Reference materials are vitally important in product and specification testing, in research and development work, in technical service work, and in quality control operations in the rubber and carbon black industries. They are especially valuable for referee purposes.
Categories, Classes, and Types of Reference Materials (RM):
Reference materials are divided into two categories:
Industry Reference Materials (IRM)8212;Materials that have been prepared according to a specified production process to generate a uniform lot; the parameters that define the quality of the lot are evaluated by a specified measurement program.
Common-Source Reference Materials (CRM)8212;Materials that have been prepared to be as uniform as possible but do not have established property (parameter) values; the knowledge of a common or single source is sufficient for certain less critical applications.
Industry reference materials (IRMs) are divided into additional classes and types according to the method of evaluating the lot parameters and according to the production process for generating the lot material. These are explained more fully (refer to Annex A3 and Annex A4 for more details on the discussion in Section 3).
The following lot parameters are important for reference material use:
Accepted Reference Value (AR Value)8212;An average IRM property or parameter value established by way of a specified test program.
Test Lot Limits (TL Limits)8212;These are limits defined as ±3 times the standard deviation of individual IRM test results across the entire lot for the property or parameter(s) that defines lot quality; the measurements are conducted in the laboratory of the organization producing the IRM.
Although the limits as defined in 3.2.3.2 are given in terms of ±3 times the standard deviation, the rejection of individual portions of the lot as being outlier or non-typical portions in assessing the homogeneity of the lot is done on the basis of ±2 times the appropriate standard deviation, that is, on the basis of a 95 % confidence interval. See Annex A3 and Annex A4 for more information and the evaluation procedures.
All IRMs have an AR value and TL limits; however the AR value may be obtained in one of two ways to produce one of two classes of AR values:
Global AR Value8212;This AR value is obtained from an interlaboratory test program where the word “global” indicates an average value across many laboratories.
Local AR Value8212;This is an AR value obtained in one laboratory or at one location, usually the laboratory responsible for preparation of the homogeneous lot.
An additional parameter is of importance for IRMs that have a global AR value:
Between-Laboratory Limits (BL)8212;The group of laboratories that conduct interlaboratory testing to establish an AR-value are not equivalent to a system or population typical of industrial production operations that use the usual ±3 standard deviation limits. Such production operations are systems that have been purged of all assignable causes of variation and are in a state of ‘statistical control’