MATRIX-ASSISTED LASER DESORPTION OF BIOLOGICAL MOLECULES IN THE QUADRUPOLE ION TRAP MASS-SPECTROMETER

Matrix-assisted laser desorption (MALD), which has been proven to be an effective ionization technique for biological molecules, has been implemented on a quadrupole ion trap mass spectrometer(ITMS). ln the instrumental configuration used for this work both the sample probe and the laser beam are brought through holes in the ring electrode, thereby enabling MALD-generated ions to expand directly into the ion trap cavity. This approach for directly introducing MALD-generated ions compliments the capabilities of the ITMS to obtain low detection limits and to perform tandem mass spectrometric analysis. For example, detection limits in the single-unit femtomole regime have been achieved for small polypeptides such as leucine enkephalin, bradykinin, and neuromedin U-8. Furthermore, structural information has been acquired via multiple stages of mass spectrometry. One limitation that currently exists is an unanticipated drop in sensitivity and resolution as the mass/charge ratio for ions exceeds 3000.