GB/T 13748.2-2026Methods for chemical analysis of magnesium and magnesium alloys - Part 2: Determination of tin, beryllium, copper, nickel and titanium content - Spectrophotometry (English PDF)

6.2.5 Sulfuric acid-hydrogen peroxide. 100 mL of sulfuric acid (

1.0 mol/L) contains 2 to 3 drops of hydrogen peroxide (rho =

6.2.6 Sulfuric acid-citric acid mixture. Weigh 25.0g of citric acid (C6H8O7) and dissolve it in 400mL of water, then slowly add 30mL of sulfuric acid. (rho=1.84g/mL), dilute with water to 500mL and mix well.

6.2.7 Sodium hydroxide solution (200 g/L).

6.2.8 Ascorbic acid solution (20 g/L). Prepare as needed.

6.2.10 Hexadecyltrimethylammonium bromide solution (

0.3 g/L). Weigh

0.15 g of hexadecyltrimethylammonium bromide (C19H42BrN) and dissolve it in... Dilute 350 mL of anhydrous ethanol (rho =

0.79 g/mL) with water to 500 mL and mix well.

6.2.11 Iron solution (1 g/L). Weigh

0.484 g of ferric chloride hexahydrate (FeCl3·6H2O) into a beaker, add 6 mL of hydrochloric acid (1.1), Dissolve and dilute with water to 100 mL, then mix well.

6.2.12 Ammonium chloride washing solution (10g/L). Weigh 1g of ammonium chloride (6.2.1) and dissolve it in 100mL of water, then add 1mL of ammonia water (6.2.2).

6.2.13 Tin Standard Stock Solution (

0.1 mg/mL). Weigh 0.1000 g of metallic tin (wSn >= 99.9%) into a 150 mL beaker, add... 10 mL of sulfuric acid (rho =

1.84 g/mL) was heated until completely dissolved and white fumes were emitted. After cooling, 25 mL of sulfuric acid (rho =

1.84 g/mL) was added. Transfer sulfuric acid (1.9) to a 1000 mL volumetric flask, dilute to the mark with sulfuric acid (1.9), and mix well. 1 mL of this solution contains

0.1 mg of tin. Or Use certified standard solutions.

6.2.14 Tin Standard Solution (5.0 µg/mL). Transfer

25.00 mL of tin standard stock solution (6.2.13) to a 500 mL volumetric flask, and precipitate with sulfur. Dilute with acid (1 9) to the mark and mix well. 1 mL of this solution contains 5.0 µg of tin. Prepare as needed.

6.3 Test Procedure

6.3.1 Sample Weigh the sample according to Table 2 (Chapter 5), accurate to 0.0001g, and record it as m0.

6.3.2 Parallel Tests Perform the experiment twice in parallel and take the average value.

6.3.3 Blank Test A blank test was performed along with the sample.

6.3.4 Measurement

6.3.4.1 Place the sample in a 300mL beaker, add approximately 50mL of water, and add 35mL of nitric acid in portions (6.2.3). Cover with a watch glass and heat. Boil until the sample is completely dissolved for 5 minutes, rinse the petri dish and cup walls with water, and add water to 150 mL.

6.3.4.2 Add 5 mL of iron solution (6.2.11) and 10 g of ammonium chloride (6.2.1), and adjust with ammonia water (6.2.2) until ferric hydroxide precipitate initially appears (at this point, the solution...). Add 6 mL to 7 mL of ammonia water (6.2.2) to the solution (pH 6-7), add water to.200 mL, and boil for 1 to 2 minutes.

6.3.4.3 Remove and let cool slightly, then filter while still warm using rapid filter paper. Wash the beaker and precipitate 8 to 10 times each with hot ammonium chloride washing solution (6.2.12), then discard. Remove the filtrate. Dissolve the precipitate in 20 mL of hot sulfuric acid-hydrogen peroxide (6.2.5) in the original beaker, and wash with water 4-5 times. Dissolve in sodium hydroxide. Adjust the solution (6.2.7) until a brown precipitate initially appears, then adjust with sulfuric acid (6.2.4) until the precipitate just dissolves and one drop in excess, and heat until the test solution is clear.

