Take the IR spectrum. N=N stretching is very characteristic. I think it is around 1580 cm-1 (from memory) Check the lit. From [email protected]

It has been a year and you might have got the answer or figured it out already. We insert diazirines in steroids. Usually we convert a keto group into diazirine group in our synthesis. In the PMR spectrum of the diazirines we prepared, we could see few up field proton resonances (0.6 to 0.2 ppm) consistently. These up field resonances belong to the protons in the neighboring region of diazirine and, I believe  they are in the "shielding cone" of  the diazirine moiety. I did not care which specific protons are they and all but I always look for those up filed proton resonances in the diazirines we prepared to confirm that the diazirine has formed.  I would say these resonances are "signature" of  the steroidal dizirines we prepare. Please keep in mind, unlike diaziridines,  diazirines are very non-polar and they dont bind well in silica gel despite the fact that  they have couple of nitrogen atoms. In other words, the introduction of diazirine functional group in a molecule does not make that molecule to become more polar.

I'm using mass spectrometry... by the way, when I test the photolabeling reaction (UV, 30 min) in water with a mixture of aminoacids I can only obtain the product of the reaction with the solvent (water) and no sign of reaction with aminoacids... this looks very strange... I mean, statistically it's quite obvious becasue the equivalents of water are much higher than eq of aminoacids but I should see some reaction with aminoacids as well, shouldn't I? do you have any tip/trick?

Use IR to detect N=N streching or mass spec to detect  R-C(+)N2 ion. Also uv will give you characteristic absorption too.Good luck. If you do not have any of this,all the diazirine have reacted.