Measurement uncertainty: Approaches to the evaluation of uncertainties associated with recovery†

Abstract

A number of approaches for evaluating recovery and its contribution to uncertainty budgets for analytical methods are considered in detail. The recovery, R, for a particular sample is considered as comprising three elements, R m , R s and R rep . These relate to the recovery for the method; the effect of sample matrix and/or analyte concentration on recovery; and how well the behaviour of spiked samples represents that of test samples. The uncertainty associated with R, u(R), will have contributions from u(R m ), u(R s ) and u(R rep ). The evaluation of these components depends on the method scope and the availability, or otherwise, of representative certified reference materials. Procedures for evaluating these parameters are considered and illustrated with worked examples. Techniques discussed include the use of certified reference materials and spiking studies, and the use of extraction profiling to predict recoveries. All the approaches discussed evaluate the recovery and its uncertainty for the analytical method as a whole. It is concluded that this is a useful approach as it reduces the amount of experimental work required. In addition, most of the required data are frequently available from method validation studies.

Operational definitions of uncertainty

“…It consists in adding the absolute value of the uncorrected bias to the expanded uncertainty, the latter being calculated assuming that the bias is zero. This approach is also followed by Barwick and Ellison [ 17 ], but they include the recovery ( expressed in a relative way ) in the standard uncertainty by taking into account the coverage factor, k, that will be used in the calculation of the expanded uncertainty. With the same approach applied here, Eq.…”

“…The IUPAC report discusses the problems related to recovery estimation and the possibilities of corrections [ 14 ]. Barwick and Ellison [ 17 ] focus on the evaluation of the uncertainties associated with recovery. Even though recovery is usually regarded in a relative way, absolute expressions are used in the following, since this corresponds with the other expressions used.…”

Measurement Uncertainty in Forensic Toxicology: Its Estimation, Reporting and Interpretation

“…This is often referred to as a "reference recovery" or a "method recovery". (Barwick and Ellison, 1999) When recovery estimates are applied to correct subsequent samples, it is very important that the concentrations and matrix are appropriately similar and that the same full analytical protocol is followed. Measurements of recovery from several spiked samples may be performed with the mean and standard deviation of the percent estimates determined, providing uncertainty estimates for the percent recovery in future measurements.…”

Validation of an analytical methodology for the quantitative analysis of petroleum hydrocarbons in marine sediment samples

“…17 The uncertainty estimation was made according to a procedure proposed in the literature. 18,19 The precision and recovery studies undertaken for the validation, were planned and executed in such a way that provide the data required to produce an estimated of the measurement uncertainty. The concentration range covered by the recovery study was used.…”