Why might Ammonium standards read high using an Ammonium ISE probe?

Document ID

Document ID TE2682

Published Date

Published Date 10/11/2021
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Question
Why might Ammonium standards read high using an Ammonium ISE probe?
Summary
Ammonium standards reading high with Ammonium ISE
Answer
Be sure to add the Ammonium ISA (Ionic Strength Adjustor) immediately before reading standards and samples. If the ISA is added and the standards sit, even for a couple minutes, the Ammonium (NH4) readings will be higher than expected. For example, a 50 mg/L standard drifted higher almost 1 mg/L per minute, but a freshly poured standard read as expected.

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