METHOD FOR TRANSFERRING A RADIOISOTOPE BETWEEN TWO STATIONARY PHASES CONTAINED IN TWO CHROMATOGRAPHY COLUMNS

Abstract

A method for transferring a radioisotope which is fixed on a first stationary phase contained in a first chromatography column to a second stationary phase contained in a second chromatography column, to fix the radioisotope on the second stationary phase, wherein the radioisotope is selected from the radioactive isotopes of thorium, radium, lead, bismuth and uranium, the method comprising at least the following steps: a) eluting the radioisotope from the first stationary phase with an aqueous solution A1 comprising an agent complexing the radioisotope, whereby an aqueous solution A2 which comprises complexes of the radioisotope is obtained; b) dissociating the complexes of the radioisotope present in the aqueous solution A2 by modifying the pH of the aqueous solution A2, whereby an aqueous solution A3 comprising the decomplexed radioisotope is obtained; c) loading the second stationary phase with the aqueous solution A3; and d) washing at least one the second stationary phase with an aqueous solution A4.

Claims

1. A method for transferring a radioisotope which is fixed on a first stationary phase contained in a first chromatography column to a second stationary phase contained in a second chromatography column, to fix the radioisotope on the second stationary phase, the radioisotope being a radioactive isotope of thorium, radium, lead, bismuth or uranium, which comprises at least the following steps: a) eluting the radioisotope from the first stationary phase with an aqueous solution A1 comprising an agent complexing the radioisotope, whereby an aqueous solution A2 which comprises complexes of the radioisotope is obtained; b) dissociating the complexes of the radioisotope present in the aqueous solution A2 by modifying a pH of the aqueous solution A2, whereby an aqueous solution A3 comprising the radioisotope in decomplexed form is obtained; c) loading the second stationary phase with the aqueous solution A3; and d) washing at least once the second stationary phase with an aqueous solution A4.

2. The method of claim 1, wherein the agent complexing the radioisotope is an aminopolycarboxylic acid or an aminopolycarboxylic acid salt.

3. The method of claim 2, wherein the aminopolycarboxylic acid is nitrilotriacetic acid, ethylenediaminetetraacetic acid or diethylenetriaminepentaacetic acid.

4. The method of claim 1, wherein the aqueous solution A1 comprises from 10 mmol/L to 100 mmol/L of ethylenediaminetetraacetic acid or a salt thereof and has a pH of 4 to 8.

5. The method of claim 4, wherein the aqueous solution A1 comprises 25 mmol/L of ethylenediaminetetraacetic acid or a salt thereof and has a pH of 6±0.5.

6. The method of claim 1, wherein the modification of the pH of the aqueous solution A2 is an acidification to bring the pH of the aqueous solution A2 to a value at most equal to 1.

7. The method of claim 6, wherein the acidification of the aqueous solution A2 comprises an addition of an acid to the aqueous solution A2.

8. The method of claim 6, wherein the acidification of the aqueous phase A2 comprises at least one washing of the first stationary phase with an acidic aqueous solution and an addition of all or part of the aqueous solution issued from the washing to the aqueous solution A2.

9. The method of claim 8, wherein the acidic aqueous solution comprises from 0.01 mol/L to 0.1 mol/L of nitric acid or from 0.1 mol/L to 1 mol/L of hydrochloric acid.

10. The method of claim 1, wherein the aqueous solution A4 comprises from 0.5 mol/L to 4 mol/L of nitric acid or from 2 mol/L to 4 mol/L of hydrochloric acid.

11. The method of claim 1, which further comprises, before step a), a step of conditioning the first stationary phase.

12. The method of claim 1, wherein the first stationary phase consists of a first stationary phase material, the second stationary phase consists of a second stationary phase material and the first and second stationary phase materials are identical.

13. The method of claim 1, wherein the first stationary phase consists of a first stationary phase material, the second stationary phase consists of a second stationary phase material and the first and second stationary phase materials are different.

14. The method of claim 1, wherein the radioisotope is thorium-228.

15. The method of claim 14, wherein at least one of the first stationary phase and second stationary phase consists of particles comprising a polymer functionalised by molecules of a ligand of thorium.

16. The method of claim 15, wherein the polymer is a polymethacrylate or a poly(styrene-co-divinylbenzene), and the ligand of thorium-228 is N,N,N′,N′-tetraoctyldiglycolamide, di(2-ethylhexyl)phosphoric acid, trioctylphosphine oxide or a mixture thereof.

