Interlaboratory measurements

Leaver ME, and Bowman WS (1994a) Interlaboratory Measurement Program for the Standard ARD Material NBM-i. Mineral Sdences Laboratories Division Report MSL 94-28 (CR) Draft. CANMET, Natural Resources Canada, Ottawa. 

LGC has been involved in the production of both pure substance and matrix reference materials (RMs) for about 15 years and during that time over 200 materials, the majority relating to food and environmental measurements, have been produced and certified. Whilst the pure materials have been certified largely on the basis of in-house measurements, the matrix materials have usually required a collaborative approach, involving interlaboratory measurement studies. The latter approach is extremely important and versatile for the production of matrix RMs, but it does raise a number of issues. Among these are the selection of appropriate procedures for as-... 

Perhaps the most pressing issue that needs urgent attention is that of quality assurance. To date, only two inter-laboratory exercises have been conducted the results from both smdies demonstrated that quantitative measurements can be quite varied. Consensus on the choice of a working standard solution, method of quantitation, and certified reference materials will go a long way to ensure that interlaboratory measurements are more comparable. 

The factors that influence the relative standard deviation for a determination and, hence, the detection limit that should be used for interlaboratory measurements are briefly reviewed. In addition, the need for a more general approach to the estimating and reporting of selectivity is pointed out. A possible basis for a suitable scheme is suggested that should be applicable to environmental and clinical samples that usually contain a large number of completely unknown species, one or more of which may interfere in the measurement of the sought-for species. 

The relative contributions of the known variables that contribute to increases in the RSD for Interlaboratory measurements are summarized in Table I. The important thing to note is that, in general, one would expect the RSD for quality assurance samples measured under truly blind conditions to be between 5 and 10 times larger than those measured on known standards by a single person in a laboratory. The resulting larger value for the RSD has an Important bearing on the limit of detection for a procedure that is to be used in interlaboratory measurements. 

The 238fj/235u jatio in standard reference materials for natural uranium has been meticulously scrutinized and revised by very precise measurements (Brennecka et al. 2010 Richter et al. 2010 Hiess et al. 2012). The NBS SRM 960 (NBL CRM 112a) served as the consensus value for of 137.88 but interlaboratory measurements with an accurate double-spike gave a slightly different average... 

NUSIMEP Nuclear Signatures Interlaboratory Measurement Evaluation Programme (intercomparison organized by the JRC)... 

R. C. Paule and J. Mandel, Analysis of Interlaboratory Measurements on the Vapour Pressure of Gold , Certification of Standard Reference Material 7451, NBS Special Publication 260-19, 1970. 

The response of ion-selective electrodes in biological fluids may be affected by a wide variety of physical and chemical factors. These may influence the indicator electrode directly or may affect the liquid junction of the reference electrode. A brief discussion is presented of the various sources of error and uncertainty in electrode measurements in biologic media especially with microelectrodes. A serious need exists for the development of practical standards for the calibration of ion-selective electrodes in physiologic media in order to ensure the consistency of interlaboratory measurements. 

In case of fast gradient (below 15 min), S could be considered constant for all the investigated molecules and wiU only have a small influence on the retention time of the compounds. Thus, the gradient retention times, of a calibration set of compounds are linearly related to the ( )o values [39]. Moreover, Valko et al. also demonstrated that the faster the gradient was, the better the correlation between t, and < )o [40]. Once the regression model was established for the calibration standards, Eq. 8 allowed the conversion of gradient retention times to CHI values for any compound in the same gradient system. Results are then suitable for interlaboratory comparison and database construction. The CH I scale (between 0 and 100) can be used as an independent measure of lipophilicity or also easily converted to a log P scale. 

Data on mineral s arates in present day volcanic rocks. Since every dating method (including the K-Ar or C systems) can be affected by several geochemical perturbations which may lead to erroneous ages, the best test for the °Th- U mineral isochrons consists in the analysis of presently erupted lavas or historic lavas of well known eruption dates. Rather surprisingly the data obtained on such samples are not so numerous (some examples are illustrated in Fig. 10). Early data showed that, in some cases, there were interlaboratory analytical discrepancies, especially in Th isotope ratios measured on mineral separates extracted from the same lava flows (this was the case for the 1971 lava from Mt. Etna and 1944 lava from Mt. Vesuvius Capaldi and Pece 1981 Hemond and Condomines 1985 Capaldi et al. 1985). This emphasizes the fact that °Th- U mineral analyses... 

