Department of Chemistry and Barnett Institute, Northeastern University, Boston, MA 02115.
Electrophoric derivatives of 5-methylcytosine and 5-hydroxymethyluracil nucleobases are determined using high-performance liquid chromatography-mass spectrometry coupled via a moving-belt interface. Standards as well as samples derived from DNA are analysed. As little as 9.9 pg (signal-to-noise ratio 5) and 180 fg (signal-to-noise ratio 10) of the respective nucleobases are detected in the electron-capture negative chemical ionization mode, and linear responses are observed over a moderate dynamic range. In a comparison study, liquid chromatography-electron-capture negative chemical ionization mass spectrometry is found to have a sensitivity comparable to gas chromatography-electron-capture negative chemical ionization mass spectrometry for 5-hydroxymethyluracil. A detection limit of 60 fg (signal-to-noise ratio 5) by gas chromatography-mass spectrometry is only three-fold better than the amount detected by liquid chromatography-mass spectrometry using the same mass spectrometer.