HIGH PRECISION ISOTOPIC REFERENCE MATERIAL PROGRAM

 

Jacqueline L. Mann and Robert D. Vocke, Division 839, CSTL, Bldg. 227 Rm B352, MS 8391, Ph:  301-975-4472, Fax:  301-869-0413, Email: jmann@nist.gov, CHEMISTRY)

 

Recent developments in thermal ionization and inductively coupled plasma multicollector mass spectrometers have lead to “high precision” isotope ratio measurements with uncertainties approaching a few parts in 106.  These new measurement capabilities have revolutionized the study of isotopic variations in nature by increasing the number of elements showing natural variations by almost a factor of two, and new research areas are actively opening up in climate change, health, ecology, geology and forensic studies.

 

Because the isotopic applications are impacting very diverse fields, there is at present little effective coordination between research laboratories over reference materials and the values to apply to those materials.  NIST had originally developed the techniques for producing accurate isotopic characterizations, culminating in the NIST Isotopic SRM series.  The values on existing materials however are insufficiently precise and, in some cases, may be isotopically heterogeneous.  A new generation of isotopic standards is urgently needed and will directly affect the quality and scope of emergent applications and ensure that the results being derived from these diverse fields are comparable.

 

A series of new isotopic reference materials similar to the NIST 3100 single element solution series is being designed for this purpose.  Twelve elements have been selected as having the most pressing need.  In conjunction with other expert users and National Metrology Institutes, an isotopic characterization of the respective 12 selected ampoules from the NIST single element solution series is currently underway.  In this presentation the primary focus will be on the suitability of these materials in terms of isotopic homogeneity and purity, long term stability and availability, and isotopic relevance.  Approaches to value assignment will also be discussed.