[en] The excitation spectra associated with the ⁷F₀→⁵D₀ transition of Eu⁺³ has been used to examine the binding sites on cell wall fragments of Datura innoxia. Both native and esterified cell wall fragments were each examined at pH 5 and pH 2 to determine the contributions to metal ion sorption from both the carboxylate and sulfonate functional groups. The excitation spectra have been deconvoluted into the individual groups responsible for metal ion uptake. At least four unique binding sites can be described as being responsible for metal ion uptake. The higher affinity sites involve carboxylates in the binding of Eu⁺³ in a tridentate (3:1 ligand-to-metal ratio) configuration. copyright 1997 Society for Applied Spectroscopy