When using the Hach TNT vials for COD, can one blank be used for the entire lot of vials or must a new blank be run each time?

Document ID

Document ID TE241

Version

Version 2.0

Status

Status Published

Published Date

Published Date 27/05/2017
Question
When using the Hach TNT vials for COD, can one blank be used for the entire lot of vials or must a new blank be run each time?
Summary
Reusing COD a blank vial
Answer
The same blank can be used repeatedly for measurements using the same lot of vials as long as the following is done:

-The blank should be stored in the dark.
-Monitor the absorbance of the blank over time to see that it is stable:
-Zero the instrument in absorbance mode using a vial containing deionized water.
-Measure the absorbance of the blank.
-Record the value.

Prepare a new blank when the absorbance has changed by about 0.01 absorbance units.