Direct analysis in real time (DART) mass spectrometry of nucleotides and nucleosides: elucidation of a novel fragment [C5H5O]+ and its in-source adducts.

Direct analysis in real time (DART) mass spectrometry is a recently developed innovative technology, which has shown broad applications for fast and convenient analysis of complex samples. Due to the ease of sample preparation, we have recently initiated an investigation of the feasibility of detecting nucleotides and nucleosides using the DART-AccuTOF instrument, which we will refer to as the DART mass spectrometer. Our experimental results reveal that the ions representing the intact molecules of nucleotides are not detectable in either positive-ion or negative-ion mode. Instead, all four natural nucleotides fragment in the DART ion source, and a common fragment ion, C(5)H(5)O (1), is observed, which is probably formed via multiple-elimination reactions. Interestingly, 1 can form adducts with nucleobases in different molar ratios in the DART ion source. In contrast to nucleotides, the ions representing the intact molecules of nucleosides are detected in both positive-ion and negative-ion mode using DART mass spectrometry. Surprisingly, the fragmentation pattern of nucleosides is different from that of nucleotides in the DART ion source. In the cases of nucleosides (under positive-ion conditions), the production of 1 is not observed, indicating that the phosphate group plays an important role for the multiple eliminations observed in the spectra of nucleotides. The in-source reactions described in the present work show the complexity of the conditions in the DART ion source, and we hope that our results illustrate a better understanding about DART mass spectrometry.