An aliquot of sample is spiked with a known concentration of target analyte(s). The spiking occurs prior to sample preparation and analysis. A matrix spike is used to document the bias of a method in a given sample matrix.
The percent recovery is calculated as:
%R = (spiked sample result - unspiked sample result)*100% / known spike added concentration
Here the difficulties are:
To identify the pair of injections "spiked sample" and "unspiked sample". It is possible to have several pairs of injections in a result set.
To define how the Spike added concentration is given.