Electrospray ionization has also been achieved at pressures as low as 25 torr and termed subambient pressure ionization with nanoelectrospray (SPIN) based upon a two-stage ion funnel interface developed by Richard D. Smith and coworkers [REF].
Extractive electrospray ionization is an spray-type, ambient ionization method that uses two merged sprays, one of which is generated by electrospray [REF].