention, the amount of nitric acid added to the aluminum standard solution can be routinely adjusted by those skilled in the art.

[0015] In some specific embodiments of the present invention, preferably, the concentration of aluminum in the aluminum standard solution is 1000 μg / L. Specifically, the aluminum standard solution can be prepared by the following steps: dissolving 1.000 g of aluminum in an appropriate amount of hydrochloric acid, and then diluting the volume with water to 1000 mL to obtain aluminum standard stock solution I; transferring 10 mL of aluminum standard stock solution I and adding an appropriate amount of nitric acid, and diluting the volume with water to 100 mL to obtain aluminum standard stock solution II; transferring 10 mL of aluminum standard stock solution II and adding an appropriate amount of nitric acid, and diluting the volume with water to 1000 mL to obtain the aluminum standard solution. The hydrochloric acid used can be a 1.16 g / mL hydrochloric acid solution, and 1.000 g of aluminum can be dissolved in 15 mL of this hydrochloric acid solution. The nitric acid used can be a 1.40 g / mL nitric acid solution, and the amount of nitric acid solution added in both steps can be 1 mL.

[0016] In some specific embodiments of the present invention, preferably, the aluminum series calibration solutions with added alkali metal nitrates are prepared by the following steps: 1 mL, 2 mL, 3 mL, 4 mL, and 6 mL of the aluminum standard solution are respectively transferred, and appropriate amounts of nitric acid and alkali metal nitrates are added. The solutions are then diluted to 100 mL with water to obtain aluminum series calibration solutions with added alkali metal nitrates containing aluminum contents of 10 μg / L, 20 μg / L, 30 μg / L, 40 μg / L, and 60 μg / L. Specifically, based on the volume of the aluminum series calibration solutions with added alkali metal nitrates, the amount of added alkali metal nitrates is 0.005-0.03 mmol / L, more preferably 0.02 mmol / L. The nitric acid used can be a 1.40 g / mL nitric acid solution, and the amount of this nitric acid solution added can be 1 mL. The alkali metal nitrate used can be a sodium nitrate solution, potassium nitrate solution, or a mixed solution of sodium nitrate and potassium nitrate with a concentration of 0.5-3 mmol / L (preferably 2 mmol / L), and the amount added is 1 mL.

[0017] In some specific embodiments of the present invention, the aluminum standard stock solution I, aluminum standard stock solution II, and aluminum standard solution described above can be prepared in advance for use, but the aluminum series calibration solutions with added alkali metal nitrates described above need to be prepared fresh for use.

[0018] In the above method, preferably, the sample to be measured includes a water sample. More preferably, the sample to be measured is a filtered water sample.

[0019] In the above method, preferably, the amount of alkali metal nitrate added is 0.005-0.03 mmol / L, more preferably 0.02 mmol / L, based on the volume of the sample to be measured.

[0020] In the above method, preferably, step (2) further includes: adding nitric acid to the sample to be tested for digestion. Preferably, the content of the added nitric acid in the sample to be tested is 0.15-0.2 mol / L.

[0021] In the above method, preferably, a matrix modifier is also added to both the aluminum-based calibration solution containing alkali metal nitrates and the sample to be tested. More preferably, the matrix modifier includes magnesium nitrate. Even more preferably, the amount of matrix modifier added is 300-700 μg / L, particularly preferably 500 μg / L, based on the volume of the aluminum-based calibration solution containing alkali metal nitrates and the volume of the sample to be tested, respectively.

[0022] In the above method, preferably, the working conditions for determining absorbance using a graphite furnace atomic absorption spectrometer include: a detection wavelength of 309.3 nm, an ashing temperature of 700-800℃ (more preferably 700℃) and a time of 20-30 s (more preferably 20 s), and an atomization temperature of 2300-2400℃ (more preferably 2350℃) and a time of 4-5 s (more preferably 5 s). In some specific embodiments of the present invention, these working conditions further include: an injection volume of 10-20 μL, argon as the carrier gas with a flow rate of 200 mL / min, a drying start and end temperature of 80-140℃ and a time of 40 s, and a purification temperature of 2600℃ and a time of 4 s.

