= Extraction recovery
\b[Extraction recovery] is the fraction of an <analyte> amount recovered after a specified extraction stage. For input amount $n_0$ and recovered amount $n_1$, write $r=n_1/n_0$ when $n_0>0$. The same quantity basis must be used in numerator and denominator. IUPAC distinguishes this preparation yield from \i[apparent recovery], an observed/reference comparison involving a calibrated analytical result.<Use of the term "recovery" and "apparent recovery" in analytical procedures by D. T. Burns and others>[Abstract, separate meanings of recovery and apparent recovery.]{ref}
Concentration alone is insufficient. In an original example, $10\,\mathrm{mL}$ at $10\,\mu\mathrm{mol\,L^{-1}}$ contains $100\,\mathrm{nmol}$ of <analyte>. A final extract of $2\,\mathrm{mL}$ at $30\,\mu\mathrm{mol\,L^{-1}}$ contains $60\,\mathrm{nmol}$. Recovery is $60/100=0.60$, or $60\%$, even though concentration increased threefold. Shrinking the volume can enrich a sample while losing material.
Measured response also need not track recovered amount with the same proportionality in different <sample matrices>. A method study explicitly distinguished matrix response from recovery in quantitative <liquid chromatography>–<mass spectrometry>.<Strategies for the assessment of matrix effect in quantitative bioanalytical methods based on HPLC-MS MS by B. K. Matuszewski and others>[Abstract, experiments separating matrix effects and true recovery.]{ref} In a matched comparison, adding equal nominal <analyte> amounts before preparation and after preparation can isolate preparation loss only if final volumes, acquisition and response conditions are adequately controlled.
A <recovery correction> divides an observed amount by an appropriate recovery estimate. A measured $6\,\mathrm{nmol}$ with $r=0.60$ gives $10\,\mathrm{nmol}$ before that loss, under the model. This is an inference, not recovered physical material. If the estimated recovery changes with sample composition or <analyte> level, applying one constant can introduce error. A measured apparent recovery above 100% need not represent creation of <analyte> during extraction; background, calibration, chemical conversion and the reference basis require examination.
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