On the other hand, reproducibility is the closeness of the agreement between the results of measurements of the same measurand carried out under changed conditions of measurement . The changed conditions include principle of measurement, method of measurement, observer, measuring instrument, reference standards, location, conditions of use, and time. Such variable conditions are typical for interlaboratory studies (laboratory intercomparisons). 

Analytical laboratories need to check their performance with regard to the production of accurate results with satisfactory precision. The most desirable way to ensure the reliability of analytical results is the participation of laboratories into regular interlaboratory tests. An interlaboratory study has to be understood as a study in which several laboratories measure a quantity in one or more identical portions of homogeneous, stable materials under documented conditions, the result of which are compiled into a single document (IUPAC [1994] Prichard et al. [2001]). 

Horwitz claims that irrespective of the complexity found within various analytical methods the limits of analytical variability can be expressed or summarized by plotting the calculated mean coefficient of variation (CV), expressed as powers of two [ordinate], against the analyte level measured, expressed as powers of 10 [abscissa]. In an analysis of 150 independent Association of Official Analytical Chemists (AOAC) interlaboratory collaborative studies covering numerous methods, such as chromatography, atomic absorption, molecular absorption spectroscopy, spectrophotometry, and bioassay, it appears that the relationship describing the CV of an analytical method and the absolute analyte concentration is independent of the analyte type or the method used for detection. 

IMEP 9, Trace Elements in Water III, Cd, Certified Range 81.0-85.4 nmol l-1 , European Commission, Joint Research Centre, Institute for Reference Materials and Measurements (EC-JRC-IRMM), Geel, Belgium (1998). [www.irmm.jrc.be/html/interlaboratory comparisons/imep/ index.htm] (accessed 30 November, 2006). 

In addition, a system for making sure staff are appropriately qualified and trained for the work that they are doing must be in place. This will enable an auditor to see clearly the demonstrated competence of the staff and how this has been checked. The requirements for all major items of equipment must be listed, to ensure that the equipment in use is suitable for the task, is in working condition and, where necessary, is calibrated. For all of the instrumentation there needs to be a documented schedule for maintenance. Measurements must be traceable, that is, the laboratory must be able to show how the calibration of measurement instruments is traceable to National or International Standards. Where this presents practical problems, as in some chemical measurements for example, interlaboratory comparison and the use of reference materials (and preferably Certified Reference Materials) will be required. 

Fukai, R., B. Oregioni, and D. Vas. 1978. Interlaboratory comparability of measurements of trace elements in marine organisms results of intercalibration exercise on oyster homogenate. Ocean. Acta 1 391-396. 

From the available literature it becomes clear that method evaluation studies do not surpass the level of within-laboratory performances. Although several of these (see Table 3.3.1) reveal satisfactory levels of quality and environmentally relevant limits of detection, a genuine quality assurance of these methods is still lacking. There are no reports of interlaboratory studies and certified reference materials for surfactants are not available on the market yet. It can therefore be concluded that there remains much to be done in the field of improving and evaluating quality of analytical measurements of surfactants in biota. 

Quality control, however, needs more attention. For example, it has been reported that much of the chemical data produced by the International Indian Ocean Expedition is unusable because of doubts about its accuracy. Such reports are a perennial source of confusion in marine chemistry. Better calibration, universal standards, and interlaboratory comparison are essential if we are to continue our present field methods, in which independent investigators make measurements that are presumably comparable (NRC, 1971, pp. 54-55). 

Stichler, W. 1995. Interlaboratory comparison of new materials for carbon and oxygen isotope ratio measurements. Pp. 67-74 in Reference and Intercomparison Materials for Stable Isotopes of Light Elements, Vienna International Atomic Energy Agency, LAEA-TECDOC-825. 

Interlaboratory Test Series of measurements of one or more quantities performed independently by a number of laboratories on samples of a given material. 

For some compounds in the Wilschut database more than one permeability coefficient was gathered from literature. In some cases, the differences in kp were greater than one log unit underlining the interlaboratory variations of such measurements. For the development of a new QSPR model one may now either choose one representative data point for each molecule or combine the multiple data points in a reasonable way. In some cases authors even employed all the available data for a single compound. Apart from the permeability data, the data on the partition coefficient and even on the molecular weight may vary from one report to another. Differences in the partition coefficient are easily explained Some collections list experimentally determined values which depend on the experimental procedure employed... 

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