Development of a kelp powder (Thallus laminariae) Standard Reference Material.

A Standard Reference Material (SRM) of seaweed, SRM 3232 Kelp Powder (Thallus laminariae) has been developed to support food and dietary supplement measurements in compliance with the Food Safety Modernization Act (FSMA) and the Dietary Supplement Health and Education Act of 1994 (DSHEA). The material was characterized for nutritional minerals, arsenic species, isomers of vitamin K1, proximates, and toxic elements. Kelp is a rich source of vitamins and minerals, and it is an excellent source of dietary iodine. Kelp also contains a large amount of arsenic, which is toxic as inorganic species but much less so as organic species. To capture the dietary profile of kelp, certified values were issued for As, Ca, Cd, Cr, Cu, Fe, Hg, I, K, Mg, Mn, Mo, Na, Pb, and Zn. Reference values for proximates were assigned. For the first time, a certified value for iodine, reference values for isomers of vitamin K1, and reference values for arsenic species including arsenosugars were assigned in a seaweed. SRM 3232 fills a gap in Certified Reference Materials (CRMs) needed for quality assurance and method validation in the compositional measurements of kelp and similar seaweeds used as food and as dietary supplements. Graphical Absract Arsenic species and isomers of vitamin K1 were determined in the development of SRM 3232 Kelp Powder (Thallus laminariae).

Elemental characterization of single-wall carbon nanotube certified reference material by neutron and prompt γ activation analysis.

Instrumental neutron activation analysis with both relative and k0 standardization was used in four experienced laboratories to determine element mass fractions in single-wall carbon nanotube certified reference material (CRM) SWCNT-1. Results obtained were evaluated using the National Institute of Standards and Technology (NIST) "Type B On Bias" approach and yielded consensus values in agreement with National Research Council Canada (NRCC) certified values for Fe, Co, Ni, and Mo and provided mass fraction values for 13 additional elements, namely, Na, Mg, Al, K, Ca, Ti, V, Cr, Mn, Br, La, W, and Au. In addition, prompt γ neutron activation analysis was employed to determine mass fractions of H, B, Co, Ni, and Mo. Results of this work provide a basis for the establishment of reference values of element mass fractions in CRM SWCNT-1, thus expanding its usability for more accurate characterization and benchmarking of similar nanotechnology materials.

Structure and stability of SnO2 nanocrystals and surface-bound water species.

The structure of SnO2 nanoparticles (avg. 5 nm) with a few layers of water on the surface has been elucidated by atomic pair distribution function (PDF) methods using in situ neutron total scattering data and molecular dynamics (MD) simulations. Analysis of PDF, neutron prompt gamma, and thermogravimetric data, coupled with MD-generated surface D2O/OD configurations demonstrates that the minimum concentration of OD groups required to prevent rapid growth of nanoparticles during thermal dehydration corresponds to ~0.7 monolayer coverage. Surface hydration layers not only stabilize the SnO2 nanoparticles but also induce particle-size-dependent structural modifications and are likely to promote interfacial reactions through hydrogen bonds between adjacent particles. Upon heating/dehydration under vacuum above 250 °C, nanoparticles start to grow with low activation energies, rapid increase of nanoparticle size, and a reduction in the a lattice dimension. This study underscores the value of neutron diffraction and prompt-gamma analysis, coupled with molecular modeling, in elucidating the influence of surface hydration on the structure and metastable persistence of oxide nanomaterials.

Certification of elements in and use of standard reference material 3280 multivitamin/multielement tablets.

Standard Reference Material 3280 Multivitamin/ Multielement Tablets was issued by the National Institute of Standards and Technology in 2009, and has certified and reference mass fraction values for 13 vitamins, 26 elements, and two carotenoids. Elements were measured using two or more analytical methods at NIST with additional data contributed by collaborating laboratories. This reference material is expected to serve a dual purpose: to provide quality assurance in support of a database of dietary supplement products and to provide a means for analysts, dietary supplement manufacturers, and researchers to assess the appropriateness and validity of their analytical methods and the accuracy of their results.

Prompt gamma ray activation analysis for determining chemical composition of 3D printing and casting materials used in biomedical applications.

