Quantitative determination of 8-hydroxyguanine and guanine by isotope dilution mass spectrometry.

8-[4,5,6,8-13C4]Hydroxyguanine and [4,5,6-13C3]guanine were prepared by total synthesis. The labeled compounds were used as internal standards in a gas-liquid chromatographic-mass spectrometric method for quantitative determination of 8-hydroxyguanine and guanine in DNA. The approach used made it possible to directly determine the ratio between 8-hydroxyguanine and guanine, expressed as the number of molecules of 8-hydroxyguanine per 10(5) molecules of guanine, in the sample of DNA analyzed. A method for trimethylsilylation of 8-hydroxyguanine and guanine at room temperature was developed. Use of this method for derivatization gave levels of 8-hydroxyguanine in calf thymus DNA which were lower than those recently found by gas chromatography-mass spectrometry but similar to those determined by high-performance liquid chromatography with electrochemical detection.