ABSTRACT
When the oligonucleotides are transferred to the gas phase during the electrospray process, cations present in the sample are attracted by the highly negative charged backbone of the oligonucleotide and give rise to so-called cation adducts. These cation adducts reduce the polarity of the highly charged DNA backbone, improving the production of gas-phase ions. However, dependent on the resolving power of the instrument, the resulting mass spectrum often exhibits broad peaks whose width and complexity reflects the degree of adduction. Moreover, these cation adducts disperse the analyte ion current of the oligonucleotide among multiple cation-containing species within each charge-state ion cluster, thus reducing the sensitivity of the mass measurement [14]. The longer the oligonucleotide, the more dramatic the results of cation adduction are. Metal-ion adduction can even lead to the impossibility to determine the mass of longer oligonucleotides.
