Voltametric determination of lead and mercury using carbon paste electrodes modified with water hyacinth, Eichhornia crassipes (Mart.) Solms.
2000
Hernandez, P.C.
Water hyacinth, Eichhornia crassipes (Mart.) Solms., considered as one of the world's worst weeds, can cause reduction of water flow and restrictions in commercial fishing. However, these plants were reported to accumulate metal ions, a property explored in the present research to address monitoring of heavy metals. This study describes the use of a carbon paste electrode modified with the roots of E. crassipes (CREMEC) for the determination of heavy metals such as lead and mercury by differential pulse anodic stripping voltammetry (DPASV). Water hyacinth obtained from Laguna de Bay [Philippines] was freeze dried to preserve the integrity of the metal-binding sites. The modifier was mixed with carbon powder in a 1:5 ratio and mineral oil added to form a paste. This was packed inside a 2-mm diameter polyethylene tube and a copper rod was inserted to provide electric contact. The CPEMEC was used in the voltammetric measurements of Pb(2) and Hg(2) in aqueous solutions. For lead analysis, the sensitivity and detection limits were found to be 6 micron A/10E-6 M and 3.0 x 10E-9 M, respectively. On the other hand, mercury (2) analysis gave a sensitivity of 10 micron A/10E-6 M and a detection limit of 1.2 x 10E-8 M. Voltammetric response was analyzed with respect to electrode composition, accumulation time, deposition time, pH, and deposition potential. DPASV using the modified electrode was used in the analysis at actual laboratory sample. The result obtained by DPASV was compared with standard AAS method and was found to be 30% lower. The ability of water hyacinth to accumulate metals was attributed to the ion-exchange properties of various functional groups present in the plant material. The ion exchange capacity of E. crassipes roots was also determined and found to be 2.72 + or - 0.21 meq/g using atomic absorption spectometry
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