Chiral recognition of amino acids by electrospray ionisation mass spectrometry/mass spectrometry
The influence of solvent composition and surface tension upon the signal intensity of deprotonated molecules [M -H] -in electrospray ionization mass spectrometry (ESI MS) was evaluated using alanine (Ala), threonine (Thr) and phenylalanine (Phe) differing levels of hydrophobicity. The surface tension of ESI solution was varied by changing the ratio of the organic solvents methanol (MeOH) and acetonitrile (MeCN) in water (H2O). In ESI MS, the signal intensity of all the amino acids increased by
... acids increased by decreasing the surface tension in two solutions, H2O/MeOH and H2O/MeCN. The use of H2O/MeCN was more favorable for the signal intensity of analytes than that of H2O/MeOH. A smaller vaporization enthalpy of MeCN compared to MeOH was proposed as one of the most plausible reasons. The order of the signal intensity of amino acids was Phe>Thr>Ala in relation to the order of hydrophobicity of amino acids. It can be practically concluded that the use of solutions with lower surface tensions and lower vaporization enthalpies results in higher signal intensities in ESI MS. 14) N. B. Cech, J. R. Krone, C. G. Enke. Predicting electrospray response from chromatographic retention time. Anal. Chem. 73: 208-213, 2001. 15) L. Tang, P. Kebarle. Dependence of ion intensity in electrospray mass spectrometry on the concentration of the analytes in the electrosprayed solution. Anal. Chem. 65: 3654-3668, 1993. 16) L. Tang, P. Kebarle. Effect of the conductivity of the electrosprayed solution on the electrospray current. Factors determining analyte sensitivity in electrospray mass spectrometry. Anal Chem. 63: 2709-2715, 1991. 17) I. Osaka, M. Takayama. Influence of hydrophobicity on positive-and negativeion yields of peptides in electrospray ionization mass spectrometry. Rapid Commun. Mass Spectrom. 28: 2222-2226, 2014. 18) T. Nishikaze, M. Takayama. Study of factors governing negative molecular ion yields of amino acid and peptide in FAB, MALDI and ESI mass spectrometry. Int.