6.3.4.4 Transfer the test solution into the corresponding volumetric flask (V0) according to Table 2, dilute with water to the mark, and mix well. Dispense the test solution (V1) into 50 mL containers according to Table 2. In a volumetric flask, add

10.0 mL of sulfuric acid-citric acid mixed acid (6.2.6) and

5.0 mL of ascorbic acid solution (6.2.8), mix well, and then add

3.0 mL of... Catechol purple solution (6.2.9),

3.0 mL hexadecyltrimethylammonium bromide solution (6.2.10) (mix gently after each addition of reagent), water Dilute to the mark, mix well, and let stand for 30 minutes.

6.3.4.5 Transfer a portion of the test solution into a 1cm cuvette, using the blank test solution accompanying the sample as a reference, and measure the solution at wavelength (4.1) on a spectrophotometer. The absorbance was measured at 662 nm, and the mass of tin (mSn) was obtained from the working curve.

6.3.5 Plotting the Working Curve

6.3.5.1 Transfer 0 mL,

5.00 mL of tin standard solution (6.2.14) to a set of... In a 50 mL volumetric flask, add

10.0 mL of a sulfuric acid-citric acid mixture (6.2.6) and

5.0 mL of ascorbic acid solution (6.2.8), respectively, mix well, and then divide into portions. Do not add

3.0 mL of catechol purple solution (6.2.9) or

3.0 mL of hexadecyltrimethylammonium bromide solution (6.2.10). (Each reagent should be added gently.) Mix lightly, dilute with water to the mark, mix well, and let stand for 30 minutes.

6.3.5.2 Transfer a portion of the series of standard solutions into a 1cm cuvette, using the "zero" concentration solution in the working curve series of standard solutions as a reference. The absorbance was measured at a wavelength of 662 nm using a spectrophotometer (4.1). A plot was created with the mass of tin on the x-axis and the corresponding absorbance on the y-axis. Operating curve. The linear correlation coefficient of the operating curve should not be less than 0.999.

6.5 Precision

6.5.1 Repeatability The measured values of two independent test results obtained under repeatability conditions, within the range of the average values given in Table 3, represent the values of the two test results. The absolute difference does not exceed the repeatability limit (r), and the number of cases exceeding the repeatability limit (r) does not exceed 5%. The repeatability limit (r) is determined by linearity based on the data in Table 3. Obtained by interpolation or extrapolation.

6.5.2 Reproducibility The measured values of two independent test results obtained under reproducibility conditions, within the range of average values given in Table 4, represent the values of the two test results. The absolute difference does not exceed the reproducibility limit (R), and the number of cases exceeding the reproducibility limit (R) does not exceed 5%. The reproducibility limit (R) is calculated using linearity based on the data in Table 4. Obtained by interpolation or extrapolation.

7.2.7 Elixirin R solution (2 g/L). Weigh

0.50 g of Elixirin R (C23H15O9SNa3, abbreviated as SCR) into a beaker. Add 4 mL of nitric acid (1.1), mix well, dissolve completely in water, filter into a 250 mL volumetric flask, dilute to the mark with water, and mix well.

7.2.8 Hexadecyltrimethylamine bromide solution (3 g/L). Weigh

0.75 g of hexadecyltrimethylamine bromide (C19H42BrN) and dissolve it in.200 mL of warm water. Add 10 mL of anhydrous ethanol (rho =

0.79 g/mL) to the water, filter into a 250 mL volumetric flask, dilute with water to the mark, and mix well.

7.2.9 Ammonia-Ammonium Nitrate Buffer Solution. Weigh 45g of ammonium nitrate and dissolve it in 400mL of water, then add 65mL of ammonia solution (rho=0.90g/mL). Mix well, adjust the pH to

9.6 using ammonia (7.2.4) or nitric acid (1 1) on a pH meter (4.2), dilute with water to 500 mL, and mix well.

7.2.10 Magnesium solution (10 mg/mL). Weigh

2.50 g of metallic magnesium (wMg >= 99.9%, wBe < 0.0001%) into a 500 mL beaker. Cover the watch glass and add 75 mL of hydrochloric acid (7.2.3) in portions. After the vigorous reaction stops, slowly heat until completely dissolved, cool, and transfer to a 250 mL container. Dilute with water to the mark in a volumetric flask and mix well.

