When does a blank or zero need to be performed on a Pocket Colorimeter II?

Document ID

Document ID TE9442

Version

Version 1.0

Status

Status Published

Published Date

Published Date 03/01/2018
Question
When does a blank or zero need to be performed on a Pocket Colorimeter II?
Summary
When blanks needs to be redone and when blanks can be reused.
Answer
This depends on if the pocket colorimeter method being performed uses a sample blank or a reagent blank.
See also: What is the difference between a reagent blank and a sample blank?

In summary a sample blank is when the zero is performed on sample without the reagent added. An example of a method that uses a sample blank is Pocket Colorimeter DPD, Low Range DPD.
A reagent blank is when the zero is performed on Demineralized water with reagent added. An example of a method that uses a reagent blank is 8311 Ozone AccuVac® Pocket Colorimeter.

For methods that use a sample blank, the instrument should be re-zeroed for each sample. For these methods it's important that the zero is performed using the same sample that is being read on for the measurement.

For methods that use a reagent blank, the instrument should be re-zeroed whenever the zero is lost by the instrument or when changing from one lot of reagent to another. The reagent blank is assumed to be identical for the rest of the reagent of that lot. When changing the lot (including if only one reagent is changing for a test that uses multiple reagents) the reagent blank from previous lots are not longer valid. Additional reagent blanks can be performed but aren't necessary. Sometimes the Pocket Colorimeter II will lose the stored blank information, when this happens it will display a flashing zero in the bottom left hand side of the display. This will require the reagent blank to be re-taken. (See also: The display on my Pocket Colorimeter II™ shows a flashing square or zero. What does this mean?)
 

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