Abstract: An ion mobility analyzer includes at least one of a “differential mobility analyzer”, an “ion mobility spectrometer” and a “differential mobility spectrometer”, to which charged molecules of interest are fed. Ions are fed to the ion mobility analyzer from a “droplet pickup ion source” including an electrospray ion source at a capillary end, from which charged droplets formed from a solvent mixture having substantially none of the molecules of interest emerge. The charged droplets are pulled by an electric field into a “pickup region” filled with a buffer gas at a pressure or a region close to the surface of a sample, where the charged droplets incorporate the molecules of interest and transfer the charge of the charged droplets to the molecules of interest, when the liquid in the charged droplets has evaporated in a heated desolvation region that is separate or integral with respect to the “pickup region”.