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Limitations of electrospray ionization in the analysis of a heterogeneous mixture of naturally occurring hydrophilic and hydrophobic compounds
Author(s) -
Nebbioso Antonio,
Piccolo Alessandro,
Spiteller Michael
Publication year - 2010
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.4749
Subject(s) - chemistry , electrospray ionization , tripeptide , molecule , electrospray , aqueous solution , chromatography , ionization , mass spectrometry , hydrophilic interaction chromatography , hydrophobic effect , ion , organic chemistry , amino acid , high performance liquid chromatography , biochemistry
A model heterogeneous mixture of a hydrophilic tripeptide (phenylalanine‐glycine‐glycine, PGG) and hydrophobic organic acids ( 12 C‐ and 13 C‐octanoic acid and pentadecanoic acid) was subjected to electrospray ionization mass spectrometry (ESI‐MS). The objective was to verify the previously noted inconsistencies in ESI‐MS of complex environmental samples such as humic materials from either aquatic or terrestrial origins. The hydrophobic organic acids, either alone or together, reduced significantly the ESI‐MS detection of the tripeptide molecular and self‐associated ions at a concentration that was an order of magnitude lower than that of PGG. The most intense peaks were invariably those of the octanoic acid as either deprotonated, self‐associated, or acetate‐clustered molecules. The presence of equimolar amounts of PGG and organic acids yielded similar results, but with a significant increased detection of PDA and a smaller depression of the PGG signals. This behaviour is attributed to a different electrospray ionization of the mixture compounds depending on their most probable positioning at the surface of the evaporating droplet. The most favoured positioning of hydrophobic molecules at the aqueous‐gas interphase allows preferential evaporation of hydrophobic ions whereas the hydrophilic molecules are retained in the droplet interior, and, their ESI‐MS detection depressed. These findings suggest that the electrospray ionization of different molecules present in complex heterogeneous mixtures of environmental significance such as humic substances is limited by their concentration and reciprocal attracting forces. Copyright © 2010 John Wiley & Sons, Ltd.