Comparison between capillary and nano liquid chromatography–electrospray mass spectrometry for the analysis of minor DNA–melphalan adducts

Nano liquid chromatography (nanoLC) coupled to electrospray mass spectrometry (ES-MS) was evaluated for the analysis of DNA adducts in melphalan-treated Jurkat cells. The detection limit of the nanoLC–ES-MS–MS system was assessed using a dAMP–melphalan adduct. Compared to capillary liquid chromatography (capLC) ES-MS the absolute detection limit could be improved by a factor 10, leading to the detection of 395 fg dAMP–melphalan adduct under single-ion monitoring conditions at a S/N of 14. Minor adducts such as cross-linked adducts could be detected in in vitro solutions of 2′-deoxynucleotides (dNMP) treated with melphalan using column-switching nanoLC–ES-MS. These adducts were not found using capLC–ES-MS. More detailed structural information of the alkylation sites was obtained by examining the nanoLC–ES-MS–MS data. Jurkat cells were treated with melphalan, the modified DNA was isolated and enzymatically hydrolyzed. Several modified dinucleotides were identified, the most abundant adducts were pdGMel(Cl)pdC (m/z=453, tr=17.0 min) and pdGMel(OH) pdC ring opened (m/z=453, tr=39.5 min).