GB/T 13748.15-2026Methods for chemical analysis of magnesium and magnesium alloys - Part 15: Determination of zinc content (English PDF)

5.3.5 Zinc Standard Solution (50 µg/mL). Transfer

25.00 mL of zinc standard stock solution (5.3.4) to a 500 mL volumetric flask and dilute with water. Fill to the mark and mix well. 1 mL of this solution contains 50 µg of zinc.

5.4 Test Procedure

5.4.1 Sample Weigh 0.25g of sample (Chapter 4), accurate to 0.0001g, and record it as m0.

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

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

5.4.4 Measurement

5.4.4.1 Place the sample in a 250mL beaker, cover with a watch glass, and add 20mL of hydrochloric acid (5.3.3) and 5 drops of peroxide in portions. Hydrogen (5.3.2), heat at low temperature, add 2 drops of hydrofluoric acid (5.3.1) if necessary, continue heating until completely dissolved, boil for 5 minutes, and cool.

5.4.4.2 Based on the mass fraction of zinc in the sample, proceed as follows:

---When the zinc mass fraction is 0.0050%~0.100%, transfer the test solution to a 100mL volumetric flask, filter if necessary, and dilute with water to the specified concentration. Scale the mixture, mix it thoroughly, and record the volume as V0.

---When the zinc mass fraction is greater than 0.100%~10.00%, transfer the test solution into the corresponding volumetric flask according to Table 1, filter if necessary, and use... Dilute with water to the mark, mix well, and record the volume as V0; then transfer a certain volume (V1) of the test solution into the corresponding volumetric flask according to Table 1, and dilute with water. Dilute to the mark, mix well, and record the volume as V2.

5.4.4.3 Operate simultaneously with the corresponding standard curve using an air-acetylene lean flame at a flame atomic absorption spectrometer wavelength of 213.9 nm. Zero the instrument with water, measure the absorbance of zinc, subtract the absorbance of the blank test solution that accompanied the sample, and then find the corresponding zinc absorbance from the working curve. Mass concentration (rho).

5.4.5 Plotting the Working Curve

5.4.5.1 Based on the mass fraction of zinc in the sample, the standard solutions for the working curve series are prepared as follows:

---Zinc mass fraction is 0.0050%~0.010%. Transfer 0 mL,

0.25 mL,

0.50 mL,

2.00 mL of zinc standard. The solution (5.3.5) was placed in a set of 100mL volumetric flasks, diluted with water to the mark, and mixed well.

---For zinc concentrations greater than 0.010%~10.00% by mass. transfer 0 mL,

0.50 mL,

5.00 mL of zinc standard solution (5.3.5) was placed in a set of 250 mL volumetric flasks, diluted with water to the mark, and mixed well.

5.4.5.2 The series of standard solutions were analyzed on a flame atomic absorption spectrometer using an air-acetylene lean flame at a wavelength of 213.9 nm. Zero the instrument with water and measure the absorbance of a series of standard solutions. Plot the zinc mass concentration on the x-axis and subtract the absorbance of the "zero concentration" solution from the corresponding absorbance. Using luminance as the ordinate, plot the working curve.

5.6 Precision

5.6.1 Repeatability The measured values of two independent test results obtained under repeatability conditions, within the range of the average values given in Table 2, 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 calculated using linear data from Table 2. It can be obtained by interpolation or extension.

5.6.2 Reproducibility The measured values of two independent test results obtained under reproducibility conditions, within the range of the average values given in Table 3, represent the two test results. The absolute difference should not exceed the reproducibility limit (R), and the number of cases exceeding the reproducibility limit (R) should not exceed 5%. The reproducibility limit (R) is determined according to the data in Table 3. Obtained by linear interpolation or extrapolation. 6.PAN spectrophotometry

6.1 Method Overview The sample was dissolved in hydrochloric acid and hydrogen peroxide, zinc was extracted with tri-n-octylamine xylene solution, and zinc was back-extracted into the solution using a potassium nitrate-potassium iodide mixture. Aqueous phase. At approximately pH 10, the colored complex of 1-(2-pyridiniazo)-2-naphthol (PAN) and zinc was extracted with chloroform and analyzed spectrophotometrically. The absorbance was measured at a wavelength of 550 nm. The mass of zinc was obtained from the working curve, and the mass fraction of zinc was calculated.

