WATER QUALITY MONITORING ON BORON-DOPED DIAMOND ELECTRODES

Elizabeth A. McGaw

Affiliation: CSTL/Analytical Chemistry Division, NIST Gaithersburg, MD 20899.

         On-board the International Space Station (ISS), potable water is used for drinking, food preparation, and hygiene.  There are several potential sources of contamination, both organic as well as inorganic, that are potentially toxic to the crew.  Several heavy metal ion contaminants have been detected in the ISS water (e.g. Ag(I), Pb(II), and Cd(II)) [1]. The latter two were found at concentrations much higher than the EPA action levels. Presently the water is tested for contamination when samples collected on ISS are returned to earth which can have a lag time of several months. On-board monitoring of these contaminants is essential for crew health and safety however there is no on-board water quality monitoring system.

         Electrochemical methods are attractive for use in environmental monitoring in space as they are versatile, energy efficient, easy to be automated, environmentally compatible, and cost effective.  Traditionally, anodic stripping voltammetry (ASV) with a Hg electrode has been employed for trace metal ion analysis.  Alternate electrodes, however, are being investigated because of the stability, toxicity, and volatility of Hg.  A boron-doped diamond electrode has many beneficial properties such as a wide working potential window, a low background current, and a reusable surface, that make it well suited as an alternative to Hg.  Boron-doped diamond has been used successfully for terrestrial ASV analysis of heavy metals found in water, sludge, and soil samples [2] and is a viable alternate electrode for space application.

         Specifications for water quality monitoring on-board ISS will require additional modifications and optimization to the current assay.  The effects of solution pH, dissolved oxygen, and salt content on the diamond electrode response (e.g., Ag(I), Cu(II), Pb(II), Cd(II) and Zn(II)) were investigated.  The results for diamond electrodes will be compared with the results for the state-of-the-art Hg electrode.

[1] D. Plumlee, P.D. Mudget, J.R. Shultz, SAE Technical Paper, 2002-01-2537 (2002)

[2] P. Sonthalia, E. McGaw, G.M. Swain, Analytica Chimica Acta, 522, 35 (2004)

Category: Chemistry

Author: Elizabeth A. McGaw

Mentor: Michele Schantz

Division: Analytical Chemistry Division (839)

Laboratory: Chemical Science and Technology Laboratory (CSTL)

Address: Building 227, Room A123

Mail Stop: 8392

Telephone: 301-975-4167

Fax: 301-977-0685

Email: elizabeth.mcgaw@nist.gov

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