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5.3 Standard Reference Materials

Carroll Croarkin, Staff of Statistical Engineering Division
Statistical Engineering Division, ITL

The Statistical Engineering Division supports the Standard Reference Materials Program and the other NIST laboratories by collaborating directly with chemists and other scientists engaged in the certification of Standard Reference Materials (SRMs). SRMs are artifacts or chemical compositions that are manufactured according to strict specifications and certified by NIST for one or more chemical or physical properties. SRMs are a primary vehicle for disseminating measurement technology to industry.

Development of a new SRM typically takes two to five years and encompasses: 1) validation of a measurement method; 2) design of a prototype; 3) stability testing; 4) study of measurement error; 5) certification and uncertainty analysis. Statisticians advise on the design and analysis of experiments at all phases; develop estimation methods; reconcile interlaboratory differences; and combine all information to produce a certified value and statement of uncertainty.

The largest number of SRMs come from the Chemical Science Technology Laboratory; (e.g. Ni/Cr thin film depth profile standard and numerous chemical composition SRMs), but SRMs also come from other NIST laboratories covering a variety of applications, for example: Manufacturing Engineering Laboratory (e.g. sinusoidal roughness); Material Science Engineering Laboratory (e.g. Secondary ferrite number standard); Electronics and Electrical Engineering Laboratory (e.g. resistivity of silicon wafers); Physics Laboratory (e.g. optical density filters); Building and Fire Research Laboratory (e.g. thermal resistance of fibrous glass insulation).

In 1999, work was completed on the certification of approximately thirty SRMs including a series of lead paint films analyzed by Nien Fan Zhang for CSTL and a series of electro-deposited coating thickness SRMs analyzed by Stefan Leigh for MSEL. A series of SRMs on Rockwell B scale hardness were undertaken by Walter Liggett where the success of the certification depends on modeling the shape of the indenter. Many SRMs are in process, and some, such as trace elements in mussel tissue, require separate analyses on as many as fifty or more constituents.

Tracking the number and status of SRMs has always been challenging because the responsibility for the status of the certification process often shifts back and forth between scientist and statistician as follow-on data are taken and analyzed or more analytes are added to the certification process. SED maintains an internal web page for this purpose that has recently been revised by Alan Heckert to provide more relevant information to NIST staff.

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Date created: 7/20/2001
Last updated: 7/20/2001
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