ESI-MS of peptides in the presence of L-ascorbic acid

A mass spectrometric method with electrospray ionisation (ESI-MS) is described for detection and quantification of selected peptides [glutathione, phytochelatin 2, bombesin, salmon luteinising hormone, and peptide fragment CYS(Xx)(12)]. A reaction coil was used to introduce a solution of sample in mobile phase consisting of acetonitrile (ACN) and an aqueous solution of trifluoroacetic acid (TFA). L-Ascorbic acid (AA), which substantially increased the abundance of the molecular ions of the peptides analysed, was added to aqueous solutions of the peptides or amino acids at a final concentration of 10 mM. This addition probably eliminated the negative effect on the ionisation processes of the strong acid TFA present in the mobile Phase, thus enabling analysis of lower concentrations of the peptides.