On-line determination of mercury(II) by membrane separation flow injection analysis

A rapid and inexpensive gas-diffusion (GD) flow injection method for the on-line determination of Hg(II) in aqueous samples is described. The analytical procedure involves the injection of a Hg(II) sample into a 1.5 M H2SO4 carrier stream which is merged with a reagent stream containing 0.6% SnCl2 and 1.5 M H2SO4. Under these conditions Hg(II) is reduced to metallic mercury which partially evaporates through a Teflon membrane into an acceptor stream containing 1.75×10−4 M KMnO4 in 0.3 M H2SO4. The decrease in the absorbance of the acceptor stream at 528 nm corresponding to the absorption maximum of the permanganate anion can be related to the original concentration of Hg(II) in the sample. The method is characterized by a detection limit of 4 μg l−1 and a sampling frequency of 8 h−1. The flow system was successfully applied to the analysis of river samples spiked with Hg(II).