Intralaboratory testing

The (intralaboratory tested) behavior of analytical process when small changes in environmental and/or operating conditions are made (generally used term)... 

Accuracy is the ability of any assay to provide the correct result. Ideally, the assay should detect all of the analyte (100% recovery) and nothing else (no interference or cross-reactivity). To estimate the method accuracy, a comparison of method results with tme sample concentrations must be completed. A straightforward procedure involves the use of a standard reference material, in which the analyte concentration is known with high accuracy and precision. Standard reference materials are not generally available for biochemical analytes, however. When a reference material is not available, accuracy can be established by comparison with alternative previously validated analytical techniques, or currently accepted methods. Intralaboratory tests of matrix effects and interferences are also conducted in order to establish the accuracy of a new method. 

Standard reference materials provide a necessary but insufficient means for achieving accuracy and measurement compatibiUty on a national or international scale. Good test methods, good laboratory practices, well-qualified personnel, and proper intralaboratory and intedaboratory quaUty assurance procedures ate equally important. A systems approach to measurement compatibiUty is ikustrated in Figure 2. The function of each level is to transfer accuracy to the level below and to help provide traceabiUty to the level above. Thus traversing the hierarchy from bottom to top increases accuracy at the expense of measurement efficiency. 

The results of local tissue irritation tests are subject to considerable variability due to relatively small differences in test design or technique. Weil and Scala (1971) arranged and reported on the best known of several intralaboratory studies to... 

Intralaboratory or within-laboratory precision refers to the precision of a test method when the results are obtained by the same operator in the same laboratory using the same apparatus. In some cases, the precision is applied to data gathered by a different operator in the same laboratory using the same apparatus. Thus, intralaboratory precision has an expanded meaning insofar as it can be applied to laboratory precision. 

The in vitro bioassay for dioxins with cleaned sediment extracts (DR-CALUX) proved to comply with the QA/QC criteria needed to guarantee the reliability of data in an inter- and intralaboratory study (Besselink et al., 2004). The chemical stability of dioxins makes it possible to apply destructive clean-up procedures which remove all matrix factors. Sample extraction and cleanup for other in vitro bioassays for specific mechanisms of toxicity require further development to make sure that the chemicals of interest are not lost or unwanted chemicals included in the sediment extract to be tested. Table 4 summarizes possible bioassays that could be performed in addition to chemical analyses with the dredged sediment in a licensing system. 

Agencies or authorities such as ISO or lUPAC still do not provide any definition of ruggedness. In the chemical literature however, a ruggedness test was defined as [4,12] An intralaboratory experimental study in which the influence of small changes in the operating or environmental conditions on measured or calculated responses is evaluated. The changes introduced reflect the changes that can occur when a method is transferred between different laboratories, different experimentators, different devices, etc. . 

Robustness-based approach Based on robustness tests as intralaboratory simulations of interlaboratory studies Simple, time-efficient approach Some sources of uncertainly may be overlooked method must first show to be robust Hund et al. [39]... 

Any or all of these conditions can be varied. To provide some guidance, intralaboratory reproducibility is used to express changes only within a laboratory, and interlaboratory reproducibility" is used to refer to the changes that occur between laboratories, for example in proficiency testing, interlaboratory method validation studies, and the like. Interlaboratory reproducibility is usually two to three times the repeatability. 

Mitchell. A.D., Rudd, C.J. Caspary, W.J. (1988) Evaluation of the L5178Y mouse lymphoma cell mutagenesis assay intralaboratory results for sixty-three coded chemicals tested at SRI International. Environ, mol. Mutag., 12 (Suppl. 13). 37-101... 

Rue, W.J., Fava, J.A. and Grothe, D.R. (1988) A review of inter- and intralaboratory effluent toxicity test method variability, in M.S. Adams, G.A. Chapman and W.G. Landis (eds.), Aquatic Toxicology and Hazard Assessment l(fh Volume, ASTM STP 971, American Society for Testing and Materials,... 

Repeatability (intralaboratory precision) is the degree of agreement between independent test results produced by the same analyst using the same test method and equipment on random aliquots of the same sample within a short time period (EPA, 1998a). Repeatability is calculated as the RPD for two measurements, as the variance or the standard deviation for more than two measurements. 

