Introduction
The effective specific activity of a radioisotope is an indirect and highly useful way to describe a radioactive sample’s purity. A high effective specific activity combines the concept of an isotopically pure product with suitability via selectivity of a particular chelating body. The primary goals of this work are twofold: 1) To determine which metallic impurities have the largest impact on the effective specific activity for a given chelator, and 2) to form a model based on the binding affinities of each metal for to calculate a ‘theoretical effective specific activ-ity’ from broad band trace metal analysis. If successful, this information can be used to guide the production of high specific activity products through the systematic elimination of high-impact metallic impurities.
Material and Methods
Phosphor plate thin layer chromatography (TLC) was used to measure the effective specific activ-ity of 64Cu by NOTA and DOTA, and 89Zr by des-feral (DF). Typical measured effective specific activities are 2–5 Ci/μmol for 64Cu and 1–2 Ci/μmol for 89Zr.
Samples were created containing increasing cod competitive burdens (X) of CuCl2, ZnCl2, FeCl2, NiCl2, CrCl3, CoCl2, MnCl2, and YCl3. Standard concentrations were measured by microwave plasma atomic emission spectrometry. 50 pmol of NOTA, DOTA, or DF were added following the activity aliquots of 64Cu or 89Zr. Labeling efficien-cies (64Cu-NOTA, 64Cu-DOTA, 89Zr-DF) were measured using TLC’s, and were fit by linear regression to the form f(X) = b/(1 − AX), where A is the chelation affinity (inverse of dissociation constant) and X is the molar ratio of the metallic impurity to the amount of chelator.
Results and Conclusion
Affinity of Zr for DF was assumed to be unity, while the affinities of Cu for NOTA and DOTA were explicitly measured and were found to be 0.93 ± 0.13 and 5.2 ± 3.2 respectively.
It was found that Cu had the highest affinity for NOTA by a factor of 266, and that Zr had the highest affinity for DF by a factor of 40.
• In order of decreasing affinity to NOTA: Cu, Zn, Fe, Co, Cr, Y, and Ni
• In order of decreasing affinity to DOTA: Cu, Y, Zn, Co, Ni, Cr, and Fe
• In order of decreasing affinity to DF: Zr, Y, Cu, Zn, Ni, Fe, Co, Cr
These results suggest that aside from the carrier element it is most important to remove zinc from 64Cu products prior to chelation with NOTA and yttrium from 64Cu and 89Zr products prior to chelation with DOTA and DF, respectively. Therefore, it is logical to believe that 89Zr effective specific activities could be greatly improved by secondary separations with the goal of re-moving additional yttrium target material.
Chelation affinities of NOTA, DOTA, and DF for several common metals have successfully been investigated. These values will guide our future attempts to provide high effective specific activity 64¬Cu and 89Zr. Furthermore, a preliminary model has been formed to calculate effective specific activity from the quantitative broad band analysis of trace metals. Future work will include chelator affinity measurements for other likely contaminants, such as scandium, titanium, zirconium, molybdenum, niobium, gold, gallium, and germanium. Details will be presented.
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa.de:bsz:d120-qucosa-166419 |
| Date | 19 May 2015 |
| Creators | Graves, S., Valdovinos, H., Cai, W., Barnhart, T., Nickles, R. |
| Contributors | Medical Physics, University of Wisconsin – Madison, USA,, Helmholtz-Zentrum Dresden - Rossendorf, |
| Publisher | Helmholtz-Zentrum Dresden - Rossendorf |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | doc-type:conferenceObject |
| Format | application/pdf |
| Source | WTTC15 |
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