How are compounds that are unstable at room temperature characterised using HPLC?

Answer 1

A simple answer to this question is that they aren't. However, by knowing something about how the molecule in question will decompose at room temperature, we can potentially use HPLC to separate the mixture of compounds formed in the decomposition, and HPLC can be used in tandem with analytic methods such as Mass Spectrometry to ascertain the molecular mass of the analyte and it's daughter ions.