ES&T MEASUREMENT FOCUS
Rethinking Traceability
Lawrence H. Keith
T
he demand for new analytical reference m a t e r i a l s has steadily increased to keep pace with advances in the sensitivity, accuracy, and precision of instruments used for conducting chemical analyses. In the realm of environmental science and technology this demand is further stimulated by constantly improving analytical m e t h o d s and changing regulations. Analytical reference materials are critically important to almost all environmental measurements because they are the primary basis for evaluating the comparability of analyte identifications and concentrations in environmental samples. Comparability is evaluated both qualitatively (identification of analytes) and quantitatively (measurements of purity or concentration). Analytical comparability is also evaluated among different laboratories using analytical reference materials that have common links with other analytical reference materials. In spite of their importance, analytical reference materials are typically viewed in much the same way as you view your toaster. As long as your toaster continues to provide reproducible, high-quality toast every day, you take it for granted. You have little interest in learning about any special features it may have; you just use it in the same way every day and don't want to think about it until something happens that requires your attention. Defining traceability Last year we began to feel the need to pay attention to issues in590 A
volving the traceability and stability of environmental reference materials. As chair of the American Chemical Society (ACS) subcommittee on Environmental Monitoring and Analysis within the Committee on Environmental Improvement, I worked with Bill Reed, head of the Environmental Reference Materials Division at the National Institute of Standards and Technology (NIST), to organize the joint NIST/ACS "Workshop on the Traceability and Stability of Environmental Reference Materials" in October 1993. Producers and users of reference materials as well as regulators attended the workshop, which was held at NIST headquarters in Gaithersburg, MD. Among the consensus recommendations from the meeting were that ACS and NIST adopt the International Organization for Stand a r d i z a t i o n (ISO)-REMCO ISO Guide 30 definition of traceability and that they continue (1) defining specific technical problems regarding traceability and stability of environmental reference materials and (2) exploring viable solutions to them. ISO defines traceability as the "property of the result of a measurement or the value of a standard whereby it can be related, with a stated uncertainty, to stated references, usually national or international standards, through an unbroken chain of comparisons" (2). A good feature of this definition is the reference to "a stated uncertainty"; often this is ignored, and then one cannot tell whether a particular value agrees within 10% or 100% to the value of the standard with which it is being compared. The problems with this definition are that often no national or international standards exist with which comparisons can be made, and no guidance exists for basic technical levels of acceptable comparison criteria. For example, a claim to using NIST-traceable analytical standards might be based on simply using NIST-traceable weights when preparing commercial standard solu-
Environ. Sci. Technol., Vol. 28, No. 13, 1994
tions for chemical analysis; this provides no chemical traceability. A few months after the NIST/ACS workshop, EPA announced that "EPA-certified" standards produced by its Cooperative Research and Development Agreement contractors were being discontinued. That makes the ISO definition of traceability even more difficult to meet than it was before, because many groups (e.g., several branches of the U.S. government, the state of Illinois, and Taiwan) used EPA-certified standards as de facto "national standards," even though the Office of the Inspector General found that some of the standards weren't adequately tested for purity, identity, or stability (2). Nevertheless, many standards that, for good or bad, were used as traceable sources are now disappearing, leaving an even smaller fraction of standards from commercial vendors that will be traceable by the very vague ISO definition. Three criteria What is the solution? We must rethink the functional definition of "traceability" and consider its purpose for today's needs. When NIST provides a standard to which other secondary s t a n d a r d s are made traceable by means of an unbroken chain of comparisons according to acceptable (as yet undefined) criteria, it guarantees three things: 1. That measurements were made ab initio by NIST (or under NIST control) according to certain NIST criteria; 2. That those measurements define the properties of the identification and purity of the analytes (or concentrations, if solutions or mixtures are involved) according to NIST criteria; and 3. That those measurements are thoroughly documented according to NIST criteria and are available for technical scrutiny. Ab initio, or "from the beginning," here means that nothing is taken for granted. Original analyses are performed to establish defini-
0013-936X/94/0927-590A$04.50/0 © 1994 American Chemical Society
