Kinetic Stability Studies on Yttrium(III)−1,4,7,10- Tetraazacyclododecane-1,4,7,10-tetraacetic Acid by Free-Ion Selective Radiotracer Extraction

Free-ion selective radiotracer extraction (FISRE) using no-carrier-added 90Y has been applied to assess the dissociation kinetics of yttrium(III)−1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (Y−DOTA), a radiopharmaceutical precursor with a remarkable kinetic stability. In order to extend the operationally defined detection window, a complemental FISRE-based experiment has been succesfully developed. Within a time frame of approximately 10 half-times of 90Y (t 1/2 = 61.4 h), the complex Y−DOTA has been observed to form two kinetically distinguishable species with significantly different kinetic properties. The time-dependent speciation was measured to be sensitive to pH variations even in the neutral pH range (4.5−7.4) whereas the impact of ionic strength changes is negligible.