HPLCMS techniques in DOM analysisESIITMS and DOM

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HPLC-MS techniques in DOM analysis/ESI-ITMS and
DOM

• Leif Kronberg, Åbo Akademi University

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• ESI-ITMS Electro Spray Ionisation Ion
  Trap Mass Spectrometry
• A new method for characterisation of NOM
• Only a few reports have been pulished on the
  method till now
• One of the most important is
• Jerry A. Leenheer et al. Anal. Chem. 2001, 73,
  1461

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ESI

• An extremely soft ionisation method
• Produces MH and M-H- ions
• These ions are very stable ? in many cases no
  fragmentation is observed
• The MS of one compound gives only one peak

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ESI-Mass Spectrum of a Single Compound, M-H-
The molecular weight of the compound is 300
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ESI-Mass Spectrum of Two Compounds, M-H-
The molecular weight of the compounds are 200 and
300, resp.
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ESI-Mass Spectrum of Three Compounds, M-H-
The molecular weight of the compounds are 140,
200 and 300, resp.
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ESI-Mass Spectrum of Short-Chained Polymers,
MH
The molecular weights of the polymers are 1711,
1564, 1448, 1301 ....
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ESI-Mass Spectrum of Natural Polymers Fulvic
Acids

• Most of the peaks represent M-H- ions.
• It is possible to determine the average molecular
  weight distribution (Mw) ? m/z 914
• This value is slightly lower than the value given
  by other methods

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It is most likely that the Mw of NOM is affected
by photochemical processesThis can be studied
by electrospray mass spectrometry
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Further applicabilities of Ion Trap MS

• The ion trap has a built in function of ion
  storage and ion fragmentation
• A single preselected ion, M-H- can be stored
  and fragmented
• We get a mass spectrum of M-H-

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The MS/MS spectrum of the polymer at m/z 1565.9
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The MS/MS Spectrum of 1565.9 Interpretation of
the Fragmentation
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Application of the MS/MS/MS... feature to NOM
fulvic acids (1/4)
M-H- 329 was isolated and fragmented ?
MS2 m/z 311 ? loss of water
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Application of the MS/MS/MS... feature to NOM
fulvic acids (2/4)
MS3 (329 ? 311)
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Application of the MS/MS/MS... feature to NOM
fulvic acids (3/4)
MS4 (329 ? 311 ? 293) m/z 109, 165, 205 and
275 The simplicity of the spectra indicates that
the ion at m/z 293 is due to a single compound
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Application of the MS/MS/MS... feature to NOM
fulvic acids (4/4)
MS5 (329 ? 311 ? 293 ? 275) m/z 109 m/z
109 can not be further fragmented
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• As the number of MS stages increases, the spectra
  become increasing simple until only one product
  ion is detected which cannot further fragment
• Starting form the simple spectra, molecular
  structures of increasing complexity can be
  elucidated

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Leenheer et al. have proposed a structure for m/z
329 which accounts for the observed
fragmentation pattern
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Further fragmentation of m/z 293
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• It might be the case that there are unique
  structures in NOM that arise from photochemical
  degradation of humic material
• These may be identified by mass spectrometry
  using ion traps

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Further applications of ESI-ITMS

• SEC-LC ?
• we get the masses of the fractions
• more simple mass spectra ? easier to interpret
• Neutral loss scan ?
• identification of ions, masses, containing a
  specific functional group