SEARCH Articles Figures Tables Fractionation isotope Isotope isotopic fractionation Isotopes natural Isotopic fractionation Isotopic specification Site fractions Site specificity Site-specific natural isotope Site-specific natural isotope fractionation Site-specific natural isotope fractionation Site-specific natural isotope fractionation NMR Site-specific natural isotope fractionation by nuclear magnetic Site-specific natural isotope fractionation nuclear magnetic resonance