Robustness and Ruggedness

For a method to be useful it must provide reliable results. Unfortunately, methods are subject to a variety of chemical and physical interferences that contribute uncertainty to the analysis. When a method is relatively free from chemical interferences, it can be applied to the determination of analytes in a wide variety of sample matrices. Such methods are considered robust. 

Random variations in experimental conditions also introduce uncertainty. If a method s sensitivity is highly dependent on experimental conditions, such as temperature, acidity, or reaction time, then slight changes in those conditions may lead to significantly different results. A rugged method is relatively insensitive to changes in experimental conditions. 

As expected, the concept of selectivity and specificity is closely related to that of sensitivity. The same may be anticipated for the concept of robustness and ruggedness. 

Methods can only usefully applied in analytical practice when they are sufficiently robust and therefore insensitive to small variations in method conditions and equipment (replacement of a part), operator skill, environment (temperature, humidity), aging processes (GC- or LC columns, reagents), and sample composition. This demand makes robustness (ruggedness) to an important validation criterion that has to be proved by experimental studies. The concepts of robustness and ruggedness mostly have been described verbally where it must be stated that their use is frequently interchangeably and synonymously (e.g., Hendricks et al. [1996] Kellner et al. [1998] EURACHEM [1998] ICH [1994, 1996] Wunsch [1994] Wildner and Wunsch [1997] Valcarcel [2000] Kateman and Buydens [1993]). 

Only in a few cases was there a distinction made between both concepts by their use in intra laboratory studies (robustness) and interlaboratory studies (ruggedness) see USP 23-NF18 [1995] USP 24-NF19 [2000] Rodriguez et al. [1998] Zeaiter et al. [2004]. Wahlich and Carr [1990] seem to be the first to use robustness and ruggedness in a hierarchical sense but in a reverse meaning as given above. 

ICH [1994] defines robustness as follows The robustness of an analytical procedure is a measure of its capacity to remain unaffected by small, but deliberate variations in method parameters and provides an indication of its reliability during normal use . 

Whereas this definition of ruggedness directly refers to infer-laboratory studies, the ICH definition of robustness clearly is related to infra-laboratory studies. 

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A calibration procedure has to be validated with regard to general and specific requirements under which the calibration model has been developed. For this purpose, it is important to test whether the conditions represented in Fig. 6.6 are fulfilled. On the other hand, it is to assure by experimental studies that certain performance features (accuracy, precision, sensitivity, selectivity, specificity, linearity, working range, limits of detection and of quantification, robustness, and ruggedness, see Chap. 7) fulfil the expected requirements. 

The problem, particularly in analytical practice is that most of the parameters needed for the calculation of relative robustness and ruggedness may frequently be unknown. 

In such cases it may be possible to check on robustness and ruggedness by means of statistical tests (see Sect. 4.3). All the variations to the measured signal, apart from that of the analyte, can be considered in form of error terms see Eq. (3.6) ... 

In the following example, robustness and ruggedness of a procedure used in two laboratories, LI and L2, will be considered. It is supposed that they use the same procedure to determine the analyte A in the presence of the interferents B and C under the influence of the factors a, b, and c. The input data for the computation are given in the following table. 

Burns DT, Danzer K, Townshend A (2005) IUPAC, Analytical Chemistry Division Use of the terms Robust and Rugged and the associated characteristics of Robustness and Ruggedness in descriptions of analytical procedures. Draft 2005... 

Ruggedness can be determined by an interlaboratory study with a sufficient in > 8) participating laboratories following one and the same procedure as performed by different analysts, and using operational and environmental conditions that may differ but are still within the specified parameters of the assay [1, 41]. Detailed guidance for robustness and ruggedness testing is available [42, 43],... 

Method validation Basic method validation (short-term use, fit for purpose, little robustness), data will see expert eye prior to release Extended method validation, robustness and ruggedness tests important for unsupervised operation... 

This review describes the determination of robustness and ruggedness in analytical chemistry. The terms ruggedness and robustness as used in method validation are sometimes considered to be equivalent [1,2], In other publications a difference is made between the two terms [3]. In the following only the term ruggedness will be used. 

What is the difference between an instrument detection limit and a method detection limit What is the difference between robustness and ruggedness ... 

The outcome of the different exercises should be discussed among all participants in technical meetings, in particular to identify random and/or systematic errors in the procedures. Whereas random errors can be detected and minimised by intralaboratory measures, systematic errors can only be identified and eliminated by comparing results with other laboratories/techniques. When all steps have been successfully evaluated, i.e. all possible sources of systematic errors have been removed and the random errors have been minimised, the methods can be considered as valid. This does not imply that the technique(s) can directly be used routinely and further work is likely to be needed to test the robustness and ruggedness of the method before being used by technicians for daily routine measurements . 

Preliminary analyte stability in biological matrix Parallelism/dilutional linearity Robustness and ruggedness... 

Robustness and ruggedness are two analytical performance characteristics that are related closely, and often not easy to distinguish. The main focus of any robustness/ ruggedness investigation is to address the question of whether the assay will be able to withstand changes in the standard laboratory conditions. The robustness of an... 

During the prestudy evaluation phase, an attempt should be made to evaluate the variety of conditions that may reflect the execution and performance of the method during the in-study phase. The final conditions should be clearly documented in the analytical procedures prior to in-study sample analysis. As an example, robustness assessment could include incubation time tolerances, while ruggedness assessment could include changes in analysts and batch size (Table 4.7). Most robustness and ruggedness evaluations are empirical in nature however, more formal evaluations can also be used [29]. 

The optimization and validation of immunoassays for immunogenicity (ADA) testing has been described in detail in several publications [9,14,33,34]. In this section, we will describe the evaluation of relevant performance characteristics (validation parameters) that require the most effort. Some of these are different from the validation of traditional bioanalytical pharmacokinetic (PK) methods for macromolecules [35 37]. Precision, specificity, robustness, and ruggedness are determined similarly between ADA and PK methods. However, recovery/accuracy, sensitivity, stability, linearity, system suitability controls, and selectivity are treated differently between these two types of assays. 

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