ABSTRACT
A liquid chromatography-tandem mass spectrometry ( LC-MSMS ) method has been developed for the simultaneous determination of N3-methyladenine ( N3-MeA ) and N3-ethyladenine ( N3-EtA ) in calf thymus DNA. The DNA samples has been purified and enriched by cation exchange cartridge ( Waters Oasis MCX) . d3-N3-MeA and d5-N3-EtA were used as isotope internal standard. The DNA samples were injected with autosampler. The injected volume was 3 μL and analysis time was 13 min. The sample separation was carried out on hydrophilic interaction chromatograph ( Waters XBridge HILIC ) with 10 mmol/L ammonium formate-acetonitrile (5:92, V/V, pH=4. 0) as mobile phase. The flow rate was set at 250 μL/min. Mass spectrometry was performed by electrospray ionization ( ESI ) with multi-reactions monitoring ( MRM ) . The optimized operation conditions of MS were as follows: nebulizer gas 369 Pa; curtain gas 185 Pa, turbo ionspray temperature 400 ℃, ionspray voltage 5500 V, dwell time 40 ms. The limits of detection were 0. 043 and 0. 007 μg/L for N3-MeA and N3-EtA, respectively. The recoveries were between 87. 8% and 103. 0%for N3-MeA and N3-EtA. This method was successfully applied to the determination of N3-MeA and N3-EtA in calf thymus DNA by cigarette smoke condensate ( CSC) exposure. This method is appropriate for routine analysis and accurate quantification of N3-MeA and N3-EtA by CSC exposure.