Methods of static potentiometry and UV-VIS spectrophotometry were applied for the determination of protonation
constants of (10-[4-aminobenzyl(hydroxyl)phosphonylmethyl]-1,4,7,10-tetraazacyclo-1,4,7-triacetic acid)
(DOTA(NH2)) and stability constants of holmium and yttrium complexes with DOTA(NH2). The DOTA(NH2) protonation
constants of [HA] (log β1 = 12.7); [H2A] (log β2 = 21.4) and [H3A] (log β3 = 27.9) were experimentally determined
by the static potentiometry. The stability constants of Ho-DOTA(NH2) (log KHo DOTA(NH2) = 18.0) and Y-DOTA(NH2) (log
KY-DOTA(NH2) = 17.8) complexes were determined by UV-VIS spectrophotometry using the competitive reaction of the
DOTA(NH2) – metal complexes with Arsenazo III.