ARTICLE IN PRESS

0969-8043/$ - se

doi:10.1016/j.ap

�CorrespondE-mail addr

Applied Radiation and Isotopes 64 (2006) 431–434

www.elsevier.com/locate/apradiso

Analysis of metal radioisotope impurities generated in [18O]H2O duringthe cyclotron production of fluorine-18

J.M. Gilliesa,�, N. Najima,b, J. Zweita,b

aCancer Research-UK/UMIST Radiochemical Targeting and Imaging Group, Christie Hospital NHS Trust, Paterson Institute for Cancer Research,

Wilmslow Road, Manchester, M20 4BX, UKbSchool of Chemical Engineering and Analytical Sciences, University of Manchester, P.O. Box 88, Manchester, M60 1QD, UK

Received 7 January 2005; accepted 30 August 2005

Abstract

We show the separation of metal radioistope impurities using capillary electrophoresis (CE). The methodology used is an improvement

of existent protocols for separation of stable metal ions. Production of fluorine-18 using [18O]H2O-enriched water encased in a titanium

target body results in the production of several metal radioisotope impurities. Optimisation of the conditions for CE separation of the

metal radioisotope impurities incorporated the use of 6mM 18-Crown-6 in combination with 12mM glycolic acid as complexing agents

within the running buffer (10mM pyridine, pH 4.0). Using this optimised procedure, we were able to separate and detect a number of

metal radioisotopes, including chromium, cobalt, manganese, vanadium and berillium, within the fM concentration range.

r 2005 Elsevier Ltd. All rights reserved.

Keywords: Capillary electrophoresis; Gamma-ray spectroscopy; Metal radioisotopes

1. Introduction

Positron emission tomography (PET) (Gambhir, 2002) isan imaging technique that uses positron-emitting radio-nuclides linked to specific molecules, ranging from smallinorganic compounds to macromolecules including pro-teins and peptides. PET scanning allows for the biodis-tribution of the labelled compound to be imaged as afunction of time. PET therefore provides measurement onin vivo biochemistry within specific normal or diseasedtissues (Massoud and Gambhir, 2003; Reader and Zweit,2001).

2-[18F]fluoro-2-deoxy-D-glucose (2-[18F]FDG) is themost widely used radiopharmaceutical for PET. 2-[18F]FDG is produced from fluorine-18 (t1/2 109.8min)which decays by b+-emission (Hamacher et al., 1986).

Fluorine-18 can be obtained with very high specificactivity by bombarding enriched oxygen-18 in the form of

e front matter r 2005 Elsevier Ltd. All rights reserved.

radiso.2005.08.008

ing author. Tel.: +44 161 446 3150; fax: +44 161 446 3109.

ess: jgillies@picr.man.ac.uk (J.M. Gillies).

a water target [18O]H2O, with protons in a cyclotron usingthe 18O(p, n)18F nuclear reaction (Roberts et al., 1995).Fluorine-18 is produced by irradiation of a 96% enriched[18O]H2O target using an 18MeV incident proton beam.During proton bombardment, trace amount of metal

radioisotopes are produced due to radio activation on themetal target housing.Ion-exchange column-based chromatography is the

principal method currently used in the separation of metalimpurities including 56Co, 57Co, 58Co, 51Cr, 52Mn, 54Mn,48V and 7Be, from enriched target [18O]H2O (Timerbaev,1996).This work was undertaken to investigate the feasibility

of using capillary electrophoresis (CE) (Zweit, 1992)as an alternative to ion-exchange chromatography for theanalysis of the metal radioisotope impurities formedduring the production of fluorine-18. Such a developmentcould then be utilised as a more efficient qualityassessment of the quantitative analysis of radioisotopeimpurities generated during the clinical production of2-[18F]FDG.

ARTICLE IN PRESS

Fig. 1. Separation of metal ion standards using CE.

J.M. Gillies et al. / Applied Radiation and Isotopes 64 (2006) 431–434432

2. Experimental

2.1. Instrumentation

Experiments were performed with an ABI-270A-HT CEsystem (ABI, USA). Separations were carried out on fusedsilica capillaries of 72 cm (50 cm effective length) 50 mm i.d.(Composite Metal Services Inc., UK).

