Application of energy dispersive X-ray spectrometry for quantitative evaluation of sorption phenomena at solid–liquid interfaces

A new application of X-ray detection technique and theoretical calculation method is presented for the quantitative determination of the surface excess concentration (e.g. surface-concentration of the adsorbed atoms on the solid surface) of the radiolabelled Zn2+ ions on a polycrystalline gold substrate. A mathematical model was developed describing the absolute dependence of the detected characteristic X-ray flux on the amount of the adsorbed Zn species labelled with 65Zn. The theoretical calculation considers the geometrical parameters of the applied electrochemical cell such as its diameter and the volume of the radioactive solution over the Au-substrate foil and attenuation by the holder foil and the ring-shaped Al collimator. The background flux of the characteristic X-rays originating from the 65Zn-containing solution layer located over a gold-covered polyethylene foil was calculated similarly. In order to test the present theoretical calculation, 2.7 μl radioactive ZnCl2 solution with 51.6 kBq activity was dropped on a polyethylene holder foil simulating a sorbed layer of 65Zn. Measuring the diameter of the dropped and dried spot, the calculated amount of layered Zn agreed with the nominal value within 10%.