Single laboratory approach

In all cases, only laboratories of the highest and proven quality should be involved. 5.].4.1. Single laboratory approach 

The first two approaches using definitive or primary or reference methods within one single laboratory require that in this laboratory everything is done to eliminate sources of systematic errors. Experience has demonstrated that it is very difficult to achieve 100% certainty and that within the laboratory a systematic bias does not remain. An additional confirmation through an — even limited — interlaboratory study is therefore advisable. Such an approach is used by NIST the single laboratory certification complies with the demand of US law that results and certificates must be NIST traceable . 

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Food methods validated by a collaborative trial study and those validated using the single-laboratory approach have been adopted as national and international standards by, e.g. CEN, International Organisation for Standardisation (ISO), AOAC International and by the Joint FAO/WHO Codex Alimentarius Food Standards Programme. A number of EN Standards developed by CEN relate to the organisation of controls. It is however important to keep in mind that, in addition to the method performance criteria, economical and prevention strategy... 

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. 

Both within a single laboratory or in an interlaboratory study, the approach to assessing bias and recovery is similar. The method is assessed using either reference materials with known quantity values, or the analysis of a test material is compared with the results of analysis of the same material... 

Whilst this may be sustainable (albeit undesirable) for some applications within a single laboratory, discipline becomes a necessity when methods have to be transferred reliably between laboratories in an organisation. When the scope of operation encompasses different organisations, national boundaries, etc., a uniformity of approach is essential if comparable results are to be obtained. 

There are two approaches to single-laboratory method validation The traditional one that identifies and then evaluates the set of analytical parameters, and a more recent one that is based on the evaluation of uncertainty. 

Unlike the majority of contributors to technical symposia, the authors of the chapters of both volumes are largely the members of a single Laboratory. This has provided the opportunity to achieve a greater unity in the discussions than is commonly found among symposia reports. It has also imposed more than normal demands on the authors, and our thanks are due to them for their endurance of the irksome process of developing a consistency of theme and style. We hope the result approaches a unified whole, yet retains the dynamism, the differences of opinion, and the subtleties of viewpoint of a living research program. 

For plant metabonomics studies, the principal approach has been to make extracts of the samples followed by chemical derivatization, and then to employ separation using GC with molecular identification using MS by comparing spectra against publically available and single-laboratory databases [10,11]. 

One other issue, also linked to the lack of standards, is the need of internationally validated methods. Several approaches can be used to validate a method, but the single-laboratory validation... 

Evolution of Single-Laboratory Validation and the Criteria Approach ... 

The fundamental problem with determining a detection limit for a method applied to trace quantities of an analyte extracted from a complex matrix is that many variables may affect the result on any given day. These include (but are not limited to) variability in matrix coextractives, variations in the source or the detector response, cleanliness of the detector cell, and variations between instruments if more than one instrument is available for use in the laboratory (particularly an issue for LC-MS and LC-MS/MS). The many issues that render determination of a detection limit more complex than it may initially appear are discussed in the lUPAC guidance on method validation in a single laboratory, where it is also suggested that for analytical systems where the validation range does not include or approach it, the detection limit does not need to be part of a validation. However, if a detection limit specification is critical to a regulatory result, it becomes important to include a sample fortified at the detection limit in each analytical run to demonstrate that in the set of samples analyzed in that run, detection of a positive result at the claimed detection limit was achieved. To demonstrate that a detection limit is realistic, 19 of 20 typical samples fortified at that concentration should be detected as positive. 

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