The Role of Reference Materials and Reference Methods in Chemical Analysis

I. INTRODUCTION

A. Scope and Purpose of the Review

The purpose of this paper is to provide a brief overview and review of the role of reference materials and reference methods in chemical analysis. Our primary concern is with the use of reference materials and reference methods in transferring accuracy and precision throughout large multilaboratory measurement networks. Although reference materials and reference methods can be effectively used to assure accuracy and precision within an individual laboratory, the great demand for compatible national measurement systems has led to their increased utilization in a total systems approach to accurate measurements in a variety of areas of chemical analysis. This paper first describes the concepts that provide the basis for the use of reference methods and reference materials to achieve measurement compatibility in multilaboratory networks. The basic concepts necessary to understand the measurement process itself are described. A conceptual systems model involving a hierarchy of reference materials and analytical methods which are utilized to transfer accuracy from a primary measurement standards laboratory into the field is presented. The basic philosophical and technical concepts underlying the systems approach to accurate measurement are evaluated and described without the use of detailed mathematical or statistical models. The role of federal laboratories, regulatory agencies, voluntary standards organizations, professional societies, and individual analytical laboratories is described in the context of a reference material-analytical method hierarchy. Criteria and guidelines that should be used for the selection and evaluation of reference materials and reference methods are reviewed. A comprehensive, technical evaluation of all the applications of reference materials and reference methods to chemical measurement systems is beyond the scope of any single review. However, some examples of recent applications of reference methods and materials are presented from the areas of industrial materials analysis (primarily metals), clinical analysis, and environmental analysis. Elemental analysis is emphasized. However, analogous conclusions can be drawn for other applications in chemical analysis. Some future needs for the development and utilization of reference materials and reference methods are presented. Also discussed is the growing need to establish mechanisms for achieving traceability of field measurements to primary reference materials and reference methods, and the role of federal laboratories, regulatory agencies, and commercial laboratories in helping to assure traceability.