17. The method of claim 3, wherein the aminopolycarboxylic acid is ethylenediaminetetraacetic acid

18. The method of claim 7, wherein the acid is nitric or hydrochloric acid.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0058] FIG. 1, previously described, represents the radioactive decay chain of thorium-232.

[0059] FIG. 2 schematically represents the different steps of an example of implementation of the method according to the invention.

DETAILED DISCLOSURE OF A SPECIFIC IMPLEMENTATION

[0060] Reference is made to FIG. 2 which represents schematically the different steps of an example of implementation of the method according to the invention for transferring thorium-228 from a first DGA DN resin, referenced 20, contained in a first chromatography column, referenced 10, to a second DGA DN resin, referenced 50, contained in a second chromatography column 40.

[0061] The first chromatography column 10 is, for example, a used radium-224 generator whereas the second chromatography column 40 is intended to constitute a new radium-224 generator.

[0062] In this implementation, the method comprises the following steps:

[0063] 1. conditioning the resin 20 with an aqueous nitric or hydrochloric acid solution;

[0064] 2. eluting the thorium-228 fixed on the resin 20 with an aqueous solution A1 which comprises EDTA, and collecting in a receptacle, referenced 30, such as a beaker, flask or similar, the eluate—or aqueous solution A2—comprising thorium-228 in the form of EDTA-.sup.228Th complexes;

[0065] 3. dissociating the EDTA-.sup.228Th complexes by acidifying the eluate to bring its pH to a value at most equal to 1, whereby an aqueous solution A3 comprising decomplexed thorium-228 is obtained;

[0066] 4. loading the resin 50 with the aqueous solution A3 to fix on this resin the decomplexed thorium-228 resin present in this solution; and

[0067] 5. washing the stationary phase 50 with an aqueous nitric or hydrochloric acid solution A4.

[0068] All these steps, which are detailed hereinafter, are performed at ambient temperature, i.e. at a temperature of 20° C. to 25° C.

[0069] *Step 1:

[0070] The column 10 comprises a DGA DN resin (Triskem International/Eichrom) 20 loaded with thorium-228.

[0071] This type of resin, which is presented in particle form, retains thorium, regardless of the isotope, but does not retain radium, regardless of the isotope.

[0072] The resin 20 was subjected to several production cycles of radium-224 each comprising a period during which thorium-228 was allowed to produce radium-224 by radioactive decay followed by an elution of the radium-224 thus produced.

[0073] These elutions having been carried out with 2 mol/L nitric acid or 3 mol/L hydrochloric acid solutions, the resin 20 is firstly conditioned to lower the acidity prevailing in the interstitial volume of this resin so as to prevent the EDTA used in step 2 hereinafter from precipitating during this step.

[0074] This conditioning is carried out by circulating in the column 10 several BVs, for example 3 BVs, at a flow rate between 0.1 mL/min and 5 mL/min, of an aqueous solution which comprises either nitric acid or hydrochloric acid—with a preference for nitric acid—at a concentration substantially less than or equal to that exhibited by the solutions having been used for the elutions of radium-224.

[0075] This concentration is, for example, 0.5 mol/L for an aqueous nitric acid solution and 2 mol/L for an aqueous hydrochloric acid solution.

[0076] *Step 2:

[0077] The elution of the thorium-228 from the resin 20 is carried out by circulating in the column 10 several BVs of aqueous solution A1, which typically comprises from 10 mmol/L to 100 mmol/L and, preferably, 25 mmol/L of EDTA and has a pH of 4 to 8 and, preferably, equal to 6±0.5.

[0078] For an optimal elution, 10 BVs of aqueous solution A1 are used at a flow rate ranging from 0.1 mL/min to 5 mL/min and, preferably, equal to 1 mL/min, the 10 BVs optionally being circulated continuously (i.e. in one go) or discontinuously, i.e. in two goes separated by one another by a break of a few minutes.

[0079] *Step 3:

[0080] As mentioned above, this step consists of acidifying the eluate—or aqueous solution A2—collected in step 2 in the receptacle 30 to bring the pH of this eluate to a value at most equal to 1.

[0081] This acidification makes it possible not only to obtain a dissociation of the EDTA-.sup.228Th complexes present in the eluate since the EDTA is in cationic form at a pH equal to or less than 1 but also to give the eluate a favourable pH for a retention of thorium-228 on a DGA DN resin. These two combined effects therefore make it possible to refix thorium-228 on the resin 50 in step 4 hereinafter.