tively the identity and purity (or concentrations) of the analytes or, often, their impurities. When any source of an analytical standard performs the kind of ab initio analyses that NIST does, and does so under strictly defined conditions developed by and acceptable to the community that uses them (e.g., EPA, private labs), logically a " g r a d e " of analytical standard should be produced to which other secondary standards could be made traceable. Whenever a NIST or other national or international reference material is available, it is the traceable source of choice. However, reference materials that meet ISO traceability criteria frequently do not exist, resulting in the need for other traceable sources. These new sources might not be equivalent to NIST or other national or international standards. However, they would need to be comparable in quality or "grade" in a manner similar to the way "ACS reagent grade" specifies, for a wide variety of chemicals, the requirements and test procedures needed to ensure suitability for use in analytical procedures. Recent events The ACS Committee on Analytical Reagents, through its chair, Paul A. Bouis, was asked to join in the work to help recommend viable technical procedures and criteria to develop such a concept. We know that the problems in producing "ACS Environmental Reference Materials" (or some other terminology) will be very different from those involved in producing ACS reagent chemicals, but the analytical experience of the committee could provide invaluable contributions. Another recent event is the formation of the Chemical Reference Materials Manufacturers Association (CRMMA), which is expected to officially start in January 1995. CRMMA also will form committees to study technical and policy issues such as those outlined here. Together, CRMMA, ACS, and NIST should provide the leadership and expertise to solve the traceability problem. A clearly defined set of criteria is needed that will cover all three basic types of environmental reference materials: neat chemicals, synthetic standards (e.g., solutions and mixtures), and natural matrix standards (where the true values are not known but are assigned). Criteria for neat chemicals will be the easiest to define and, no doubt,
will be tackled first. Different criteria will be needed for synthetic standards and natural matrices, but a big step was taken at the October 1993 NIST/ACS workshop when specific consensus recommendations were made to tackle ab initio criteria for those types of standards. Much work needs to be done, but I think the technical approaches, which recommended using two or more methods (involving different physical and/or chemical properties of the analytes) are viable. Lyle Phifer comments that the technical solutions we arrive at will be applicable to many types of standards other than just environmental reference materials; many of these same standards are finding increased use for food analysis, drugs, and industrial products (Phifer, L. H., ChemService, Inc., personal communication, Sept. 1994). Avoiding burnt toast Two more o p p o r t u n i t i e s to widely discuss these problems and issues will occur next year. Dave Henderson (at Supelco) and I will conduct a "Workshop on Environmental Reference Standards" at the PittCon meeting in New Orleans (March 1995). An international symposium on the "Science and Technology of Environmental Reference Materials" will be held at Pacifichem '95 in Honolulu December 18-19, 1995. If we don't solve our traceability problems soon, EPA and the regulated community may decide to solve them for us. If the "toaster that burned the toast" doesn't get fixed pretty quickly, it could be replaced, and a new one might be pretty expensive. We must solve these problems before that happens. We must take an innovative approach, cooperate, and keep focused on what the technical community needs in order to have standards that contribute to analytical solutions rather than to problems.
Industry's Future: Changing Patterns of Industrial Research This fascinating volume provides the readers with an understanding of the dynamic processes that make industrial research a principal driving force in creating technical change, producing economic growth, and strengthening the technical institutions in society. It describes and analyzes the major factors that shape the conduct and organization of industrial research, including the internationalization of R&D, restructuring of industry, declining defense expenditures and the pressure to develop access to sources of technical change outside the corporation. The volume presents approaches for improved industry relations with government and academia, discusses complex conditions for conducting industrial research effectively and analyzes potential new conditions that can shape future industrial research. The experiences of specific corporations with modern management of technology are also described. Herbert I. Fusfeld 384 pages (1 994) C l o t h b o u n d : ISBN 0-841 2-2983-X $39.95 Paperbound: ISBN 0 - 8 4 1 2 - 2 9 8 4 - 8 $24.95
References (1) (2)
Just Published!
ISO Guide 1992, 30, Section 3.8. Noble, D. Anal. Chem. 1994, 66, 868A-72A.
Lawrence H. Keith is principal scientist at Radian Corporation, He is editor of the ACS Division of Environmental Chemistry newsletter, EnvirofACS, and chairs the CEI Subcommittee on Environmental Monitoring and Analysis. His Ph.D. is from the University of Georgia.
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Environ. Sci. Technol., Vol. 28, No. 13, 1994
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