[0023] According to a specific embodiment of the present invention, preferably, the above method further includes the following steps: zeroing with a blank solution and measuring absorbance to subtract the blank; or zeroing with a zeroing solution first, and then measuring absorbance with a blank solution to subtract the blank. Zeroing can be performed using either a blank solution or a zeroing solution. If the aluminum content in the blank solution is negligible, zeroing can be performed using the blank solution; otherwise, zeroing should be performed using the zeroing solution first. Zeroing is required for the measurement of absorbance of the aluminum series calibration solution with added alkali metal nitrates, and for the measurement of absorbance of the sample to be measured with added alkali metal nitrates, and the blank needs to be subtracted during calculation. Specifically, the blank solution includes a 14 g / L nitric acid solution. More specifically, the blank solution can be prepared by the following steps: transferring 1 mL of a 1.40 g / mL nitric acid solution and diluting it to 100 mL with water to obtain the blank solution. The zeroing solution is water.

[0024] This invention provides a method for determining aluminum content using graphite furnace atomic absorption spectrometry (GFAAS) of alkali metal oxides. The technical solution of this invention has at least the following beneficial effects:

[0025] The method of this invention involves adding alkali metal nitrates to both the calibration solution and the sample to be tested. During the detection process using graphite furnace atomic absorption spectrometry (Graphite Furnace Atomic Absorption Spectrometry), alkali metal oxides are formed after ashing. The compounds of these alkali metal oxides and aluminum then form aluminates at high temperatures, with the aluminates serving as the final state for atomic excitation. This method significantly reduces the graphite furnace measurement temperature, allowing aluminum to be fully atomized at 2350°C, maximizing its atomization rate. This results in a high degree of overlap between the slopes of the standard curve and the sample, improving measurement accuracy and providing a standard curve with better linearity compared to existing techniques. Furthermore, this method addresses the issue of differing atomization rates between the sample water and the calibration solution, masking interference from other metal oxides. Simultaneously, the method exhibits good spike recovery rates, ranging from 97.85% to 101.55%. In summary, the method of the present invention improves the accuracy of aluminum content determination by graphite furnace atomic absorption spectrometry by generating the same atomization environment and increasing the atomization rate when testing the calibration solution and the sample for aluminum element. Furthermore, the method of the present invention is scientific, reasonable, has a high spike recovery rate, and is easy to operate, and has broad application prospects. Attached Figure Description

[0026] Figure 1 The standard curves are those obtained from Example 1 and Comparative Example 1.

[0027] Figure 2 The curve shows the absorbance of the standard sample in Example 1 as a function of atomization temperature.

[0028] Figure 3 The curve shows the absorbance of the standard sample in Comparative Example 1 as a function of atomization temperature.

[0029] Figure 4 The graph shows the effect of copper and calcium ions on the determination of aluminum content without the addition of sodium nitrate.

[0030] Figure 5 The graph shows the effect of copper and calcium ions on the aluminum content determination results when sodium nitrate is added. Detailed Implementation

[0031] In order to provide a clearer understanding of the technical features, objectives and beneficial effects of the present invention, the technical solution of the present invention will now be described in detail below, but it should not be construed as limiting the scope of implementation of the present invention.

[0032] Example 1

[0033] This embodiment provides a method for determining aluminum content using graphite furnace atomic absorption spectrometry, which includes the following steps:

[0034] (1) Prepare aluminum series calibration solutions with added sodium nitrate.

[0035] Weigh 1.000g of aluminum and dissolve it in 15mL of 1.16g / mL hydrochloric acid solution. Transfer the entire solution to a 1000mL volumetric flask, dilute with water, and bring the volume to the mark to obtain aluminum standard stock solution I. The concentration of aluminum in aluminum standard stock solution I is 1000mg / L.

