Sonic Spray Mass Spectrometry Mechanism and Characteristics

1
Sonic Spray Mass Spectrometry Mechanism and
Characteristics

• Sonic Spray Ionization
• Sonic Spray Setup and conditions
• How? Charged Droplet Formation and Ionization
  process
• Example Spectral Characteristics

2
Atmospheric Pressure Sonic Spray Conditions

• Sonic Spray Flow Conditions
• Coaxial flow of nitrogen at 3-4 L/min
• Fused silica capillary (0.1mm ID)
• Voltage can be used to enhance droplet charge
  density
• Multi-hole plate to diffuse spray gas

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Mechanism of Charged Droplet Formation by Sonic
Spray

• Charged Sonic Sprayed Droplets
• Dependent on surface potential and non-uniform
  ion concentrations at surface
• Fission of droplets
• Shear stress ? charged droplets
• Non-uniformity of positive and negative ion
  concentrations can be enhanced by an external
  electric field
• At Sonic gas flow, a droplet undergoes fission
  and charged droplets produced

Non-uniformity of positive and negative ion
concentrations are generated near the droplet
surface due to the surface potential
Formation of fine charged droplet from a neutral
droplet in which the positive and negative ion
concentrations are not uniform
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Sonic Spray Characteristics

• Characteristic Features
• Shear stress --? charged droplet formation
• Ion Intensity dependent on gas velocity
• Fine charged droplets dependent on gas velocity
  (based on ion current measurements) and much less
  dependent on solution flow rate
• Droplet size minimum at sonic velocity
• Sonic Spray Ionization - Fine charged droplets
  and ions are produced. Ion Desorption Ion
  Evaporation Model

Ion Intensity as a function of the gas flow rate.
It has also been shown that Ion current shows a
very similar dependency on flow rate
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Sonic Spray Spectral Characteristics Example
of Similarity to ESI
Okadaic Acid SSI-MS Spectrum
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Sonic Spray Spectral Characteristics - Chitosan
Oligosaccharide
Chitosan Pentamer C30H57N5O21 M.W.823
Chitosan Hexamer C36H68N6O25 M.W.984
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SSI-MS Spectrum of Ganglioside-GM1
Sonic Spray Ionization Negative ion mode
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Acknowledgment
Central Research Laboratory, Hitachi Tokyo
Japan Atsuma Hirabayashi, CRL, Hitachi Tokyo
Japan