Hach DR 2800 user manual Standard Addition monitoring/checking results, Method

Advanced Operations

6.3 Standard Addition – monitoring/checking results

The accuracy of measured values (their correspondence with the actual concentration of the analyte in the sample) and their precision (correspondence of the measurement 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 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 should be close to 100%.

Measured value after a standard addition

Detection rate = ------------------------------------------------------------------------------------------------------------

Expected value after a standard addition

Detection rate	Conclusion
100%	Probability that the measurement results are correct
	is high.
	Assumption: The analysis was falsified by
	substances in the sample (sample matrix effect)
< 100%	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
		Ions in the sample are
	100%	interfering with the
		analysis, causing false
		results to be obtained.
		No interfering ions -
	≠ 100%	consider other
		interference factors.

Measures to identify other interference factors:

Checklist:

1.Check if the procedure is completed correctly:

a.Are the reagents added in the correct order?

b.Is enough time allowed for color development?

c.Is the correct glassware in use?

d.Is the glassware clean?

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