A survey of readily available chelators for buffering calcium ion concentrations in physiological solutions

Stability constants are reported for the binding of H+, Ca2+ and Mg2+ ions to the chelators commonly abbreviated EGTA, EDTA, HEDTA, DPA, NTA, ADA, and citrate, under uniform conditions of physiological temperature and ionic strength. Other compounds usable as calcium buffers are listed. The theoretical and practical considerations that influence the actual pCa attained in a chelator solution are discussed and a Hepes-buffered saline solution is suggested as a standard of "physiological pH". With these figures it is possible to make a rational choice of chelator to control the pCa and pMg of solutions for investigations in cell physiology, drug action, virus reproduction, and ion binding to proteins.