[0036] Transfer 10 mL of aluminum standard stock solution I to a 100 mL volumetric flask, add 1 mL of 1.40 g / mL nitric acid solution, dilute with water and bring to volume to obtain aluminum standard stock solution II, in which the concentration of aluminum is 100 mg / L;

[0037] Transfer 10 mL of aluminum standard stock solution II to a 1000 mL volumetric flask, add 1 mL of 1.40 g / mL nitric acid solution, dilute with water and bring to volume to obtain an aluminum standard solution with an aluminum concentration of 1000 μg / L.

[0038] Transfer 1 mL, 2 mL, 3 mL, 4 mL, and 6 mL of aluminum standard solution to 100 mL volumetric flasks, respectively. Add 1 mL of 1.40 g / mL nitric acid solution, 10 μL of 5 mg / mL magnesium nitrate solution as a matrix modifier, and 1 mL of 2 mmol / L sodium nitrate solution to each flask. Dilute with water, bring to volume, and mix well to prepare a series of aluminum calibration solutions with aluminum contents of 10 μg / L, 20 μg / L, 30 μg / L, 40 μg / L, and 60 μg / L, containing sodium nitrate. The 5 mg / mL magnesium nitrate solution was prepared as follows: Weigh 500 mg of anhydrous magnesium nitrate and dissolve it in an appropriate amount of water. Transfer the solution to a 100 mL volumetric flask, dilute with water, and bring to volume.

[0039] The aluminum standard stock solution I, aluminum standard stock solution II, and aluminum standard solution mentioned above can be prepared in advance for use, but the aluminum series calibration solutions containing sodium nitrate mentioned above need to be prepared fresh for use.

[0040] (2) The absorbance of the aluminum series calibration solution with added sodium nitrate was measured using a graphite furnace atomic absorption spectrometer. Then, a standard curve was plotted with the measured absorbance as the ordinate and the aluminum content in the aluminum series calibration solution with added sodium nitrate as the abscissa.

[0041] (3) Filter the water sample to be tested, and then take an appropriate amount of the filtered water sample, add an appropriate amount of 1.40 g / mL nitric acid solution, an appropriate amount of magnesium nitrate solution with a concentration of 5 mg / mL as a matrix modifier, and an appropriate amount of sodium nitrate solution with a concentration of 2 mmol / L, shake well, and obtain the sample to be measured by graphite furnace atomic absorption spectrometry; wherein, the content of the added nitric acid in the filtered water sample is 0.15-0.2 mol / L, and based on the volume of the filtered water sample, the amount of magnesium nitrate added is 500 μg / L and the amount of sodium nitrate added is 0.02 mmol / L;

[0042] (4) Use a graphite furnace atomic absorption spectrometer to measure the absorbance of the sample obtained in step (3), and then calculate the aluminum content in the water sample to be measured based on the standard curve obtained in step (2).

[0043] In specific embodiments of the present invention, the reagents used should be analytical grade reagents and water conforming to the Class II water standard in GB / T 6682. The aluminum content in the water and reagents used should be negligible compared to the detection limit (i.e., the lower limit of quantitation) of the method of the present invention.

[0044] The method of this embodiment further includes the following steps: zeroing with a blank solution and measuring absorbance to subtract the blank; or zeroing with a zeroing solution first, and then measuring absorbance with a blank solution to subtract the blank. Zeroing can be performed using either a blank solution or a zeroing solution. If the aluminum content in the blank solution is negligible, the blank solution can be used for zeroing; otherwise, the zeroing solution should be used first. For the measurement of absorbance of the aluminum series calibration solution with added sodium nitrate, and for the measurement of the sample absorbance, zeroing is required, and the blank must be subtracted during calculation. Specifically, the blank solution is prepared as follows: 1 mL of 1.40 g / mL nitric acid solution is transferred to a 100 mL volumetric flask, diluted with water, and brought to the mark to obtain the blank solution. The zeroing solution is water.

