GB 46997-2025Limits of certain heavy metal in printing ink (English PDF)

6.1.1 Sample preparation

6.1.1.1 Reagents and materials Unless otherwise specified, only the confirmed analytically-pure reagents or higher, and distilled water, deionized water, or water of equivalent purity, shall be used in the analysis. 6.1.1.1.1 Nitric acid (HNO3). guaranteed reagent. 6.1.1.1.2 Hydrogen peroxide (H2O2). approximately 30% (mass fraction), analytically pure. 6.1.1.1.3 Hydrofluoric acid (HF). guaranteed reagent. 6.1.1.1.4 Nitric acid solution (1+1) (volume ratio). 6.1.1.1.5 Water. meets, at a minimum, the requirements for Grade 2 water as specified in GB/T 6682.

6.1.1.2 Instruments and equipment 6.1.1.2.1 Drying oven. 0°C~200°C; temperature control accuracy at ±2°C. 6.1.1.2.2 Pressure digestion vessel. equipped with a polytetrafluoroethylene (PTFE) inner digestion vessel. 6.1.1.2.3 Microwave digestion system. equipped with polytetrafluoroethylene (PTFE) digestion inner vessels. 6.1.1.2.4 Hot plate (for acid wet digestion method) or muffle furnace (for ashing method). 6.1.1.2.5 UV curing unit 6.1.1.2.6 Analytical balance. accuracy is

0.1 mg. 6.1.1.2.7 Volumetric flasks (25 mL, 50 mL, etc.). 6.1.1.2.8 All glassware, glass containers, glass plates, or PTFE plates shall be soaked in a nitric acid solution (1+1) for 24 h prior to use. They shall then be washed with water and dried.

6.1.1.3 Sampling procedure for test specimens After thoroughly mixing the test specimen, prepare a coating film of appropriate thickness on a glass plate or a polytetrafluoroethylene (PTFE) plate. Once completely dry [if oven-drying is required, the temperature shall be (60 ± 2)°C; alternatively, the printing ink shall be dried in accordance with its specific drying characteristics], collect the printing ink sample. Pulverize the sample at room temperature, then sieve it through a

0.5 mm ×

0.5 mm metal sieve. Set it aside for further processing. NOTE. If the coating film cannot be easily pulverized into

0.5 mm ×

0.5 mm pieces, prepare the sample in dimensions of no less than 1 mm × 1 mm but no greater than 2 mm × 2 mm, and then proceed with the test.

6.1.1.4 Digested specimen 6.1.1.4.1 Pressure vessel digestion method Weigh

0.5 g of the specimen (accurate to

0.1 mg) and place it into a PTFE digestion liner. Add 5~8 mL of nitric acid and 2 mL of 30% hydrogen peroxide. For materials with a high silica content, an additional 3 mL of hydrofluoric acid must be added. Alternatively, depending on the sample matrix, select an appropriate sample mass and acid addition method to ensure complete digestion of the sample. Cover with the PTFE lid, then tighten the stainless-steel outer jacket. Place the assembly in a constant- temperature drying oven and heat at (180 ± 2)°C for 4 h. Once the pressure digestion vessel has cooled to room temperature, transfer the digest solution into a 50 mL volumetric flask. Rinse the PTFE liner and lid 3~4 times with water, and transfer the rinsings into the volumetric flask. Dilute to the mark with water. If the solution is not clear or if a precipitate forms, filter the solution and retain the digested specimen solution for subsequent analysis. 6.1.1.4.2 Microwave digestion method Weigh

0.5 g (accurate to

0.1 mg) of the specimen and place it into a PTFE digestion liner. Add 5~8 mL of nitric acid and 2 mL of 30% hydrogen peroxide. For materials with a high silica content, an additional 3 mL of hydrofluoric acid must be added. Alternatively, depending on the sample matrix, select an appropriate sample mass and acid addition method to ensure complete digestion of the sample. Cover the vessel and allow it to stand for 1 h. Seal the digestion vessel and place it into a microwave digestion system. Proceed with the digestion according to the standard operating procedures for the microwave digester. Upon completion of the digestion, remove the vessel from the digester. Allow the vessel to cool completely before slowly opening the inner lid. Transfer the digest solution into a 50 mL volumetric flask. Rinse the digestion vessel and lid 3~4 times with water, and transfer the rinsings into the volumetric flask. Dilute to the mark with water. If the solution is not clear or if a precipitate forms, filter the solution and retain the digested sample solution for analysis. 6.1.1.4.3 Other digestion methods Provided that the specimen can be completely digested, other digestion methods, such as wet acid digestion or ashing, may also be employed to treat the specimen and obtain the digest solution for subsequent analysis. 6.1.1.4.4 Blank test With the exception of omitting the test specimen, proceed in accordance with 6.1.1.4.1, 6.1.1.4.2, or 6.1.1.4.3 to obtain the blank digested solution. NOTE. The digestates obtained from 6.1.1.4.1, 6.1.1.4.2, 6.1.1.4.3, and 6.1.1.4.4 are used for the determination of the elements listed in Annex A ~ Annex C.

6.1.2 Determination of lead The lead content in the printing ink shall be determined in accordance with Annex A or Annex B. The method specified in Annex B serves as the arbitration method.