Although high mass species are easily ionised by electrospray ionisation it is not trivial to detect them with standard mass spectrometers. The ions are too energetic and can not be contained in the transfer region between source and analyser. With the high mass upgrade package, transmission and stability of large non-covalently bound complexes is greatly improved by a localised sleeve around the source hexapole. This increases the pressure leading to better collisional cooling of the ions. This effect is further exploited by adding a precision throttle valve in the source backing line, providing improved control over the pressure behind the sample cone. Additionally, a Pirani gauge is fitted for direct monitoring of the pressure inside the source.
