Collision surface for improved ionisation

A method of spectrometric analysis comprises obtaining one or more sample spectra for an aerosol, smoke or vapor sample obtained using an ambient ionisation source, e.g. a rapid evaporative ionization mass spectrometry (REIMS) ion source. The one or more sample spectra are subjected to pre-processing and then multivariate and/or library-based analysis so as to classify the aerosol, smoke or vapour sample. The pre-processing of the one or more sample spectra comprises applying a non-linear (e.g. logarithmic- or power-based), variance stabilising function to the intensity values in said spectra to remove a correlation between intensity and intensity variance therein. The results of the analysis are used for various surgical or non-surgical applications.