Investigation of the electrospray response of lysine-, arginine-, and homoarginine-terminal peptide mixtures by liquid chromatography/mass spectrometry.

Guanidination has been used to investigate how modification of the lysine eta-amino group into the corresponding guanidino group affects response in electrospray (ES) mass spectrometry (MS). Selected ion monitoring (SIM) analysis of equimolar mixtures containing arginine-, lysine- and the corresponding homoarginine-terminal peptides following liquid chromatography (LC) showed differences in ES response. The ionisation behaviour of the standard peptides is in accordance with the postulated higher stability of the guanidino group present on arginine- and homoarginine-terminal peptides. Modification of the separation conditions employed during LC demonstrates that relative abundances of electrosprayed peptides ions rely mostly on peptide structure.