Simultaneous multi-element detection of metal ions bound to a Datura innoxia material

An on-line detection scheme has been developed for the determination of metal ion affinities for binding to a plant-based substrate. This involves monitoring the effluent of a column packed with cell-wall fragments from the plant Datura innoxia for 27 different elements simultaneously by coupling the column to an ICP emission spectrometer. Previously accepted procedures for removing native metal ions from biological materials by washing the material with a pH 2 solution were found to be insufficient for this material. Measurable amounts of Na, Mg, Al, Ca, Mn, Fe, Ni, Cr, Zn, Cd, Pb, Ba, Sr, and Si were all detected in an effluent from the introduction of 1.0M HCl following washing the material in a pH 2 solution. Metal ion breakthrough curves for Cd(2+), Zn(2+), Ni(2+), Cu(2+), and Pb(2+) were found to exhibit an affinity order of Pb(2+)>Cu(2+)>Zn(2+) congruent with Cd(2+)>Ni(2+) for an equimolar mixture of these metal ions. This configuration also enabled the displacement of metal ions to be detected as the breakthrough curve for a subsequent metal ion was monitored. Comparison of Ni and Zn binding indicates a simple ion exchange model is insufficient to explain sequential binding of these metal ions.