7.2.11 Beryllium standard stock solution (100 µg/mL). Prepare and calibrate as follows, or use a certified standard solution.

a) Preparation. Weigh 0.500g of beryllium sulfate (BeSO4·4H2O), dissolve it in 50mL of water, filter it into a 250mL volumetric flask, and add... Add 85 mL of hydrochloric acid (7.2.3), dilute with water to the mark, and mix well.

b) Standardization. Transfer

50.00 mL (V) of beryllium standard stock solution to a 250 mL beaker, add 30 mL of water, heat to boiling, remove from heat, and add... Add 4 mL of EDTA solution (7.2.5), 3 drops of thymol blue ethanol solution (1 g/L), and ammonia solution (7.2.4) until the solution turns clearly blue. Add 5 drops of the blue dye in excess, heat to a gentle boil, maintain near boiling for 30 minutes, remove, and let stand for at least 12 hours. Use a medium-speed quantitative filter. Paper filtration was performed, and the beaker was washed 5-6 times with ammonia water (5.95), followed by washing the precipitate 7-8 times. The precipitate, along with the filter paper, was then transferred to a preheated container. The sample was dried and ashed in a heavy porcelain crucible, then ignited at 1000°C for 45 minutes. It was then removed and allowed to cool slightly. Finally, it was placed in a desiccator and cooled for 40 minutes before being weighed. The sample was repeatedly heated until a constant weight (m) was achieved.

7.2.12 Beryllium Standard Solution A (0.5 µg/mL). Transfer

2.50 mL of beryllium standard stock solution (7.2.11) to a 500 mL volumetric flask, add... Dilute 150 mL of hydrochloric acid (7.2.3) to the mark with water and mix well. 1 mL of this solution contains 0.5 µg of beryllium. Prepare fresh before use.

7.2.13 Beryllium Standard Solution B (0.2 µg/mL). Transfer

1.00 mL of beryllium standard stock solution (7.2.11) to a 500 mL volumetric flask, add... Dilute 150 mL of hydrochloric acid (7.2.3) to the mark with water and mix well. 1 mL of this solution contains 0.2 µg of beryllium. Prepare fresh before use.

7.2.14 p-Nitrophenol solution (2 g/L).

7.3 Test Procedure

7.3.1 Sample Weigh the sample according to Table 5 (Chapter 5), accurate to 0.0001g, and record it as m1.

7.3.2 Parallel Tests Perform the experiment twice in parallel and take the average value.

7.3.3 Blank Test Transfer magnesium solution (7.2.10) into the corresponding volumetric flask according to Table 5, and proceed according to steps

7.3.4.3 to 7.3.4.5.

7.3.4 Measurement

7.3.4.1 Place the sample in a 250mL beaker, add 20mL of water, cover with a watch glass, and slowly add 25mL of hydrochloric acid along the beaker wall (7.2.3). After the vigorous reaction stops, add 1 drop of hydrogen peroxide (7.2.2) [for zirconium-containing magnesium alloys, add 2 drops of hydrofluoric acid (7.2.1)], and heat until completely dissolved. Remove and allow to cool to room temperature.

7.3.4.2 Transfer the test solution into the corresponding volumetric flask (V2) according to Table 5 (filter if turbid), dilute with water to the mark, and mix well. Dispense the test solution according to Table 5. Pour the solution (V3) into the corresponding volumetric flask, add the corresponding volume of magnesium solution (7.2.10), and mix well.

7.3.4.3 Add 2 mL of sodium tartrate solution (7.2.6), add EDTA solution (7.2.5) and 1 drop of p-nitrophenol solution (7.2.14) according to Table 5. Adjust the solution to a light yellow color with ammonia (7.2.4) and add an excess of

7.3.4.4 Add 4 mL of ammonia-ammonium nitrate buffer solution (7.2.9) and 4 mL of hexadecyltrimethylamine bromide solution (7.2.8), mix slowly, and let stand. Let stand for 5 minutes, then add 5 mL of elixir cyanide blue R solution (7.2.7) while shaking continuously. Mix well, let stand for 5 minutes, then dilute with water to the mark. Mix well and let stand for 10 minutes.

7.3.4.5 Transfer a portion of the solution into a 1cm cuvette, using the blank test solution accompanying the sample as a reference, and measure the solution at wavelength (4.1) on a spectrophotometer. The absorbance was measured at 558 nm, and the mass of beryllium (mBe) was obtained from the working curve.

7.3.5 Plotting the Working Curve

7.3.5.1 Based on the mass fraction of beryllium, the standard solutions for the working curve series are prepared as follows:

---When the beryllium mass fraction is 0.0002%~0.0050%. transfer 0 mL,

4.00 mL, respectively.

