Cl. Liu et al., ON LINE MICRODIALYSIS SAMPLE CLEANUP FOR ELECTROSPRAY-IONIZATION MASS-SPECTROMETRY OF NUCLEIC-ACID SAMPLES, Analytical chemistry, 68(18), 1996, pp. 3295-3299
A major limitation of electrospray ionization mass spectrometry (ESI-M
S) for oligonucleotide analysis arises due to sodium adduction, a prob
lem that increases with molecular weight. Sodium adduction can preclud
e useful measurements when-limited sample sizes prevent off-line clean
up. A novel and generally useful on-line microdialysis technique is de
scribed for the rapid (similar to 1-5 min) DNA sample cleanup for ESI-
MS. Mass spectra of oligonucleotides of different size and sequence sh
owing no significant sodium adduct peaks were obtained using the on-li
ne 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 ga
the dialysis buffer, it was also found that the noncovalent associati
on of double-stranded oligonucleotides could be preserved during the m
icrodialysis process, allowing analysis by ESI-MS.