VOLTAMMETRIC STRIPPING (VS) AS A LOW-COST ALTERNATIVE TO ATOMIC EMISSION SPECTROGRAPHIC ANALYSIS

Traditionally, heavy metals in rocks and sediments are determined using atomic absorption spectrophotometry (AA), plasma spectrophotometry (ICP), or X-ray fluorescence (XRF). While these methods provide excellent detection levels, each is expensive to purchase, operate, and maintain. Voltammetric methods have not been used extensively in the geological sciences but offer an attractive alternative for some types of metal analyses. A complete system can be acquired for less than $25,000 and determination of metals can be carried out well down into the ppb range.

Following sample digestion, a very negative voltage is initially applied to an electrode. This causes all metal ions in solution to be reduced to metal atoms on the electrode surface. These atoms are then reoxidized (i.e., "stripped") by quickly scanning the voltage in a positive direction. The current is monitored during the stripping step and each metal oxidizes when the voltage on the electrode coincides with its unique reduction potential. A series of "peaks" are produced, with each being characteristic of the metal present and the maximum current of each representing the metal concentration. On the negative side, analytical times are slow and only one sample can be analyzed at a time. Further, certain combinations of elements may introduce chemical interferences (however these may often be eliminated by pre-treatment techniques). Examples are presented from bottom sediment analyses from Mobile Bay, Alabama and Apalachicola Bay, Florida and are compared with those obtained by AES-ICP analyses to demonstrate the cost-effectiveness and accuracy of the procedure.