Labeling proteins at high specific activity using N-succinidyl 4-[18F](fluoromethyl) benzoate

High effective specific activity N-succinimidyl 4-[18F](fluoromethyl)benzoate was prepared using a reversed phase HPLC procedure. Reversed phase HPLC removed several additional impurities not removed by normal phase HPLC, thereby increasing the effective specific activity. Small amount (< 100 μg) of sensitive proteins such as erythropoietin can be labeled with this reagent in high yield without aggregation.