Inter-laboratory study results

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. 

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]). 

An inter-laboratory study to determine benzoie acid in orange juices was reported, where a Hamilton PRP-1 column and a mobile phase mixture of 4 + 6 of aeetonitrile / phosphate buffer was used [36]. In this work, the juices were fortified with 0.5-10 ppm of benzoic acid. Statistical analysis of the results showed a relative reproducibility between laboratories ranged in the range of 6.92% to 15.97% for juice fortified with 1-10 ppm and 27.90% for juice fortified with 0.5 ppm. Mean recoveries ranged from 94.5% to 114%. 

The factor 2I/Z is based on the fact that r and R are related to the difference between two measurement results. For distributions which are approximately normal and in the case of not too small a number of measurements, the factor f does not vary much from 2 and one can use the approximate value of 2.8 for f-2I/2. Because in practice the true repeatability and reproducibility standard deviations are not known, they are replaced with estimated values sr and sR from the inter-laboratory study and one obtains then ... 

Table 3. Results of an inter-laboratory study on quantification of PCAs in a synthetic product (PCA-1), a commercial products (PCA 70) and fish tissue sample [70]a... 

SUMMARY OF THE RESULTS OF THE SECOND INTER LABORATORY STUDY. THE RESULTS ARE GIVEN IN nmol kg ... 

Following the guidelines of ASTM D 6300, repeatability (r) and reproducibility (R) were determined from the data shown in Table 6. The results are given in Table 7 along with the mean of each sample and the standard deviations of r and R. The repeatability results show significant improvement over that of the ASTM D 7039-04. The reproducibility results are similar to that of inter-laboratory study (ILS) in 2002 [3]. Further interlaboratory round robin studies will be needed to confirm the reproducibility. 

Table 25.4 Comparison of labelled folic acid data with those obtained by stable isotope dilution assay (SIDA) and by HPLC-UV in an inter-laboratory study (internal standard). SIDA results generally are in good accordance with the labels. Differences for corn flakes, noodles and bread to HPLC-UV were attributable to interfering compounds.

Different biological samples were analyzed via the ICP-IDMS approach depicted in Figure 8.8 and the results obtained were compared with those of an interlaboratory study in which 14 laboratories using various non-IDMS techniques participated. In this study, a silicon content of 5.3 + 1.0 pg (mean + standard deviation based on five independent analyses) was found for a homogeneous pork liver sample via ICP-IDMS, which agreed well with the result of the inter-laboratory study of 5.1 + 2.8 pg g (mean of the means of individual laboratories + corresponding standard deviation). In contrast to this agreement, the results for a spinach powder were 333 + 11 pg g for ICP-IDMS and 176 + 189 pg g for the inter-laboratory study. The reason for this extreme difference between the ICP-IDMS result and the mean value, and also for the unacceptable standard deviation in the inter-laboratory study, is the presence of considerable amounts of silicate in spinach. Many laboratories had not adequately dealt with this silicate portion due to analytical difficulties with and errors in the sample preparation. 

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... 

Methods of analysis also differ. The two analytical techniques most often employed are atomic absorption spectrometry and anodic stripping voltammetry. One inter-laboratory study using a (supposedly) homogenized tooth powder showed that the measurements obtained from different laboratories varied very significantly, with the results ranging from 4 to 15 iUg/g (Stack and Delves, 1982). However, subsequently there has been a suggestion that the tooth powder was not adequately homogenized, and this... 

Within CEN TC 275, a distinct protocol for the conduct of inter-laboratory method validation trials is not selected or required, but it is recommended to apply ISO 5725 or the ISO/International Union for Pure and Applied Chemistry (lUPAC) harmonized protocol. " In the past, results of several national and international interlaboratory trials had been accepted. Nevertheless, the following fundamental aspects of the harmonized protocol for the design of method-performance studies should be fulfilled ... 

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). 

If analytical methods are validated in inter-laboratory validation studies, documentation should follow the requirements of the harmonized protocol of lUPAC. " However, multi-matrix/multi-residue methods are applicable to hundreds of pesticides in dozens of commodities and have to be validated at several concentration levels. Any complete documentation of validation results is impossible in that case. Some performance characteristics, e.g., the specificity of analyte detection, an appropriate calibration range and sufficient detection sensitivity, are prerequisites for the determination of acceptable trueness and precision and their publication is less important. The LOD and LOQ depend on special instmmentation, analysts involved, time, batches of chemicals, etc., and cannot easily be reproduced. Therefore, these characteristics are less important. A practical, frequently applied alternative is the publication only of trueness (most often in terms of recovery) and precision for each analyte at each level. No consensus seems to exist as to whether these analyte-parameter sets should be documented, e.g., separately for each commodity or accumulated for all experiments done with the same analyte. In the latter case, the applicability of methods with regard to commodities can be documented in separate tables without performance characteristics. 

To facilitate a standardisation of inter-laboratory results of permeability, it is now common practice to include a range of model drugs as internal standards in initial validation (i.e. method suitability) of intestinal perfusion techniques [116]. A list of 20 model drugs has been reported by the FDA for the standardisation of the in situ intestinal perfusion experiment, whereas six drugs are recommended for human studies. Once the method has been... 

This method was developed to replace the hazardous mercury catalyst required in the original mercuric oxide Kjeldahl method. It has been evaluated through an interlaboratory comparison of catalysts and has been adopted as the official replacement for the mercuric-oxide catalyzed Kjeldahl method. An inter-laboratory evaluation (Berner, 1990) indicated that this method (which uses the copper/titanium catalyst mixture) produces results more closely in agreement with the mercuric oxide catalyst method than methods using a copper sulfate catalyst. As a result of this study, mercuric... 

Oberacher H, Pavlic M, Libiseller K, Schubert B, Sulyok M, Schuhmacher R, Csaszar E, Kofeler HC (2009) On the inter-instrument and inter-laboratory transferability of a tandem mass spectral reference library 1. Results of an Austrian multicenter study. J Mass Spectrom 44 485-493... 

Once a method is established, precision may be determined by suitable replicated experiments. However it is in inter-laboratory trails that the problems with environmental methods often show up. It is accepted that for trace analysis RSD values of tens of percent are likely. In studies conducted in Western Australia on pesticide residues in bovine fat RSD values for dieldrin were 12% and for dia-zonium were 28%. It is typical to see a quarter of the laboratories in such a trial producing values that could be termed outliers. In the previously mentioned study, 5 laboratories out of 26 had z> 3 for aldrin. In a parallel study RSD values for petroleum in dichloromethane and water were 40% and 25%, respectively. The conclusions of these studies was that there was poor comparability because of the different methods used, that accreditation apparently made no difference to the quality of results, and that a lack of understanding of definitions of the quantities to be analysed (for example gasoline range organics ) caused non-method errors. In relation to methods, this is contrary to the conclusion of van Nevel et al. who asserted that the results of the IMEP round of analyses of trace elements in natural and synthetic waters showed no dependence on method [11]. If properly validated methods do yield comparable results, then one conclusion from the range of studies around the world is that many environmental methods are not validated. It may be that validated methods are indeed used, but not for exactly the systems for which they were validated. 

Weil CS, Scala A (1971) Study of intra- and inter- laboratory variability in the results of rabbit eye and skin irritation tests. Toxicol Appl Pharmacol 19 276-360... 

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