CATION-EXCHANGE RESINS FOR REMOVAL OF ALKALI-METAL CATIONS FROM OLIGONUCLEOTIDE SAMPLES FOR FAST-ATOM-BOMBARDMENT MASS-SPECTROMETRY

Cation-exchange resins are useful matrix additives for the positive an d negative ion FAB-MS determination of nucleotides. Several factors in cluding the amount and type of matrix, the amount and type of the resi n, the molecular weight of the nucleotide, and the salt content of the nucleotide sample are investigated, For positive ions, the mast abund ant [M + H](+) ions are obtained with 1 mu L of DTT/DTE with 75-100 re sin beads in the H+ form is used. For negative ions, the most abundant [M - H](-) ions are produced from 1 mu L TEA and 75-100 resin beads i n the NH4+ form. In several cases, the use of cation-exchange resins g ive superiors results compared to those obtained with other matrix add itives.