6.2 Instruments Spectrophotometer.

6.3 Reagents Unless otherwise specified, only reagents confirmed to be of superior purity and grade II water as specified in GB/T 6682 shall be used in the analysis.

6.3.1 Chloroform.

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

6.3.3 Hydrochloric acid (1 1).

6.3.4 Hydrochloric acid (1 5).

6.3.5 Ammonia (1 1).

6.3.6 PAN ethanol solution (1 g/L).

6.3.7 Tri-n-octylamine-xylene solution (1.20). Used tri-n-octylamine-xylene solution can be recycled after purification. Purification method. Shake the tri-n-octylamine xylene solution with an equal volume of sodium carbonate solution (

0.5 mol/L), discarding the aqueous phase. Then add an equal volume of hydrochloric acid (1.10) and shake. Shake, discard the aqueous phase, and repeat the shaking process several times. After the last shaking with sodium carbonate solution, wash with water until no metal ions react in the aqueous phase. [The washed water should be yellow when tested with PAN ethanol solution (6.3.6)]. Then, add an equal volume of hydrochloric acid (6.3.4), shake for 2 minutes, let stand, and discard. Store in aqueous and organic phases for later use.

6.3.8 Potassium nitrate-potassium iodide mixed solution. Dissolve 50g of potassium nitrate and 10g of potassium iodide in water, then dilute to 1000mL and mix well. Purification method. Method. Add 3-5 mL of PAN ethanol solution (6.3.6) to the mixed solution, and extract twice with chloroform (6.3.1) (30 mL each time). Discard the organic phase (50 mL), filter the aqueous solution into a reagent bottle, and store for later use.

6.3.10 BCO ethanol solution (1 g/L). Weigh

0.5 g of BCO (bicyclohexanone oxaloyl dihydrazone) and dissolve it in 250 mL of ethanol (95%), then add water. Dilute to a 500 mL volumetric flask and mix well.

6.3.11 Zinc Standard Stock Solution (1 mg/mL). Weigh 0.5000 g zinc (wZn >= 99.99%) into a beaker, add 20 mL hydrochloric acid (6.3.3) Heat to dissolve completely, cool, transfer to a 500mL volumetric flask, dilute to the mark with water, and mix well. 1mL of this solution contains... 1 mg zinc. Or use a certified standard solution.

6.3.12 Zinc Standard Solution (4 µg/mL). Transfer

4.00 mL of zinc standard stock solution (6.3.11) to a 1000 mL volumetric flask and dilute with water. Dilute to the mark and mix well. 1 mL of this solution contains 4 µg of zinc.

6.4 Test Procedure

6.4.1 Sample Weigh 0.50g of sample (Chapter 4), accurate to 0.0001g, and record it as m1.

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

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

6.4.4 Measurement

6.4.4.1 Place the sample in a 100mL beaker, cover with a watch glass, add 10mL of hydrochloric acid (6.3.3), and add 3-4 drops of hydrogen peroxide. (6.3.2) Heat to dissolve completely. Evaporate to near dryness, then dissolve in hydrochloric acid (6.3.4) and cool.

6.4.4.2 Transfer the test solution into a volumetric flask according to Table 4, dilute to the mark with hydrochloric acid (6.3.4), mix well, and record the volume as V

6.4.5 Plotting the Working Curve

6.4.5.1 Transfer 0 mL,

0.50 mL,

5.00 mL of zinc standard solution (6.3.12) to aliquots. Do not place in a 125mL separatory funnel, add 7mL of hydrochloric acid (6.3.3), dilute with water to 20mL, and proceed according to 6.4.4.3~6.4.4.5.

6.4.5.2 Using the zero concentration in the standard solutions of the working curve series as a reference, the absorbance was measured at a wavelength of 550 nm using a spectrophotometer. (The last part, "zinc," appears to be incomplete and requires further context.) Plot a working curve with mass as the x-axis and absorbance as the y-axis. The linear correlation coefficient of the working curve should be no less than 0.999.

6.6 Precision

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

6.6.2 Reproducibility The measured values of two independent test results obtained under reproducibility conditions, within the range of the average values given in Table 6, represent the two test results. The absolute difference should not exceed the reproducibility limit (R), and the number of cases exceeding the reproducibility limit (R) should not exceed 5%. The reproducibility limit (R) is determined according to the data in Table 6. Obtained by linear interpolation or extrapolation.

7.2.14 Dithizone ethanol solution (

0.25 g/L).

