How will sulfides effect the performance of a differential pHD sensor?

Document ID

Document ID TE2144

Published Date

Published Date 03/30/2018
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Question
How will sulfides effect the performance of a differential pHD sensor?
Summary
pHD sensors and sulfides in sample
Answer
Hach’s pHD differential electrode is nearly ideal for samples containing sulfide. The upper limit for sulfide in the sample for these probes is about 1 molar. The problem is not the sulfide itself, but the high pH associated with concentrated sulfide. The reason why Hach’s pHD differential electrode can do well in samples containing sulfide is the silver chloride wire inside the probe is encased in a glass electrode. The glass protects the silver from the sulfide. Conventional reference electrodes do not have this glass protection around the silver chloride wire, so the internal silver chloride wire converts to silver sulfide, which causes disastrous results, leading to large errors in the pH reading. Once the electrode of these probes is contaminated with sulfide, there is no way to fix it.

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