An attractive approach for HPLC detection of both β+/β- emitters

Objectives For metabolic studies of tracers labeled with PET radionuclides and “classic” radionuclides such as C-14 and tritium, on-line detection of β+/β- particles in radio-HPLC is essential.Since special Li-glasses (GS1) are available as internal solid scintillators, we evaluated the applicability of such a detector for metabolites labeled with N-13, C-14 and tritium, F-18, C-11 as well as in dual isotope studies.

Methods HPLC system was used with a Ramona as β-detector (raytest, Germany) in line. For calibration, 13NH3, [18F]FDG (140MBq/0.1mL), [11C]choline (108MBq/0.1mL), [3H]acetic acid (185MBq/mL), and [14C]aspartic acid (3.7MBq/mL),were used. Dilutions by a factor up to 10-100,000 were made. For analysis of 14C-labeled and 3H-labeled amino acids, SCX Partisil column was used. The system was also utilized for assessing the purity of commercially available [14C]proline, [14C]glutamic acid, [14C]aspartic acid, [14C]glutamine, [14C]alanine, [14C]urea (37MBq/mL), [3H]glutamic acid, and [3H]alanine. For dual isotope studies, a mixture of 13N- and 14C-amino acids was analysed by same HPLC conditions. Similar system was used for analysis of 13N-labeled amino acids in animal experiments.

Results Though certified with a purity of 99%, [14C]glutamic acid, [14C]aspartic acid and [14C]proline showed impurities of 20%, 10% and 72%, respectively. Calibration was carried out for 13N with 13NH3 (linear response interval:0.7-10kBq). A good recognition of an activity peak was possible at 40Bq for both 13N and 14C, 5kBq for 3H, 20Bq for both 11C and 18F. In dual isotope studies with 13N and 14C amino acids, the mixture of β+ and β- emitters was registered and after decay of 13N, analysis was repeated for measurement of 14C. That type of radiochemical standard approach allowed to detect even low activities (40Bq) of 14C.

Conclusions Detection of β+/β- by Ramona was performed with a high sensitivity substituting the need of final liquid scintillator. For biological applications, the data illustrated the need to critically check the purity of commercially obtained radio-labeled tracers