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The detection of iron protoporphyrin (heme b) in phytoplankton and marine particulate material by electrospray ionisation mass spectrometry – comparison with diode array detection

The detection of iron protoporphyrin (heme b) in phytoplankton and marine particulate material by electrospray ionisation mass spectrometry – comparison with diode array detection
The detection of iron protoporphyrin (heme b) in phytoplankton and marine particulate material by electrospray ionisation mass spectrometry – comparison with diode array detection
A mass spectrometric (MS) method for the identification of iron protoporphyrin (IX) (FePTP, heme b) in marine particulate material and phytoplankton is described. Electrospray ionisation of FePTP produced the molecular Fe(III)PTP+ ion (m/z = 616) or the pseudomolecular [Fe(II)PTP + H]+ ion (m/z = 617), depending on the oxidation state of the central iron ion. Collision induced dissociation (CID) in the ion trap mass spectrometer resulted in a single detected product ion (m/z = 557) indicative of loss of ethanoic acid from a carboxylic acid side chain. Widening the isolation width to 616 ± 3 resulted in production of a mass spectrum demonstrating the distinctive isotopic ratio of the iron containing fragment, further increasing the specificity of the analysis. Selective reactant monitoring (SRM) of the fragment ion (m/z = 557) was applied to the detection of FePTP after chromatography of ammoniacal OGP extracts of marine samples. The detection limit for FePTP analysed by SRM after chromatography was 1.2 ± 0.5 fmol. For phytoplankton samples, reasonably good agreement was achieved between results obtained with SRM and those obtained by monitoring absorbance at ? = 400 nm using a diode array detector (DAD). Use of SRM for analysis of particulate material obtained from the high latitude North Atlantic allowed for the analysis of FePTP in the presence of a co-eluting compound that interfered with detection by DAD. Simultaneous collection of mass spectra from m/z = 300 to 1500 resulted in identification of the pseudomolecular ion for the interfering compound. The CID fragmentation pattern and UV–visible mass spectra indicated that the interfering compound was a previously unidentified chlorin type compound. Comparison of FePTP determined by SRM and DAD on samples where this compound could not be detected showed that results collected using the two methods correlated. The use of both MS and DAD results in a powerful tool for quantifying this important biogenic component of the particulate iron pool.
Iron, Ocean, Porphyrin, Chromatography, Tetrapyrrole
0003-2670
33-43
Gledhill, Martha
da795c1e-1489-4d40-9df1-fc6bde54382d
Gledhill, Martha
da795c1e-1489-4d40-9df1-fc6bde54382d

Gledhill, Martha (2014) The detection of iron protoporphyrin (heme b) in phytoplankton and marine particulate material by electrospray ionisation mass spectrometry – comparison with diode array detection. Analytica Chimica Acta, 841, 33-43. (doi:10.1016/j.aca.2014.06.045).

Record type: Article

Abstract

A mass spectrometric (MS) method for the identification of iron protoporphyrin (IX) (FePTP, heme b) in marine particulate material and phytoplankton is described. Electrospray ionisation of FePTP produced the molecular Fe(III)PTP+ ion (m/z = 616) or the pseudomolecular [Fe(II)PTP + H]+ ion (m/z = 617), depending on the oxidation state of the central iron ion. Collision induced dissociation (CID) in the ion trap mass spectrometer resulted in a single detected product ion (m/z = 557) indicative of loss of ethanoic acid from a carboxylic acid side chain. Widening the isolation width to 616 ± 3 resulted in production of a mass spectrum demonstrating the distinctive isotopic ratio of the iron containing fragment, further increasing the specificity of the analysis. Selective reactant monitoring (SRM) of the fragment ion (m/z = 557) was applied to the detection of FePTP after chromatography of ammoniacal OGP extracts of marine samples. The detection limit for FePTP analysed by SRM after chromatography was 1.2 ± 0.5 fmol. For phytoplankton samples, reasonably good agreement was achieved between results obtained with SRM and those obtained by monitoring absorbance at ? = 400 nm using a diode array detector (DAD). Use of SRM for analysis of particulate material obtained from the high latitude North Atlantic allowed for the analysis of FePTP in the presence of a co-eluting compound that interfered with detection by DAD. Simultaneous collection of mass spectra from m/z = 300 to 1500 resulted in identification of the pseudomolecular ion for the interfering compound. The CID fragmentation pattern and UV–visible mass spectra indicated that the interfering compound was a previously unidentified chlorin type compound. Comparison of FePTP determined by SRM and DAD on samples where this compound could not be detected showed that results collected using the two methods correlated. The use of both MS and DAD results in a powerful tool for quantifying this important biogenic component of the particulate iron pool.

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Published date: 2 September 2014
Keywords: Iron, Ocean, Porphyrin, Chromatography, Tetrapyrrole
Organisations: Ocean and Earth Science

Identifiers

Local EPrints ID: 368127
URI: http://eprints.soton.ac.uk/id/eprint/368127
ISSN: 0003-2670
PURE UUID: 53a49de1-b0aa-46ca-8399-2a416bb3b584

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Date deposited: 18 Aug 2014 10:07
Last modified: 15 Jul 2019 21:47

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Author: Martha Gledhill

University divisions

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