Viability of permanently installed platinum redox electrodes

Electrodes used continuously in the field for up to 5 Sr were removed, exam ined visually, and tested in both a quinhydrone solution and a 1:5 soil-wat er slurry. Comparison with pre-installation quinhydrone readings showed tha t all but 3 of 102 electrodes tested were still within +/-10 mV of the stan dard value. Water observed inside more than half the electrodes had no appa rent adverse impact on electrode performance. The post-removal quinhydrone test correctly identified one electrode that developed faulty readings in t he first year of field use. Test values for two other potentially defective electrodes fell within acceptable standards after rinsing them in an HCl- HNO3 solution and retesting. Platinum poisoning with coatings could not be detected visually, and we conclude that poisoning, though possibly present at minimal levels, did not significantly impair electrode performance after 5 yr, Post-removal testing in a constantly stirred slurry gave readings th at were a little more variable than quinhydrone readings but were much less variable than actual field readings. Anomalous slurry readings within repl icated electrode sets suggest that, despite good quinhydrone readings, some electrodes may not have responded properly under actual field use, Field d ata from one such set confirmed the presence of a defective electrode, We c onclude that the slurry test provides valuable information that complements the quinhydrone test and could be used as a pre-installation test to help identify potentially faulty electrodes.