Metabolomic studies of human gastric cancer: Review

Table 2 Comparison of different analytical techniques employed in metabolomics

Method	Sampling characteristics	Sensitivity	Advantages	Disadvantages	Ref.
Nuclear magnetic resonance (NMR) spectroscopy	Non-destructive; minimum sample required	10-6	Fully automated with a high degree of reproducibility; relatively easy to identify metabolites from simple one-dimensional spectra	Lower sensitivity than mass spectrometry; co-resonant metabolites can be difficult to quantify; drug metabolites can be co-resonant with metabolites of interest	[20,41,105]
Gas chromatography-mass spectrometry (GC-MS)	Requires extraction, sample dried and chemical derivation	10-12	A relatively cheap and reproducible method with a high degree of sensitivity	Sample preparation can be time consuming; not all compounds are suitable for gas chromatography	[20,41,106,107]
Liquid chromatography-mass spectrometry (LC-MS)	Requires extraction and concentration (vacuum drying), liquid-liquid extraction	10-15	This method is increasingly being used in place of GC-MS as sample preparation is not as time consuming; has a sensitivity similar to GC-MS	More costly than GC-MS and depends on the reproducibility of liquid chromatography (more difficult to control than GC); can also suffer from ion suppression	[20,41,108,109]
Fourier-transform infrared (FT-IR) spectrometry	Uses vibrational frequencies of metabolites to produce a fingerprint of metabolism	10-6	Cheap and good for high-throughput first screening	Very difficult to identify which metabolites are responsible for causing changes; very poor at distinguishing metabolites within a class of compounds	[20,41,110,111]
Raman spectroscopy	Non-destructive; minimum sample required, occasionally hydration is needed	10-6	Has the advantage over FT-IR in that water has only a weak Raman spectrum; therefore, many functional groups can be observed	Very poor at distinguishing classes of compounds	[20,41,110,111]