Simply put, it is three steps.
1, actually measure the cross-sectional area of the conductor.
. 2. Measure the conductor resistance
3. Specify the resistance value corresponding to the cross-sectional area. If it is less than the standard value, the purity of the copper wire is qualified. If the conductor resistance is too large, it means that the purity is not enough.
If you want to accurately measure the specific copper content, you still have to go to some laboratories to measure it, but the charge is not cheap.