0
$\begingroup$

I’m testing on samples that require a concentration of 1000 ppb (or 1 mg/L) of Pb 2+. My first thought was to simply dissolve 1 mg of Lead nitrate in 1 L of deionized distilled water to create 1 L of stock solution at the desired 1000 ppb (1 mg/L) concentration.

Is the process as simple as that, or is 1 mg proportionally too small a mass of solute to dissolve in 1 L of distilled water? Should I create a more concentrated stock solution and dilute it to 1000 ppb by adding requisite amounts of water? What concentration stock solution would be recommended in this case?

All the best!

$\endgroup$
1
$\begingroup$

Making the solution in a single step is inaccurate up to impossible.

  • Try to find a crystal of lead nitrate with the mass close enough to $\pu{1 mg}$
  • Try to weight up $\pu{1 mg}$ on scales with good enough accuracy.
  • Try to make such $\pu{1 ppm}$ solution stable enough.

The usual thing is to create a concentrated stock solution ( e.g $\pu{1000 ppm}$ and creating the working solution in 1 (1000 times) or 2 step ( 20x50 times) dilution whenever needed.

There is need to consider stabilizing by an acid, to prevent hydrolysis and adsorption. Very diluted solutions, like for AAS, are often stored in PE instead of laboratory glass to prevent ion Vs glass surface interactions.

| improve this answer | |
$\endgroup$
  • $\begingroup$ When you say “steps”, do you mean creating a moderately concentrated stock solution (e.g. 1000 ppm) and diluting it to create a solution of the desired concentration? $\endgroup$ – Thunderbolt114 Apr 5 at 6:28
  • $\begingroup$ I mean, using 1 or 2 stock concentrations, if dilution in 1 step would be too big to be practical or accurate. E.g. you may dilute it 1000 times in 1 step, or 20x50 times in 2 steps. $\endgroup$ – Poutnik Apr 5 at 6:31
  • $\begingroup$ That makes sense. Would dissolving a “1 mg crystal of lead nitrate” in 1 L of water be an accurate way to create a stock solution at 1000 ppb? Will every volume of water in that 1 L contain the same concentration of lead if the container was perhaps shaked/agitated thoroughly? $\endgroup$ – Thunderbolt114 Apr 5 at 6:36
  • $\begingroup$ It would, IF... But as the premise is false, it would not. $\endgroup$ – Poutnik Apr 5 at 6:41
  • $\begingroup$ Alright. So if I understand correctly, my best bet would be to dilute 1000 ppm of solution with the necessary amount of distilled water to yield a 1000 ppb stock solution? $\endgroup$ – Thunderbolt114 Apr 5 at 6:44

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.