91Ó°ÊÓ

A spike, also called a fortification, is a known quantity of analyte added to a sample to test whether the response to the spike is the same as that expected from a calibration curve.

Spiked samples are analysed in the same manner as unknowns.

For example, if drinking water is found to contain $\mathbf{10}\mathbf{.}\mathbf{0}\mathbf{μ²\mu }$of nitrate, a spike of$\mathbf{5}\mathbf{.}\mathbf{0}\mathbf{μ²\mu }\mathbf{/}\mathbf{L}$could be added. Ideally, the concentration in the spiked portion found by analysis will be$\mathbf{15}\mathbf{.}\mathbf{0}\mathbf{μ²\mu }\mathbf{/}\mathbf{L}\mathbf{.}$If a number other than $\mathbf{15}\mathbf{.}\mathbf{0}\mathbf{μ²\mu }\mathbf{/}\mathbf{L}$is found, then the matrix could be interfering with the analysis.

$\%\mathrm{recovery}=\frac{{\mathrm{C}}_{\mathrm{spiked}\mathrm{sample}}-{\mathrm{C}}_{\mathrm{unspiked}\mathrm{sample}}}{{\mathrm{C}}_{\mathrm{aded}}}×100$

The percent of the spike found by analysis is

$$\begin{gathered} \%recovery \\ =\frac{15.3\mathrm{μ}g/L-10.0\mathrm{μ}g/L}{5.0\mathrm{μ}g/L}×100 \\ =106\% \end{gathered}$$

If the acceptable recovery is specified to be in the range from$96\%\mathrm{to}115\%\mathrm{then}106\%$ is unacceptable. Something in your method or techniques needs improvement.