Preparation of solutions with free calcium concentration in the nanomolar range using 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid

Anal Biochem. 1991 Feb 15;193(1):61-71. doi: 10.1016/0003-2697(91)90044-t.


There are many uses for solutions with a known free calcium concentration ([Ca2+]free) in the nanomolar range. Most frequently ethylene glycol bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA) has been used as a buffer for the control of [Ca2+]free; however, under a variety of conditions the use of 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) for this purpose would be advantageous. The theory and calculations necessary to make solutions with known [Ca2+]free appropriate for given conditions of pH, ionic strength, and temperature for use with EGTA or BAPTA are reviewed. Practical considerations and methods for making such solutions are detailed. The advantages and disadvantages associated with the use of each of the two chelators are discussed. As one example of the application of solutions with free calcium in the nanomolar range, the dissociation constant of the fluorescent indicator fura-2 for calcium has been determined in a physiologic buffer at 22 and 37 degrees C. For practical reasons, the use of BAPTA is advantageous when solutions with different known [Ca2+]free must be used on a daily basis.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Calcium / chemistry*
  • Calcium Chloride / chemistry
  • Egtazic Acid*
  • Hydrogen-Ion Concentration
  • Magnesium / chemistry
  • Osmolar Concentration
  • Solutions*
  • Temperature
  • Thermodynamics


  • Solutions
  • Egtazic Acid
  • Magnesium
  • 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid
  • Calcium Chloride
  • Calcium