[0045] In this embodiment, the working conditions for measuring absorbance using a graphite furnace atomic absorption spectrometer include: using an aluminum hollow cathode lamp, a detection wavelength of 309.3 nm, an injection volume of 20 μL, argon as the carrier gas with a flow rate of 200 mL / min, a drying start and end temperature of 80-140 °C for 40 s, an ashing temperature of 700 °C for 20 s, an atomization temperature of 2350 °C for 5 s, and a purification temperature of 2600 °C for 4 s.

[0046] The method in this embodiment yielded aluminum content in water samples ranging from 19.65 to 21.87 μg / L, as shown in Table 1.

[0047] Comparative Example 1

[0048] This comparative example provides a method for determining aluminum content using graphite furnace atomic absorption spectrometry.

[0049] The specific steps of this method are basically the same as those in Example 1, except that sodium nitrate is not added to the aluminum series calibration solution and the water sample to be tested; and the atomization temperature in the working conditions for measuring absorbance using a graphite furnace atomic absorption spectrometer is 2500℃.

[0050] The method used in this comparative example determined the aluminum content in the water sample (which was the same as that in Example 1) to be 22.85-25.57 μg / L, and the specific results are shown in Table 2.

[0051] The standard curves (i.e., aluminum content-absorbance curves of aluminum-based calibration solutions) obtained in Example 1 and Comparative Example 1 are as follows: Figure 1 As shown. By Figure 1 It can be seen that the slope of the standard curve obtained by adding sodium nitrate to the aluminum series calibration solution in Example 1 is significantly greater than that of the standard curve in Comparative Example 1 without adding sodium nitrate, and the linear relationship is also better than that of the standard curve in Comparative Example 1 without adding sodium nitrate.

[0052] Test Example 1: Absorbance of Standard Sample as atomization Temperature

[0053] In this test example, aluminum calibration solutions with an aluminum content of 30 μg / L, containing sodium nitrate and without sodium nitrate (i.e., the standard samples in this test example) from Example 1 and Comparative Example 1 were used. The absorbance of these solutions was measured at different atomization temperatures, and the highest absorbance point was observed to investigate the temperature at which aluminum achieves full atomization.

[0054] (1) Absorbance curve of the standard sample in Example 1 as a function of atomization temperature

[0055] Al₂O₃, a high-boiling-point substance, is difficult to atomize. Keeping other conditions constant as in Example 1, an aluminum calibration solution with 30 μg / L aluminum content and added sodium nitrate was used. The absorbance was measured at different atomization temperatures, increasing in increments of 100 °C. The results are as follows: Figure 2 As shown. By Figure 2 It can be seen that the standard sample shows a high absorbance point between 2300-2400℃, proving that the method of the present invention achieves full atomization of aluminum at a relatively low atomization temperature of 2300-2400℃. Therefore, the present invention selects 2350℃ as the optimal atomization temperature.

[0056] (2) Absorbance curve of Comparative Example 1 standard as a function of atomization temperature

[0057] Al₂O₃, a high-boiling-point substance, is difficult to atomize. Using a calibration solution of aluminum with a concentration of 30 μg / L (without added sodium nitrate) and no other conditions specified in Comparative Example 1, absorbance was measured at different atomization temperatures, increasing in increments of 100 °C. The results are as follows: Figure 3 As shown. By Figure 3 It can be seen that the standard sample shows a high absorbance point between 2700℃ and 2800℃, proving that the method of Comparative Example 1 can only achieve full atomization of aluminum at an atomization temperature of 2700℃-2800℃.

[0058] Test Example 2: The Influence of Interfering Metal Ions on Measurement Results

[0059] This test case analyzes the effect of interfering metal ions on the determination results of the methods in Example 1 and Comparative Example 1.

[0060] The reagents used in this test case include:

[0061] The copper nitrate interference solution is prepared as follows: Weigh 100 mg of anhydrous copper nitrate and dissolve it in an appropriate amount of water. Transfer the solution to a 100 mL volumetric flask, dilute with water, and bring the volume to the mark.