5.00 mL of beryllium standard solution B (7.2.13) was placed in a set of 100 mL volumetric flasks, and

10.0 mL of magnesium solution (7.2.10) was added and mixed. Mix evenly, following steps

7.3.4.3 to 7.3.4.4.

---When the beryllium mass fraction is >0.0050%~0.020%. transfer 0 mL,

8.00 mL, respectively.

10.00 mL of beryllium standard solution A (7.2.12) was added to a set of 50 mL volumetric flasks, followed by

2.0 mL of magnesium solution (7.2.10). The mixture was then thoroughly mixed. Follow the steps in

7.3.4.3 to 7.3.4.4.

7.3.5.2 Transfer a portion of the series of standard solutions into a 1cm cuvette, using the "zero" concentration solution in the working curve series of standard solutions as a reference. The absorbance was measured at a wavelength of 558 nm using a spectrophotometer (4.1). A plot was created with the mass of beryllium on the x-axis and the corresponding absorbance on the y-axis. Operating curve. The linear correlation coefficient of the operating curve should not be less than 0.999.

7.5 Precision

7.5.1 Repeatability The measured values of two independent test results obtained under repeatability conditions, within the range of the average values given in Table 6, represent the values of the two test results. The absolute difference does not exceed the repeatability limit (r), and the number of cases exceeding the repeatability limit (r) does not exceed 5%. The repeatability limit (r) is determined by linearity based on the data in Table 6. Obtained by interpolation or extrapolation.

7.5.2 Reproducibility The measured values of two independent test results obtained under reproducibility conditions, within the range of average values given in Table 7, represent the values of the two test results. The absolute difference does not exceed the reproducibility limit (R), and the number of cases exceeding the reproducibility limit (R) does not exceed 5%. The reproducibility limit (R) is calculated using linearity based on the data in Table 7. It can be obtained by interpolation or extrapolation.

8.1 Photometric method for extraction of copper sulfate from neodiatomaceous earth

8.1.1 Method Overview The sample was dissolved in hydrochloric acid and hydrogen peroxide, ferric ions were masked with ammonium citrate, and divalent copper ions were reduced to monovalent copper with hydroxylamine hydrochloride. Ions, after adjusting the solution pH to 5, copper reacts with neo-cupranium to form a yellow complex, which is extracted with chloroform and analyzed at a spectrophotometer wavelength of 460 nm. The absorbance was measured, and the mass of copper was determined based on the working curve. The mass fraction of copper was then calculated.

8.1.2 Reagents or materials Warning. Chloroform is a highly toxic substance. When handling it, it is imperative to wear protective equipment as required, avoid contact with skin and clothing, and [further precautions should be taken]. The operation is completed inside the fume hood. Unless otherwise specified, only reagents confirmed to be of analytical grade and grade II water conforming to GB/T 6682 shall be used in the analysis.

8.1.2.1 Chloroform.

8.1.2.2 Hydrogen peroxide (rho=1.10g/mL), analytical grade.

8.1.2.3 Hydrochloric acid (1 1). Transfer 500 mL of hydrochloric acid (rho=

1.19 g/mL, analytical grade) to 500 mL of water and mix well.

8.1.2.4 Hydroxylamine hydrochloride solution (100g/L), prepare fresh before use.

8.1.2.5 Ammonium citrate solution (500 g/L).

8.1.2.6 Ammonia (1 1). Transfer 500 mL of ammonia (rho=

0.90 g/mL, analytical grade) to 500 mL of water and mix well. 8.1.2.7 2,9-Dimethyl-1,10-diazaphenanthrene (neo-copper phenanthrene) ethanol solution (1 g/L).

8.1.2.8 Copper Standard Stock Solution (1 mg/mL). Weigh 1.0000 g of metallic copper (wCu>=99.99%) into a 250 mL beaker, add... Dissolve 15 mL of nitric acid (rho =

1.42 g/mL) by slow heating until completely dissolved. Cool, transfer to a 1000 mL volumetric flask, and dilute to the mark with water. Mix thoroughly. This solution contains 1 mg of copper per mL. Alternatively, use a certified standard solution.

8.1.2.9 Copper Standard Solution A (10 µg/mL). Transfer

10.00 mL of copper standard stock solution (8.1.2.8) into a 100 mL volumetric flask. Dilute to the mark with water and mix well. Then, transfer

25.00 mL of this solution to a 250 mL volumetric flask, dilute to the mark with water, and mix well. 1 mL contains 10 µg of copper. Prepare fresh before use.

