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Dissolved organic matter (DOM) is linked to the heterogeneous distribution of elevated arsenic (As) in groundwater used for drinking and irrigation purposes, but the relationship between DOM characteristics and arsenic mobility has yet to be fully understood. Here, DOM from groundwater sampled in the Bengal Basin region was characterized using both conventional bulk emission–excitation (EEM) spectroscopy and high-performance size-exclusion chromatography coupled to spectroscopy (HPSEC–EEM). Notably, application of the novel HPSEC–EEM approach permitted the total fluorescence of individual samples to be independently resolved into its underlying components. This allowed the external validation of the bulk-sample fluorescence decomposition and offered insight into the molecular size distribution of fluorescent DOM. Molecular size distributions were similar for the UVA fluorescent (C₃₁₀ and C …