Determination of Trace Metals (Cu, Pb, Zn and Ni) in Soil Extracts by Flow Analysis with Voltammetric Detection

Abstract

It is shown here that flow analysis with voltammetric detection can be used to determine Cu, Pb, Zn and Ni in soil extracts. Cu, Pb and Zn were detected by square-wave anodic stripping voltammetry (SWASV), and Ni by square-wave cathodic stripping voltammetry (SWCSV). Advantages of the method are good sensitivity and the possibility to take the instrumentation into the field for on-site measurement. The reagents were: 0.2 M acetate buffer at pH 5.0 for Cu, Pb and Zn, and 0.04 M pH 9.0 ammonia buffer containing 20 μM DMG (dimethylglyoxime) for Ni. The reactive metal fraction was determined in 0.5 M HCl extracts (25 min extraction time) of soil samples from six different sites characterised by varying degrees of heavy metal pollution. The reactive metal fractions amounted to 23–73% of the metals in 5 of the 6 sites, whereas it was much lower (9–30%) at the other site. Organic matter did not interfere with the measurements as it was not extracted significantly by the 0.5 M HCl and as the extracts were diluted prior to analysis. The formation of intermetallic compounds at high levels of Cu and Zn was minimised by determining these metals in separate sample aliquots with calibration using separate standard additions, and by using different plating potentials and short plating times. Good accuracy was verified by analysis of reference materials.