Polarographic and potentiometric investigation of Co(II) complexes with 5-hydroxytryptophan.

The formation of the complexes between Co(II) and 5-hydroxytryptophan has been studied by means of polarographic and potentiometric methods. The real stability constants of mono and bis-chelato complexes of Co(II) with 5-hydroxytryptophan, obtained by polarographic method, in Britton-Robinson buffer were found to be, log beta 1 = 4.98 and log beta 2 = 8.45. By applying the potentiometric method, in aqueous medium of ionic strength mu = 0.2, the stability constants, log beta 1 = 4.42 and log beta 2 = 8.57 were obtained. The complexes defined by polarographic method have been used in a purpose of analytical determination of 5-hydroxytryptophan.