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 and negative ion FAB‐MS determination of nucleotides. Several factors including the amount and type of matrix, the amount and type of the resin, the molecular weight of the nucleotide, and the salt content of the nucleotide sample are investigated. For positive ions, the most abundant [M + H]⁺ ions are obtained with 1 μL of DTT/DTE with 75–100 resin beads in the H⁺ form is used. For negative ions, the most abundant [M − H]⁻ ions are produced from 1 μL TEA and 75–100 resin beads in the NH₄⁺ form. In several cases, the use of cation‐exchange resins give superiors results compared to those obtained with other matrix additives.