8.1.2.10 Copper Standard Solution B (1 µg/mL). Transfer

25.00 mL of copper standard solution A (8.1.2.9) to a 250 mL volumetric flask, and use... Dilute with water to the mark and mix well. 1 mL of this solution contains 1 µg of copper. Prepare fresh before use.

8.1.3 Test Procedure

8.1.3.1 Sample Weigh the sample according to Table 8 (Chapter 5), accurate to 0.0001g, and record it as m2.

8.1.3.2 Parallel Tests Perform the experiment twice in parallel and take the average value.

8.1.3.3 Blank Test A blank test was performed along with the sample.

8.1.3.4 Measurement 8.1.3.4.1 Place the sample in a 250mL beaker, add hydrochloric acid according to Table 8 (8.1.2.3), and add 3 to 5 drops of hydrogen peroxide (8.1.2.2). Heat slowly until the sample is completely dissolved, then heat to evaporate until the volume of the sample solution is about 5 mL, and then cool. 8.1.3.4.2 When the mass fraction of copper is not greater than 0.05%, place the test solution in a 125 mL separatory funnel and dilute with water to approximately 30 mL. When the mass fraction is greater than 0.05%, transfer the test solution to a 100 mL volumetric flask (V4), dilute to the mark with water, and mix well. Distribute according to Table 8. Place

10.00 mL of test solution (V5) into a 125 mL separatory funnel and dilute with water to approximately 30 mL. 8.1.3.4.3 Add 15 mL of ammonium citrate solution (8.1.2.5) and 5 mL of hydroxylamine hydrochloride solution (8.1.2.4) to a separatory funnel, and then use ammonia water. (8.1.2.6) Adjust the pH of the solution to 5, and add the neocaprin ethanol solution according to Table 9 (8.1.2.7) (mix gently after each addition of reagent), then add... Add

10.00 mL of chloroform (8.1.2.1), shake for 2 min, allow to stand for layering, then filter the organic phase through filter paper into a dry 10 mL colorimetric solution. In the tube. 8.1.3.4.4 Transfer a portion of the solution into a dry 1cm cuvette, using the blank test solution accompanying the sample as a reference, and analyze it using a spectrophotometer. (4.1) Measure its absorbance at a wavelength of 460 nm. Find the mass of copper (mCu) from the working curve.

8.1.3.5 Plotting the Working Curve 8.1.3.5.1 Based on the mass fraction of copper, the standard solutions for the working curve series are prepared as follows:

---When the mass fraction of copper is 0.00030%~0.0010%. transfer 0 mL,

6.00 mL, respectively.

10.00 mL of copper standard solution B (8.1.2.10) were placed in a set of 125 mL separatory funnels and diluted with water to approximately [amount missing]. 30 mL, proceed according to steps 8.1.3.4.3.

---When the mass fraction of copper is >0.0010%~0.200%. transfer 0 mL,

3.00 mL, respectively.

5.00 mL of copper standard solution A (8.1.2.9) were placed in a set of 125 mL separatory funnels and diluted with water to approximately [amount missing]. 30 mL, proceed according to steps 8.1.3.4.3. 8.1.3.5.2 Transfer a portion of the series of standard solutions into a dry 1cm cuvette, using the "zero" concentration solution from the standard solutions in the working curve series. For reference, its absorbance was measured at a wavelength of 460 nm using a spectrophotometer (4.1). The mass of copper is plotted on the x-axis, and the corresponding absorbance on the y-axis. Plot the working curve. The linear correlation coefficient of the working curve should not be less than 0.999.

8.1.5 Precision

8.1.5.1 Repeatability The measured values of two independent test results obtained under repeatability conditions, within the range of the average values given in Table 10, represent the two test results. The absolute difference does not exceed the repeatability limit (r), and the number of cases exceeding the repeatability limit (r) does not exceed 5%. The repeatability limit (r) is defined using linear data from Table 10. It can be obtained by interpolation or extension.

8.1.5.2 Reproducibility The measured values of two independent test results obtained under reproducibility conditions, within the range of the average values given in Table 11, represent the two test results. The absolute difference shall not exceed the reproducibility limit (R), and the number of cases exceeding the reproducibility limit (R) shall not exceed 5%. The reproducibility limit (R) shall be determined according to the data in Table 11. Obtained by linear interpolation or extrapolation.

