Speciation of no-carrier-added 68Ga prior to its labeling for PET imaging

Abstract

The present article describes the probable speciation of 68 Ga radionuclide just before labeling to DOTA peptides for PET imaging. The 68 Ga eluted from an anion exchange column after its purification was analyzed for its elemental composition and pH at several stages. Neutron activation analysis of the eluted fractions yields the concentrations of Na and Cl, pH measurements indicate the concentration of free H ? ions in the medium and specific activity calculations indicate the concentration of 68 Ga in the solution. Using all these information we get the idea of speciation of no carrier added Ga in the eluted fractions from CHEAQS programme. The estimations indicate that Ga is mostly present as GaCl 2? in the total MiliQ eluate. However, just before labeling of DOTA the pH of the Ga-containing eluate is adjusted to *3.5 using HEPES buffer and at that condition Ga remains as Ga 3? species which is responsible for a successful and efficient labeling. The MilliQ eluate collected before actual labeling was estimated for trace elements using inductively coupled plasma atomic emission spectrometry was found to contain a few ppb of Al, Co, Pd and Pt that did not interfere in the actual labeling. A clear idea about the prerequisite of 68 Ga species before labeling to a peptide might be of special interest for its judicious application as a radiopharmaceutical.

Prospective of 68Ga-Radiopharmaceutical Development

“…The stabilization of pH and omission of strong sodium hydroxide use was achieved by the addition of a cartridge washing step using 5 M sodium chloride solution. The content and type of gallium chemical species under this conditions was investigated and shown to be prevailed by [GaCl] 2+ and Ga 3+ , respectively before and after the buffering (pH 3) 104 . Another advantage of the anion exchange method is that the highly concentrated 68 Ga in small volume can directly be used for production of 68 Ga-carbon nanoparticle aerosol for the examination of acute pulmonary emboli 91 , 105 .…”

Radiochemistry

“…Production of copper-67 using the [Zn 68 (p,2p)Cu 67 ] has been proposed 24 using a high energy proton accelerator. Whilst gallium-68 can readily be made care is being taken to determine its speciation 25 before use for nuclear medicine, and other routes are being sought for its production in a low energy accelerator 26 (irradiation of copper) or for very high specific activity 27 from zinc.…”