Chemistry of inorganic compounds – Halogen or compound thereof – Elemental halogen
Reexamination Certificate
1999-03-11
2001-02-20
Nguyen, NgocYen (Department: 1754)
Chemistry of inorganic compounds
Halogen or compound thereof
Elemental halogen
C536S018400, C536S122000, C210S685000, C210S682000, C423S580200
Reexamination Certificate
active
06190637
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for preparing [F-18]-fluoride ion used for producing radiofluorinated organic compounds.
2. Related Art Statement
Radiofluorinated organic compounds are used in position emission tomography (PET), one of the medical diagnostic imaging technologies.
Currently, most radiofluorinated organic compounds are produced by organic chemical reactions of their precursors with [F-18]-fluoride ion. [F-18]-fluoride ion is formed by proton irradiation of [O-18]enriched water as target and obtained in the form of [O-18]-enriched water containing [F-18]-fluoride ion. To use the [F-18]-fluoride ion thus formed for labelling organic compounds, it is necessary to concentrate and separate [F-18]-fluoride ion from the [O-18]-enriched water containing [F-18]-fluoride ion obtained above. Furthermore, since [O-18]-enriched water is very expensive, it is desirable to recover and reuse [O-18]-enriched water after [F-18]-fluoride ion has been concentrated and separated therefrom.
A method of concentrating and separating [F18]-fluoride ion with the object of recovering and reusing [O-18]-enriched water has been already reported in the literature.
Schlyer et al. (Appl. Radiat. Isot., Vol. 41, No. 6, pp. 531-533 (1990)) reported that [O-18]-enriched water containing [F-18]-fluoride ion (about 0.5 ml) is brought into contact with a strongly basic anion exchange resin (hydroxyl form or carbonate form) to make [F-18]-fluoride ion adsorbed to the resin and, along therewith, to recover the [O-18]-enriched water which has passed through the resin and then the [F-18]-fluoride ion adsorbed to the strongly basic anion exchange resin is eluted with an aqueous solution of cesium carbonate or potassium carbonate, so that [F-18]-fluoride ion can be concentrated and separated at a collection efficiency of 95% or more. Hamacher et al. (Appl. Radiat. Isot., Vol. 41, No. 1, pp. 49-55 (1990)) reported that from about 2 ml of [O-18]-enriched water containing [F-18]-fluoride ion, in the same manner as above, [F-18]-fluoride ion can be concentrated and separated at a collection efficiency of 95% or more.
In the above-mentioned method, however, the recovered [O-18]-enriched water contains cations etc. as impurities, so that purification by distillation or the like is necessary to reuse the recovered [O-18]-enriched water for preparing radioactive fluoride ion.
On the other hand, with the increase of demand for radiofluorinated organic compounds, an increase in the production of [F-18]-fluoride ion has become necessary. Consequently, an increase in the amount of [O-18]-enriched water used in each production of [F-18]-fluoride ion is eagerly desired.
When it is intended, according to the method described above, to concentrate and separate [F-18]-fluoride ion from the larger amount of [O-18]-enriched water containing [F-18]-fluoride ion than that (about 2 ml) already reported in the literature, it may be assumed that the intention can be attained simply by increasing the amount of the resin. However, an increase in the amount of the resin makes it necessary to use an excess of aqueous basic solution as the eluent in eluting the adsorbed [F-18]-fluoride ion; this not only hinders the labelling reaction of organic compounds with the eluted [F-18]-fluoride ion but also is liable to lead to an increase in an amount of contamination with non-radioactive impurities.
OBJECT AND SUMMARY OF THE INVENTION
In view of the situations, the object of the present invention is to provide a method for preparing [F-18]-fluoride ion used for producing radiofluorinated organic compounds according to which [F-18]-fluoride ion can be collected at a high efficiency from a larger amount (about 2 ml or more) of [O-18]-enriched water containing [F-18]-fluoride ion than the amount in the prior method without increasing the amount of the resin and, at the same time, [O-18]-enriched water reusable for preparation of [F-18]-fluoride ion can be recovered without subjecting to any purification such as distillation.
DETAILED DESCRIPTION OF THE INVENTION
According to the present invention, there is provided a method for preparing [F-18]-fluoride ion used for producing radiofluorinated organic compounds which comprises the step of bringing [O-18]-enriched water containing [F-18]-fluoride ion formed by proton irradiation of [O-18]-enriched water into contact with a strongly acidic cation exchange resin to remove impurity cations, the step of then bringing the [O-18]-enriched water containing [F-18]-fluoride ion treated above into contact with a weakly basic anion exchange resin to make [F-18]-fluoride ion adsorbed to the resin and, along therewith, to recover the [O-18]-enriched water which has passed through the resin, and the step of eluting and collecting the [F-18]-fluoride ion adsorbed to the weakly basic anion exchange resin.
As compared with the prior method of concentrating and separating [F-18]-fluoride ion from [O-18]-enriched water containing [F-18]-fluoride ion by using a strongly basic anion exchange resin, which method shows a low collection efficiency, the method for preparing [F-18]-fluoride ion according to the present invention makes it possible to prepare [F-18]-fluoride ion at a high collection efficiency even from a larger amount (about 2 ml or more) of [O-18]-enriched water containing [F-18]-fluoride ion than previously.
In the prior method, moreover, a purification operation, such as distillation, is necessary for reusing the recovered [O-18]-enriched water for preparing [F-18]-fluoride ion. According to the present invention, on the other hand, since impurity cations are removed by the treatment with the strongly acidic cation exchange resin as the preliminary step for making [F-18]-fluoride ion adsorbed to the weakly basic anion exchange resin, the recovered [O-18]-enriched water can be reused without purification.
Therefore, according to the present invention, [O-18]-enriched water, which is very expensive, can be reused while the loss of the water is suppressed to the minimum.
The [O-18]-enriched water used in the present invention is a water in which 99.7% of oxygen atoms constituting water molecules consist of an oxygen isotope of mass number 18. Proton irradiation of the water forms [F-18]-fluoride ion, which are obtained in the form of anion contained in [O-18]-enriched water.
In the proton irradiation of [O-18]-enriched water, the water is placed in a target box made of metal, such as stainless steel or silver, so that the irradiated water contains cations as impurities which have dissolved out of the target box. When the impurity cations form salts with fluoride ions, it is difficult to adsorb [F-18]-fluoride ion with a weakly basic anion exchange resin. Further, when impurity cations are present as a contaminant in the recovered [O-18]-enriched water obtained after concentration and separation of [F-18]-fluoride ion, the [O-18]-enriched water cannot be reused for the preparation of [F-18]-fluoride ion unless having been subjected to purification, such as distillation.
The present inventors have succeeded in solving the above-mentioned problems by bringing [O-18]-enriched water containing [F-18]-fluoride ion into contact with a strongly acidic cation exchange resin and thereby removing impurity cations therefrom.
The strongly acidic c
Ino Sento
Itoh Osamu
Tamura Masahiko
Nguyen Ngoc-Yen
Nihon Medi+Physics Co., Ltd.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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