EGTA

EGTA or Ethyleneglycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, has the structure:

As a chelating agent, it preferentially binds Ca⁺² with a significantly greater affinity than the other divalent cations, due to the high value of the formation constant (K_f = 1.0·10¹¹).