Chemical derivatization and mass spectral libraries in metabolic profiling by GC/MS and LC/MS/MS

An overview is presented of gas chromatography/mass spectrometry (GC/MS) and liquid chromatography/mass spectrometry (LC/MS), the two major hyphenated tech-niques employed inmetabolic profiling that complement direct ‘fingerprinting ’ methods such as atmospheric pressure ionization (API) quadrupole time-of-flight MS, API Fourier transform MS, and NMR. In GC/MS, the analytes are normally derivatized prior to analysis in order to reduce their polarity and facilitate chromato-graphic separation. The electron ionization mass spec-tra obtained are reproducible and suitable for library matching, mass spectral collections being readily avail-able. In LC/MS, derivatization and librarymatching are at an early stage of development and mini-reviews are provided. Chemical derivatization can dramatically in-crease the sensitivity and specificity of LC/MS methods for less polar compounds and provides additional struc-tural information. The potential of derivatization for metabolic profiling in LC/MS is demonstrated by the enhanced analysis of plant extracts, including the po-tential to measure volatile acids such as formic acid, difficult to achievebyGC/MS. The important role ofmass spectral library creation and usage in these techniques is discussed and illustrated by examples. Key words: Derivatization, electrospray ionization, food analy-sis, gas-liquid chromatography-mass spectrometry, ion trap, liquid chromatography-mass spectrometry, urine analysis, mass spectral library, metabolic profiling, tandem mass spec-trometry, time-of-flight