A) The chemical structure of Vitamin K1, and the m/z = 170–240 region of the FT–ICR MS2 spectrum of B) vitamin K1, and C) S881. Dissociation ions at m/z = 172, 185, 196, 223, and 238 are consistent with dissociation of the isoprene unit alpha–linked to the napthoquinone moiety, and are present in both spectra.