GB/T 43085-2023Plastics - Polymer dispersions - Determination of the content of free formaldehyde (English PDF)

0.1

g) of sample into a 25 mL volumetric flask. Add approximately 10 mL of standard diluent (5.11) (Method B) or water (Method A) to dilute. Mix thoroughly for at least 30 min. The diluted polymer dispersion shall be a clear, particle-free aqueous solution. Depending on the difficulty of filtering the sample, use one of the three methods in 7.1.2~

7.1.4 to prepare a test solution suitable for analysis.

5.5 Phosphoric acid solution: Dissolve

2.3 mL of 85% phosphoric acid (H3PO4) in water. Use water to dilute to 1 L. Prepare an aqueous solution with a concentration of 33 mmol/L.

5.6 Potassium ferrocyanide trihydrate solution (Carrez solution I): Dissolve 36 g of potassium ferrocyanide trihydrate [K4Fe(CN)6 · 3H2O] in water. Use water to dilute to 1 L. Prepare a solution with a concentration of 36 g/L.

5.7 Zinc sulfate heptahydrate solution (Carrez solution II): Dissolve 72 g of zinc sulfate heptahydrate (ZnSO4 · 7H2O) in water. Use water to dilute to 1 L. Prepare a solution with a concentration of 72 g/L.

5.8 Sodium hydroxide solution: Dissolve 4 g of sodium hydroxide (NaOH) in water. Use water to dilute to 1 L. Prepare an aqueous solution with a concentration of

0.1 mol/L.

5.9 Disodium hydrogen phosphate.

5.10 Nash reagent Transfer

62.5 g of ammonium acetate (5.2) into a 1 L brown reagent bottle (6.1) equipped with stirring. Add 600 mL of water. Stir to dissolve. After the ammonium acetate is dissolved, add

7.5 mL of glacial acetic acid (5.1), 5 mL of 2,4-pentanedione (5.4) and 387.5 mL of water to the bottle. Mix thoroughly (recommended 45 min). NOTE: If necessary, use Nash reagent containing varying concentrations of ammonium acetate, glacial acetic acid, and acetylacetone. Since 2,4-pentanedione is photosensitive, Nash reagent shall be stored protected from light. Fresh Nash reagent needs to be prepared weekly. Degas the Nash reagent with helium before use. When using Method B, transfer the Nash reagent to the post-column reactor (6.6.2). The reactor shall be protected from light.

5.11.1 Preparation of mobile phase Transfer

1.78 g of disodium hydrogen phosphate (5.9) to a 2 L mobile phase reservoir equipped with stirring. Add 2 L of water and mix until disodium hydrogen phosphate is completely dissolved.

6.6 High performance liquid chromatography system (Method B)

6.6.1 Liquid chromatograph It is equipped with an injection valve, a post-column reactor, a tungsten lamp or deuterium lamp detector capable of providing a wavelength of 410 nm, and an infusion pump capable of providing a flow rate of

0.6 mL/min.

6.6.2 Post-column reactor (PCR) It consists of an infusion pump providing a flow rate of

0.5 mL/min, a sample derivation tube that can be heated to 95°C, and a matching static mixing tee.

6.6.3 Chromatographic column It is a C18 pH reversed phase column with a particle size of 5 µm. The length is 250 mm. The inner diameter is

4.6 mm. When applicable, other suitable chromatographic columns can also be used (such as a special column for acid analysis, with a length of 100 mm and an inner diameter of

6.6.4 Guard column It is a C18 pH reversed phase guard column with a particle size of 5 µm. The length is 10 mm. The inner diameter is

4.6 mm. When applicable, other guard columns can also Keys: 1 - Mobile phase; 2 - Pump; 3 - Straight-through one-way valve; 4 - Injector; 5 - Chromatographic column; 6 - Nash reagent; 7 - Post-column derivatization pump; 8 - Pulse damper; 9 - Straight-through one-way valve; 10 - Mixing tee; 11 - Derivative tube; 12 - Oven (temperature 95°C); 13 - Water bath (room temperature); 14 - UV/visible light detector; 15 - Data system; 16 - Waste liquid. Figure 1 -- Schematic diagram of liquid chromatograph and post-column reaction system

7.1 Preparation of specimens

7.1.1 Dilution of specimens According to the characteristics and measurement range of the polymer dispersion, weigh

0.1 g~

1.0 g (accurate to

7.1.2 Filtration Dilute the solution prepared in

7.1.1 to the mark with sample diluent (5.12) (Method B) or water (Method A) (with given volume). Use the 0.1 µm filter (6.2) to filter the solution. If necessary, the filtrate can be further diluted with sample diluent.

7.1.3 Centrifugation Dilute the solution prepared in

7.1.1 to the mark with sample diluent (5.12) (Method B)

7.4.1.2 Standard curve Determine the absorbance of the standard solution. Draw a standard curve of formaldehyde mass fraction and absorbance in the standard solution (5.13.2). The standard curve shall appear linear.

7.4.2 Method B

7.4.2.1 Test conditions Adjust the liquid chromatography according to the manufacturer's instructions and the following parameters: - Column temperature: room temperature; - Mobile phase:

6.3 mmol/L Na2HPO4 (pH = 7) or water; - Flow rate:

0.6 mL/min; - Injection volume: 50 µL; - Post-column reaction temperature: 95°C; - Post-column reaction flow rate:

0.5 mL/min; - Detector: UV/visible light (410±5) nm. Equilibrate the instrument until a stable baseline is obtained in the data system.

7.4.2.2 Standard solution testing and standard curve Before testing, ensure that the entire chromatography system is operating normally and that the formaldehyde concentration in the test solution does not exceed the linear response range of any component of the system (such as the chromatographic column, detector, integrator, and other components). According to the conditions of 7.4.2.1, inject 50 µL of each standard solution (5.13.2) and blank reagent (standard diluent) (5.11) into the liquid chromatograph for testing. Measure the formaldehyde peak area. Draw a standard curve with the formaldehyde peak area as the ordinate and the mass fraction of formaldehyde (mg/kg) as the abscissa, as shown in Figure 3. The standard curve shall appear linear. Calculate the formaldehyde mass fraction in the sample according to formula (1): Where, omegaf,o - The mass fraction of formaldehyde in the sample, in milligrams per kilogram (mg/kg); omegaf,d - The mass fraction of formaldehyde in the diluted polymer dispersion, in milligrams per kilogram (mg/kg); omega0 - The mass fraction of formaldehyde in the blank solution, in milligrams per kilogram (mg/kg); k - The dilution coefficient of diluted polymer dispersion. The arithmetic mean of the two measurements is used as the test result, in mg/kg. NOTE: The dilution factor depends on the method of preparation of the test solution (7.1.2,

7.1.3 or 7.1.4).