The TOF-MS 5000 is a simple mass spectrometer with a relatively narrow mass range (m/z 50–800), a reduced size (70 cm length × 65 cm width × 75 cm height), and lighter weight (85 kg), and thus no tandem mass spectrometry experiment could be implemented in this compact TOF-MS instrument. Detailed description of the TOF-MS instrument was documented elsewhere . The voltages were set as follows for this work: capillary voltage 140 V, focusing mirror voltage 135 V; positive pulse voltage 950 V, negative pulse voltage –950V, acceleration zone voltage −4100 V, grid voltage −90 V, reflex zone voltage 1340 V. No other optimization was made to the TOF-MS instrument. Thermo Finnigan LTQ-XL mass spectrometer is a widely available bench-top type commercial instrument, with advanced functions including multi-stage tandem mass spectrometry. The LTQ-XL instrument worked under the following conditions: the mass range was m/z 50–1000 with a positive ion detection mode, the temperature of the heated capillary was 150 °C, the lens voltage was 60 V. Other LTQ-XL parameters were automatically optimized by the system.