Design Of Novel GD-ESI Ionization Source And Its Application In MS Of Small Molecules

Mass spectrometry has made great breakthrough and innovation in the past century since it was introduced by J.J.Thomson in 1912.It is increasingly applied as a rapid,effective,and sensitive analytical method.Mass spectrometry is an analytical technique that ionizes the molecules and sorts the charged ions based on their mass to charge ratio.A mass spectrum is finally displayed as a plot of ion abundance versus mass-to-charge ratio.Organic mass spectrometry method is an important branch of mass spectrometry,which is widely used in the analysis of diverse organic compounds and bio-molecules,such as small organic molecules,hydrocarbons,polymers,proteins,polysaccharides,and DNA,etc.The ionization methods of a mass spectrometer for analyzing organic compounds are classified to soft ionization methods and hard ionization methods.Generally,a mass spectrometer consists of six major parts,including an ion source,a mass analyzer,a detector,a vacuum system,control and data acquisition systems.The advance of modern mass spectrometers allows flexible combinations of different types of ion sources,mass analyzers,and detectors.In spite of these advanced commercial instruments,there are still some problems,such as(i)some species are hard to be ionized by traditional ionization methods,(ii)some compounds fail to produce molecular ions as they are fragile,(iii)different ion sources must be selected according to the properties of the analytes.Therefore,new ionization methods to obtain the molecular ions for kinds of analytes are highly desirable.To solve these problems,we have developed a dual electrospray(ESI)-glow discharge(GD)ionization ion source.In our ion source,a direct current glow discharge is generated by a couple of concentric electrodes similar to the reported FAPA method.Then,the GD ion source is coupled to an electrospray ion source.Glow discharge is a kind of self-maintained gas discharge phenomenon,discovered by Faraday.It is produced by the passage of electric current through a low-pressure gas.The new designed ion source in this work combine the advantages of ESI in the polar molecules analysis and the advantages of GD in the non-polar molecules analysis.This technique largely broaden the range of the analyte in the presence of diverse reagents.In GD mode,molecular ions in the form of oxidation peaks of weakly-polar or nonpolar compounds like alkanes,can be generated.Instead of fragment ions obtained by electron ionization(EI)mode,the proposed ion source provides an excellent approach for accurate measurement of molecular weights from which element compositions can be deduced.Besides,ESI spectra can be readily available by adjusting the voltages applied on this ion source.Therefore,it can be used for different analytes with diverse polarities by GD ionization mode coupled to ESI mode and applied in a wider area.