With the large increase in the use of chemicals for the production and manufacture of foodstuffs, pharmaceuticals and consumer products the potential for contamination of air, water, food and the general environment has dramatically increased. Regulation of the level of chemicals in biological and environmental samples is important in trade, community health and pollution prevention. Consequently the trace analysis of both metals and organic contaminants in complex biological and environmental samples is fundamental. One of the key factors affecting a laboratory’s capability to produce realistic test results is the availability of reference materials with property values that can be relied upon by users.

It is important that reference material uses understand that certified reference material (CRM) certificates provide considerable information about the particular standard. Compositional values with uncertainty limits are given for all certified values; these limits are normally 95% confidence intervals. Many reference material suppliers include analyte values for “informational purposes” only, normally these values are not certified because:

• Value determined by only one technique.
• Sample homogeneity problems.
• Discrepancies between different analytical techniques.

Certificates also often describe restrictions on the use of the reference material that must be observed to maintain sample integrity and to ensure results are consistent with certified values. These restrictions include:

• Drying.
• Homogeneity.
• Segregation.
• Storage.
• Shelf life.

This paper also explores the five main purposes for reference materials in a laboratory:

• To assist with the development and validation of accurate methods of analysis, ensuring traceable measurement results at a working level.
• To verify that test methods in current use are performing according to validated performance levels.
• To calibrate measurement systems.
• To assure the long-term adequacy and integrity of measurement quality assurance programs.
• To use as test materials for inter-laboratory comparisons and proficiency test programs.

Reference materials, which are produced by laboratories in-house, are generally used on a day-to-day basis. The attraction of using in-house reference materials is that they provide a relatively cheap option as compared to using certified reference materials and can closely resemble the laboratory’s routine test samples. Laboratories must remember that in-house reference materials do not replace CRM’s, but merely enable CRM’s to be used on a less frequent basis. It is vitally important that in-house standards are appropriately prepared to ensure that they are fit for purpose.