 Michael Thompson

Michael Thompson is an analytical chemistry researcher named at Birkbeck College in the 1999 international guidelines on using recovery information in analytical measurement. The paper addresses how losses during sample preparation affect reported results, their comparability and their measurement uncertainty. Its authorship and affiliation identify this contribution without conflating other scientists of the same name.^[ref]

A central distinction is between correcting an estimated loss and treating the correction as perfectly known. In a specified recovery correction model,where $x$ is the uncorrected result and $r$ the estimated fractional recovery. The guide treats the determination's uncertainty and the recovery estimate's uncertainty separately. For independent inputs, first-order propagation givesThis states an uncertainty calculation, not a rule that every analytical measurand must be defined identically.^[ref]

For an original example, stipulate $x=8.0mg/kg$ with standard uncertainty $u(x)=0.20mg/kg$ and $r=0.80$ with $u(r)=0.04$. The corrected result is $10.0mg/kg$ andTreating recovery as exact would give only $u(x)/r=0.25mg/kg$. The added uncertainty describes limited knowledge of the correction; omitting it does not make the physical measurement more reliable. Correlated estimates require the appropriate covariance term instead of this independent-input formula.

The experiment used to estimate recovery also matters. An added, readily dissolved analyte may not behave like native analyte strongly bound within the sample matrix. The guidelines discuss this limitation of surrogate recovery studies and the need to consider matrix variation.^[ref] A useful validation therefore specifies what material was added, when it was added, which matrices were represented and whether the procedure had time to equilibrate.

Thompson and his collaborators' reporting recommendations call for identifying whether results are recovery corrected and how the correction was obtained. This makes two laboratories' numbers interpretable: a corrected estimate of total analyte and a reproducible result defined by a particular extraction procedure can otherwise look like measurements of the same quantity when they are not.^[ref]