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Chapter 3.5. EXAMPLES FOR THE STANDARD ADDITION METHOD

United Kingdom

Original text. Later amendments are not shown.

A test sample with a content T of the analyte is divided in two test portions 1 and 2 of respective masses m1 and m2. The test portion 2 is spiked with a volume VA of a solution of concentration ρA of the analyte. Two extracts of the test portions of respective volumes V1 and V2 are obtained after extraction and purification steps of the method. The recovery of the analyte is supposed to be rc. Both extracts are assayed with a measurement method of sensitivity b and give an analytical response of x1 and x2 respectively.

If assumed that rc and b are the same for the analyte in the native sample and in the spiked sample, then the content T can be calculated as:

T =  x 1 . V 1 . ρ A . V A /( x 2 . V 2 . m 1 -  x 1 . V 1 . m 2 )

The method will allow the determination of the recovery rc. Then, in addition with the assay described above, part of the extract of the test portion 1 (volume V3) is spiked with a known amount ρB.VB of the analyte and assayed. The analytical response is x3 and the recovery is:

rc =  x 2 . V 1 . V 2 . ρ B . V B /[ x 3 . V 1 . V 3 (T. m 2 + ρ A . V A ) -  x 2 . V 2 .T. m 1 ( V 3 - V B )]

Moreover, it is possible to calculate the sensitivity b, as:

b =  x 1 . V 1 /rc.T. m 1

All conditions of application and details have been described (18).

Notes on Annex I

Textual amendments

F1

Replaced by virtue of 2003/181/EC: Commission Decision of 13 March 2003 amending Decision 2002/657/EC as regards the setting of minimum required performance limits (MRPLs) for certain residues in food of animal origin (Text with EEA relevance) (notified under document number C(2003) 764)