What is the signal at around 2090 wavenumbers in the nitroguanidine FTIR spectrum? There is a signal at around 2090 apparent in the FTIR spectrum of nitroguanidine  from Sigma-Aldrich (first image). It's also apparent in FTIR spectra we've taken in the lab (second image), but when assigning peaks to bonds, we are unclear to what it is.

We are unsure of how Sigma-Aldrich prepared their pellets, but we used KBr. We are thinking perhaps KCN, but then again - how could that possible form?
Its common Nujol, a hydrocarbon oil used to prepare paste-samples for IR from powdered materials. Hence the C-H valence around 2090 cm-1