Anal. Chem. 1996, 68, 3295-3299
On-Line Microdialysis Sample Cleanup for Electrospray Ionization Mass Spectrometry of Nucleic Acid Samples Chuanliang Liu, Qinyuan Wu, Amy C. Harms, and Richard D. Smith*
Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99352
A major limitation of electrospray ionization mass spectrometry (ESI-MS) for oligonucleotide analysis arises due to sodium adduction, a problem that increases with molecular weight. Sodium adduction can preclude useful measurements when limited sample sizes prevent off-line cleanup. A novel and generally useful on-line microdialysis technique is described for the rapid (∼1-5 min) DNA sample cleanup for ESI-MS. Mass spectra of oligonucleotides of different size and sequence showing no significant sodium adduct peaks were obtained using the on-line microdialysis system with sodium chloride concentrations as high as 250 mM. Signal-to-noise ratios were also greatly enhanced compared to direct infusion of the original samples. By using ammonium acetate as the dialysis buffer, it was also found that the noncovalent association of double-stranded oligonucleotides could be preserved during the microdialysis process, allowing analysis by ESI-MS. The application of electrospray ionization mass spectrometry (ESI-MS) for the characterization of DNA has grown rapidly in recent years due to its capabilities for studying increasingly large oligonucleotides with high sensitivity (90%. CONCLUSIONS We have developed a new and efficient on-line microdialysis method for the rapid desalting of oligonucleotides for ESI-MS studies. This approach was demonstrated to provide effectively complete “on-line” salt removal in
