Method for measuring thallium content in nickel sulfate product by graphite furnace atomic absorption method

Abstract

The invention relates to the technical field of chemical analysis, in particular to a method for measuring thallium content in a nickel sulfate product by a graphite furnace atomic absorption method, which comprises the following steps: optimizing test conditions, preparing a standard solution and drawing a standard curve; weighing a nickel sulfate sample, and dissolving to obtain a green and transparent nickel sulfate sample solution; taking the nickel sulfate sample solution into an automatic sample injection cup, measuring the absorbance of the sample under the set condition of an instrument by using a graphite furnace atomic absorption spectrometer, and automatically calculating the concentration value of thallium in the nickel sulfate sample according to the drawn standard curve instrument; and calculating the content of thallium in the sample according to the weight of the weighed sample and the constant volume. According to the graphite furnace atomic absorption method, the thallium content in the nickel sulfate product can be efficiently and accurately measured. The method has the advantages of high sensitivity, low detection limit, simplicity in operation, low detection cost, wide detection range and wide applicability.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical analysis, and particularly relates to a method for determining the thallium content in nickel sulfate products by graphite furnace atomic absorption spectrometry. Background Art

[0002] Thallium (Tl) is one of the heavy metals with high toxicity and has strong neurotoxicity. At the same time, the widespread use of thallium increases the risk of environmental pollution and has been listed in the blacklist of priority pollutants to be controlled in water in China. However, it widely exists in many industrial fields, and trace amounts of thallium elements also exist in nickel sulfate products. Nickel sulfate is widely used in fields such as electroplating and battery production. Due to the high toxicity of thallium, the detection of thallium content in nickel sulfate products is very important. At present, the detection of thallium generally uses the ICP method or the ICP-MS method, but the detection limit of the ICP method is relatively high, and the thallium content in nickel sulfate is low, so it cannot be detected. The instrument used in the ICP-MS method is expensive and the detection cost is high, making it difficult to meet the use requirements of grass-roots inspection units. Therefore, there is an urgent need for a method for determining low-content thallium that is efficient, accurate and has a low detection cost. Summary of the Invention

[0003] The present invention provides a method for determining the thallium content in nickel sulfate products by graphite furnace atomic absorption spectrometry, which overcomes the deficiencies of the above-mentioned prior art and can effectively solve the problems of low efficiency and high cost in the existing detection methods for thallium content in nickel sulfate products.

[0004] To solve the above problems, a method for determining the thallium content in nickel sulfate products by graphite furnace atomic absorption spectrometry according to the present invention includes the following steps: Prepare a standard solution and draw a standard curve; Weigh a nickel sulfate sample and dissolve it to obtain a green and transparent nickel sulfate sample solution; Take the nickel sulfate sample solution in an automatic sampler cup, use a graphite furnace atomic absorption spectrometer, measure the absorbance of the sample under the set conditions of the instrument, and the instrument automatically calculates the concentration value of thallium in the nickel sulfate sample according to the drawn standard curve; Calculate the thallium content in the sample based on the weight of the sample taken and the volume of constant volume.

[0005] The above set conditions include: the lamp current of the hollow cathode lamp is 3.0 - 6.0 mA, the slit width is 0.5 - 1.0 nm, the drying temperature is 90 - 120 °C, the ashing temperature is 400 - 700 °C, the atomization temperature is 1200 - 1500 °C, the sample weight is 2.0 - 10.0 g, the volume of constant volume is 200 - 500 ml, the matrix modifier is NH4H2PO4 or ascorbic acid with a certain concentration, and the measurement wavelength is 276.8 nm.

[0006] Prepare a standard solution and plot a standard curve, including stepwise diluting a thallium element standard solution of 1×10^6 ug / L to 50 ug / L of thallium, putting this solution and the prepared nickel sulfate matrix solution into an auto-sampler cup respectively, and using the instrument's automatic online dilution function to obtain a series of standard solutions with concentration values of 0, 5, 10, 20, and 40 ug / L respectively. Taking the concentration of the standard solution as the abscissa and the absorbance as the ordinate, the instrument automatically plots the standard curve.

