Susan F. Stone

The use of high accuracy NAA for the certification of nist botanical standard reference materials

Neutron activation analysis is one of many analytical techniques used at the National Institute of Standards and Technology (NIST) for the certification of NIST Standard Reference Materials (SRMs). NAA competes favorably with all other techniques because of its unique capabilities for high accuracy even at very low concentrations for many elements. In this paper, instrumental and radiochemical NAA results are described for 25 elements in two new NIST SRMs, SRM 1515 (Apple Leaves) and SRM 1547 (Peach Leaves), and are compared to the certified values for 19 elements in these two new botanical reference materials.

Radiochemical and instrumental neutron activation analysis procedures for the determination of low level trace elements in human livers

A comprehensive approach to the analysis of human livers was developed in a pilot program for the National Environmental Specimen Bank that employed a combination of four analytical techniques. Refinements in this approach were needed for improvement in detection limits, more effective sample usage and to reduce the number of analytical steps that were involved. Since neutron activation analysis (NAA) had determined most of the elements, expansion of NAA was chosen to achieve these goals. Modifications in the instrumental NAA procedures, including the use of a Compton Suppressor System, gave increased sensitivity for some low level elements, such as arsenic and chromium. Radiochemical procedures that followed the instrumental counts increased the sensitivity for the elements chromium, selenium, arsenic, molybdenum, silver, antimony, and tin. Results are given for two radiochemical procedures that were applied following the modified procedure, either the use of an inorganic ion exchange column or a liquid/liquid extraction, and these are compared to instrumental results.

Long-term stability of the elemental composition in biological materials

SummaryLyophilized and radiation sterilized biological certified reference materials (CRMs) are believed to be stable in their chemical composition. Generally, the certifying agencies consider the certificates of these biological CRMs valid for a 5-year shelf life, i.e., apart from measurable moisture content, the chemical composition should not change during that time. The long-term behavior of fresh frozen material is not known. In this study the elemental compositions of the Bovine Liver Standard Reference Material (SRM 1577) and human liver tissue samples are evaluated over a time period of more than 7 years. The concentrations of selected elements were determined by neutron activation analysis at various times. The initial evaluation of zinc, selenium and arsenic results gives no indication of changes during 7 years storage of fresh frozen tissues, however, a trend towards lower arsenic concentrations has been observed in SRM 1577 during a 10-year period.

Application of polyacrylamide gel electrophoresis/neutron activation analysis for protein quantification.

A combination of two methods, polyacrylamide gel electrophoresis (PAGE) and neutron activation analysis (NAA), has been applied to solutions containing phosphoproteins for the purpose of protein quantification. The proteins were separated by molecular weight using PAGE, and then the whole gel was activated by neutron bombardment. Densitometric measurements of the developed bands from32P, taken from autoradiographs of the activated gels, resulted in quantification of the phosphorus, and then the related protein. This PAGE/NAA method was applied to several phosphoprotein-containing materials, including commercial milk products and reference materials, i.e., IAEA A-11, milk powder, and SRM 1845, Cholesterol in Egg Powder.

SOL PARTICLE IMMUNOASSAYS USING COLLOIDAL GOLD AND NEUTRON ACTIVATION

The feasibility of performing immunoassays with colloidal gold labels and detection of198Au by neutron activation has been demonstrated with measurements of human immunoglobulin and of serum antibodies to human immunodeficiency virus type 1. The detection sensitivity achieved after activation in a high flux reactor or with a water moderated252Cf source, by gamma-counting or by autoradiography, is similar to the sensitivity obtained with absorbance measurements in the more common enzyme immunoassays. The reactor based neutron activation assay allows detection of 10−16 mol of analyte in routine operation with possible extension to 10−20 mol. The sensitivity with the 1.3 Ci252Cf source is limited to about 10−15 mol. The practical limitations of the assays sensitivity at this point are due to background signals from reagents and/or nonspecific binding of the gold labeled reagent.

Instrumental neutron activation analysis of Standard Reference Material 1941, Organics in Marine Sediment. Element content and homogeneity.

The National Institute of Standards and Technology has developed a new Standard Reference Material 1941, “Organics in Marine Sediment.” In addition to the organic constituents, over 30 elements have been determined by instrumental neutron activation analysis and prompt-gamma activation analysis. The homogeneity of the material was investigated and relative standard deviations of single-element concentrations in 250-mg samples were found to be 1% or less with regard to major inorganic constituents and rare earth elements. A slightly higher relative SD was found for elements that may stem from biological or anthropogenic input. The element concentrations determined in this work are discussed in comparison to concentrations in other similar reference materials. Concentrations for 31 elements will be included for information on the certificate.

Nuclear Analytical Methods in Environmental Specimen Banking

Several nuclear analytical methods have been applied to determine elemental concentrations in samples from the National Biomonitoring Specimen Bank. Various combinations of neutron activation analysis (NAA), prompt gamma activation analysis (PGAA), and X-ray fluorescence (XRF) used to obtain information on the inorganic constituents in four types of samples, human livers, marine bivalves, fish livers, and sediments, are described. Concentrations of at least 20–30 elements from a small test portion (~ 1 g wet weight) can be obtained by combining these methods. The dynamic ranges, sensitivities and multielement capabilities of the described methods are shown to provide the high quality data needed in a banking program.

Instrumental neutron activation analysis of Standard Reference Material 1941, Organics in Marine Sediment

The National Institute of Standards and Technology has developed a new Standard Reference Material 1941, “Organics in Marine Sediment.” In addition to the organic constituents, over 30 elements have been determined by instrumental neutron activation analysis and prompt-gamma activation analysis. The homogeneity of the material was investigated and relative standard deviations of single-element concentrations in 250-mg samples were found to be 1% or less with regard to major inorganic constituents and rare earth elements. A slightly higher relative SD was found for elements that may stem from biological or anthropogenic input. The element concentrations determined in this work are discussed in comparison to concentrations in other similar reference materials. Concentrations for 31 elements will be included for information on the certificate.