On-line [11C]methylation using [11C]methyl iodide has been successfully applied to the preparation of l-[methyl-11C]-methionine (11C-Met). [11C]Methyl iodide is first trapped in a short column that contains Porapak Q and l-homocysteine thiolactone coated on inert support. The column is then charged with NaOH dissolved in a mixture of ethanol and water to cause the [11C]methylation. The present method can provide practically pure 11C-Met in radiochemical yield of over 98%. The whole procedure including the sterilization of final product has been completely automated for routine PET use.
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