3.5.2.1 The limit of reporting (LOR)
The LOR is the practical limit of quantitation at or above the LOQ.
3.6
Ruggedness
The ruggedness (a measure of robustness) of a method is the degree to which results are unaffected by
minor changes from the experimental conditions described in the method, for example, small changes in
temperature, pH, reagent concentration, flow rates, extraction times, composition of mobile phase.
Ruggedness testing provides an indication of the methods reliability during normal usage. The aim of
ruggedness testing is to identify and, if necessary, better control method conditions that might otherwise lead
to variation in measurement results, when measurements are carried out at different times or in different
facilities. It can also be used to identify factors which need to be addressed to improve precision and bias.
Ruggedness is investigated by measuring the effects of small, planned changes to the method conditions on
the mean of the results. Trials need to be conducted with the aid of blank specimens, (certified) reference
materials, specimens of known composition, etc. To evaluate the degree of ruggedness, significance testing
may be carried out. In some cases, information may be available from studies conducted during in-house
method development. Intra-laboratory reproducibility investigations, by their nature, take into account some
aspects of a method’s ruggedness.
Ruggedness testing can be carried out by considering each effect separately, by repeating measurements
after varying a particular parameter by a small amount and controlling the other conditions appropriately
(single variable tests). However, this can be labour intensive as a large number of effects may need to be
considered. Experimental designs are available, which allow several independent factors to be examined
simultaneously. Hibbert (2007) describes Plackett-Burman experimental designs that provide an economical
Technical Note 17 - Guidelines for the validation and verification of quantitative and qualitative test methods
June 2012
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and efficient approach whereby (4n -1 ) variables are evaluated by conducting only 4n analyses. Both
approaches assume independence of effects.
In practice, an experienced analyst will be able to identify those method parameters with the potential to
affect results and introduce controls, e.g. specified limits for temperature, time or pH ranges, to guard against
such effects.
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