Ruggedness of method

In summary, official German analytical methods for pesticide residues are always validated in several laboratories. These inter-laboratory studies avoid the acceptance of methods which cannot readily be reproduced in further laboratories and they do improve the ruggedness of analytical procedures applied. The recently introduced calibration with standards in matrix improves the trueness of the reported recovery data. Other aspects of validation (sample processing, analyte stability, extraction efficiency) are not considered. 

Sample preparation consists of homogenization, extraction, and cleanup steps. In the case of multiresidue pesticide analysis, different approaches can have substantially different sample preparation procedures but may employ the same determinative steps. For example, in the case of soil analysis, the imidazolinone herbicides require extraction of the soil in 0.5 M NaQH solution, whereas for the sulfonylurea herbicides, 0.5M NaOH solution would completely decompose the compounds. However, these two classes of compounds have the same determinative procedure. Some detection methods may permit fewer sample preparation steps, but in some cases the quality of the results or ruggedness of the method suffers when short cuts are attempted. For example, when MS is used, one pitfall is that one may automatically assume that all matrix effects are eliminated because of the specificity and selectivity of MS. 

Some more recent field techniques have focused on the location of the preparation of field fortification samples and have taken some of the responsibility for the preparation of the field fortification samples from the field personnel and placed them with the analytical laboratory. For example, it is becoming more common for the analytical laboratory to prepare air sample field fortifications in the analytical laboratory, freeze them, and ship them to the field for use in a frozen state. Whereas there may be some advantage to this technique in that the air tube fortification samples may possibly be fortified more accurately in the laboratory under controlled conditions than if done in the field, there are some inherent scientific problems with this method. First, one reason for the field fortification is to test the ruggedness of the field techniques of the researcher under extreme field conditions. Second, the act of freezing and thawing the sorbent matrix within the air mbe itself may have an impact on the recovery of the analyte from the air tube after exposing the sorbent to field conditions... 

Consequently, it was proposed to define (Burns et al. [2005]) Robustness of an analytical procedure is the property that indicates insensitivity against changes of known operational parameters on the results of the method and hence its suitability for its defined purpose and Ruggedness of an analytical procedure is the property that indicates insensitivity against changes of known operational variables and in addition any variations (not discovered in intra-laboratory experiments) which may be revealed by inter-laboratory studies (Burns et al. [2005]). 

The range of relative ruggedness is range rug = (0... 1), too. According to Burns et al. [2005], the relative ruggedness of an analytical procedure is given by the ratio of the ideal signal for an uninfluenced method corn-... 

The robustness of an analytical method can be defined as a measure of the capability of the method to remain unaffected by small, but deliberate, variations in method parameters. The parameter therefore provides an indication of the method reliability during normal usage. The ruggedness of a method is the degree of reproducibility of test results obtained by the analysis of the same samples under a variety of conditions, such as different laboratories, different analysts, different instruments, different lot of reagents, different days, etc. 

Precision estimates are key method performance parameters and are also required in order to carry out other aspects of method validation, such as bias and ruggedness studies. Precision is also a component of measurement uncertainty, as detailed in Chapter 6. The statistics that are applied refer to random variation and therefore it is important that the measurements are made to comply with this requirement, e.g. if change of precision with concentration is being investigated, the samples should be measured in a random order. 

The chromatogram of Cabernet Sauvignon wine is shown in Fig. 2.100. It was concluded from the results that the baseline separation of each analyte under investigation, and the good linearity and ruggedness of the method allow its application for the routine analysis... 

Method precision refers to the variability in measurement of the same sample. There are three main components of method precision repeatability (also known as system or intraassay precision), intermediate precision (also known as inter-assay or intra-laboratory precision), and reproducibility precision (also known as ruggedness, overall or inter-laboratory... 

A review of ruggedness testing methods is presented in Chapter 3 and in Chapter 5 examples are given. In these chapters procedures are described that test the robustness or ruggedness of existing methods. Hence, incorporating robustness explicitly in analytical techniques (see Section 1.1) is not discussed. 

If robustness has to be build in, then the concept of robustness has to be formalized and optimized. This is contrary to the class of methods that check the robustness or ruggedness of existing methods then the influence... 

The ruggedness of an analytical method can generally be described as the ability to reproduce an analytical method in different laboratories or in different circumstances without the occurrence of unexpected differences in the obtained results. 

A ruggedness test is a part of method validation (Table 3.1) and can be considered as a part of the precision evaluation [2,4,5]. Ruggedness is related to repeatability and reproducibility. Some definitions for ruggedness come very close to those for reproducibility. Certain interpretation methods to identify the significant factors in a ruggedness test use criteria based on results for repeatability or reproducibility. These two items will be considered in Section 3.4.7. 

The Canadian Acceptable Methods document [14] gives more or less a combination of the two definitions described above and considers 3 levels in the testing of the ruggedness of a method, with the third level being performed only rarely. Level one requires verification of the basic insensitivity of the method to minor changes in environmental and operational conditions and should include verification of reproducibility by a second analyst . The first part of this definition resembles the French Guide s definition. The second part is a check on the adequacy of the method description and should be done without input from the original analyst. 

To examine the ruggedness of the factors that were selected one could test these factors one variable at a time, i.e. change the level of one factor and keep all other factors at nominal level. The result of this experiment is then compared to the result of experiments with all factors at nominal level. The difference between the two types of experiments gives an idea of the effect of the factor in the interval between the two levels. The disadvantage of this method is that a large number of experiments is required when the number of factors is large. 

Inserting tolerance intervals of the chromatographic responses in this equation results in rugged intervals for the factors. By comparing these intervals with the inaccuracy of the settings of the experimental conditions a statement about the ruggedness of the method is made. The tolerance intervals of the responses are defined by the experimentator, e.g. 2.5% difference in the area response between two independent analyses is considered acceptable in reference [16], i.e. a value of 0.025 0.307=0.0076 for the above mean response. The rugged interval for the injection temperature is then obtained from equation (29) ... 

The ruggedness of a method can be tested using two types of experimental designs. Procedure related factors at the one hand are examined mainly in screening designs of the Plackett-Burman or... 

The study of the precision of a method is often the most time and resource consuming part of a method validation program, particularly for methods that are developed for multiple users. The precision is a measure of the random bias of the method. It has contributions fi om the repeatability of various steps in the analytical method, such as sample preparation and sample injection for HPLC [5-9], and from reproducibility of the whole analytical method fiom analyst to analyst, fiom instrument to instrument and fiom laboratory to laboratory. As a reproducibility study requires a large commitment of time and resources it is reasonable to ensure the overall ruggedness of the method before it is embarked upon. 

---