[0082] The acidification of the eluate can be carried out: [0083] either by simply adding nitric or hydrochloric acid—with a preference for nitric acid—to the eluate present in the receptacle 30; [0084] or, as illustrated in FIG. 2, by subjecting the resin 20 to two successive washings, each of these washings being carried out with an acidic aqueous solution, and adding the solutions from these washings to the eluate present in the receptacle 30.

[0085] The first washing is, for example, carried out by circulating in the column 10 several BVs, for example 3 BVs, of an aqueous solution comprising: [0086] either from 0.01 mol/L to 0.1 mol/L and, preferably, 0.1 mol/L of nitric acid; [0087] either from 0.1 mol/L to 1 mol/L and, preferably, 0.1 mol/L of hydrochloric acid.

[0088] The second washing is, for example, carried out by circulating in the column 10 several BVs, for example 3 BVs, of an aqueous solution comprising: [0089] either from 0.5 mol/L to 4 mol/L and, preferably, 0.5 mol/L of nitric acid; [0090] either from 2 mol/L to 4 mol/L and, preferably, 2 mol/L of hydrochloric acid.

[0091] In both cases, preference is given, once again, to aqueous nitric acid solutions.

[0092] The circulation rates in the column 10 of the aqueous solutions used for the washings are advantageously from 0.1 mL/min to 5 mL/min.

[0093] As illustrated in FIG. 2, the solutions issued from the washings can be collected directly, at the outlet of the column 10, in the receptacle 30 wherein the eluate is located.

[0094] Alternatively, they can be collected in a receptacle other than the receptacle 30 and then be added to the eluate present in the receptacle 30.

[0095] It should be noted that, during the acidification of the eluate, EDTA can precipitate then be redissolved virtually entirely. Also, regardless of the methods selected to acidify the eluate, it is preferable for this acidification to be carried out under stirring to ensure a homogeneity of the acidified eluate—or aqueous solution A3—and, therefore, its stability, once the EDTA has redissolved.

[0096] As a precautionary measure, the aqueous solution A3 can optionally be filtered, for example by means of a filter of porosity 0.2 μm, before proceeding with step 4.

[0097] *Step 4:

[0098] The column 40 is, preferably completely identical to the column 10, with the same bed volume and the same mass quantity of DGA DN resin, except that this resin is free from any prior use.

[0099] The loading of the column 40 with the aqueous solution A3 is carried out by circulating this solution in the column 40, preferably at a low flow rate, for example from 0.1 mL/min to 5 mL/min, so as to favour the retention of the thorium-228 at the head of the column.

[0100] *Step 5:

[0101] The washing of the resin 50 is carried out by circulating in the column 40 several BVs of aqueous solution A4, which typically comprises: [0102] from 0.5 mol/L to 4 mol/L and, preferably, 0.5 mol/L of nitric acid; or [0103] from 2 mol/L to 4 mol/L and, preferably, 2 mol/L of hydrochloric acid.

[0104] Once again, preference is given to nitric acid.

[0105] For optimal washing, 20 BVs of aqueous solution A4 are used at a flow rate ranging from 0.1 mL/min to 5 mL/min and, preferably, equal to 2.5 mL/min.

[0106] The implementation of the method according to the invention using a column 10 and a column 40 each having a BV of 7.2 mL and each containing 3.3 g of DGA DN resin (particle size: 50-100 μm) as well as the following operating parameters: [0107] step 1: conditioning of the resin 20 by circulation in the column 10 of 5 BVs of an aqueous solution comprising 0.5 mol/L of nitric acid, at a flow rate of 0.5 mL/min; [0108] step 2: elution of thorium-228 by circulation in the column 10 of 10 BVs of an aqueous solution A1 comprising 25 mmol/L of EDTA and of pH equal to 6±0.5, at a flow rate of 1 mL/min; [0109] step 3: addition to the aqueous solution A2 from step 2 of 2 BVs of a nitric acid solution comprising about 14 mol/L of HNO.sub.3 (i.e. 65% by mass); [0110] step 4: loading of the resin 50 by circulation in the column 40 of the 12 BVs obtained in step 3, at a flow rate of 2.5 mL/min; [0111] step 5: washing of the resin 50 by circulation in the column 40 of 5 BVs of an aqueous solution A4 comprising 0.5 mol/L of nitric acid, at a flow rate of 0.5 mL/min; made it possible to transfer more than 99% of the activity of the thorium-228 retained by the resin contained in the column 10 at the time t0 of the implementation of the method to the resin contained in the column 40.