The use of silica-gel cartridges for the preparation of gallium chloride from the citrate solution

Objectives There are two gallium radio-nuclides, Ga-67 and Ga-68 possessing favorable nuclear properties for nuclear medicine applications. A procedure is necessary for converse the commercial gallium-67 or gallium-68 citrate to the chloride solution. The need for such a conversion relates to the formation of a strong complex between gallium ions and citrate preventing Ga-67(3 plus) or Ga-68(3 plus) from binding to selected molecules in radiolabeling procedures.

Methods We attempting to label TOTATOC with Ga-67 or Ga-68 and likewise required substitution of the citrate ions for Cl (1 minus) prior to the radio-labeling procedure. We use a simple two-step procedure involving absorption on a silica-gel, removal of the citrate ions with water and elution of the Ga-67 or Ga-68 ions with diluted HC1.

Results This rapid procedure characterizes a minimum amount of manipulation of the radioactivity and is high efficiency reproducible. The two steps: 1. To 5 mL of Ga-67(100 MGq, INER, Taiwan) or Ga-68 citrate (100 MGq, INER, Taiwan) was added 10 mL of distilled water, whereafter the solution was filtered over a 500mg silica-gel cartridge (J.T.Baker, USA) fitted with a 6-ml plastic syringe, at a flow rate of 1 mL per minute. 2. The retained radioactivity was eluted from the cartridge with 3 ml of 0.1 M HC1 and the pH of the eluate was adjusted to pH 5 with 0.1 M NaOH to yield a Ga-67or Ga-68 chloride solution free from citrate ions.

Conclusions This simple procedure was completed in 20 min and the overall recovery of the radioactivity exceeded 91%. We are currently using silica-gel (SiOH) J.T.Baker cartridges routinely in our laboratory for the preparation of Ga-67or Ga-68 chloride from the citrate solution for the radiolabeling of TOTATOC