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Electrodes used continuously in the field for up to 5 yr were removed, examined visually, and tested in both a quinhydrone solution and a 1:5 soil–water slurry. Comparison with pre‐installation quinhydrone readings showed that all but 3 of 102 electrodes tested were still within ±10 mV of the standard value. Water observed inside more than half the electrodes had no apparent adverse impact on electrode performance. The post‐removal quinhydrone test correctly identified one electrode that developed faulty readings in the 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 that were a little more variable than quinhydrone readings but were much less variable than actual field readings. Anomalous slurry readings within replicated electrode sets suggest that, despite good quinhydrone readings, some electrodes may not have responded properly under actual field use. Field data from one such set confirmed the presence of a defective electrode. We conclude 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.

Results are presented from a series of experiments that were designed to characterise quadrupole analyzers. Three different analyzers have been studied. The first, typical of the small quadrupoles often used for residual gas analysis, has rods 50 mm long and 6.25 mm in diameter. The second uses rods of similar diameter, but 125 mm long. The third uses rods of diameter 12 mm and length 230 mm. Simple ion sources were used. All had cylindrical ionization regions with external filaments, in a configuration similar to an extractor ion gauge. All were operated under similar conditions. The sensitivity and linearity of the instrument is found to depend in a complex way on the operating conditions of the ion source. The observed behavior is explained qualitatively by the presence of both electronic and ionic space charge in the ion source.

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