[0062] The calcium nitrate interference solution is prepared as follows: Weigh 100 mg of anhydrous calcium nitrate and dissolve it in an appropriate amount of water. Transfer the solution to a 100 mL volumetric flask, dilute with water, and bring the volume to the mark.

[0063] This test case includes the following steps:

[0064] (1) Investigate the effects of copper and calcium ions on the aluminum content determination results without the addition of sodium nitrate.

[0065] Transfer 3 mL of the aluminum standard solution (aluminum concentration of 1000 μg / L) from Example 1 to a 100 mL volumetric flask, add 1 mL of 1.40 g / mL nitric acid solution, 10 μL of 5 mg / mL magnesium nitrate solution as a matrix modifier, and 1 mL of the copper nitrate interference solution mentioned above. Dilute with water, bring to volume, and shake well to obtain the copper interference sample. Measure its absorbance using a graphite furnace atomic absorption spectrometer under the same working conditions as Comparative Example 1.

[0066] Transfer 3 mL of the aluminum standard solution (aluminum concentration of 1000 μg / L) from Example 1 to a 100 mL volumetric flask, add 1 mL of 1.40 g / mL nitric acid solution, 10 μL of 5 mg / mL magnesium nitrate solution as a matrix modifier, and 1 mL of the above-mentioned calcium nitrate interference solution. Dilute with water, bring to volume, and shake well to obtain the calcium interference sample. Measure its absorbance using a graphite furnace atomic absorption spectrometer under the same working conditions as Comparative Example 1.

[0067] Using the standard curve in Comparative Example 1, we investigated the effects of copper and calcium ions on the aluminum content determination results without the addition of sodium nitrate.

[0068] (2) Investigate the effects of adding sodium nitrate on the aluminum content determination results.

[0069] Transfer 3 mL of the aluminum standard solution (aluminum concentration of 1000 μg / L) from Example 1 to a 100 mL volumetric flask, add 1 mL of 1.40 g / mL nitric acid solution, 10 μL of 5 mg / mL magnesium nitrate solution as a matrix modifier, 1 mL of 2 mmol / L sodium nitrate solution, and 1 mL of the above-mentioned copper nitrate interference solution. Dilute with water, bring to volume, and shake well to obtain the copper interference sample. Measure its absorbance using a graphite furnace atomic absorption spectrometer under the same working conditions as in Example 1.

[0070] Transfer 3 mL of the aluminum standard solution (aluminum concentration of 1000 μg / L) from Example 1 to a 100 mL volumetric flask, add 1 mL of 1.40 g / mL nitric acid solution, 10 μL of 5 mg / mL magnesium nitrate solution as a matrix modifier, 1 mL of 2 mmol / L sodium nitrate solution, and 1 mL of the above-mentioned calcium nitrate interference solution. Dilute with water, bring to volume, and shake well to obtain the calcium interference sample. Measure its absorbance using a graphite furnace atomic absorption spectrometer under the same working conditions as in Example 1.

[0071] Using the standard curve in Example 1, we investigated the effects of the addition of sodium nitrate on the determination results of aluminum content.

[0072] In step (1) of this test example, the absorbance and aluminum content of the copper interference sample and the calcium interference sample are compared with the standard curve of Comparative Example 1. The results are as follows: Figure 4 As shown. By Figure 4 It can be seen that, using the method of Comparative Example 1, other metal ions have a significant impact on the determination results of aluminum content, and the measured value of aluminum content differs greatly from the true value.

[0073] In step (2) of this test example, the absorbance and aluminum content of the copper interference sample and the calcium interference sample are compared with the standard curve of Example 1. The results are as follows: Figure 5 As shown. By Figure 5 It can be seen that the method of Example 1 effectively masks the interference of other metals, resulting in high accuracy and stability of the detection results.

[0074] Test Example 3 Spike Recovery

[0075] This test case provides spike recovery tests for the methods of Example 1 and Comparative Example 1.

