Mass spectra of 5′-CCTT4CTT7G8C9T10TCTCC-3′ (ODN15) (a) and the reaction mixture of ODN15 and cisplatin incubated at 310 K for 72 h (b). Mass peaks of unreacted ODN15, mono-platinated ODN15, and di-platinated ODN15 were labeled by orange, green, and purple circles, respectively, with the corresponding negative charge number inserted in each circle. Representative theoretical (top) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) observed (bottom) isotope pattern of [ODN15 − 5H]5− (inset in (a)), [ODN15 + Pt(NH3)2 − 7H]5− (left inset in (b)), and [ODN15 + 2Pt(NH3)2 − 9H]5− (right inset in b) are also shown.