An ion-exchange chromatograph/electrospray ionization
mass spectrometer (IC/ESI-MS) was used successfully to
identify organic and inorganic species present in topiramate tablets. An ion suppressor is placed between the
column and detectors to replace sodium ions in the
mobile phase with hydrogen ions supplied by the suppressor. The ensuing combination of the hydrogen ions
with the mobile phase hydroxide ions produces water and
thus allows simultaneous ion detection by an ion conductivity detector and a mass spectrometer. Analytes,
including lactate, glycolate, chloride, formate, sulfate, and
oxalate, were unambiguously identified by matching the
mass spectra and retention times with those of the
authentic compounds. Due to its capability of
detecting
positive and negative as well as neutral species, ESI-MS
provides valuable information which is not available with
ion conductivity detection alone. Though the coupling
of
ion-exchange chromatography to mass spectrometry has
been reported previously, this is the first demonstration
of IC/ESI-MS for the identification of unknown species
in real samples. Finally, with the use of deuterium/carbon-13 labeling and MS/MS techniques, we have
confirmed that oxalic acid (HOOC-COOH) is formed from
formic acid (HCOOH) at the electrospray interface in the
presence of the electric field. This observation not
only
confirms the identity of an unknown peak, but it also
provides new insight into chemistry that can take place
during electrospray ionization.
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