• Analytical Science and Technology
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• v.25 no.2
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• pp.114-120
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• 2012

For the qualitative analysis of peptides in matrix-assisted laser desorption/ionization-mass spectrometry (MALDI-MS), O-methylisourea, which is chemically bound to a specific site of an amino acid (e.g. lysine) of peptides and improves the intensities of the modified peptides, is frequently used prior to the MALDI-MS analysis of peptides, where the process is called guanidination. The reaction efficiency of guanidination varies depending on the reaction conditions. We investigated the efficiencies of guanidination of tryptically digested myoglobin using three different reagents (O-methylisourea, S-methylisothiourea, and 2-methyl-2-imidazoline) at $65^{\circ}C$ for 1 h with various pH conditions (pH 4.0, 7.0, and 10.5), where O-methylisourea and pH 10.5 were found to be most effective. The guanidination with O-methylisourea at pH 10.5 were then applied with different reaction conditions such as heating, microwave and ultrasound at various times, where heating for 60 min was found to be most effective. Conclusively, guanidination with O-methylisourea at $65^{\circ}C$ for 1 h at pH 10.5 was found to be the optimized condition.