[0007] According to the above-mentioned plotted standard curve, the instrument automatically calculates the concentration value of thallium in the nickel sulfate sample, including extending the standard curve to intersect with the abscissa and obtaining the concentration value at the intersection point, which is the concentration of thallium in the nickel sulfate sample, with the unit of ug / L.

[0008] Calculate the content of thallium in the sample based on the sample weight and the fixed volume of the solution, which is calculated by the following formula: In the formula, c is the measured element concentration, in ug / L; V is the sample volume, in mL; m is the sample amount, in g.

[0009] The present invention has the following advantages compared with the prior art: (1) High sensitivity: Under the test conditions of this study, the graphite furnace atomic absorption spectrometry has high sensitivity when determining the thallium content in nickel sulfate products and can accurately measure trace thallium elements.

[0010] (2) Low detection limit: Compared with the existing metal element detection technology - ICP method, the detection limit of this method is lower and it is more suitable for the detection of low-content metal thallium elements.

[0011] (3) Simple operation: Compared with the traditional method, the steps of the present invention are simplified and the operation is simple, which is suitable for large-scale industrial applications.

[0012] (4) Low detection cost: Compared with the existing trace metal element detection technology - ICP-MS method, the instrument used in this method is cheap, the detection cost is low, and it is more suitable for wide use in grass-roots inspection units.

[0013] (5) Wide determination range and applicability: This method can determine the thallium content in the range of 0.00002% - 0.001%. At the same time, this method is not only applicable to nickel sulfate samples, but also applicable to the detection of low-content thallium elements in other solutions. Description of the Drawings

[0014] The following further elaborates on the specific implementation manners of the present invention in conjunction with the drawings.

[0015] Figure 1 It is the influence curve diagram of the lamp current on the absorbance value in Example 2 of the present invention.

[0016] Figure 2 It is the influence curve diagram of the slit width on the absorbance value in Embodiment 3 of the present invention.

[0017] Figure 3 It is the influence curve diagram of the ashing temperature on the absorbance value in Embodiment 4 of the present invention.

[0018] Figure 4 It is the influence curve diagram of the atomization temperature on the absorbance value in Embodiment 5 of the present invention. Specific Embodiments

[0019] The present invention is not limited by the following embodiments, and the specific implementation manners can be determined according to the technical solution of the present invention and the actual situation.

[0020] Embodiment 1: Overall testing process The embodiment of the present invention discloses a method for determining the thallium content in nickel sulfate products by graphite furnace atomic absorption spectrometry, including the following steps: Prepare a standard solution and draw a standard curve; Weigh a nickel sulfate sample, and after dissolution, obtain a green transparent nickel sulfate sample solution; Take the nickel sulfate sample solution in an automatic sampling cup, use a graphite furnace atomic absorption spectrometer, measure the absorbance of the sample under the set conditions of the instrument, and the instrument automatically calculates the concentration value of thallium in the nickel sulfate sample according to the drawn standard curve; Calculate the thallium content in the sample based on the weighed sample weight and the constant volume.

[0021] Among them, preparing a standard solution and drawing a standard curve includes gradually diluting a 1×10^6 ug / L Tl element stock solution to 50 ug / L, putting this solution and the prepared nickel sulfate matrix solution into automatic sampling cups respectively, and using the automatic online dilution function of the instrument to obtain a series of standard solutions with concentration values of 0, 5, 10, 20, 40 ug / L. Taking the concentration of the standard solution as the abscissa and the absorbance as the ordinate, the instrument automatically draws a standard curve.

[0022] Among them, weighing the nickel sulfate sample includes weighing a certain amount of nickel sulfate crystal sample (accurate to 0.0002 g) and placing it in a 250 mL beaker, adding water to dissolve it completely, and making it up to a certain volume, shaking well to obtain a green transparent nickel sulfate sample solution.

[0023] Among them, the set conditions include that the lamp current of the hollow cathode lamp is 3.0 - 6.0 mA, the slit width is 0.5 - 1.0 nm, the ashing temperature is 400 - 700 °C, the atomization temperature is 1200 - 1500 °C, the sample weight is 2.0 - 10.0 g, the constant volume is 200 - 500 ml, the matrix modifier is NH4H2PO4 or ascorbic acid at a certain concentration, and the measurement wavelength is 276.8 nm.

