Comparative evaluation of Tc-99m-ethylene bis-l-cysteine and Tc-99m-ethylene bis-l-beta-homocysteine during reversed phase HPLC analysis and electrophoresis at various pH conditions

Ethylene bis-L-beta -homocysteine (L,L-EH) differs from ethylene bis-L-cyst eine (L,L-EC) in having an extra methylene group between each pair of amine and carboxyl groups. The objective of this study was to determine the effe ct of the extra methylene groups on the characteristics of the complex of t hese compounds with technetium-99m during analysis by reversed phase HPLC a nd by electrophoresis at various pH values. Up to pH 5.5, Tc-99m-L,L-EH exh ibits a substantially longer retention time during reversed phase HPLC than Tc-99m-L,L-EC, suggesting a more lipophilic character for Tc-99m-L,L-EH un der these conditions. On the other hand, Tc-99m-L,L-EH clearly possesses a higher negative charge in the pH range 3-6.5 as shown by the markedly great er migration towards the anode in electrophoresis experiments. A rational e xplanation for these seemingly opposing observations can not yet be offered .