Hey Akito I Sema why didn’t you consider the molar mass of the salts and the metal?

Yes Akito I Sema if both depends on the molar mass then why didn’t consider it in your calculations to get the exact value for the metal

I would use chloride or better nitrate salts

Solubility in water

0.051 g/100 mL (25 °C) sulphate salt

7.4 g/100 mL (20 °C) chloride salt

prepare a stock of 100 mg/L

for instance mercury (II) chloride

Formula: HgCl2

Molar mass: 271.52 g/mol

purity 98% (may vary)

atomic weight of Hg 200.59

No of Hg atom in compound= 1

to prepare 100 mg/L

dissolve [0.1 x (271.52/200.59)]x[100%/98%] = 0.138 g in 800 mL of deionized water in 1 L of class A volumetric flask, add a few drops of conc nitric acid, top up to 1 L (meniscus).

working stock 1 mg/L use M1V1=M2V2

https://www.physiologyweb.com/calculators/dilution_calculator_mass_per_volume.html

dilute to 2 ppb fresh-

double check the calculation with a chemist and dispose properly. All the best