0.025 g of dithizone (diphenylthiocarbazone) is dissolved in ethanol (95%) and diluted to [the desired concentration]. 100mL. Prepare fresh before use.

7.2.15 Litmus paper.

7.2.16 Precision pH test paper (pH 5~6,

0.2 units apart).

7.3 Instruments A glass column with a piston, 20mm in diameter and about 400mm in height.

7.4 Test Procedure

7.4.1 Preparation of Ion Exchange Columns First, use hydrochloric acid (7.2.3) to continuously wash away the fine particles from the strongly basic anion exchange resin (7.2.1) until the solution is clear after washing. Transparent. Then immerse the resin in hydrochloric acid (7.2.9) for several hours or overnight. Place a small amount of glass at the bottom of the glass column (7.3), above the piston. Glass fibers are used to support the resin. While shaking, the resin suspension is poured into the prepared glass column (taking care to avoid forming air bubbles or air channels), allowing the resin to... The column is approximately 150 mm high. Wash the exchange column with approximately 100 mL of hydrochloric acid (7.2.9) at a rate of 7 mL/min. Then wash with pre-added

0.5 mL of nitric acid. 200 mL of hydrochloric acid (7.2.7) was passed through the exchange column at the same rate as acid (7.2.4) to achieve the required working conditions. After the exchange column preparation was completed... During the analysis, the resin was completely soaked in hydrochloric acid (7.2.9).

7.4.2 Samples Weigh 4.00g of sample (Chapter 4), accurate to 0.0001g, and record it as m3.

7.4.3 Blank Test Prepare a reagent blank along with the sample.

7.4.4 Preparation of test solution

7.4.4.1 Place the sample in a 400mL beaker, add about 50mL of water, cover with a glass watch glass, and slowly add 30mL of hydrochloric acid (7.2.3). After a vigorous reaction, add 2 drops of hydrogen peroxide (7.2.6) and slowly heat to boiling. Continue boiling until all the hydrogen peroxide (7.2.6) is decomposed. If zinc... If the content is greater than 1.00%, transfer the solution to a 250mL volumetric flask, cool, dilute with water to the mark, mix well, and the volume is V4.

7.4.4.2 Transfer a portion of the test solution into a 250 mL beaker according to Table 7, evaporate it in a boiling water bath until crystals just precipitate, cool it, and add 100 mL of the solution. Dissolve hydrochloric acid (7.2.7) and

0.5 mL nitric acid (7.2.4) by heating.

7.4.4.3 If the test solution contains insoluble zirconium or silica precipitates during evaporation, filter it with dense filter paper and rinse with a small amount of hot salt. Wash thoroughly with acid (7.2.7).

7.4.5 Ion Exchange

7.4.5.1 Cool the test solution (7.4.4.3), pass it through an ion exchange column (7.4.1) at a rate of 5 mL/min to 7 mL/min, and use four 25 mL aliquots of salt. The beaker and exchange column were continuously washed with acid (7.2.7), and then the resin was washed with 100 mL of hydrochloric acid (7.2.8) at a rate of 5 mL/min to 7 mL/min. [If the sample contains lead, the amount of hydrochloric acid (7.2.8) used should be increased from 100 mL to.200 mL].

7.4.5.2 Elute the zinc adsorbed by the resin by passing 250 mL of hydrochloric acid (7.2.9) through the exchange column at the same rate. Collect the eluent in... Concentrate in a 400mL beaker until the volume is 100mL.

7.4.6 Titration Place the litmus paper (7.2.15) into the eluent, and while stirring, add ammonia water (7.2.5) dropwise until the paper changes color. Remove the litmus paper. (7.2.15) Wash with water, then add 20 mL of acetic acid solution (7.2.10) and 10 mL of ammonium acetate solution (7.2.11). Use precision pH test paper. (7.2.16) Check the pH of the solution; it should be between

5.0 and 5.5.If necessary, adjust by adding acetic acid solution (7.2.10). Then add 50 mL of [amount missing]. Acetone (7.2.2), 2 mL dithizone ethanol solution (7.2.14), titrated with EDTA standard titration solution (7.2.13) until the test solution changes from red to green. The color continues until it reaches an orange-yellow hue. This color remains unchanged even with an excess of 2 drops of EDTA standard titration solution (7.2.13), consuming the EDTA standard titration solution. The volume of (7.2.13) is denoted as V

6.The volume of EDTA standard titration solution (7.2.13) consumed by the blank test solution of the titration reagent is denoted as V7.