The application of instrumental neutron activation analysis for the certification of the new NIST Fly Ash SRM

The National Institute of Standards and Technology (NIST) recently released the second renewal of its Trace Elements in Coal Fly Ash Standard Reference Material (SRM 1633b). This new material is currently certified for 23 major, minor and trace elements, and concentrations of an additional 24 elements are provided for information only purposes. Current plans are to certify the concentrations of a number of rare earths upon completion of additional analytical work now in progress. Instrumental neutron activation analysis (INAA) has played a major role in the certification of this new material in view of its potential for accuracy, multielemental capability, ability to assess homogeneity, high sensitivity for many elements, and essentially blank-free nature. For an element to be certified in a NIST SRM its concentration is usually determined by at least two independent analytical techniques. INAA has provided analytical information for 15 of the 23 elements certified, as well as for 22 of the 24 elements listed for information only. In addition, INAA has provided much of the homogeneity information for this SRM. This paper will describe these analytical procedures, and highlight those designed to optimize and assess the accuracy of the INAA measurements.