High sensitivity mass spectrometric determination of peptides: direct analysis of aqueous solutions

The high sensitivity analysis of peptides by fast atom bombardment mass spectrometry has been achieved using a continuous flow probe for the introduction of samples contained in aqueous solutions. Small aliquots of sample (0.5-1 microliter) are injected into a solvent flow containing water/glycerol (8:2). For several peptide samples tested whose molecular weights were between 1000 and 1500 daltons, molecular ions were selectively monitored at the 20 fmol level with a signal-to-chemical noise of about 4:1, and full scan data were obtained on about 5 pmol of sample. The increase in sensitivity observed using the continuous flow probe is shown to be a consequence of both the decrease in the chemical background noise and to the increase in ion yields obtained from the bombardment of aqueous sample solutions.