The outcome of the different exercises should be discussed among all participants in technical meetings, in particular to identify random and/or systematic errors in the procedures. Whereas random errors can be detected and minimised by intralaboratory measures, systematic errors can only be identified and eliminated by comparing results with other laboratories/techniques. When all steps have been successfully evaluated, i.e. all possible sources of systematic errors have been removed and the random errors have been minimised, the methods can be considered as valid. This does not imply that the technique(s) can directly be used routinely and further work is likely to be needed to test the robustness and ruggedness of the method before being used by technicians for daily routine measurements . 

Accurate temperature calibration using the ASTM temperature standards [131, 132] is common practice for DSC and DTA. Calibration of thermobalances is more cumbersome. The key to proper use of TGA is to recognise that the decomposition temperatures measured are procedural and dependent on both sample and instrument related parameters [30]. Considerable experimental control must be exercised at all stages of the technique to ensure adequate reproducibility on a comparative basis. For (intralaboratory) standardisation purposes it is absolutely required to respect and report a number of measurement variables. ICTA recommendations should be followed [133-135] and should accompany the TG record. During the course of experiments the optimum conditions should be standardised and maintained within a given series of samples. Affolter and coworkers [136] have described interlaboratory tests on thermal analysis of polymers. 

Table I lists the catalyst materials characterized and available for use as reference materials. For each property measured, the number of the ASTM Standard Test Method used in the determination is identified the material is specified the consensus mean value determined is listed the interlaboratory reproducibility and the intralaboratory repeatability from round robin tests are presented and the number of the ASTM research report describing the round robin data is listed. These round robins were conducted in accordance with ASTM E-691 -- Standard Practice for Conducting an Interlaboratorv Study to Determine the Precision of a Test Method.

E646 Lanphear, B., Laessig, R., Ehrmeyer, S. and Hassemer, D. (1990). The application of proposed CDC/HCFA criteria to assess intralaboratory performance through proficiency testing programs. Clin. Chem. 36, 1005, Abstr. 250. 

The results of local tissue irritation tests are subject to considerable variability due to relatively small differences in test design or technique. Well and Scala arranged and reported on the best known of several intralaboratory studies to clearly establish this fact. Though the methods presented previously have proven to give reproducible results in the hands of the same technicians over a period of years and contain some internal controls (the positive and vehicle controls in the PDI) to minimize large variations in results or the occurrence of either false positives or negatives, it is still essential to be aware of those factors that may systematically alter test results. These factors are summarized as follows ... 

Note-. The coefficient of variation following multiple runs using the indicated positive control test substances in one laboratory is shown. The overall average of the intralaboratory CVs listed is 17%. n is the number of times the assay has been conducted with the indicated positive control material units indicates the measurement units obtained from the alternative method mean indicates the average value obtained for all the indicated runs SD is the standard deviations calculated associated with the mean of the alternative method sources CV is the coefficient of variation (mean/SD) SLS is sodium lauryl sulfate. 

As described by Osborne RM, Perkins MA, and Roberts DA (1995) Development and intralaboratory evaluation of an in vitro human cell-based test to aid ocular irritancy assessments. Fundamental and Applied Toxicology 28 139-153. 

Many validation studies use a nested or hierarchical design (Figure 5). These studies usually involve several laboratories that independently conduct the same alternative method on all the substances in an RSTS. There are four sources of variability in such studies. These include variation in the test substances, variation within experiments within a laboratory (intraexperiment variability), variation between experiments within a laboratory (intralaboratory variability), and variation between laboratories (interlaboratory variability). Reviewed next is the nature and importance of each. The differences between chemicals are ignored in this discussion since they can generally be minimized with well-controlled test article distribution and storage. Attention is concentrated on the variability in results obtained by testing a single chemical in a number of different laboratories. 

Ehrmeyer SS> Laessig RH. A computer model to translate federal proficiency testing performance standards for pH/blood gases into intralaboratory precision and accuracy requirements. In Methodology and clinical applications of blood gases, pH, electrolytes and sensor technology. 

The revised version of this guide gives an approach for the use of CRMs. After having validated his method (see Chapter 2) with intralaboratory tools, the analyst analyses the CRM. He calculates the mean value X of at least five determinations, possibly ten. These determinations have to be fully independent. This means that he starts five or more times from a fresh test sample and does a new calibration of the instrument. If the same operator does the job, in a short period of time, it can be considered as having being done under repeatability conditions (r). Otherwise a reproducibility value is established (R). Having calculated the mean X and the standard deviation... 

This material is dealt with in the chapter Interlaboratory and Intralaboratory Surveys and Reference Methods by R.A. Braithwaite. The only statement we will make here is that a sufficient number of this kind of control specimen should be incorporated, e.g. one control specimen for 10 test specimens. 

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