Extraction recovery

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 apparent recovery, an observed/reference comparison involving a calibrated analytical result.^[ref]

Concentration alone is insufficient. In an original example, $10\mathrm{mL}$ at $10\mu \mathrm{mol}{\mathrm{L}}^{-1}$ contains $100\mathrm{nmol}$ of analyte. A final extract of $2\mathrm{mL}$ at $30\mu \mathrm{mol}{\mathrm{L}}^{-1}$ 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.^[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.