Simultaneous Determination of Low Parts-per-Billion Level Pb and as in Waters Using Energy-Dispersive X-Ray Fluorescence Spectrometry

A simple method is described for the simultaneous determination of low parts-per-billion levels of As and Pb in waters. The method is based on the preconcentration of analytes by adsorbing them onto hydrous ferric hydroxide (HFO) impregnated into the 13 mm diameter area at the center of 32 mm diameter circular disks cut from Whatman filter papers. The adsorbed analytes are determined by using thin-layer energy-dispersive X-ray fluorescence spectrometry. The X-ray intensity of As and Pb adsorbed onto HFO is linearly proportional to the concentration up to 80 μg/L. The precision of the method is ∼ 0.5–5%, and the method detection limit for Pb and As in seawater is 0.63 and 0.21 μg/L, respectively. The method was validated by analyzing the certified reference materials SLRS-3 (riverine water), CASS-4 (nearshore seawater), and NASS-5 (offshore seawater) for As. The adsorption characteristics of Pb, As(III), As(V), Se(IV), Se(VI), and Hg onto the HFO impregnated disks, the interspecies adsorption effects, and the use of the standard addition method to compensate for matrix effects are also presented.