How many Mg2+ ions can EDTA bind?

Pete pkursula at
Fri Dec 19 06:22:32 EST 1997

Is this also true for Ca2+ and EGTA?


> >Hello,  I need to re-adjust the [Mg2+] in my PCR rxns to correct for
> >EDTA carryover.  Different people have told me, each with great
> >certainty, that one molecule of EDTA (pKa's 2.0, 2.7, 6.1, and 10.2) at
> >pH 9 will chelate one, two, or four Mg2+ ions.  I, myself, have no idea
> >how EDTA coordinates Mg2+. Can someone give a definitive stoichiometry
> >or point me to any references?
> >Thanks for your help. 
> EDTA forms complexes with 2 and 3 valent kations 1:1, so in other
> words one EDTA molecule will omplex one Mg 2+ ion! The pH value does
> not change the stoichiometry of the reaction but only the
> efficiency-if the pH is not optimal the equilibrium will be shifted to
> the right side leaving more free Mg2+ and EDTA!
> Martin

|)    |/
|etri |\ursula

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