What is the impact of surrogate recovery?

Modified on: Wed, 30 Jan, 2019 at 2:29 PM

Surrogates are compounds added to the sample either at the initiation of the sample extraction process (Extraction Surrogate), or at a  step immediately prior to loading on the instrument (Instrument Surrogate). Surrogates  are selected using the following criteria:

1. The surrogate should be chemically similar to  the test code parameters. This is of particular importance with respect to the  Extraction Surrogate as its recovery is a key indicator regarding the  effectiveness of the extraction process. 

2. The surrogates should chromatograph or respond on the test instrument similarly to the test parameters. 

3. The surrogate’s response on the instrument should be stable, reproducible and resolve effectively, or has inherent properties, to allow it to be differentiated from the parameters of interest. 

There are allowances for the failure of surrogates in specific situations. 

If an analysis should have a minimum of four Instrument  Surrogates, one is allowed to fail. 

Failure of the Extraction Surrogate is only  allowed under specific circumstances. An Extraction Surrogate make fail “high” if a high background concentration of native components exists within the test  sample that interfere with the surrogate. 

An Extraction Surrogate may fail  “low” if a test sample or extract requires a large dilution factor to bring the  concentration of a test parameter within the instrument’s calibration range.  Dilution of the Extraction Surrogate may not be allowed if contractually not  permitted.

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