[0024] According to the concentration value of thallium content in the nickel sulfate sample solution measured by the instrument, the weight of the sample taken and the constant volume, calculate the thallium content in the sample, and calculate it through the following formula: In the formula, c is the measured element concentration, μg / L; V is the sample volume, mL; m is the sample amount, g.

[0025] Example 2: Optimization process of test conditions This embodiment of the present invention discloses taking different selections of the lamp current of the hollow cathode lamp as an example. Specifically: Prepare a 10 μg / L thallium standard solution as a sample, set the standard series concentrations to 0, 5, 10, 20, 40 μg / L, ensure that other test conditions are the same, and adjust the lamp current of the hollow cathode lamp to 2.0 mA, 3.0 mA, 4.0 mA, 5.0 mA, 7.0 mA respectively, measure the sample concentration and absorbance under different conditions to determine a more appropriate lamp current, and obtain the absorbance data at different lamp currents as shown in Table 1. Draw the influence curve of the lamp current on the absorbance according to Table 1 to obtain Figure 1 The described curve graph.

[0026] It can be seen from Figure 1 that the hollow cathode lamp provides a sharp-line light source for atomic absorption. The luminous intensity of the hollow cathode lamp is related to the lamp current. Within a certain range, increasing the lamp current can increase the spectral line intensity. The absorbance value first increases and then decreases with the increase of the lamp current of the hollow cathode lamp. This is because when the lamp current is small, the radiated sharp-line spectral line is narrow, the discharge is unstable, and the spectral output intensity is small. And when the lamp current is too small, the transmitted light is too weak, and the gain of the photomultiplier tube sensitivity needs to be increased. At this time, the noise will increase and the signal-to-noise ratio will decrease; if the lamp current is too large, it will cause thermal broadening and collision broadening of the radiated spectrum, increase the self-absorption in the lamp, reduce the intensity of the radiated sharp-line light, increase the background, reduce the sensitivity, and also accelerate the consumption of the inert gas in the lamp and shorten the service life of the lamp. From the experimental results, it can be seen that when the lamp current is selected as 4.0 mA, the absorbance value is relatively large. Therefore, the hollow cathode lamp is selected as 4.0 mA to measure the thallium content in the sample.

[0027] Example 3: Optimization process of test conditions An embodiment of the present invention discloses an embodiment of the influence of slit width on the absorbance value. Specifically: An experiment on the selection of slit width was carried out under the condition that the hollow cathode lamp was 4.0 mA, and then an experiment on the selection of ashing temperature was carried out according to the optimal slit width. A thallium standard solution with a concentration of 10 μg / L was prepared as a sample, and the standard solution concentrations were set to 0, 5, 10, 20, and 40 μg / L. While ensuring that other test conditions were the same, the slit widths were adjusted to 0.2 nm, 0.5 nm, 0.8 nm, and 1.2 nm respectively, and the sample concentrations and absorbances under different conditions were measured to determine a more appropriate slit width. The absorbance data under different slit widths are shown in Table 2. According to Table 2, a curve of the influence of lamp current on absorbance was plotted to obtain Figure 2 the described curve graph.

[0028] It can be seen from Figure 2 that within a certain range, the absorbance value first increases and then decreases with the increase of the slit width. This is because when the slit width is small, to a certain extent, the light flux becomes smaller, the signal becomes smaller, and the sensitivity decreases. When the slit width is large, to a certain extent, the light flux is also large, and the monochromatic light is impure. At this time, when other spectral lines or non-absorbing light enter the spectral bandpass, the absorbance will immediately decrease, the signal value is also large, but the corresponding background signal is also large, and the accuracy decreases. From the experimental results, it can be seen that when the slit width is 0.8 nm, the absorbance value reaches the highest value and the interference is small. Therefore, a slit width of 0.8 nm is selected to measure the thallium content in the sample.

