587 08 wk05aa mass spec contd std

587 08 wk05aa mass spec contd std - Mass Spectrometry...

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1 Mass Spectrometry continued… Electrospray Ionization ESI Utilizes an electric field to spray fine droplets a dilute solution is sprayed from a fine needle Evaporation of the volatile solvent occurs H 2 O, CH 3 OH, or CH 3 CN Results in increased Coulombic repulsion between the positive charges This causes fragmentation of the droplet, generating smaller droplets when the needle carries a positive potential droplets have an excess of positive charges (protons)
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2 ESI ESI ion formation theories (not completely known) the ionized sample molecules are expelled from the droplets, or the single ionized sample molecules remain after continuous solvent evaporation and droplet fragmentation ESI facts: the ions generated by ESI carry multiple charges provided the MW is > 1000 amu ESI spectral features generally the larger the MW, the more charges it accrues charge increases proportionally with MW ESI key points it is the multi-charging phenomenon that allows the
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587 08 wk05aa mass spec contd std - Mass Spectrometry...

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