Radiochemical purity, determination

Radiochemical purity determinations consist of separating the different chemical substances containing the radionuclide. The radiochemical purity of labeled pharmaceuticals is typically determined by paper chromatography (paper impregnated with silica gel or silicic acid). The most frequently used radioisotope is technetium-99m obtained by daily elution with saline... 

Table 3.1 summarizes the radiochemical purity, determined by electrophoresis, of the reaction mixtures prepared with different molar peptide to radionuclide ratios. Figure 3.1 shows the various HPLC profiles that were observed for the different molar peptide to radionuchde ratios. 

Silica Gel. The chemical properties are based on siloxane (Si-O-Si) and silanol (Si-OH). Polar groups are responsible for the interaction of the adsorbent with water and with the sample to be analyzed. Silica stationary phases (3-8 pm) have been produced for ITLC as silica gel (ITLC-SG) and silicic acid (ITLC-SA). ITLC-SG is the most frequently used adsorbent for routine radiochemical purity determinations (Table 9.1.1.1). 

Radiochemical Purity Determination of the percentage of fixed iodine on the molecule is usually done by the radiochromatographic method. It can also be done by a precipitation test for proteins. Proteins are precipitated with trichloroacetic acid, and the different phases are counted in a gamma counter. 

Mah, G., Reilly, R. M., Wong, G. L. and Houle, S. A comparison of three methods to determine the radiochemical purity of 99mTc-hexamethylpropylene amine oxime (99mTc-HMPAO). Nucl. Med. Commun. 10 733-740,1989. 

F. Fuchtner, P. Angelberger, H. Kvaternik, F. Hammerschmidt, B. Peric-Simovc, J. Steinbach, Aspects of 6-[ F]fluoro-L-DOPA preparation Precursor synthesis, preparative HPLC purification and determination of radiochemical purity, Nucl. Med. Biol. 29 (2002) 477-481. 

The tiyptophol was condensed with methyl propionylacetate using boron trifluoride etherate as the catalyst to produce tetrahyropyranoindole. Basic hydrolysis of the ester gave [3-14C] etodolic acid (overall yield 26% from the labeled starting material). The compound was recrystallized in presence of an antioxidant to prevent formation of peroxides and stored at -10°C. The radiochemical purity was determined to be 99%. 

In order to determine the half-life, the decay scheme, and other nuclear characteristics of a radioactive nuclide, it is important to use a sample of very high radiochemical purity. In addition in the measurement of nuclear reaction cross sections, fission yields and in activation analysis, the amounts of the radioactive nuclide produced must be determined. Thus It Is also necessary to determine the yield of... 

Compound 232 has been obtained232 in 19.7% overall yield from uniformly labelled 14C-L-alanine according to the reaction scheme of equation 96. The acid 232 had specific activity of 66.7 /iCimmol-1 and radiochemical purity of 98% as determined by radio-... 

The quality control tests fall in two categories biological tests and physiochemi-cal tests. The biological tests establish the sterility and apyrogenicity, while the physiochemical tests include radionuclidic, chemical, and radiochemical purity tests along with determination of pH, osmotic pressure, and physical state of the sample (for colloids). 

Azaconazole, C4abelled at the 2-caibon of the dioxolane ring (Fig. 1), was obtained from the Janssen Radiosynthesis Group. It showed a specific activity of 449 kBq/mg (12.1 pCi/mg) and a radiochemical purity exceeding 96%, as determined by radio-HPLC. The impurity was C-R 33 277, the 4H-1,2,4-triazole isomer of azaconazole. Unlabelled azaconazole was found to have a purity in excess of 99%. 

Determination of the radiochemical purity using fast protein liquid chromatography (FPLC) and instant thin layer chromatography (ITLC), and purification using the SepPak procedure and size exclusion chromatography. 

The radiochemical purity of the Rc-HEDP was determined by instant thin layer chromatography (ITLC) using ITLC sihca gel strips developed in 95% acetone. The strips were dried and cut into 0.5 cm long segments, and the radioactivity was measured using a gamma counter (Ecko Electronics). The Re-HEDP remained at the origin (Rj = 0) and the ReO moved to the solvent front (Rf = 0.9). 

The main aim of the stability studies of Re-HEDP was to determine its optimal storage conditions and shelf-life prior to its administration to patients. For this purpose, Re-HEDP was stored under different environmental conditions, namely, at 20-25°C in darkness, at 4°C in darkness, at 20-25°C in light and at 20-25°C in human serum in darkness. Instant thin layer chromatographic analysis of radiochemical purity was performed at 1,3,6,24,48 and 72 h after preparation of the Re-H EDP. 

Various parameters such as ligand concentration, incubation time and temperature were varied extensively to arrive at the protocol for maximum complexation. The estimation of the radiochemical purity of the labelled product was carried out by HPLC analysis using the gradient elution technique described above. Complexation yields were determined by using different amounts of ligand (25-100 pg) in order to determine the optimal ligand concentration for obtaining maximum complexation. 

The Lu obtained from a commercial suppher was added to 50% gentisic acid in acetate buffer in order to adjust the pH to approximately 4.5. DOTATATE was added to the buffered Lu to achieve a specific activity of 1 mCi/pg. Tlie mixture was then incubated at 90°C for 30 min in a thermostatic bath, after which the radiochemical purity was determined by either SepPak CIS cartridge or HPLC. 

The labelled compounds were purified on a SepPak CIS cartridge. The radiolabelled DOTATATE preparations were eluted with methanol, with greater than 9S% purity after evaporation of the methanol. To determine its stability, the radiolabelled preparation was stored at room temperature and at 37°C for 72 h for Lu. The stability of the preparation, described as the radiochemical purity, was determined by SepPak separation. 

The peptide was reconstituted in saline at pH7.2 and used for labelling. Parameters such as peptide concentration, temperature and pH were varied to arrive at the optimal conditions for labelling DOTATATE with Ho and 1. The radiochemical purity of the labelled biomolecules was determined by HPLC and ITLC-SG analysis. 

Radiochemical purity was also determined by reversed phase HPLC on a C18 column (gBondapak C18, 10 gm, 3.9 mm x 300 mm, Waters, Milford, MA,... 

---