Hach-Lange DR 3900 User Manual - Manual (Page 93)

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Expanded programs
4. Press OK to confirm.
Note: If a Favorite Program is deleted, it will stay in the User
Programs or Stored Programs.
Note: If the stored program is deleted in User Programs, it will also
be deleted in Favorites Programs.
6.3 Standard Addition - monitoring/checking results
The accuracy of readings (their correspondence with the actual
concentration of the analyte in the sample) and their precision
(correspondence of the reading results obtained from several
samples containing the same concentration of the test analyte)
can be determined or improved using the standard addition
method
This method (also known as standard-addition or spiking) serves
to detect sample-specific faults:
• The analysis was compromised by substances or
interferences in the sample (sample matrix effect),
• defective measuring device,
• impure reagents.
Method:
Add a defined quantity (concentration) of the substance to be
tested to the sample as a standard solution. The detection rate
(concentration of the added standard solution) should be close to
100 %.
Detection rate =
Reading of successful standard addition
Expanded value after successful standard
addition
Detection rate Conclusion
100 %
Probability that the reading results are correct
is high.
≠ 100 %
Assumption: The analysis was compromised
by substances or interferences in the sample
(sample matrix effect)
Test to determine whether a sample matrix
effect is present:
Use distilled water instead of the sample. Add
standard solution as described in the
procedure.
Detection rate Conclusion
100 %
Ions in the sample are
interfering with the
analysis, causing false
results to be obtained.
≠ 100 % No interference ions.