The accuracy of the procedure was assessed by
performing recovery experiments. Two different concentration
levels of the analytes, together with a fixed
concentration of the internal standard, were added to the
samples both before and after the extraction procedure.
The results obtained for the samples spiked after the
extraction procedure were considered to represent 100%
recovery. The recoveries were calculated according to
Eq. 1.
Recoveryð%Þ ¼ Cbefore
Cafter
100 ð1Þ
where Cbefore and Cafter are the analyte concentrations of
the samples spiked before and after the extraction
procedure, respectively.