[0029] Example 4: Process of optimizing test conditions An embodiment of the present invention discloses an embodiment of the influence of ashing temperature on the absorbance value. Specifically: A thallium standard solution with a concentration of 10 μg / L was prepared as a sample, and the standard solution concentrations were set to 0, 5, 15, and 20 μg / L. While ensuring that other test conditions were the same, the ashing temperatures were adjusted to 400 °C, 500 °C, 600 °C, and 700 °C respectively, and the sample concentrations and absorbances under different conditions were measured to determine a more appropriate ashing temperature. The absorbance data under different ashing temperatures are shown in Table 3. According to Table 3, a curve of the influence of ashing temperature on absorbance was plotted to obtain Figure 3 the described curve graph.

[0030] It can be seen from Figure 3 that within a certain range, the absorbance value first increases and then decreases with the increase of the ashing temperature. This is because when the ashing temperature is too low, the matrix is not completely ashed, resulting in a large background absorption. When the ashing temperature is too high, ashing loss occurs and the data reproducibility becomes poor. From the experimental results, it can be seen that when the ashing temperature is 600 °C, the absorbance value reaches the highest value. At this temperature, it can not only ensure that the matrix is completely ashed but also is not easy to cause sample loss.

[0031] Example 5: Process of optimizing test conditions The embodiment of the present invention discloses an embodiment of the effect of atomization temperature on absorbance value, specifically: Prepare 10ug / L thallium standard solution as sample, set the standard solution concentration to 0, 5, 15, 20, 40 ug / L, ensure that other test conditions are consistent, adjust the ashing temperature to 1200℃, 1300℃, 1400℃, 1500℃, respectively, measure the sample concentration and absorbance under different conditions to determine the atomization temperature with a more appropriate size, and obtain the absorbance data at different atomization temperatures as shown in Table 4. According to Table 4, draw the influence curve of atomization temperature on absorbance, and get Figure 4 The curve graph described.

[0032] Depend on Figure 4 It can be seen that the absorbance value first increases and then decreases with the increase of atomization temperature. The atomization temperature is determined by the properties of the measured elements and compounds, and is an important factor affecting the atomization efficiency and signal value of the measured object. When the atomization temperature is too high, the ground state atoms are ionized, the concentration of the ground state atoms decreases, and the absorbance value decreases accordingly, thereby reducing the measured concentration and shortening the service life of the graphite tube. When the atomization temperature is too low, the optimal atomization temperature is not reached, the atomization will be incomplete, the detected absorbance value will decrease, and the measured concentration will also decrease. From the experimental results, it can be seen that when the atomization temperature reaches 1300℃, the absorbance value reaches the highest value and a platform appears. Under this condition, the sensitivity of thallium determination can be improved and the service life of the graphite tube can be guaranteed.

[0033] Example 6: Method Validation Process The present invention discloses an embodiment of the detection of low-content thallium in a nickel sulfate sample. Specifically, the detection limit and the lower limit of determination experiment are carried out under the above-mentioned setting conditions. Weigh 10.0000 g of nickel sulfate product and dissolve it in a 250 ml beaker. After it is completely dissolved, transfer it to a 500 ml volumetric flask, add 10 ug / L of thallium standard, and measure it according to the sample analysis steps. Record the absorbance and concentration values respectively, calculate the standard deviation of the 7 measurement results, and calculate the method detection limit and determination limit according to the following formula.

[0034] Calculation formula: Method detection limit (MDL) = t (6,0.99)* S MQL = 4*MDL In the above formula, t （6,0.99） is the one-sided t distribution value with 6 degrees of freedom and 99% confidence level; S is the standard deviation of 7 parallel measurements.

[0035] As can be seen from Table 5, the method detection limit of the graphite furnace atomic absorption method is 0.012 ppm, and the determination lower limit is 0.048 ppm. That is, the nickel sulfate products with thallium content above 0.048 ppm can be accurately determined by the graphite furnace atomic absorption method, meeting the current production requirements.

[0036] Example 7: Method verification process The embodiment of the present invention discloses an embodiment for detecting low-content thallium in a nickel sulfate sample. Specifically: The method precision test is carried out under the above-set conditions. Nickel sulfate products with different thallium contents are tested, and parallel determinations are made 7 times to calculate their precision. As can be seen from Table 6, the measured values of the 4 nickel sulfate samples are all within the allowable error range, and the relative error is between 0.37% and 3.86%. At the same time, the relative deviation range is between 0.31% and 2.06%. Therefore, it shows that the precision of the determination of thallium content in nickel sulfate products after optimizing the conditions is relatively high, meeting the analysis requirements of actual samples.

