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

We have investigated the feasibility of simplifying the electrospray ionization (ESI) mass spectra for mixture analyses through charge state reduction, Two methods for charge state reduction of gasphase oligonucleotide negative ions were evaluated: (1) the addition of acids to the oligonucleotide solution and (2) the formation of diamine adducts followed by dissociation in the interface region, In the first method, the efficiency of charge state reduction depends on the pK(a), the concentration, and the nature of the acids. Acetic and formic acids were found to be better reagents than HCl, CF3CO2H, and H3PO4. The second method has the advantage that the stability of oligonucleotides is not affected but requires the optimization of the interface dissociation:conditions and the amounts of diamine added to the oligonucleotide solution. Both methods show promise for charge state reduction, and results are presented for two oligonucleotides: d(pT)(12) and d(AGCT). Substantial reduction in spectral complexity upon charge state reduction was also observed for a four-component mixture of oligonucleotides.