Three-dimensional printing and casting materials were analyzed by prompt gamma-ray activation analysis (PGAA) to determine their suitability as human tissue surrogates for the fabrication of phantoms for medical imaging and radiation dosimetry applications. Measured elemental compositions and densities of five surrogate materials simulating soft tissue and bone were used to determine radiological properties (x-ray mass attenuation coefficient and electron stopping power). When compared with radiological properties of International Commission on Radiation Units and Measurements (ICRU) materials, it was determined that urethane rubber and PLA plastic yielded the best match for soft tissue, while silicone rubber and urethane resin best simulated the properties of bone.

Determination of moisture content of single-wall carbon nanotubes.

Several techniques were evaluated for the establishment of reliable water/moisture content of single-wall carbon nanotubes. Karl Fischer titration (KF) provides a direct measure of the water content and was used for benchmarking against results obtained by conventional oven drying, desiccation over anhydrous magnesium perchlorate as well as by thermogravimetry and prompt gamma-ray activation analysis. Agreement amongst results was satisfactory with the exception of thermogravimetry, although care must be taken with oven drying as it is possible to register mass gain after an initial moisture loss if prolonged drying time or elevated temperatures (120 °C) are used. Thermogravimetric data were precise but a bias was evident that could be accounted for by considering the non-selective loss of mass as volatile carbonaceous components. Simple drying over anhydrous magnesium perchlorate for a minimum period of 8-10 days is recommended if KF is not available for this measurement.

Evaluation of radiochemical neutron activation analysis methods for determination of arsenic in biological materials.

Radiochemical neutron activation analysis (RNAA) with retention on hydrated manganese dioxide (HMD) has played a key role in the certification of As in biological materials at NIST. Although this method provides very high and reproducible yields and detection limits at low microgram/kilogram levels, counting geometry uncertainties may arise from unequal distribution of As in the HMD, and arsenic detection limits may not be optimal due to significant retention of other elements. An alternate RNAA procedure with separation of arsenic by solvent extraction has been investigated. After digestion of samples in nitric and perchloric acids, As(III) is extracted from 2 M sulfuric acid solution into a solution of zinc diethyldithiocarbamate in chloroform. Counting of (76)As allows quantitation of arsenic. Addition of an (77)As tracer solution prior to dissolution allows correction for chemical yield and counting geometries, further improving reproducibility. The HMD and solvent extraction procedures for arsenic were compared through analysis of SRMs 1577c (bovine liver), 1547 (peach leaves), and 1575a (pine needles). Both methods gave As results in agreement with certified values with comparable reproducibility. However, the solvent extraction method yields a factor of 3 improvement in detection limits and is less time-consuming than the HMD method. The new method shows great promise for use in As certification in reference materials.

Characterization of SiGe films for use as a National Institute of Standards and Technology Microanalysis Reference Material (RM 8905).

Bulk silicon-germanium (SiGe) alloys and two SiGe thick films (4 and 5 microm) on Si wafers were tested with the electron probe microanalyzer (EPMA) using wavelength dispersive spectrometers (WDS) for heterogeneity and composition for use as reference materials needed by the microelectronics industry. One alloy with a nominal composition of Si0.86Ge0.14 and the two thick films with nominal compositions of Si0.90Ge0.10 and Si0.75Ge0.25 on Si, evaluated for micro- and macroheterogeneity, will make good microanalysis reference materials with an overall expanded heterogeneity uncertainty of 1.1% relative or less for Ge. The bulk Ge composition in the Si0.86Ge0.14 alloy was determined to be 30.228% mass fraction Ge with an expanded uncertainty of the mean of 0.195% mass fraction. The thick films were quantified with WDS-EPMA using both the Si0.86Ge0.14 alloy and element wafers as reference materials. The Ge concentration was determined to be 22.80% mass fraction with an expanded uncertainty of the mean of 0.12% mass fraction for the Si0.90Ge0.10 wafer and 43.66% mass fraction for the Si0.75Ge0.25 wafer with an expanded uncertainty of the mean of 0.25% mass fraction. The two thick SiGe films will be issued as National Institute of Standards and Technology Reference Materials (RM 8905).

Glassy carbon, NIST Standard Reference Material (SRM 3600): hydrogen content, neutron vibrational density of states and heat capacity.