3. Chemicals

All chemicals were supplied by Sigma-Aldrich, UK

3.1. Solution preparation

All solutions and standards were prepared using double-distilled deionised water produced on the Elix waterpurification system. Stock solutions of each stable cation(Zn, As, Mo, Cu, Co, Fe, Mn, Se, Cr, Be and V) wereprepared by diluting atomic absorption standard solutionsto the desired concentration (10mM).

4. Electrophoretic procedure

A new capillary (50 mm i.d., 72 cm long, 50 cm to detectorwindow) was rinsed for 5min intervals with 1.0M NaOHfollowed by 0.1M NaOH and finally water. The carrierelectrolyte (10mM pyridine pH4.0, 12mM glycolic acidand 6mM 18-Crown-6) was flushed through the capillary5min prior to start of analysis. The separation was run at20 kV and 25 1C (constant temperature). Samples, eitherstandard or Sep cartridge eluant, were injected into thecapillary using hydrodynamic pressure at 5 bar for 2 s(1 s ¼ 4 nL injection volume, UV detection at 254 nm wasused).

5. Radioisotope analysis

During the routine clinical production of 2-[18F]FDG,using a GEMS TracerLab MX FDG Synthesizer (GeneralElectric, USA), the enriched [18O]H2O was passed throughan Accell Plus QMA Sep-Pak cartridge (Waters, USA) andthe fluorine-18 was extracted using a solution of kryptofix2.2.2 (22.0mg), K2CO3 (7.0mg) in 600 mL acetonitrile/water (50:50). The Accell Plus QMA Sep-Pak cartridgeretained all metal impurities within its matrix.

These cartridges were then analysed using a gammaspectrometer equipped with pure germanium detector (EG& G ORTEC, UK) to identify and quantify all g-emittingradioisotope impurities extracted from the enriched[18O]H2O.

The metal impurities were extracted from the cartridgesusing 12M HCl. The fraction collected was then passedthrough an anion-exchange column (Bio-Rad, UK) and theindividual metal species were eluted using ion-exchangechromatography providing a final eluant volume of 1ml.

The individual radioisotope impurities collected from theanion-exchange column were analysed using the optimisedCE method developed from the analysis of the stable metalstandards.

6. Results and discussion

Lee and Lin (1994) have shown the separation of amixture of stable metal ions by CE using a running buffercontaining pyridine (10mM), as a UV chromophore, whichhas a maximum absorption wavelength of 254 nm at pH4.0 and 12mM glycolic acid as complexing agent. Themethod developed within the study by Lee and Lindemonstrated the separation of a range of stable metalions in less than 15min. This method has been used for thequantifiable determining alkali, alkaline earth and transi-tion metal ions.In order to further enhance and optimise conditions

for the separation and detection of trace radioisotopecomplexes, we investigated the effects of severalrunning buffers and complexing agents on stable metalion separation. From this work, it was seen that theoptimal separation conditions, using CE, for metal ionseparation involved a running buffer of 10mM pyridine inthe presence of the complexing agents glycolic acid(12mM) and 18-Crown-6 (6mM) with an applied voltageof 20KV.We show a two-fold reduction in the separation time of a

range of metal standards when using 10mM pyridine as therunning buffer in the presence of the complexing agentsglycolic acid (12mM) and 18-Crown-6 (6mM) for CEseparation. Separation was achieved for a range of stablestandard metal ion in less than 7min (Fig. 1).Once the CE parameters for the analysis of the stable

metal cations had been established, identification of themetal radioisotopes present in the enriched [18O]H2O wascarried out. This involved the gamma-ray spectrographic

ARTICLE IN PRESS

Fig. 3. CE analysis of metal impurities from a Sep-Pak cartridge used in

the production of 2-[18F]FDG.

Table 1

Absolute radioactivity (Bq) and concentration (fM) of radioisotopes

extracted from Sep-Pak cartridges

Metal isotope Activity (KBq) Concentration (fM)

51Cr 1.32 2.347Be 8.16 26.856,57,58Co 18.75 8.1552,54Mn 0.64 2.3848V 0.07 0.38

J.M. Gillies et al. / Applied Radiation and Isotopes 64 (2006) 431–434 433

analysis of the Sep-Pak cartridges used to trap the traceimpurities during clinical production of 2-[18F]FDG.

