Patent Number: 056195451
Section: summary

FIELD OF THE INVENTION The invention is in the field of radioisotopes. More particularly, the invention relates to a process for purifying radioiodides. BACKGROUND OF THE INVENTION Routine manufacturing of Iodides also results in production of iodate ions (IO.sub.3 -) and other impurities. If the end use for the Iodide is for medical diagnostic purposes, any iodate ions or other impurities must be below mandated limits. Also, iodide ions adversely affect radiolabelling of organic molecules. The present invention provides a new process for purifying desired radioiodide from iodate and other impurities. SUMMARY OF THE INVENTION The invention relates to a process for purifying radioiodides which comprises: a) passing a recovered solution of iodide over a anion exchange resin; PA1 b) washing the ion exchange resin in (a) with a solution comprising a weak base solution or anionic ion; PA1 c) washing the ion exchange resin in (a) with a stronger solution than used in (b); and PA1 d) recovering a solution containing the desired iodide ion. Benefits of the new process include the recovery of the desired iodide ion without the iodate and other impurities. DETAILED DESCRIPTION OF THE INVENTION The general process for the manufacture of iodides can be exemplified by the manufacture of .sup.123 I produced in a cyclotron. The production of .sup.123 I iodide involves proton irradiation of a cyclotron target vessel that has been filled with pure .sup.124 Xe gas. A mixture of product isotopes is produced. The isotopes produced include .sup.123 Xe, .sup.123 Cs and .sup.123 I. For a final product of .sup.123 I, the .sup.123 Xe isotope and .sup.123 Cs isotope are allowed to decay to .sup.123 I. The target .sup.124 Xe gas is recovered, with the desired .sup.123 I product left in the target vessel. The target vessel is filled with pure water and heated to absorb the iodide products. The water, now containing the iodide products, is washed through an ion exchange resin to absorb the iodide ions. At this point, the ion exchange resin is generally eluted with a 0.02N sodium hydroxide solution in order to release the desired iodide solution in a concentration suitable for further use. The process of the invention comprises a pre-wash step, before the 0.02N sodium hydroxide solution wash. The pre-wash step utilizes a solution that comprises a dilute base that removes impurities before the concentrated radioiodide solution is released by way of the 0.02N sodium hydroxide solution wash. The present invention is also applicable to other iodides besides the above described .sup.123 I. Other iodides that can be purified with the process of the invention include .sup.131 I, .sup.126 I, .sup.125 I.sup.124 I and .sup.121 I. The production of iodides can utilize any production method including cyclotrons and reactors. Typical cyclotron procedures are disclosed in "Cyclotron Production of Medically Useful Halogen Radioisotopes"; R. Weinreich, S.M. Qaim, and G. Stocklin, Nuclearmedizin (16) 1978, 226-31, "Cyclotron Production of High-Purity Iodine-123 for Medical Application"; J. A. Jungerman, M.C. Lagunas-Solar, Journal of Radioanalytical Chemistry, Vol. 65, No. 1-2 (1981) 31-45, and "Recent Developments in the Production of .sup.18 F, .sup.75,76,77 Br, and .sup.123 I", S. M. Qaim, Appl. Radiat. Sot., Vol. 37, No. 8, pp. 803-810, 1986. U.S. Pat. No. 4,622,201 also describes procedures useful in producing iodides. .sup.131 I can also be produced by neutron bombardment in a reactor and according to processes outlined in the Manual of Radioisotope Production, International Atomic Energy Commission, Vienna, Austria, 1966. Ion exchange resins useful in practicing the invention include any weak anion exchange resin. Examples of suitable ion exchange resins for use in the invention include BioRex 5, BioRex Macropore Q materials (BioRex, BioRad BioRad Laboratories, 2000 Alfred Nobel Drive, Hercules, Calif. 94547), Amberlite IRA 93, Amberlite IRA 94, Amberlite IRA 68, Amberlite IRA 35 (Sigma Chemical Co., St. Louis, Mo. 63178), Dowex WGR-2 (Sigma Chemical Co., St. Louis, Mo. 63178), Sephadex DEA A-25 and Sephadex DEA A-50 (Sigma Chemical Co., St. Louis, Mo. 63178). The goal in choosing a resin for use in the process of the invention is to match a base strength wash which is compatible with the specific weak basic resin in order to perform the separation. This separation is routinely optimized depending on the resins and base solutions chosen. Generic description of the column: The column which holds the resin is a holder, generally cylindrical in cross section, with a frit (screen) over both the top and bottom holding the resin in place. The column is constructed to provide for the eluent to be applied to the matrix material, disributed through that matrix, and collected for removal from the matrix. The matrix weight will generally be between 100 mg., and 5 grams. The weight (volume) is kept as low as practical so as to minimize the volume of eluant required for the rinsing operations since increased volumes, particularly for the iodide removal, should be as small as possible. The wash solutions useful for practice with the invention comprise any water soluble base solutions that will release iodide and/or iodate from an ion exchange resin. Examples of suitable water soluble base solutions for use in the invention include hydroxide, fluoride, acetate, formate and phosphate solutions. Typical strengths of these base solutions range from about 0.0005 to about 0.005. Typical stronger strength solutions range from about 0.005 to about 1.0N. Strengths of wash solutions employed will differ with respect to the resin used. Any anionic ion which will release iodide and/or iodate from an exchange resin can also be used with the invention. Ions such as OH.sup.-, F.sup.-, acetate.sup.-, formate.sup.-, and phosphate are examples of suitable ions for use in the invention. Recovery methods for obtaining the wash solutions include those generally known, such as those disclosed in U.S. Pat. No. 4,622,201.