The　complex　natural　organic　matter　of　the　Suwannee　River　fulvic　acid　(SRFA)　standard　was　analyzed　by　online　reversed-phase　chromatography　with　Orbitrap　MS/MS　using　collision-induced　dissociation　(CID).　The　number　of　isobars　per　nominal　mass　could　be　reduced　to　a　single　dominantly　abundant　species　in　a　chromatographic　run,　sharing　some　ions　with　signals　having　the　identical　molecular　formula　in　adjacent　chromatographic　segments　and　later　serving　as　a　precursor　ion　for　fragmentation.　A　very　large　proportion　of　the　same　fragment　ions　existed　in　adjacent　chromatographic　fractions.　The　difference　in　the　fragment　ions　in　adjacent　chromatographic　fractions　could　be　attributed　to　a　gradual　change　in　the　formula　composition　of　precursor　ions　in　a　chromatographic　run.　It　could　be　concluded　that　dissolved　organic　matter　(DOM)　molecules　with　the　same　elemental　composition　in　different　chromatographic　fractions　may　have　very　similar　molecular　structures.　In　addition,　we　propose　a　possible　DOM　model　that　might　greatly　deepen　our　understanding　of　the　behavior　of　DOM　in　aquatic　matrices.