Integrated Quantification and Identification of Aldehydes
and Ketones in Biological Samples
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Abstract
The
identification of unknown compounds remains to be a bottleneck of
mass spectrometry (MS)-based metabolomics screening experiments. Here,
we present a novel approach which facilitates the identification and
quantification of analytes containing aldehyde and ketone groups in
biological samples by adding chemical information to MS data. Our
strategy is based on rapid autosampler-in-needle-derivatization with <i>p</i>-toluenesulfonylhydrazine (TSH). The resulting TSH-hydrazones
are separated by ultrahigh-performance liquid chromatography (UHPLC)
and detected by electrospray ionization-quadrupole-time-of-flight
(ESI-QqTOF) mass spectrometry using a SWATH (Sequential Window Acquisition
of all Theoretical Fragment-Ion Spectra) data-independent high-resolution
mass spectrometry (HR-MS) approach. Derivatization makes small, poorly
ionizable or retained analytes amenable to reversed phase chromatography
and electrospray ionization in both polarities. Negatively charged
TSH-hydrazone ions furthermore show a simple and predictable fragmentation
pattern upon collision induced dissociation, which enables the chemo-selective
screening for unknown aldehydes and ketones via a signature fragment
ion (<i>m/z</i> 155.0172). By means of SWATH, targeted and
nontargeted application scenarios of the suggested derivatization
route are enabled in the frame of a single UHPLC-ESI-QqTOF-HR-MS workflow.
The method’s ability to simultaneously quantify and identify
molecules containing aldehyde and ketone groups is demonstrated using
61 target analytes from various compound classes and a <sup>13</sup>C labeled yeast matrix. The identification of unknowns in biological
samples is detailed using the example of indole-3-acetaldehyde