yes, you are right! theoretically one should have almost no UV signal, the radiodector signal in the HPLC and the LSC give you the proof. But tha tis not the problem.
I have synthesized a peptide using the SPPS protocol with Fmoc-AA labelled with 3H (2 tritium atoms). I have purified and I have 1 mCi, but incredible high UV signal...dilution series shows me a pure compound, from the amount I have really a lot (I can actually see the substance, that is in the conditions where 1 mCi is 16 nmol! and my peptide is under 2000!!) so I did a mass with the same conditions as the cold peptide and I see a mass higher with 10 amu.
So, my questions: how come I have a signal so high in the UV? and so much amount that I can measure mass....in literature there is NO report of mass of any tritium labelled peptide...or maybe you know one?