Hi,

I am producing 18F-FLT on a modified FDG synthesizer, starting with 20mg of "Boc-Tryt- Nos" precursor. Given the limitations of the box i am using, I perform the hydrolysis in 2 mL of HCl 0.2M at 105 degrees, the solution is filtered through and alumina sep-pack after cooling and the vial and alumina seppak rinsed with 1 ml of H2O. The pH of the crude solution before HPLC is 6.5.
I then inject the solution (prealalbly filtered on 0.22 microns filter) on a semi-prep Luna column RP18 5 microns on a 2 ml loop, using H2O/EtOH 92/8 as solvent at 5mL.min. I collect the 18F-FLT peak at 15-16 min. However it sometimes presents a UV impurity that comes out in the "background" during semiprep- purification but at 3.8 min in analytical HPLC same solvent (1ml.min).

The impurity is not present at every synthesis using stricly the same reaction and purification conditions. I have not been able to identify this impurity yet.

Thanks