Why does a hardness sample turn a different color than the color specified in the method?

Document ID

Document ID TE291

Version

Version 4.0

Status

Status Published

Published Date

Published Date 08/14/2018
Question
Why does a hardness sample turn a different color than the color specified in the method?
Summary
Sample color is different than what is indicated in the hardness method
Answer
An interfering substance can prevent proper color development both before titration and at the titration end point. A dilution is a common way to try to reduce an interference to a level at which the substance does not interfere. Multiply the result by the dilution factor for the final result.

If the sample turns a purplish color but never turns blue no matter how much EDTA is added, the sample could contain an interfering metal. Attempt to dilute the sample and retest.

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