Precision interlaboratory

Interlaboratory precision is the most general measure of reproducibility observed when aliquots of the same sample are analyzed by different people in different laboratories. Interlaboratory precision becomes poorer as the level of analyte decreases (Box 5-2). 

Range is the concentration interval over which linearity, accuracy, and precision are all acceptable. An example of a specification for range for a major component of a mixture is the concentration interval providing a correlation coefficient of R2 > 0.995 (a measure of linearity), spike recovery of 100 2% (a measure of accuracy), and interlaboratory precision of 3%. For an impurity, an acceptable range might provide a correlation coefficient of R2 > 0.98, spike recovery of 100 10%. and interlaboratory precision of 15%. 

Define the following terms instrument precision, injection precision, intra-assay precision, ruggedness, intermediate precision, and interlaboratory precision. 

More recently, there have been numerous collaborative studies (81-84) that have attempted to improve the accuracy and precision of this method. A typical example by MacDonald et al. (81) reported a collaborative study by seven laboratories. Samples were oxidized with performic acid for 16 hours over ice bath. After oxidation, HBr was used to destroy excess performic acid. Samples were then roto-evaporated to dryness, dissolved in 6N HC1, nitrogen purged, and then hydrolysed for 18 hours at 100°C. Interlaboratory precision for cysteic acid determination in six food ingredients ranged from 7 to 10%. For methionine sulfone, interlaboratory precisions ranged from 1 to 13% for the same six food ingredients. The mean recovery of cysteine was 95% and of... 

Intralaboratory analytical precision is the agreement between repeated measurements of random aliquots of the same sample made at a single laboratory using the same method. Interlaboratory precision is the agreement between the measurements of the same sample conducted by two or more laboratories. Intralaboratory and interlaboratory precision may be calculated as the RPD for two measurements, as variance or as the standard deviation for more than two measurements. 

Reproducibility (interlaboratory precision) is the precision that measures variability among the results obtained for the same sample at different laboratories (EPA, 1998a). It is usually statistically expressed as variance or the standard deviation. The low variance or the standard deviation value indicates a high degree of reproducibility. 

EPA round robin studies is another quality assessment tool that is effective in revealing deficiencies in laboratory s ability to correctly identify and quantify environmental pollutants. The EPA performs these studies on a regular schedule and evaluates the results for the purpose of establishing interlaboratory precision, which is a measure of variability among the results obtained for the same sample at different laboratories. (Interlaboratory precision or reproducibility is another secondary DQI.)... 

Comparability is a DQI that comprises accuracy, precision, and representativeness. It may be assessed as interlaboratory precision and calculated as the RPD between results obtained at two laboratories. But more often, comparability, similar to field duplicate precision, is evaluated qualitatively. Data are never qualified based on comparability evaluation. 

The interlaboratory precision for extrudate crush strength testing was so poor in both of the round robins, that it was decided to publish the method for regular shapes only, and have the task group continue to work to improve extrudate testing. 

The results from the study are shown in Table 3. The accuracy and precision of the analytical methods were based on the measurements reported for the PCA-1 and PCA-70 mixtures of known concentration. The PCA-70 mixture was selected because its elution profile closely resembled that of the supplied external standard (PCA-60). In contrast, PCA-1 had a profile that was very different to that of PCA-60. The rationale for using these two mixtures was to see if the quantitative data would become more accurate for mixtures with profiles more closely resembling the standard. The data derived from the quantitative measurements on the environmental samples provided an estimate on the interlaboratory precision. 

The main objective of the lEA PYRA Round Robin was to determine the interlaboratory precision and methods applied for elemental composition, water, pyrolytic lignin and main cotiqjounds. Two poplar oils were analysed by the lEA PYRA participants. It was concluded that the precision of carbon and hydrogen was very good, liquid sample handling plays a very important role in the C, H analysis, water by Karl-Fischer titration was acceptable, but should be checked carefully, and the method for the determination of pyrolytic lignin should be improved (3). 

Repeatability closeness of agreement between results of successive measurements carried out under the same conditions (i.e., corresponding to within-run precision). Reproducibility closeness of agreement between results of measurements performed under changed conditions of measurements (e.g., time, operators, calibrators, and reagent lots). Two specifications of reproducibility are often used total or between-run precision in the laboratory, often termed intermediate precision and interlaboratory precision (e.g., as observed m external quality assessment schemes [EQAS]) (see Table 14-2). 

The interlaboratory precision or between-laboratory precision is defined in terms of the variability between test results obtained on the aliquots of the same homogeneous material in different laboratories using the same test method. 

Between-laboratory precision see Interlaboratory precision, Intermediate precision, and Precision). 

Intermediate precision the precision obtained when an assay is performed by multiple analysts using several instruments in one laboratory (see also Interlaboratory precision and Precision. 

The precision of an analytical method is obtained from multiple analyses of a homogeneous sample. You can determine overall precision of the method, including sample preparation. Such precision data are obtained by one laboratory on one day, using aliquots of the homogeneous sample that have been independently prepared. Such interlaboratory precision is called repeatability. Interlaboratory precision, if appropriate, is also determined as part of a measurement of reproducibility or robustness of the method (see below). 

This method worked well for the fairly soluble compounds being studied. Interlaboratory precision was good. Therefore, this basic methodology, with minor modifications, such as the use of gas chromatography (GC) or fluorescence spectroscopy for analysis of the aqueous solutions has been generally adopted for the determination of the aqueous solubilities of PAHs (23-32), even though the solubilities of some PAHs differ from that of benzene by a factor of more than 106. In the remainder of this section some of the modifications that have been made on this basic method and some new approaches to the measurement of the aqueous solubility of aromatic hydrocarbons will be briefly reviewed. 

The recovery rate from the model-processed food should be in the range 50 to 150%. In addition, the interlaboratory precision (RSDr) value should be less than 25%. 

Thomson M, Recent trends in interlaboratory precision at ppb and sub-ppb concentrations in relation to fitness for purpose criteria in proficiency testing. Analyst 2006 125 385-386. 

Interlaboratory quality control studies are designed to determine the degree of compatibility of the data generated by participating laboratories. Furthermore, such studies help to determine interlaboratory precision and accuracy and to standardize analytical methodology. They also provide valuable data for the certification of standard reference materials. 

At present, there is no completely valid method available to directly calculate the interlaboratory precision from the intralaboratory precision or vice versa. This is unfortunate because frequently only one type of precision estimate is available for a method. ITowever, in general, the following comments are applicable. First, the intralaboratory precision should be smaller than the interlaboratory precision because of additional variables in the latter. Second, if the interlaboratory precision is much larger than the intralaboratory precision, this indicates that the method is very technique-sensitive. Such information can be very important when considering a project that might involve several laboratories analyzing the same sample. 

A semi-empirical formula that is useful in relating the intralaboratory precision with the interlaboratory precision is represented by the following relationship ... 

However, the relative deviations for interlaboratory reproducibility sr are considerable, i.e. 26.6% (AO-1) and 12.3% (AO-2). These results (Table 6.23) show that the determination of antioxidants in polyolefins is not a trivial matter. For cases where the interlaboratory precision is much larger than the intralaboratory precision there is obviously lack of robustness of the analytical methods used. 

Depending on where the method is used the precision of different operators, equipment and laboratories should also be examined. Interlaboratory precision can be determined by having different laboratories analyse the same sample. 

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