Comparative Studies on Experimental Procedures for Labeling of Tc-99m with L-Aspartic Acid

Abstract

For the labeling of Tc-99m radioisotope with L-aspartic acid (ASP), six different procedures were designed. The key points to the procedures are focused on the phase (solid or solution) used of major reactants (L-aspartic acid sodium salt monohydrate and SnCl₂) and the pH of reacting solution. Labeling experiments were carried out according to the procedures at conditions; the concentration ratio ([ASP]/[SnCl₂]) = 35-45, temperature = 80 ºC, radioactivity of ^99mTc = 5 mCi, reaction time = 1 h. The labeling was investigated by radio-ITLC using methylethyl keton (MEK) and 0.9 % saline solution as solvents, respectively. The labeling yields were determined from the radioactivity distributions in the two solvents. Solid typed SnCl₂ gave better yields than solution typed SnCl₂. While, regardless of whether L-aspartic acid sodium salt monohydrate was used as solid or solution, there was found a negligible effect on ^99mTc labeling. The pH dependence on the ^99mTc labeling with L-aspartic acid sodium salt monohydrate was found. The labeling yields were found higher in the following order; weakly acidic and neutral (pH 5-7) > alkaline (pH 10) > acidic (pH 4) media. The best yield (ca. 90 %) was obtained from the procedure that both L-aspartic acid sodium salt monohydrate and SnCl₂ were used as solid without adjustment of pH, providing a good method for the preparation of pharmaceutical kits using L-aspartic acid sodium salt monohydrate.