Hach-Lange DR 2800 eco - Manual (Page 86)

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Advanced Operations
6.2 Standard Addition – Monitoring/Checking Results (DR 2800 only)
The accuracy of measured values (their correspondence with the
actual concentration of the parameter in the sample) and their
precision (correspondence of the measurement results obtained
from several samples containing the same concentration of the test
parameter) can be determined or improved using the standard
addition method.
This method (also referred to as spiking) serves to identify
sample-specific interference factors, e.g. substances in the sample
that falsify the analysis (sample matrix effect), a defective
measuring instrument or contaminated reagents.
Method:
A defined amount (concentration) of a standard solution of the test
substance is added to the sample. The detection rate
(concentration of the added standard solution) should be close to
100%.
This procedure can be used with all HACH methods for which a
corresponding work step is included in the procedure.
Measures to identify other interference factors:
Checklist:
1. Check whether you carried out the procedure correctly:
a. Did you use the correct reagents in the correct sequence?
b. Did you adhere to the specified reaction times?
c. Did you use the correct laboratory glassware?
d. Was the laboratory glassware clean?
e. Does the test require the sample to be at a certain
temperature?
f. Was the pH of the sample in the correct range?
Detection rate Conclusion
100%
Probability that the measurement results are correct
is high.
< 100%
Assumption: The analysis was falsified by
substances 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.
¼ 100% No interference ions.