Homogeneity and Stability Tests

Selection of method appropriate for homogeneity and stability testing Design of the characterization of the reference material Sampling... 

Select a method appropriate for homogeneity and stability testing... 

Because the material will be distributed as a reference material after the study, there must be enough material to satisfy the needs of the test and its future uses. Homogeneity and stability must be demonstrated, and after the first certification round, later rounds can be planned to establish shelf life of the material. Usually one laboratory has the responsibility for performing homogeneity and stability tests. Subsamples are stored at temperatures ranging from —20°C to +50°C and analyzed once a month for a period of 3 or 4 months. 

Precht, D., Molkentin, J. and de Froidmont-Goertz, I. (1998) Anhydrous butterfat reference material CRM 519 certification of triglyceride composition and cholesterol content including homogeneity and stability tests. Fett. Lipid., 100, 546-554. 

Table 5.1.3 Homogeneity and stability testing for quality control tools produced within the SWIFT-WFD Project... 

In order to validate speciation methods more effectively, a number of certified reference materials (CRMs) have been produced to allow laboratories to measure the accuracy of their techniques. A range of sediment and biota materials are available such as the sediment materials PACS-2 from the National Research Council of Canada, NIES-12 from the National Institute for Environmental Studies, Japan and the CRM-462 from Community Bureau of Reference (BCR), EU. These materials have been rigorously homogeneity and stability tested and the levels of organotins have been certified by a range of techniques utilizing either definitive methods or multiple independent methods. 

The selection and preparation of the samples very often is the most crucial item in an interlaboratory test. All characteristics that could affect the integrity of the test have to be considered. This includes homogeneity and stability, which are dealt with in detail later. The PT provider has to look for possible changes in and the effect of ambient conditions on the samples. 

Test materials Minimum of five different materials, no stipulations for homogeneity and stability of test samples No minimum, per round often less than five test samples homogeneity and stability of materials must be assured... 

At the conclusion of the study, surplus test materials are offered for sale as reference materials for quality control and method development purposes. These materials have been studied for homogeneity and stability and have been assigned values for specific analytes. The more recently produced materials (since July 1999) have traceable assigned values with rigorously evaluated uncertainties. Older materials have consensus-based assigned values. 

In order to cope with the lack of CRMs for endogenous species, the practice of laboratory internal QC materials is developing. A Laboratory Reference Material (LRM) was prepared from Brazil nuts (Bertholletia excelsa) for QC of the selenomethionine determinations. The concentration of selenomethionine was 79.9 p,g g-1. The homogeneity and stability of this candidate CRM passed the relevant tests recommended by the Measurement and Testing Programme [97],... 

The suitability of the quality control tools prepared under the SWIFT-WFD project was proved from the homogeneity and stability studies carried out on all materials. Table 5.1.3 summarizes the tested analytes for each material, the institution responsible for the analysis, and the analytical technique and sample intake used. 

The requirements of 58.113(a) substantially changed the state of the art for the conduct of nonclinical laboratory studies. Prior to the promulgation of GLP regulations, analytical tests to establish the homogeneity and stability of article/carrier mixtures were not routine, nor were tests to determine the concentration of test and control articles in the mixtures used to deliver test and control articles to test systems. 

The preparation of each test material followed the same principles as those described in various places of this book with respect to homogenisation, stabilisation, verification of the homogeneity and stability, and establishment of assigned values. 

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