8.2 Neo-Asian Copper Spectrophotometry

8.2.1 Method Overview The sample was dissolved in hydrochloric acid and hydrogen peroxide. In the presence of ammonium citrate, hydroxylamine hydrochloride was used to reduce divalent copper ions to monovalent copper ions. When the pH of the solution is approximately 6, copper reacts with neocubic amine to form a yellow complex. The absorbance of this complex was measured at a wavelength of 455 nm using a spectrophotometer. [The last sentence appears to be incomplete and possibly refers to a working procedure.] The mass of copper is obtained from the curve, and the mass fraction of copper is calculated.

8.2.2 Reagents or materials Unless otherwise specified, only reagents confirmed to be of analytical grade and grade II water conforming to GB/T 6682 shall be used in the analysis.

8.2.2.1 Hydrogen peroxide (rho=1.10g/mL).

8.2.2.2 Hydrochloric acid (1 1).

8.2.2.3 Hydroxylamine hydrochloride solution (100 g/L). 8.2.2.4 2,9-Dimethyl-1,10-diazaphenanthrene (neo-copper phenanthrene) ethanol solution (1 g/L).

8.2.2.5 Ammonium citrate solution (500 g/L).

8.2.2.6 Copper Standard Solution (100 µg/mL). Weigh 0.0500 g of metallic copper (wCu>=99.99%) into a 300 mL beaker, add... 20 mL of water and 10 mL of nitric acid (1.1) are heated at low temperature until completely dissolved. The solution is then transferred to a 500 mL volumetric flask, diluted to the mark with water, and mixed well. This solution contains 100 µg of copper per mL. Alternatively, a certified standard solution may be used.

8.2.3 Test Procedure

8.2.3.1 Sample Weigh 0.50g of sample (Chapter 5), accurate to 0.0001g, and record it as m3.

8.2.3.2 Parallel Tests Perform the experiment twice in parallel and take the average value.

8.2.3.3 Blank Test A blank test was performed along with the sample.

8.2.3.4 Measurement 8.2.3.4.1 Place the sample in a.200mL beaker, slowly add 15mL of hydrochloric acid (8.2.2.2), and add 2-3 drops of hydrogen peroxide (8.2.2.1). Heat slowly until the sample is completely dissolved, cool to room temperature, transfer to a 250 mL volumetric flask (V6), dilute with water to the mark, and mix well. 8.2.3.4.2 Transfer

10.00 mL of the test solution (V7) to a 100 mL volumetric flask, add 5 mL of ammonium citrate solution (8.2.2.5), mix well, and add... Add 5 mL of hydroxylamine hydrochloride solution (8.2.2.3), mix well, let stand for a moment, and while shaking, add 10 mL of neocaprin ethanol solution (8.2.2.4), then add water. Dilute to the mark and mix well. 8.2.3.4.3 Transfer a portion of the solution into a 1cm cuvette, using the blank test solution accompanying the sample as a reference, and analyze it on a spectrophotometer at wave (4.1). The absorbance was measured at 455 nm, and the mass of copper (mCu) was obtained from the working curve.

8.2.3.5 Plotting the Working Curve 8.2.3.5.1 Transfer 0 mL,

8.00 mL of copper standard solution (8.2.2.6) to a container. Add 5 mL of ammonium citrate solution (8.2.2.5) to each of the 100 mL volumetric flasks, mix well, and then add 5 mL of hydroxylamine hydrochloride solution to each flask. (8.2.2.3) Mix well, let stand for a moment, and then add 10 mL of neocaprin ethanol solution while shaking (8.2.2.4). Dilute with water to the mark. Mix well. 8.2.3.5.2 Transfer a portion of the series of standard solutions into a 1cm cuvette, using the "zero" concentration solution in the working curve series of standard solutions as a reference. The absorbance of copper was measured at a wavelength of 455 nm using a spectrophotometer (4.1). The mass of copper was plotted on the x-axis, and the corresponding absorbance on the y-axis. Plot the working curve. The linear correlation coefficient of the working curve should not be less than 0.999.

8.2.5 Precision

8.2.5.1 Repeatability The measured values of two independent test results obtained under repeatability conditions, within the range of the average values given in Table 12, represent the two test results. The absolute difference does not exceed the repeatability limit (r), and the number of cases exceeding the repeatability limit (r) does not exceed 5%. The repeatability limit (r) is determined by linear data from Table 12. It can be obtained by interpolation or extension.