Mass Spectral Library of Acylcarnitines Derived from Human Urine

We
describe the creation of a mass spectral library of acylcarnitines
and conjugated acylcarnitines from the LC–MS/MS analysis of
six NIST urine reference materials. To recognize acylcarnitines, we
conducted in-depth analyses of fragmentation patterns of acylcarnitines
and developed a set of rules, derived from spectra in the NIST17 Tandem
MS Library and those identified in urine, using the newly developed
hybrid search method. Acylcarnitine tandem spectra were annotated
with fragments from carnitine and acyl moieties as well as neutral
loss peaks from precursors. Consensus spectra were derived from spectra
having similar retention time, fragmentation pattern, and the same
precursor m/z and collision energy.
The library contains 157 different precursor masses, 586 unique acylcarnitines,
and 4 332 acylcarnitine consensus spectra. Furthermore, from
spectra that partially satisfied the fragmentation rules of acylcarnitines,
we identified 125 conjugated acylcarnitines represented by 987 consensus
spectra, which appear to originate from Phase II biotransformation
reactions. To our knowledge, this is the first report of conjugated
acylcarnitines. The mass spectra provided by this work may be useful
for clinical screening of acylcarnitines as well as for studying relationships
among fragmentation patterns, collision energies, structures, and
retention times of acylcarnitines. Further, these methods are extensible
to other classes of metabolites.