[mlenos77]

I want to make a Pb complex that is stable at very low pH <2. Any suggestions?

[Borek]

How stable? At pH 2.0 around 94% of Pb²⁺ would be complexed by EDTA (assuming solution is 0.1 M in both Pb(NO₃)₂ and H₄EDTA, then pH brought up to 2.0 with NaOH).

[mlenos77]

Thanks for the reply.  If I go the other direction, first creating a Pb complex with EDTA and then lower the pH to 1.0, will it remain stable (i.e. remain complexed)?  Would HEDTA and DTPA work better or worse than EDTA at pH between 1.0 and 2.0?  Are there any other chelants that you can think of I should try in the lab experiments along with EDTA and possibly HEDTA or DTPA.

[Borek]

Route doesn't matter, equilibrium will be the same. As for other chelating agents - hard to say without having pKa and K values at hand (and I don't have them here).