[0037] Example 8: Method verification process The embodiment of the present invention discloses an embodiment for verifying the accuracy of the graphite furnace atomic absorption method. Specifically: The method accuracy test is carried out under the above-set conditions.

[0038] Accurately weigh 10.0000 g (accurate to 0.0002 g) of nickel sulfate samples (batch numbers are: 423041010232 and 423040940230, and the known thallium contents are 0.10 ppm and 0.11 ppm respectively). Take four portions of each and place them in 250 mL beakers. After completely dissolving with water, transfer them into 500 mL volumetric flasks, make up to the mark and shake well; Add 0 ml, 2.0 ml, 4.0 ml, and 8.0 ml of 100 μg / L thallium standard solution to each portion in turn to prepare a series of standard solutions with concentrations of 0 μg / L, 2.0 μg / L, 4.0 μg / L, and 8.0 μg / L for the spike recovery test, and calculate the recovery rate.

[0039] As can be seen from Table 7, when using the graphite furnace atomic absorption method to determine the thallium content in nickel sulfate products, the recovery rate is 98.20% - 103.95%, within the range of 95.0% - 105.0%. This shows that the measurement results are relatively accurate and reliable, and the accuracy is relatively high when using this method to determine low-content thallium in nickel sulfate products, meeting the production needs.

Claims

1. A method for determining the thallium content in nickel sulfate products by graphite furnace atomic absorption spectrometry, characterized in that, It includes the following steps: Prepare a standard solution and draw a standard curve; Weigh the nickel sulfate sample to be tested, and after dissolution, obtain a green transparent nickel sulfate solution to be tested; Take the nickel sulfate solution to be tested in an auto-sampler cup, use a graphite furnace atomic absorption spectrometer, measure the absorbance of the sample under the set conditions of the instrument, and the instrument automatically calculates the concentration value of thallium in the nickel sulfate sample according to the drawn standard curve; Calculate the content of thallium in the sample based on the weighed sample weight and the volume of constant volume.

2. The method for determining the thallium content in nickel sulfate products by graphite furnace atomic absorption spectrometry according to claim 1, wherein, The set conditions include that the lamp current of the hollow cathode lamp is 4.0 mA, the slit width is 0.8 nm, the drying temperature is 110 °C, the ashing temperature is 600 °C, the atomization temperature is 1300 °C, the sample weight is 10.0 g, the volume of constant volume is 500 mL, the matrix modifier is 15 μL of NH4H2PO4 with a volume fraction of 1%, and the measurement wavelength is 276.8 nm.

3. The method for determining the thallium content in nickel sulfate products by graphite furnace atomic absorption spectrometry according to claim 1, characterized in that, The preparation of the standard solution and the drawing of the standard curve include successively diluting the Tl element stock solution of 1×10^6 μg / L to 50 μg / L, putting this solution and the prepared nickel sulfate matrix solution into the auto-sampler cup respectively, and using the automatic on-line dilution function of the instrument to obtain a series of standard solutions with concentration values of 0, 5, 10, 20, 40 μg / L respectively. Taking the concentration of the standard solution as the abscissa and the absorbance as the ordinate, the instrument automatically draws the standard curve.

4. The method for determining the thallium content in nickel sulfate products by graphite furnace atomic absorption spectrometry according to claim 1, characterized in that, The automatic calculation of the concentration of thallium in the nickel sulfate sample according to the drawn standard curve includes extending the standard curve to intersect with the abscissa, and obtaining the concentration value at the intersection point, which is the concentration of thallium in the nickel sulfate sample, with the unit of μg / L.

5. The method for determining the thallium content in nickel sulfate products by graphite furnace atomic absorption spectrometry according to claim 1, characterized in that, Calculate the content of thallium in the sample according to the sample weight and the volume of constant volume, and calculate through the following formula In the formula, c is the measured element concentration, μg / L; V is the sample volume, mL; m is the sample amount, g.

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