SIMULTANEOUS DETERMINATION OF COPPER, CADMIUM, LEAD AND ZINC IN NATURAL WATERS BY DIFFERENTIAL PULSE CATHODIC STRIPPING VOLTAMMETRY (DPCSV)

Heavy metals are necessary for healthy lifestyles. However, at higher concentrations, they can be toxic to the surroundings. In a journal article written by Carlo Colombo and Constant M.G. van den Berg 1996, a method was introduced for the simultaneous determination of concentrations of several trace metals in seawater. The process used, cathodic stripping voltammetry, determines specific ionic species simultaneously due to explicitness of the ligand. A series of methods was applied to find such metals, some of which include the focus of our own study, zinc, cadmium, lead, and copper. In the existing method, square-wave techniques were used, alongside 0.01 M Tris (a buffer solution) and 0.01mM of Oxine. A suspended mercury drop was used to absorb the reducing potentials of the copper, lead, cadmium, and zinc to obtain a peak, which was then used to measure concentrations.

Individual peak locations were found by analyzing each element by itself at different concentrations. After the identification of the location of peak areas, nano-pure water was spiked with known concentrations of heavy metals to form a calibration curve. In order to optimize the prior Tris/Oxine method, all possible combinations of Tris and Oxine were tested with the following set of values: 5ul, 10ul, 20ul, 40ul, and 80ul. In addition, DPCSV (differential-pulse of cathodic-stripping voltammetry) techniques were used in place of square-wave.

Linear regression provided varying R2 values which were then used to find the optimal conditions for simultaneous determination of the four metals. Some combinations lacked peaks entirely, and were discarded. At neutral pH, in a 10mL reaction vessel, three Tris/Oxine combinations with regression values of 0.997 to 0.995 were chosen for future optimization. The importance of these results allow for determinations in different environments and at higher sensitivities.

In order for implementation to surrounding bodies of water in Queens, New York City, the concentration of Tris must be altered to maintain a neutral pH. For further studies our method will be applied to local ponds and lakes to document the concentrations of such heavy metals. It will further aid in the study of the make-up of the lakes, surrounded by human activity.