Commercial glassy carbon plates being used as absolute intensity calibration standards in small-angle X-ray scattering applications (NIST SRM 3600) have been characterized in several recent publications. This contribution adds to the characterization by measuring the hydrogen content of a plate to be (4.8 ± 0.2) × 10-4 (mol H)/(mol C), and by measuring the vibrational spectrum by neutron inelastic scattering. The spectrum bears a strong resemblance to published measurements on graphite, allowing the identification of several spectral features. The measured spectrum is used to calculate the heat capacity of low-hydrogen-content glassy carbon for comparison with measurements reported here from 20 to 295 K.

Prompt Gamma-ray Activation Analysis for Certification of Sulfur in Fuel Oil SRMs.

A combination of cold neutron prompt gamma-ray activation analysis (CNPGAA) and thermal neutron (TN) PGAA was used to determine sulfur in fuel oils to develop a method to provide values for certification. CNPGAA was used to measure S/H mass ratios, and TNPGAA to measure hydrogen mass fractions. Measurements were combined to determine sulfur mass fractions (with expanded uncertainties) of 2.159 % ± 0.072 % for SRM 1622e, 0.7066 % ± 0.0120 % for SRM 1619b, and 0.1266 % ± 0.0030 % for SRM 1617b, in agreement with certified values. The results validate the method as suitable for certification of sulfur at mass fractions ≥ 0.1 %.

Certification of Total Arsenic in Blood and Urine Standard Reference Materials by Radiochemical Neutron Activation Analysis and Inductively Coupled Plasma - Mass Spectrometry.

A newly developed procedure for determination of arsenic by radiochemical neutron activation analysis (RNAA) was used to measure arsenic at four levels in SRM 955c Toxic Elements in Caprine Blood and at two levels in SRM 2668 Toxic Elements in Frozen Human Urine for the purpose of providing mass concentration values for certification. Samples were freeze-dried prior to analysis followed by neutron irradiation for 3 h at a fluence rate of 1×1014cm-2s-1. After sample dissolution in perchloric and nitric acids, arsenic was separated from the matrix by extraction into zinc diethyldithiocarbamate in chloroform, and 76As quantified by gamma-ray spectroscopy. Differences in chemical yield and counting geometry between samples and standards were monitored by measuring the count rate of a 77As tracer added before sample dissolution. RNAA results were combined with inductively coupled plasma - mass spectrometry (ICP-MS) values from NIST and collaborating laboratories to provide certified values of (10.81 ± 0.54) µg/kg and (213.1 ± 0.73) µg/kg for SRM 2668 Levels I and II, and certified values of (21.66 ± 0.73) µg/kg, (52.7 ± 1.1) µg/kg, and (78.8 ± 4.9) µg/kg for SRM 955c Levels 2, 3, and 4 respectively. Because of discrepancies between values obtained by different methods for SRM 955c Level 1, an information value of < 5 µg/kg was assigned for this material.

Determination of boron in materials by cold neutron prompt gamma-ray activation analysis.

An instrument for cold neutron prompt gamma-ray activation analysis (PGAA), located at the NIST Center for Neutron Research (NCNR), has proven useful for the measurement of boron in a variety of materials. Neutrons, moderated by passage through liquid hydrogen at 20 K, pass through a (58)Ni coated guide to the PGAA station in the cold neutron guide hall of the NCNR. The thermal equivalent neutron fluence rate at the sample position is 9 x 10(8) cm(-2) s(-1). Prompt gamma rays are measured by a cadmium- and lead-shielded high-purity germanium detector. The instrument has been used to measure boron mass fractions in minerals, in NIST SRM 2175 (Refractory Alloy MP-35-N) for certification of boron, and most recently in semiconductor-grade silicon. The limit of detection for boron in many materials is <10 ng g(-1).

Radiochemical neutron activation analysis for certification of ion-implanted phosphorus in silicon.

A radiochemical neutron activation analysis procedure has been developed, critically evaluated, and shown to have the necessary sensitivity, chemical specificity, matrix independence, and precision to certify phosphorus at ion implantation levels in silicon. 32P, produced by neutron capture of 31P, is chemically separated from the sample matrix and measured using a beta proportional counter. The method is used here to certify the amount of phosphorus in SRM 2133 (Phosphorus Implant in Silicon Depth Profile Standard) as (9.58 +/- 0.16) x 10(14) atoms x cm(-2). A detailed evaluation of uncertainties is given.