Thomas E. Gills

A new river sediment standard reference material.

The collection, processing and certification of a new sediment Standard Reference Material (SRM), SRM 2704, is described. Collected from the bottom of the Buffalo River in New York State during the fall of 1986, SRM 2704 is certified for 25 elements with information provided on another 22 elements. Improvements in analytical methods as well as the application of well-defined quality-control procedures for collection, processing and analysis have resulted in a reference material that is more completely characterized than previous NIST sediment reference materials.

Certifying the chemical composition of a biological material — a case study

A worldwide laboratory intercomparison was organized by the International Atomic Energy Agencys Analytical Quality Control Services (AQCS) involving the determination of trace elements in plant materials used for human consumption. The National Institute of Standard and Technology (NIST) Standard Reference Materials Program donated 5 kg of spinach designated for the production of the future Standard Reference Material SRM 1570a to this intercomparison; the AQCS provided a similar amount of cabbage. For the study, 150 units of each material were distributed and 114 laboratories reported results on both materials to AQCS. The results for the spinach, encompassing more than forty elements, have been compiled and evaluated; estimates of the elemental concentrations were made based on statistical evaluations, principles of analytical procedures and the laboratory performance indicated by the results on the cabbage material. Satisfactory estimates were obtained for 27 elements. Comparison with IAEA laboratory and NIST reference data did not reveal any significant bias that might have been introduced by the intercomparison approach or its evaluation.

Determination of tin in biological materials by atomic absorption spectrophotometry and neutron activation analysis

Concentrations of Tin (Sn) were determined in botanical, dietary and biological reference materials (RMs), and in human livers from Japanese and American subjects using atomic absorption spectrophotometry (AAS) and neutron activation analysis (NAA), either in the instrumental mode (INAA) or in the radiochemical mode (RNAA). The mean Sn concentrations (+/- 1 S.D.) found in various RMs are: total diet (NIST SRM-1548) 3.57 +/- 0.52 and 3.61 +/- 0.52 microgram/g by AAS and INAA, respectively; non-fat milk powder (NIST SRM-1549) 2.5 +/- 1.4 ng/g and 1.9 +/- 0.3 ng/g; bovine liver (NBS SRM-1577) 18 +/- 2 and 20 +/- 0.3 ng/g; and citrus leaves (NIST SRM-1542) 0.25 +/- 0.02 and 0.243 +/- 0.006 microgram/g by AAS and RNAA, respectively. These comparisons demonstrate good agreement between the two methods. In apple leaves (NIST SRM-1515) and peach leaves (NIST SRM-1547), the measured concentrations by AAS were 77.1 +/- 20 and 85 +/- 15 ng/g; interferences by 160Tb did not permit an accurate assessment by INAA at this concentration. The Sn results obtained for the American human liver specimens by RNAA ranged from 0.135-0.712 microgram/g wet weight, and the Sn concentrations in Japanese human liver specimens determined by AAS ranged from 0.078-1.122 microgram/g wet weight in 23 individuals. The results from this study show that it is feasible to use INAA/RNAA and AAS in combination to establish recommended values in RMs.

Certification of a new NIST fly ash standard reference material

In June 1993 the National Institute of Standards and Technology (NIST) released the third version of “Constituent Elements in Coal Fly Ash” Standard Reference Material (SRM 1633b). This material is intended for quality assurance purposes in evaluating the analytical methods used for the determination of constituent elements in coal fly ash or in materials with similar matrices. It has been certified for 23 major, minor and trace elements using ten different analytical techniques. For an element to be certified in a NIST SRM, its concentration is usually determined by at least two independent analytical techniques. The concentrations of additional 24 elements are provided for “information only” purposes in the new fly ash. Current plans are to certify the concentrations of a number of rare earths upon completion of additional analytical work now in progress. Homogeneity testing was accomplished using instrumental neutron activation analysis and X-ray fluorescence. This presentation summarizes the preparation of this new material and the analytical results used for certification.

Certification of sulfur in SRM 2724 diesel fuel oil by isotope dilution thermal ionization mass spectrometry and X-ray fluorescence

Abstract SRM 2724 is a no. 2-D diesel fuel oil that has been certified for total sulfur concentration at 425 ± 4 μ g g −1 (95% confidence interval) by isotope dilution thermal ionization mass spectrometry, which is the most accurate and precise method for the determination of sulfur in many different matrices. The sulfur concentration in this standard has also been measured by X-ray fluorescence (XRF) using a procedure derived from ASTM method D 2622-87. The mean of the XRF measurements was 423 ± 2 (1s), which demonstrates that XRF is capable of measuring sulfur accurately and precisely at the 500 μg g −1 level when it is properly calibrated using accurately certified standards of a similar matrix. SRM 2724 will be useful in validating the measurement process for the determination of sulfur by XRF in on-road diesel fuel at the 500 μg g −1 limit as mandated by EPA, effective from October 1993.

The determination of trace elements in new food grain SRM's using neutron activation analysis

Potentially toxic metals in the food chain that can lead to deleterious effects on human health have been well documented. Because of the toxicity of some metals, levels of 1 ppm or less must be routinely monitored in foods to ensure human safety. To ensure the accuracy of measurement, NBS in a cooperative interagency agreement with the Food and Drug Administration is involved in developing and certifying selected elements in food grain as a part of the Standard Reference Material program. Both instrumental and radiochemical neutron activation analysis were used to analyze two food grain standard reference materials (Rice and Wheat Flours) for trace element certification.

Recent developments in NIST botanical SRMs

The National Institute of Standards and Technology (NIST) (formerly the National Bureau of Standards (NBS)) issued the first botanical reference material certified for elemental content in January 1971, as Standard Reference Material (SRM) 1571, Orchard Leaves. In the following years a total of nine additional botanical certified reference materials have been issued by NIST. Each of these materials was certified for major, minor and trace elements except for SRM 2695, certified for fluorine only. Botanical SRMs issued since 1991 are significantly improved over previous materials in a number of ways. Probably the most significant change is the use of a jet-milling process to grind them to extremely fine particles. This has resulted in botanical SRMs with significantly improved homogeneity. These NIST reference materials are described with information on homogeneity, drying techniques and grit content.

Mercury in Coal: A New Standard Reference Material

Abstract Sources of environmental mercury contamination are generally related to industrial and mining activity. However, close examination of the sources reveal how complex the task of dealing with mercury pollution is. For example, virtually none of the mercury in fossil fuel is trapped in the fly ash, instead it is released in gaseous form as a product of combustion. Evidence now exists that this gaseous mercury is washed from the air by rain, being cycled to rivers, lakes and oceans where further evidence indicates that it may be methylated to its most toxic form, methylmercury. Mercury releases to the environment from burning of fossil fuels have been calculated to contribute a significant portion of the total mercury released. Unfortunately, mercury concentrations in coals used to calculate mercury release differ by a wide range. This paper presents the results of a concerted analytical program by the National Bureau of Standards to develop a coal standard of proven homogeneity with an accurate valu...