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Title: Utilizing the Inherent Electrolysis in a Chip-Based Nanoelectrospray Emitter System to Facilitate Selective Ionization and Mass Spectrometric Analysis of Metallo Alkylporphyrins

A commercially available chip-based infusion nanoelectrospray ionization system was used to ionize metallo alkylporphyrins for mass spectrometric detection and structure elucidation by mass spectrometry. Different ionic forms of model compounds (nickel (II), vanadyl (II), copper (II) and cobalt (II) octaethylporphyrin) were created by using two different types of conductive pipette tips supplied with the device. These pipette tips provide the conductive contact to solution at which the electrolysis process inherent to electrospray takes places in the device. The original unmodified, bare carbon-impregnated plastic pipette tips, were exploited to intentionally electrochemically oxidize (ionize) the porphyrins to form molecular radical cations for detection. Use of modified pipette tips, with a surface coating devised to inhibit analyte mass transport to the surface, was shown to limit the ionic species observed in the mass spectra of these porphyrins largely, but not exclusively, to the protonated molecule. Under the conditions of these experiments, the effective upper potential limit for oxidation with the uncoated pipette tip was 1.1 V or less and the coated pipette tips effectively prevented the oxidation of analytes with redox potentials greater than about 0.25 V. Product ion spectra of either molecular ionic species could be used to determine the alkyl chainmore » length on the porphyrin macrocycle. The utility of this electrochemical ionization approach for the analysis of naturally occurring samples was demonstrated using nickel geoporphyrin fractions isolated from Gilsonite bitumen. Acquiring neutral loss spectra as a means to improve the specificity of detection in these complex natural samples was also illustrated.« less
Authors:
 [1] ;  [1]
  1. ORNL
Publication Date:
OSTI Identifier:
1038803
DOE Contract Number:
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Analytical and Bioanalytical Chemistry; Journal Volume: 403; Journal Issue: 2
Research Org:
Oak Ridge National Laboratory (ORNL)
Sponsoring Org:
SC USDOE - Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; CATIONS; CHAINS; COBALT; COPPER; DETECTION; ELECTROLYSIS; INFUSION; IONIZATION; MASS SPECTRA; MASS SPECTROSCOPY; NICKEL; OXIDATION; PLASTICS; PORPHYRINS; RADICALS; REDOX POTENTIAL; SPECIFICITY; SPECTRA; SURFACE COATING; TRANSPORT electrospray; electrochemistry; oxidation; porphyrins; Gilsonite