Application of pressure assisted electrokinetic injection technique in the measurements of DNA oligonucleotides and their adducts using capillary electrophoresis–mass spectrometry

The identification and measurement of negatively charged DNA oligonucleotides and their benzo[a]pyrene-7,8,9,10-tetrahydro-7,8-dihydrodiol-9,10-epoxide (BPDE) adducts by capillary zone electrophoresis (CZE) hyphenated mass spectrometry (MS) system using an on-line enrichment technique, the constant pressure assisted electrokinetic injection (PAEKI), is described here. With optimized PAEKI conditions, an on-line sample concentration power of 300–800 times could be reached for both single-stranded (ss) and double-stranded (ds) oligonucleotides during a 90-s PAEKI injection. The detection limits using single quadrupole MS in the scan mode were 0.01–0.03 μM for ss and 0.04–0.08 μM for ds oligonucleotides, respectively. The relative standard deviations at 1 μM of oligonucleotides were from 7.6 to 15.8%. A dynamic linear calibration range of about two orders of magnitude were observed. Good mass spectra of oligonucleotides and BPDE–oligonucleotide adducts at low micromolar levels could be obtained using single quadrupole MS which could be a helpful tool in DNA adducts studies.