Laboratory Quality Control Sample - Duplicates and RPD

Created by: Andrew White

Modified on: Tue, 7 May, 2019 at 1:09 PM


Laboratory Duplicates

A second aliquot from a randomly chosen sample within an analytical batch processed through the entire analytical method.


Laboratory duplicates are expressed as the Relative Percent Difference (RPD) between the two results.


Frequency and Purpose

Mandatory. Minimum of 1 in a batch of 15 to 20 samples; or at an average frequency of 5% of total samples.


Evaluates analytical precision and sample homogeneity.


Application and Regulatory Criteria


When concentrations are <5xMDL, the difference shall not be >2xRDL. (There may be allowance for less rigorous criteria for specific tests known to be challenging.  Please confirm with your local regulatory body for additional guidance.


Recommended Actions


Bureau Veritas Laboratories uses and recommends 2 to 5xRDL for each sample concentration, in order for RPDs to be calculated. This alert criteria results in less uncertainty for concentrations close to the RDL. The laboratory will repeat affected sample. If still not acceptable, inspect for homogeneity and qualify data appropriately.



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