High resolution MS scans enable a broad variety of analytical possibilities. Complex
data sets are more and more used for chemometric projections besides the general use
of structure elucidation and quantification. Well established multivariate data analysis,
e.g. metabolomics, requires commercial software tools and profound knowledge to interpret
the validity of the corresponding model. However, in the case of unknown chemical
profiles a general overview on molecular subclasses is often the first step to focus
the following evaluation. In this work we present a simple approach for the initial
characterization and profiling of herbal drugs using mass defect plots. The mass defect,
which is the result of the free binding energy of atoms, can either be calculated
for any molecule of interest by their molecular formula or from high resolution m/z values from HR-MS scan profiles. In the first step we calculated a large number of
common secondary plant metabolites that represent a varied mixture of molecular classes
in polarity, glycosylation, alkylation etc. In addition, we validated the calculation
with qualified reference substances measured with HR-ToF-MS (ESI neg. and pos.). The
plot of the relative mass defect versus the m/z of the pseudo molecular ions is the basis for further analyses and represents a kind
of “molecular map” (Fig. top). Subsequently, we analyzed a variety of herbal drugs
with well described compositions to confirm our approach (Fig. bottom). The data processing
includes automated peak detection, isotope filtering, solvent blank correction and
elimination of adduct and fragment signals. The corresponding mass defect plots allow
fast and detailed overviews of secondary plant metabolites detectable with MS.
Fig. 1: Top: Molecular map – theoretical mass defect plot of common secondary plant metabolites
which can be calculated for any substance of interest. Bottom: Mass defect plot of a flavonoid rhich plant shows its typical composition (HR-MS
data).
Keywords: High Resolution Mass Spectrometry – Analysis – Metabolites – Mass Defect Plot
