Validation method scope

Before performing a validation method for a certain application, the scope of the method and its validation criteria should be defined first. The parameters to be investigated include compounds, matrices, types of formation, qualitative or quantitative method, detection or quantitation limit, linear range, precision and accuracy, types of equipment that will be used, and the location of the system. These steps of the validation method are illustrated in Fig. 1, which has been modified from Ref. [11],... 

Before any method validation is started, the scope of validation must be fixed, comprising both the analytical system and the analytical requirement. A description of the analytical system includes the purpose and type of method, the type and concentration range of analyte(s) being measured, the types of material or matrices for which the method is applied, and a method protocol. On the basis of a good analysis lies a clear specification of the analytical requirement. The latter reflects the minimum fitness-for-purpose criteria or the different performance criteria the method must meet in order to solve the particular problem. For example, a minimum precision (RSD, see below) of 5% may be required or a limit of detection (LOD) of 0.1% (w/w) [2,4,15,58]. The established criteria for performance characteristics form the basis of the final acceptability of analytical data and of the validated method [58]. 

A question of increasing importance to both suppliers and users of RM is the scope of a matrix RM, i.e. the extent to which a reference matrix of a particular type (e.g. a sediment) may properly be used to validate methods used for the routine analysis of test sample matrices of a different type (e.g. a soil). Relating different matrix types in this way is sometimes referred to as com-... 

Parameters usually examined in the validation process are limit of detection, limit of quantitation, bias, precision, selectivity, linearity, range and ruggedness. Limits will be set for each relevant parameter, and if these are achieved during the performance tests the results are documented and the method is said to be fit for purpose and now is a validated method for a given scope (see Section 2.3). 

Validation as one of the milestones of ISO/IEC 17025 is required to be performed each time non-standard methods, procedures developed in-house or methods outside their intended scope are used. Additionally, according to the same standard, every laboratory should confirm that it can properly operate standard or validated methods (procedures) before (first) introducing the tests, which, as a consequence again include the validation principle. The scope of validation ( objective evidence )... 

As simplified validation procedures ( fast validation methods) must be used in many cases, the capability to use professional judgement in assessing whether the validation is comprehensive enough becomes pronounced. However, even when talking about simplified or fast validation procedures, the validation must be done with such a depth that the method is fit for the intended use and acceptable to the customer and/or authorities. It is clear that the definition of the use and scope of the method and assumption of uncertainty should not be misleading and too optimistic. 

Without fully documented and properly validated methods, analysts, or others who use the data provided by analysts, will not have the confidence to ensure that the results that are generated are fit for the purpose for which they were originally intended. Methods should be fully documented, and should clearly and unambiguously describe the determinand being determined as well as the concentration range of the determinand for which the method is applicable, and the matrix, or matrices, to which the method can be applied. In addition, clear details of the procedures to be followed should be documented in such a manner that the text cannot be open to mis-interpretation and that the analyst can precisely carry out that which needs to be done. Without all this information, the scope of the method cannot be clearly defined and the method will often be misused, for example, in the inappropriate determination of parameters... 

FIGURE 3.3 Steps in method development. A systematic approach for defining and devel oping a method is shown from the initial steps of determining the method scope to evaluation of reagents, method development, and optimization, and finally, transfer to prestudy validation. 

It is necessary to first understand what we should expect to achieve from method validation. There are three basic considerations (1) the validation should define the method scope, which includes the analyte/matrix combinations to which the method can be applied and the concentration range within which reliable results have been demonstrated ... 

Results from these samples should be recorded continuously, and the data are used to verify that the test works reliably. The choice of analytes to include in routine QC samples should follow the same rules as those selected for the initial or abridged validation exercise, that is, the worst-case analytes that are listed in the method scope or the most relevant analytes in a national control plan. Even if the use of spiked samples as QC is applicable, it is highly preferable to use incurred samples where possible. QC samples should be stored for a period determined by the laboratory according to stability data available for the analyte/matrix. The data obtained with the QC samples should be stored and remain traceable as long as the method is used in the laboratory. The results obtained from the QC samples should be used to supplement the initial and abridged validation data. 

The scope of this chapter is limited to troubleshooting HPLC systems using predeveloped and validated methods of analysis. We will focus on some of the most commonly encountered problems and the possible solutions. 

This method has been widely used in the past but there now are much more sophisticated and statistically-valid methods for evaluation of reactivity ratios. However, they are beyond the scope of this book and the reader is recommended to consult an up-to-date advanced review of copolymerization for details. 

It would clearly be desirable to extend the scope of the Kelvin method to include a range of adsorptives having varied physical properties, especially surface tension, molar volume, molecular shape and size. This would enable the validity of the method and its attendant assumptions to be tested more adequately, and would also allow a variation in experimental technique, for example by permitting measurements at 298 K rather than 77 K. 