[0076] (1) Spike recovery test in Example 1

[0077] Clean water samples were taken for spiked recovery tests, and the results are shown in Table 1 below. As can be seen from Table 1, the recovery rate of the method in Example 1 is between 97.85% and 101.55%, indicating that the method in Example 1 has a good recovery rate and can be applied in practice.

[0078] Table 1. Recovery rate experimental results of Example 1

[0079]

[0080] (2) Spiked recovery test of Comparative Example 1

[0081] Clean water samples were used for spiked recovery tests, and the results are shown in Table 2 below. As can be seen from Table 2, the recovery rate of the method in Comparative Example 1 is between 105.50% and 127.65%, and the lower the aluminum content, the greater the deviation from the actual value.

[0082] Table 2 shows the recovery results of Comparative Example 1.

[0083]

[0084] In summary, the method of the present invention improves the accuracy of aluminum content determination by graphite furnace atomic absorption spectrometry by generating the same atomization environment and increasing the atomization rate when testing the calibration solution and the sample for aluminum element. Furthermore, the method of the present invention is scientific, reasonable, has a high spike recovery rate, and is easy to operate, and has broad application prospects.

Claims

1. A method for determining aluminum content using graphite furnace atomic absorption spectrometry, comprising the following steps: (1) Prepare an aluminum series calibration solution with added alkali metal nitrate. Based on the volume of the aluminum series calibration solution with added alkali metal nitrate, the amount of added alkali metal nitrate is 0.005-0.03 mmol / L. Measure the absorbance of the aluminum series calibration solution with added alkali metal nitrate using a graphite furnace atomic absorption spectrometer. Then, plot a standard curve with the measured absorbance as the ordinate and the aluminum content in the aluminum series calibration solution with added alkali metal nitrate as the abscissa. (2) Add alkali metal nitrate to the sample to be tested. The amount of alkali metal nitrate added is 0.005-0.03 mmol / L, based on the volume of the sample to be tested. The alkali metal nitrate includes sodium nitrate and / or potassium nitrate. Measure its absorbance using a graphite furnace atomic absorption spectrometer. Then calculate the aluminum content in the sample to be tested according to the standard curve obtained in step (1). The working conditions for measuring absorbance using a graphite furnace atomic absorption spectrometer include: a detection wavelength of 309.3 nm, an ashing temperature of 700-800℃ and a time of 20-30 s, and an atomization temperature of 2300-2350℃ and a time of 4-5 s.

2. The method according to claim 1, wherein, The aluminum series calibration solutions with added alkali metal nitrates are prepared by the following steps: taking different amounts of aluminum standard solutions, adding appropriate amounts of nitric acid and alkali metal nitrates, and diluting with water to obtain aluminum series calibration solutions with added alkali metal nitrates with aluminum content of 1 μg / L-100 μg / L.

3. The method according to claim 2, wherein, The aluminum content in the aluminum series calibration solution containing alkali metal nitrates is 10 μg / L-60 μg / L.

4. The method according to claim 2, wherein, The aluminum concentration in the aluminum standard solution is 1000 μg / L.

5. The method according to claim 1, wherein, The samples to be tested include water samples.

6. The method according to claim 5, wherein, The sample to be tested is a filtered water sample.

7. The method according to claim 1, wherein, Step (2) further includes: adding nitric acid to the sample to be tested for digestion.

8. The method according to claim 7, wherein, The amount of nitric acid added in the sample to be tested was 0.15-0.2 mol / L.

9. The method according to claim 1, wherein, The aluminum series calibration solution containing alkali metal nitrates and the sample to be tested also contain matrix modifiers.

10. The method according to claim 9, wherein, The matrix modifier includes magnesium nitrate.

11. The method according to claim 9, wherein, The amount of matrix modifier added is 300-700 μg / L, based on the volume of the aluminum series calibration solution containing alkali metal nitrates and the volume of the sample to be tested, respectively.

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