A waste water sample from a jewelry

A waste water sample from a jewelry factory was obtained from
the Gem and Jewelry Institute of Thailand (Public Organization).
The jewelry waste sample was prepared by filtration of 20 mL of
waste water with Whatman No. 1 filter paper. Then the sample
was mixed with 20 mL of HNO3 and the solution was heated at
200 1C to evaporate the solvent. After that, the sample was made
up with 20 mL of Milli-Q water and was heated at 100 1C until
dryness (repeated three times). Next, the sample was rinsed with