ABSTRACT

The general aim of metabolomics is to analyze comprehensively all known and unknown metabolites in biological samples.1 The first generation of metabolomics research mainly focused on the development of a methodology for nontargeted

metabolome analysis to analyze all detectable metabolites without the preselection of targets. To detect a wider range of metabolites, nontargeted metabolome analyses have been performed while operating the mass spectrometer in full scan mode. Time-of-flight (TOF) analyzers are suitable for this purpose because of their higher scan speed and sensitivity.2-8 The high resolution of modern TOF analyzers is also preferred in order to characterize unknown metabolites by using accurate mass data.9,10 The nontargeted metabolome analysis strategy, using LC-TOF-MS, plays a critical role in the metabolomics research of plant secondary metabolites, because almost all detectable metabolite signals are unknown phytochemicals.11 However, in many biological applications, multitargeted or widely targeted data analyses have been performed using the raw data produced by nontargeted methodologies. The return to targeted analysis is due to the difficulty in the structural characterization of unknown metabolite signals based only on high-resolution and tandem mass spectral data.12,13 For analyses exploring the behavior of metabolic systems, the study can be performed using a data set of identified metabolites without considering the unknown metabolites.14