M
ass spectrometry (MS) has evolved into one of the most sensitive analytical methods for the structural characterization of molecules.1,2 Ionization is critical for volatilizing sample analytes into a gas-phase. This primer covers a range of options which often require complementary equipment, such as syringe pumps, for efficient ionization.
Electrospray Ionization (ESI)
ESI is the most common form of ionization used for MS.3 It employs voltage to convert a flow of liquid to generate an electrospray. A combination of heat and acceleration toward the vacuum system forces electrostatically bound particles to dissociate by releasing water and drying the sample. The ions in gaseous phase pass through a voltage gradient before being ejected into the mass analyzer for detection. The use of syringe pumps for aerosolizing the sample can greatly enhance electrospray generation. ESI is mild enough to be used with thermally labile compounds such as proteins and pharmaceuticals and is often used in combination with liquid chromatography.
Atmospheric Pressure Chemical Ionization (APCI)
A needle generates a voltage discharge at atmospheric pressures which is applied to aerosolized samples in APCI.4 Precision syringe pumps inject liquid analytes at a controlled flow rate towards a heated gas for volatilization and exposure to ions created by the discharge. The new ions formed by proton transfer are then transported to a vacuum used for electrospray. Other variations of this technique include photoionization as well as ...
