Method inter-laboratory studies

NIST has also used results obtained from inter-laboratory studies as an additional set of results in the two or more methods approach (mode 2 in Table 3.13). For example for the recent value assignment for PCBs and pesticides in SRM 1944, the mean of results from 19 laboratories participating in an inter-laboratory comparison exercise was used as an additional set of data in the determination of the certified values. Similar inter-laboratory study results were also included in the value assignment of PAHs, PCBs, and pesticides for two recently issued mussel tissue materials, SRM 2977 and SRM 2978. 

The laboratory of the European Pharmacopoeia applies the method specific approach (inter-laboratory study) as has been previously described (Technical Guide for the Elaboration of Monographs 1996). 

The NADA method approval process consists of three phases (1) method development by the sponsor and generation of information to establish that the method satisfies acceptability criteria (2) FDA review of the sponsor s data to determine suitability of the method and (3) the method trial , an inter-laboratory study, which determine whether the method meets performance criteria when used in multiple laboratories. The inter-laboratory method trial procedure provides an indication of a method s ability to be used as a practicable and reliable regulatory tool. Sponsors are urged to develop methods that are mgged and exceed rather than meet the minimal standards of acceptability. Those methods that appear marginally acceptable after review often do not pass the inter-laboratory method trial. 

The methods EN 1528 1996 and EN 12393 1998 comprise a range of old multiresidue methods of equal status, which are widely accepted throughout Europe. These are, e.g., the Luke method and the German Deutsche Forschungsgemeinschaft (DFG) methods S8 and S19 ° (all based on extraction with acetone), the Association of Official Analytical Chemists (AOAC) method 970.52 (using acetonitrile extraction and liquid-liquid partition combined with Horisil column cleanup) and the Dutch ethyl acetate extraction combined with GPC. All methods have been subjected to inter-laboratory studies, although not with all pesticide/matrix combinations, which would be impossible to achieve. 

Because of the small number of laboratories involved, validation of UK methods by inter-laboratory study has become impractical in most cases. Even where it is practical, it is usually impossible to validate all pesticide-matrix combinations. Moreover, single-laboratory validation data will have to be generated. Therefore, the CSL guidelines are one of the first that strictly focus on requirements of single-laboratory validation. Some examples of minimum requirements are given in Table 8. Additionally, these guidelines emphasize some other important aspects of validation and contain some new ideas. 

Even if most examples and procedures presented apply to in-house validation, the procedure does not distinguish between validations conducted in a single laboratory and those carried out within inter-laboratory method performance studies. A preference for inter-laboratory studies can be concluded from the statement that laboratories should always give priority to methods which have been tested in method performance studies. Within the procedure a profound overview of different categories of analytical methods according to the available documentation and previous external validation is given. For example, if a method is externally validated in a method performance study, it should be tested for trueness and precision only. On the other hand, a full validation is recommended for those methods which are published in the scientific literature without complete presentation of essential performance characteristics (Table 9). 

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. 

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. 

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]). 

At the same time. Interagency Coordinating Committee on the Validation of Alternative Methods (ICCVAM) evaluated FETAX methodology based on the inter-laboratory studies and published a review document in 2000 (5). The expert panel concluded that FETAX was not sufficiently validated for regulatory use due to the intra- and inter-laboratory variability (6). Nonetheless, the assay was developed in our laboratory for use as a predictive screening assay. 

After many years of debate and discussion, there is now an international consensus about the statistical approach and method to be employed in full collaborative trials This topic is discussed further in Section 9.5. The lUPAC protocol referred to above requires the analysis of duplicate test samples of the same material (a minimum of five materials or, exceptionally, three) in eight or more laboratories. However, there are many occasions where inter-laboratory studies are needed which, for various reasons, cannot achieve the prescribed criteria. In instances where the lUPAC criteria cannot be achieved, it is recommended that the Youden Matched Pairs procedure is used. The statistics of the method have been recently updated and a new procedure described. 

This is a less widely-used application. No inter-laboratory studies have been carried out to describe characteristics of the method. 

An international inter-laboratory study recently compared quantitative methods used for measuring short chain (C10-C ) PCAs [70]. In this study, the samples to be quantified consisted of a standard solution of a commercially available PCA product containing 70% chlorine by mass (PCA-70), a synthetic PCA mixture consisting of purified products derived from the chlorination of 1,5,9-decatriene (PCA-1) and two fish sample extracts. The fish samples consisted of a cleaned up extract (lipid-free) of muscle tissue from a yellow perch fish, collected at the mouth of the Detroit River at Lake Erie, in 1995. All participating labs were asked to quantify the PCA-1 and PCA-70 mixtures and at least one fish extract against a primary standard solution which contained a known concentration of a second short chain commercial PCA product containing 60 mass % chlorine (PCA-60) and, if desired, by using other commercially available C10-C13 PCA mixtures. 

Subsequent to the studies conducted in mice, a two-phase inter-laboratory study for quantification of rat splenic lymphocyte subpopulations using immu-nofluorescent staining and flow cytometry was conducted to determine if this method would be useful for immunotoxicology studies (Ladies et al., 1997,... 

Feier, U., and Goetsch, P. H. (1993). Inter-laboratory studies on precision characteristics of analytical methods. Determination of biogenic amines in fish and fish products—HPLC method. Arch. Lebensm. 44, 129-152. 

Work is underway to standardize the test method described here as a new ASTM standard. An Inter-Laboratory Study (ILS) is proposed to include at least nine each of gasoline and diesel Tier 2 class materials containing sulfur levels between <10 and 80 mg/kg in gasoline and between <10 and 80 mg/kg in diesels. Some blind National Institute of Standards and Technology (NIST) Standard Reference Materials (SRM) and solvent blanks are also plaimed for the cross check. The ILS will follow a protocol of an initial analysis of a set of samples and solvent blanks, and after an elapsed time of at least 12 h but no more than 72 h, a second set of measurements on the same set of samples and blanks will be completed. We expect this ILS to be completed by the end of2005. 

Standards ISO 5725-22 and ISO 21748 ° provide guidance to carry out properly designed and executed inter-laboratory studies for the estimation of method parameter statistics... 

Dehouck P, Vander Heyden Y, Smeyers Verbeke J, et al.. Inter-laboratory study of a liquid chromatography method for erythromycin Deter-mination of uncertainty, J. Chromatogr. A 2003 1010(l) 63-74. 

Figure 8.11 Palladium content in a road dust sample as obtained by different laboratories/ analytical methods in the context of an inter-laboratory study (error bars represent standard deviations). Reproduced with permission from [60].

The results ofthe inter-laboratory study showed that the exposures produced only minor ehanges in the measured thermoanalytical properties. The materials tested were generally stable under the outdoor and laboratory exposure conditions. In the ease of TG analysis of the pyrolyzable organic constituents, it was found that the method showed rather good within- and between-laboratory variability. The number of participants in the d5mamic mechanical/TPA analysis was limited hence, no conclusion was made regarding the variability within and between laboratories. In the ease of... 

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