What could cause low nitrate results on samples but good results with standards when using cadmium reduction?

Document ID

Document ID TE522

Published Date

Published Date 04/02/2019
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Question
What could cause low nitrate results on samples but good results with standards when using cadmium reduction?
Summary
Low results on nitrate samples
Answer
There have been demonstrated instances of low results on samples that have a high alkalinity or buffering capacity. After the addition of the NitriVer® 5 reagent, the expected pH is about 3. Samples that have a high buffering capacity are unable to get down to this pH and this can cause low test results as the reaction is unable to go to completion.

There are a few possible resolutions to this issue:
- Use the NitriVer® 5 AccuVac®. The buffer contained in these is slightly more acidic and can achieve better results.
- Switch to the chromotropic acid method 10020. This method uses a much stronger acid and can better buffer high alkalinity samples.
- Use sulfuric acid to pH adjust the sample to a pH of between 6 and 7 prior to starting the test. Correct for any volume addition.

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