CHARGE-STATE REDUCTION OF OLIGONUCLEOTIDE NEGATIVE-IONS FROM ELECTROSPRAY-IONIZATION

We have investigated the feasibility of simplifying the electrospray i onization (ESI) mass spectra for mixture analyses through charge state reduction, Two methods for charge state reduction of gasphase oligonu cleotide negative ions were evaluated: (1) the addition of acids to th e oligonucleotide solution and (2) the formation of diamine adducts fo llowed by dissociation in the interface region, In the first method, t he efficiency of charge state reduction depends on the pK(a), the conc entration, and the nature of the acids. Acetic and formic acids were f ound to be better reagents than HCl, CF3CO2H, and H3PO4. The second me thod has the advantage that the stability of oligonucleotides is not a ffected but requires the optimization of the interface dissociation:co nditions and the amounts of diamine added to the oligonucleotide solut ion. Both methods show promise for charge state reduction, and results are presented for two oligonucleotides: d(pT)(12) and d(AGCT). Substa ntial reduction in spectral complexity upon charge state reduction was also observed for a four-component mixture of oligonucleotides.