Hach DR/700 Procedures Manual page 23

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.
Figure 1
Standard Additions
Decision Tree
B
No
D
Is the Procedure in
Use Correct?
No
Use Correct
Procedure and
Repeat B
E
Are the Reagents Working Properly?
No
Repeat B with
New Reagents
Did a Single Standard Addition Give the Correct Recovery?
No
A
Are
Interferences
Present?
No
Do Multiple
Standard Additions
On DI Water Give
Correct Recovery?
C
Give Uniform Increments?
F
Analysis
Is Incorrect
Yes
H
Is Instrument Apparatus Working Properly?
No
Repair/Replace
Instrument Apparatus
and Repeat B
Yes Yes Yes
Do Multiple Standard
Additions On Sample
No Yes
G
Analysis May
be Correct
Yes
Yes
I
Standards Defective
Repeat B with New
Standards
1-5
Yes
J
Are
Interferences
Present?
No
K
Analysis
Is Correct