Reagent And Standard Stability; Interferences - Hach DR/850 Procedures Manual

CHEMICAL ANALYSIS INFORMATION
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Reagent and Standard Stability

Interferences

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Hach always strives to make stable formulations and package them to
provide maximum protection. Most chemicals and prepared reagents do
not deteriorate after manufacture. However, the way they are stored and
the packaging can affect how long the reagents are stable. Light, bacterial
action, and absorption of moisture and gases from the atmosphere can
affect shelf life. Some chemicals may react with the storage container or
they may react with other chemicals.
Chemicals supplied with the colorimeter have an indefinite shelf life
when stored under average room conditions, unless the packaging says
something different. Product labels state any special storage conditions
required. Otherwise, store reagents in a cool, dry, dark place for
maximum life. It is always good practice to date chemicals when you
receive them. Use older supplies first. If in doubt about the reagent shelf
life, run a standard to check its effectiveness.
Substances in the sample may interfere with a measurement. Hach
mentions common interferences in the test procedures. The reagent
formulations eliminate many interferences. You can remove others with
sample pretreatments described in the procedure.
If you get an unusual answer, a color that you don't expect, or you notice
an unusual odor or turbidity, the result may be wrong. Repeat the test on a
sample diluted with deionized water; see Sample Dilution Techniques.
Compare the result (corrected for the dilution) with the result of the
original test. If these two are not close, the original result may be wrong
and you should make an additional dilution to check the second test (first
dilution). Repeat this process until you get the same corrected result twice
in a row.
More information about interferences and methods to overcome them is
contained in Standard Additions of this manual and the General
Introduction section of APHA Standard Methods. Hach urges the analyst
to obtain this book and refer to it when problems are encountered.
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