EXACT MASS DETERMINATION FOR ELEMENTAL ANALYSIS OF IONS PRODUCED BY MATRIX-ASSISTED LASER-DESORPTION

The exact masses of bastadins, cyclic peptides from marine sponges Ian thella basta, are determined using matrix-assisted laser desorption io nization (MALDI) coupled to a Fourier transform mass spectrometer. Two known compounds were mixed with the unknown to serve as internal cali brants. The mass of the calibrants bracketed the mass of the unknown c ompound. With this method, exact masses were obtained to within 5 ppm for single determinations, and less than 3 ppm for multiple determinat ions, allowing the derivation of elemental composition. This method is viable for routinely obtaining the exact masses of new compounds with MALDI.