GB/T 40231-2021Restricted substance in electrical and electronic products—Determination of hexavalent chromium—Ion chromatography method (English PDF)

7.1 Sample Pre-treatment

7.1.1 Extraction of hexavalent chromium in soluble polymers (ABS, PC and PVC)

The extraction of hexavalent chromium in soluble polymers (ABS, PC and PVC) shall be carried out in the following steps:

a) Accurately weigh-take 0.1 g of sample, then, put it into the glass bottle with a screw mouth (5.9).

NOTE: for samples, whose concentration of hexavalent chromium may be extremely low or extremely high, other sample sizes may be used.

b) Pour 10 mL of NMP (4.2) into the glass bottle with a screw mouth (5.9); tightly fasten down the cap of the container.

c) Shake the sample container by hand for about 10 s, so as to suspend the insoluble particles. Then, at a temperature of 60 °C, use the ultrasonic water bath constant temperature oscillator (5.2) to conduct treatment for 1 h. Before proceeding to the next step, the sample shall be completely dissolved.

d) Shake the glass bottle with a screw mouth (5.9) by hand to mix it well, then, add 200 mg of MgCl2 (4.6) and 0.5 mL of 0.5 mol/L phosphate buffer solution (4.7) to each glass bottle with a screw mouth (5.9). Re-shake the glass bottle with a screw mouth (5.9) to mix it well.

e) Use a measuring cylinder (5.8) to measure-take 20 mL of the extraction solution (4.8) and slowly pour it into the glass bottle with a screw mouth (5.9); mix it well.

f) Place the sample solution prepared in Step e) in the ultrasonic water bath constant temperature oscillator (5.2); at a temperature of 60 °C, conduct ultrasonic treatment for 1 h. When the ultrasonic treatment reaches 0.5 h, shake the glass bottle with a screw mouth (5.9) by hand to evenly mix the liquid.

g) Transfer the sample solution processed through Step f) into a 150 mL beaker (5.7); constantly stir it up and monitor the pH value. Meanwhile, dropwise add HNO3 (4.3) to the beaker. Adjust the pH value of the solution to 7.5 ± 0.5.

h) Pour the sample solution into a 100 mL volumetric flask; use pure water (4.1) to reach a constant volume to the scale. Use the 0.45 µm filter membrane or filter syringe (5.12) and the RP solid phase extraction column (5.13) for purification.

i) Take an appropriate volume of the filtered sample and dilute it by 10 times; reserve it for the later test.

7.1.2 Extraction of hexavalent chromium in antimony-free insoluble polymers / unknown polymers and electronic parts

The extraction of hexavalent chromium in antimony-free insoluble polymers / unknown polymers, and electronic parts shall be carried out in the following steps:

a) Accurately weigh-take 0.15 g of sample, then, pour it into the microwave digestion tank equipped by the microwave digestion apparatus (5.14).

NOTE: for samples, whose concentration of hexavalent chromium may be extremely low or extremely high, other sample sizes may be used.

b) Use the measuring cylinder (5.8) to respectively measure-take 10 mL of the extraction solution (4.8) and 5 mL of toluene (4.9); add it to the microwave digestion tank.

c) Add 400 mg of MgCl2 (4.6) and 0.5 mL of 0.5 mol/L phosphate buffer solution (4.7); mix it well.

d) Use the microwave digestion apparatus (5.14) or the heating device (5.1) to heat the sealed microwave digestion tank to 160 °C; maintain it for 1.5 h. Then, cool the sample to room temperature.

e) Use the separatory funnel (5.11) to separate the organic phase from the container and discard it. Filter the inorganic phase through the 0.45 µm filter membrane or filter syringe (5.12). Use water to rinse the filter and the microwave digestion tank for 3 times. If clogging occurs when using the 0.45 µm filter syringe, large-pore-size filter papers may be used to filter the sample.

f) Use water to rinse the inside of the filter bottle and filter pad; transfer the filtrate and rinsing fluid into a clean 150 mL beaker (5.7).

g) Constantly stir it up and monitor the pH value, meanwhile, dropwise add HNO3 (4.3). Adjust the pH value of the solution to 7.5 ± 0.5.

7.2 Drawing of Standard Working Curve

Use the pipette (5.10) to transfer-take an appropriate amount of the hexavalent chromium certified reference substance (4.14). Use water (4.1) to dilute it to standard solutions with different concentrations. The specific concentrations are shown in Table 1. Generate a standard working curve of the standard solution series concentrations through linear regression; the correlation coefficient of the curve shall be not less than 0.999. The standard solution should be prepared right before use. […]