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Improved detection of glucuronide and glutathione conjugates with thermospray ionization following esterification
Author(s) -
Haroldsen Peter E.,
Baillie Thomas A.
Publication year - 1994
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.1290080506
Subject(s) - chemistry , conjugate , glucuronide , thermospray , glutathione , yield (engineering) , protonation , chromatography , ion , stereochemistry , mass spectrometry , organic chemistry , biochemistry , metabolite , tandem mass spectrometry , selected reaction monitoring , enzyme , mathematical analysis , materials science , mathematics , metallurgy
Abstract Analysis by thermospray of glucuronide and glutathione conjugates as the corresponding methyl‐, propyl‐, or hexyl esters is demonstrated to yield a remarkable increase in positive pseudomolecular ion production and to result in a dramatic improvement in detectability of these thermally labile compounds as intact molecular structures. In the most extreme examples a 450‐fold increase in the [M + NH 4 ] + ion intensity was observed for mycophenolic acid glucuronide bis‐propyl esters vs. the native conjugate and an 860‐fold increase in the [M + H] + ion intensity was achieved for acetaminophen glutathione bis‐hexyl ester vs. the native conjugate. Following esterification, seventeen of the eighteen glucuronide esters analyzed demonstrated an increase in totalion‐current yield ranging from 1.1‐ to 8.3‐fold while eighteen of the twenty‐one glutathione esters examined demonstrated an increase in totalion‐current yield from 2.0‐ to 26.3‐fold. For both types of conjugates a trend in increased relative abundance of the positive pseudomolecular ion intensity is observed as the hydrophobicity of the ester increases from methyl to hexyl. For the glutathione conjugate esters, the [M + H] + ion represented the base peak in the mass spectra of the majority of samples analyzed. This approach improves the protonated‐ or ammoniated‐molecular‐ion abundances of the conjugates to such an extent that it provides a means for unambiguous molecular weight assignments to be made. Although the exact mechanism(s) for the observed phenomenon is not known, it appears that the improvement in sensitivity for the conjugate esters over the corresponding native conjugates involves an increase in pseudomolecular‐ion stability and also in part an increased ionization efficiency of the esterified molecule.