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Platinum Microelectrode Poisoning Factors¹

ABSTRACT

The oxide coating that occurs on platinum electrodes would be expected to influence oxygen diffusion rate (ODR) measurements on the basis of electro-chemistry literature. However, no consistent influence of condition of electrode oxidation on ODR measurement in clay suspension was found by the authors. The current density on electrodes in clay suspensions was suspected of being below that density where the oxide would exhibit an influence on current.

A deposit of salts, principally calcium bicarbonate, and clay particles, principally biotite, on electrodes left in place in a loamy sand reduced measured ODR's by an average of more than 50% after 2 months compared to ODR's from reinserted electrodes in the same soil. The deposits did not form to such an extent on electrodes in a clay and ODR measurements from in-place electrodes remained comparable to those from reinserted ones throughout the 2-month period.

A nitric acid pretreatment procedure provided an electrode cleaning technique without any abrasion and brought electrodes to an oxidized condition after prolonged use or disuse.

¹ Contribution from the Department of Soils & Plant Nutrition, University of California, Riverside.

² Formerly Graduate Student, Department of Soils & Plant Nutrition, University of California, Riverside, presently Research Soil Scientist, USDA, ARS, SWC, Snake River Conservation Research Center, Kimberly, Idaho.

³ Associate Professor and Professor of Soil Physics, Department of Soils and Plant Nutrition, University of California, Riverside.

⁴ Research Soil Scientist, Northeastern Forest Exp. Sta., Columbus, Ohio.

Received for publication July 28, 1967. Accepted for publication December 5, 1967.