It would be difficult to over-estimate the extent to which the BET method has contributed to the development of those branches of physical chemistry such as heterogeneous catalysis, adsorption or particle size estimation, which involve finely divided or porous solids in all of these fields the BET surface area is a household phrase. But it is perhaps the very breadth of its scope which has led to a somewhat uncritical application of the method as a kind of infallible yardstick, and to a lack of appreciation of the nature of its basic assumptions or of the circumstances under which it may, or may not, be expected to yield a reliable result. This is particularly true of those solids which contain very fine pores and give rise to Langmuir-type isotherms, for the BET procedure may then give quite erroneous values for the surface area. If the pores are rather larger—tens to hundreds of Angstroms in width—the pore size distribution may be calculated from the adsorption isotherm of a vapour with the aid of the Kelvin equation, and within recent years a number of detailed procedures for carrying out the calculation have been put forward but all too often the limitations on the validity of the results, and the difficulty of interpretation in terms of the actual solid, tend to be insufficiently stressed or even entirely overlooked. And in the time-honoured method for the estimation of surface area from measurements of adsorption from solution, the complications introduced by... 

The mathematical principles of convective heat transfer are complex and outside the scope of this section. The problems are often so complicated that theoretical handling is difficult, and full use is made of empirical correlation formulas. These formulas often use different variables depending on the research methods. Inaccuracy in defining material characteristics, experimental errors, and geometric deviations produce noticeable deviations between correlation formulas and practice. Near the validity boundaries of the equations, or in certain unfavorable cases, the errors can be excessive. 

The BET method has its limitations and several improvements exist, but these are beyond the scope of our treatment. We note that the BET isotherm is valid under the following assumptions ... 

Because the validation of the last technique requires a different approach to chromatographic and spectrometric methods, several important points are described in SANCO/825/00 which should be taken into account when such methods are used. The authors do not wish to go into detail on this subject, since on the one hand very few methods have been submitted up to the present, and on the other hand it would go beyond the scope of this article. 

Most often studies will be accepted by regulatory authorities even if they do not contain all information. For example, a summary, the scope, a separate notice regarding the residue definition or a schematic diagram of the analytical procedure are helpful and may avoid additional questions, but they are not essential. Also, detailed specification of standard glassware or chemicals commonly used in residue analysis is less important. Finally, data about extraction efficiency or analyte stability can be offered in separate studies or statements, which are also valid for other methods. However, each method must precisely describe at the minimum ... 

In contrast to multi-analyte/multi-matrix methods, a more or less complete validation of methods with limited scope is possible. For this reason, TC 275 decided that... 

The sensitivity achieved (LOD) is not normally presented. It is recognized that different laboratories determine dissimilar values for this parameter and even within a laboratory the repeatability of the LOD is low. Most often, the lowest validated concentration gives an impression about the lowest levels that can be analyzed generally with acceptable results. A measure of selectivity is the intensity of blank results. This intensity is discussed by the participants of inter-laboratory validation studies. However, results are not reported and limits are not defined by CEN TC 275. The results of method validations of the several multi-residue/multi-matrix methods are not reported in the same way, but newer methods with limited scope generate analogous tables with validation results (as an example, see Table 7). 

Different sample materials often need some adjustment of pesticide residue methods. The insufficient consideration of matrices in thcNKML method validation protocol may be a tribute to the wide scope of this standard. 

Any validation and verification work performed must always be documented in such a way that the results can be checked and the scope of a method is clear. International standards, e.g., ISO 17025, contain separate sections regarding documentation, which should be observed. The NMKL procedure on method validation states that It is of particular importance that the report includes all raw data from the experimental work, or references to where such data can be found . In some circumstances this complete documentation is impractical. Even where it is practical, it is usually impossible to publish these results together with the methods. 

In Europe, very different concepts of method validation are in use. The extent of validation depends upon legal requirements (e.g., for enforcement methods provided by the applicant), upon the required level of acceptance (e.g., for CEN methods) and upon national resources. Undoubtedly, the best method validation is performed with the help of inter-laboratory studies of performance, but such studies can be uneconomic, too slow to reach completion or restricted in scope. 

The workhorses in national monitoring programs are multi-residue methods. Any official method collection of any EU Member State contains at least one multi-residue method. For multi-analyte and/or multi-matrix methods, it is likely to be impractical to validate a method for all possible combinations of analyte, concentration and type of sample matrix that may be encountered in subsequent use of the method. Therefore, initial validation should incorporate as many of the target analytes and matrices as practicable. For practical reasons this validation and the evaluation of other methods with limited scope often cannot be conducted in inter-laboratory studies. Other concepts based on independent laboratory validation or validation in a single laboratory have been developed and can provide a practical and cost-effective alternative (or intermediate) approach. 

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