Preconcentration of Trace Metal Ions from Natural Waters: Studies on the Application of an Acrylic Ester Macroreticular Resin

Abstract

<p>A new preconcentration method has been developed for the determination of trace metals from natural waters. The method is based on the direct uptake of metal ions on a column packed with the macroporous acrylic ester resin, XAD-7, after interfering humic substances are removed on a XAD-7 precolumn. The retained metal ions are subsequently eluted with 1% v/v HNO₃ and the trace metals determined by graphite-furnace atomic absorption spectroscopy. The effects of various parameters such as pH, ionic strength, anions, organic substances, flow rate, column bed-size and resin particle size on the adsorption and elution of metal ions were examined. Based on these investigations, optimal conditions for the group preconcentration of Cr, Fe, Cd, Co, Cu, Mn, Ni and Pb were established.</p> <p>The method was successfully applied to various natural waters and was found to be simpler and less susceptible to contamination than the Chelex-100 method. In addition, a larger preconcentration factor was obtained. The accuracy and precision of the XAD-7 method were found to be at least competitive with the Chelex-100 method.</p> <p>The mechanism of adsorption was investigated and adsorption isotherms and distribution ratios of selected metal ions were measured. The adsorption process is complex and likely involves charge-dipole interactions.</p> <p>A simple model was developed to illustrate the rationale of the method of standard additions in a preconcentration procedure. It was shown that a high degree of spike reaction with the sample matrix and a reasonable degree of analyte separation are vital for the successful application of standard additions. If the degree of separation is very high, the method of standard additions is not required and only a simple calibration curve is necessary.</p>