GB/T 10656-2022Analysis of water used in boiler and cooling system - Determination of zinc (English PDF)

5.2 Reagents or materials

5.2.1 Hydrochloric acid solution: 1+1.

5.2.2 Sulfuric acid solution: 1+35.

5.2.3 Sodium hydroxide solution: 40 g/L.

5.2.4 Ammonium persulfate solution: 4 g/L, ready-to-use.

5.2.5 Boric acid-potassium chloride-sodium hydroxide buffer solution (pH8.8 ~ pH9.0). Prepare according to HG/T 4015.

5.2.6 Zinc standard stock solution:

0.1 mg/mL. Prepare according to GB/T 602, or buy commercially available solution.

5.2.7 Zinc standard solution:

0.01 mg/mL. Pipette

10.00 mL of zinc standard stock solution into a 100 mL volumetric flask; use water to dilute to the mark; mix well. Formulate the solution when needed.

5.2.8 Methyl orange indicator solution: 1 g/L.

5.2.9 Zinc reagent solution:

0.8 g/L. Weigh

0.2 g of zinc reagent and dissolve it in 250 mL of absolute ethanol; cover and place overnight to make it completely dissolved (or ultrasonically shake for 1 min ~ 5 min to dissolve completely). Store the solution in a brown bottle and place it in a refrigerator at 0 °C ~ 4 °C for one month. When the solution turns from red to yellow, it shall be re-prepared.

5.4 Test procedures

6.2.7 Acetic acid-sodium acetate buffer solution (pH = 5.5): Weigh 200 g of sodium acetate (CH3COONa·3H2O) and dissolve it in 150 mL of water; add 9 mL of glacial acetic acid; transfer it into a 1 000 mL volumetric flask; use water to dilute to the mark.

6.2.8 Ethylene Diamine Tetraacetic Acid standard titration solution: c(EDTA) =

0.001 mol/L. Before use, use boiled and cooled water to dilute the Ethylene Diamine Tetraacetic Acid standard titration solution, of a concentration of

0.1 mol/L, which is prepared according to GB/T 601.

6.2.9 Xylenol orange indicator solution: 6 g/L. Weigh

0.6 g of xylenol orange; dissolve in water and dilute to 100 mL; mix well; store in a brown bottle.

6.3 Apparatus Micro burette: 5 mL or 10 mL.

6.4 Preparation of samples The sample for the single-item analysis measurement shall not be less than 300 mL; the sample storage bottle shall be a stoppered glass bottle or a polyethylene plastic bottle. The determination of zinc content should be completed as soon as possible. Under normal circumstances, the sample shall not be stored for more than 24 h. For the measurement of the content of soluble zinc, an appropriate amount of sample shall be determined after filtration through the medium-speed filter paper.

6.5 Test procedure Pipette 100.0 mL of sample; put it in a 250 mL conical flask; add 2 mL of tartaric acid solution, 4 mL of potassium fluoride solution and

0.5 mL of thiourea solution; use sodium hydroxide solution or hydrochloric acid solution to adjust the pH of the test solution to 5 ~ 6. Then, add 20 mL of acetic acid-sodium acetate buffer solution; shake well; heat to 30 °C ~ 40 °C on an electric hot plate or water bath. Add 10 drops of trisodium citrate solution; then, add three to four drops of xylenol orange indicator solution; use Ethylene Diamine Tetraacetic Acid standard titration solution to titrate until the sample changes from purple red to bright yellow as the end point. When there is no organic phosphonate in the sample, tartaric acid solution may not be added; when there is no copper ion, thiourea solution may not be added; when the content of aluminum ion and iron ion is less than 1 mg/L, trisodium citrate solution may not be added.