Intralaboratory studies

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... 

The infralaboratory calibration study was performed by the Institute for Environmental Studies. Sediment was extracted and cleaned up as indicated here. The determination of dioxin and/or dioxin-like content was according to the method indicated under the section DR CALUX analysis. For the intralaboratory study, the following parameters were investigated limit of detection (LOD), limit of quantitation (LOQ), and reproducibility and repeatability of the bioassay. 

The results of the multiple analysis of the standard 2,3,7,8-TCDD calibration curves are also be used to determine the per-participant LOD and LOQ taking into account interlaboratory variation (Table 3). This results show that on average, the partieipants of the calibration study meet the set LOD and LOQ derived from the intralaboratory study. 

TCDD calibration curves. From these data, a per-participant LQD and LQQ could be determined. Qn average, the participants of the calibration study met the set LQD and LQQ derived from the intralaboratory study. Furthermore, analysis of variance indicated that no significant differences in LOD between laboratories could be identified. 

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. 

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 ... 

Precision studies can be performed under different conditions, and are strongly influenced by variables such as temperature, source and quality of reagents, reproducibility of reagent delivery, and instrumental noise. Therefore, if all precision studies are done in the same laboratory (intralaboratory study) higher precision is expected in comparison with interlaboratory studies, where several laboratories produce the data used to prepare the method precision profile. 

The AMDA concept of ANSI is attractive, and the writer would like to expand upon it. First, if the RSD and the MDA have been based on intralaboratory studies, a procedure for estimating the Interlaboratory RSD and the AMDA could be done by applying an appropriate series of approximate corrections shown in Table 1. Such corrections could be applied to either the original procedure for which an AMDA was to be stated or to the alternate less sensitive procedure which was to be used for the AMDA. Of course, if an AOAC-type interlaboratory study were conducted to determine a pooled RSD, only the corrections for variables not included in the AOAC-type study would be used. 

It is well known that the actives used in hair dye formulations can penetrate into and permeate across the skin (Dressier, 1998 Yourick and Bronaugh, 2000). The rate and total cumulative amount of dye that has been shown to be absorbed, however, is variable and also dependent on the study protocol. When similar protocols have been used, in inter- and intralaboratory studies variability is considerably reduced (Beck et al., 2000). Calculation of safety margins for hair dyes using in vitro skin permeation data is somewhat more complex than that illustrated above for a sunscreen agent. Whereas a typical sunscreen agent is applied as a leave-on product over a large area of the body, hair dye products are applied to the hair over a relatively small (but certainly an area rich in hair follicles) area of skin and remain in place for a short period of time. Thus, to determine the potential systemic load using in vitro skin permeation measurements, the experiments should follow as closely as possible the in-use scenario. 

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. . 

Validation-based approach Based on inter- or intralaboratory validation studies (precision, trueness, robustness) An extension of validation work, no extra work needed Some sources of uncertainly may be overlooked Eurachem [14], Barwick and Ellison [47]... 

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. 

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.

Reproducibility is defined as the long-term variability of the measurement process, which may be determined for a method run, within a single laboratory, but on different days. Reproducibility also applies to a method, either run by different operators, different instruments, or a combination of the above. The reproducibility standard deviation is typically twofold to threefold larger than that for repeatability. Precision is often expressed relative to 1 day as intraday (within-day) precision or relative to a period of days, as interday (between days) precision. Reproducibility, in the sense of intralaboratory precision, is related to the procedure being performed at two or more laboratories as in, e.g., a collaborative study. 

Friedberg T, Pritchard MP, Bandera M, et al. Merits and limitations of recombinant models for the study of human P450-mediated drug metabolism and toxicity - An intralaboratory comparison. Drug Metab Rev. 1999 31 523-544. 

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. 

Intralaboratory precision studies are classified as intraassay, where the profile is obtained doing the replication in only one run, using the same batch of reagents, or interassay, where the precision profile is obtained by comparison of runs done on different days. Poorer precision is generally obtained in interassay studies. 

In samples 1, 4, 6, and 10, the expected activity is 5000 NLU/g, whereas in the rest of the samples the expected activity is 2000 NLU/g. The data presented are averages of two replicates samples. The underlined data were later identified as outliers and were not used in further calculations. Intralaboratory (RSDr) and interlaboratory (RSDr) precision values are also shown. [Reprinted, with permission, from A. J. Engelen and P.H.G Randsdorp, Journal of AOAC International 82 No. 1, 1999, 112—118. Determination of Neutral Lactase Activity in Industrial Enzyme Preparations by a Colorimetric Enzymatic Method Collaborative Study . 1999 by Association of Official Analytical Chemists.]... 

Reference materials find their utility because the analyst can use them when he wants. Therefore, they must be stable. CRMs have a guaranteed — certified — content of a substance the producer must guarantee the stability of this substance and of the matrix. RMs for intralaboratory and interlaboratory studies must also be stable. As already mentioned above, stabilisation of the material must be done in such a way that it does not affect the representativeness of the material. In the food/feed control field, as well as in the... 

As palaeoceanographic reconstructions based on bulk fossil chemistry proliferate, comparability of measurements between laboratories has become an important issue. A recent calibration exercise involving thirteen laboratories by Rosenthal et al. (2004) evaluated the reproducibility of analyses of synthetic standard solutions within and between laboratories. The study found that intralaboratory instrumental precisions were generally better than 0.5% for both Mg/Ca and Sr/Ca measurements, but interlahoratory precisions (r.s.d) were significantly worse (up to 3.4% and 1.8%, respectively). This could be a result of differences between cahbration standards used by laboratories, or because the circulated standard solutions had become contaminated in the interval between their... 

CRMs are products of very high added value. Their production and certification is very costly. Therefore, except for calibration materials for comparative methods, they should be reserved for the selected verification of analytical procedures and not for daily checks, e.g. intralaboratory statistical control, nor for interlaboratory studies (round-robins). 

Several standards arc available for intralaboratory and intcr-laboralyry quality control studies, which also include day-to-day control of the precision and accuracy of within-run and between-run imprecision of activity measurements. Commercially available standard.s also provide information on the activity of the standards for a given substrate at specified experimental conditions. 

Since important decisions affecting the health and welfare of humanity must be made on the basis of analytical results, considerable effort must be directed toward assuring greater confidence in the reliability of the output of analytical laboratories. The Commission of the European Communities, after performing a study to determine the comparability of chemical analyses for drinking water quality, concluded that analytical quality control must be required as a routine component of analytical work. They state ( ), "Only the combination of intralaboratory controls of precision and accuracy complemented by interlaboratory intercomparison tests can lead to a significant evaluation and improvement of analytical results."... 

---