Ionization Methods for Mass Spectrometry Methods

Ionization Methods for Mass Spectrometry Methods

1. Electrospray

   • a solution is passed through a fine needle in an electric field, generating a spray of small droplets
     • the charged droplets evaporate almost instantly, leaving ions in the vapor phase
       • M/Z is then analyzed in the mass spectrometer
   • ions often have multiple charges
   • Advantages
     • good sensitivity
     • softest ionization method, capable of maintaining non-covalent complexes in gas-phase
     • easily adaptable to liquid chromatography
     • multiple charging allows for analysis of high mass ions with relatively low m/z range instrument
   • Disadvantages
     • presence of salts can reduce sensitivity
     • multiple charging can create confusion especially in mixture analysis
     • requires fairly pure samples

2. MALDI

   • Matrix Assisted Laser Desorption and Ionization
   • protein is diluted into a solid matrix (such as dihydroxybenzoic acid) and vaporized with a laser pulse
   • Advantages
     • particle mass range up to 300,000 Dа
     • good sensitivity
     • soft ionization-little to no fragmentation observed
     • salt tolerant to mM concentrations
     • suitable for analysis of complex mixtures
   • Disadvantages
     • photodegredation of sample can be observed at high laser fluence*/power
     • sample preparation methods are empirical (trial and error)

3. Electrospray and MALDI differ in the way that they generate ions