Gamma-ray spectroscopy is an analysis technique usedfor radionuclide identification and quantification, throughthe analysis of gamma-ray energies emitted from radio-nuclides. A hyper pure germanium detector and multi-channel analyser software are used to detect and analysegamma-ray energies in a given sample. The system iscalibrated for energy and efficiency, in order to determineabsolute activity using calibrated standards of 241Am,133Ba, 22Na, 60Co and 137Cs.

The spectrum was compiled using Gamma Vision-32Programme. Data were obtained from the spectrum ofthree individual measurements. These data were used tocalculate the detector efficiency in counts per minute permicrocurie (cpm mCi�1), and used to construct an efficiencycalibration curve (data not shown).

Ten Sep-Pak cartridges used during the synthesis of 2-[18F]FDG were monitored using gamma-ray spectroscopy.Isotopes were identified based on the characteristic g-emissions (Fig. 3). Each peak was analysed by marking theregion of interest and recording the count rate. An exampleof the data obtained from an individual cartridge isdisplayed in Fig. 2.

The detector efficiency was measured for various g-rayenergies and this was used to determine absolute activitythrough count rate measurement of the area under theenergy peak taking into account the detector efficiency atthat energy and the abundance of the particular gamma-ray energy.

Radioisotopes retained on the Sep-Pak cartridges wereeluted and ion-exchange chromatography was used toseparate the various metal species from each other.Further, gamma-ray spectroscopy was then obtained oneach of the purified metal ions to measure thier overallactivity. This activity was then used to calculate theconcentration in fM of each species present in the Sep-Pak cartridge (Table 1).

The CE analysis protocol was also applied to a solutionof the Sep-Pak extract prior to ion-exchance chromato-graphy to see if detection in the fM region was possible

Fig. 2. Gamma-ray spectrum of individual Sep-Pak cartridges used during

the synthesis of 2-[18F]FDG.

using a CE instrument. Fig. 3 shows the electroferogramfor the separation of a two second injection (8 nL) of asolution of the metal species containing the concentrationsshown in Table 1.

7. Conclusion

The CE method was successfully applied to analyse thestable metal isotopes (Co, Cr, Mn, V and Be) with a two-fold decrease in separation time (total separation time of7min) from previous studies. The buffer system required toachieve the improved separation contains 10mM pyridineof pH 4 as the running buffer (carrier electrolyte) and,12mM glycolic acid and 6mM 18-Crown-6 as complexingagents.This work shows the potential of CE methodology to

demonstrate faster analysis times and greater sensitivitythan conventional ion-exchange chromatographic meth-odologies.

Acknowledgements

This work is funded by Cancer Research UK. Thanks toElizabeth A. Keenan of Mem-Teq Ventures Ltd., 15

ARTICLE IN PRESSJ.M. Gillies et al. / Applied Radiation and Isotopes 64 (2006) 431–434434

Kingfisher Court, Ashton-on-Makerfield, Wigan, WN49DW, and Dr. Graham Cowling for proof reading themanuscript.

References

Gambhir, S.S., 2002. Molecular imaging of cancer with positron emission

tomography. Nat. Rev. Cancer 2, 683.

Hamacher, K., Coenen, H.H., Stocklin, G., 1986. Efficient stereospecific

synthesis of no-carrier-added 2-[18F]-fluoro-2-deoxy-D-glucose using

aminopolyether supported nucleophilic substitution. J. Nucl. Med. 27,

235–238.

Lee, Y.H., Lin, T.I., 1994. Determination of metal cations by capillary

electrophoresis effect of background carrier and completing agents. J.

Chromatogr. A 675, 227.

Massoud, T.F., Gambhir, S.S., 2003. Molecular imaging in living subjects:

seeing fundamental biological processes in a new light. Genes Dev. 17,

545.

Reader, A.J., Zweit, J., 2001. Developments in whole-body molecular

imaging of live subjects. Trends Pharmacol. Sci. 22, 604.

Roberts, A.D., Oakes, T.R., Nickles, R.J., 1995. Development of an

improved target for [18F]F2 production. Appl. Radiat. Isot. 46, 87.

Timerbaev, A.R., 1996. Advanced possibilities on multi-element separa-

tion and detection of metal ions by capillary zone electrophoresis using

precapillary complexation I. Separation aspects. J. Chromatogr. A

756, 300.

Zweit, J., 1992. Eur. J. Nucl. Med. 19, 418.