1-5
approach whether the fault lies in the reagent, the instrument and
apparatus, the test procedure or an interfering substance present in the
test sample. A decision tree, such as the one in Figure 1, establishes a
systematic method for identifying the problem. Request Hach
Publication 7004 for additional information on standard additions.
Explanations of the various steps follow.
A
B
D
C
E
H
I
F
G
K
J
Standards Defective
Repeat B with New
Standards
Repair/Replace
Instrument Apparatus
and Repeat B
Is Instrument Apparatus Working Properly?
Repeat B with
New Reagents
Use Correct
Procedure and
Repeat B
Are
Interferences
Present?
Analysis
Is Correct
Analysis
Is Incorrect
Analysis May
be Correct
Do Multiple Standard
Additions On Sample
Give Uniform Increments?
Is the Procedure in
Use Correct?
Are the Reagents Working Properly?
Yes
No
No
No
Yes
No
Yes
Yes
No Yes
Do Multiple
Standard Additions
On DI Water Give
Correct Recovery?
Yes
No
Are
Interferences
Present?
Yes
No
No
Yes
Did a Single Standard Addition Give the Correct Recovery?
Figure 1
Standard Additions
Decision Tree
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