Certification Of Standard Reference Materials Research Articles

Nuclear analysis at NBS and NIST

For more than 50 years, nuclear methods have been applied to chemical analysis at the National Institute of Standards and Technology. Radiochemical, instrumental, and prompt-gamma activation analysis are used, as well as neutron depth profiling and other techniques. The history of this group in methods development and the certification of Standard Reference Materials, among other applications, is reviewed.

Preparation and Certification of Standard Reference Material 3278 Tocopherols in Edible Oils

Standard Reference Material (SRM) 3278 Tocopherols in Edible Oils has been issued for use as a quality assurance tool in the measurement of tocopherols. Like other natural-matrix SRMs, this material can be used in method validation or in assignment of tocopherol values to in-house quality control materials. Because most edible oils contain one predominant tocopherol isoform, the SRM is a blend of sunflower, soy, canola, and safflower oils to provide roughly comparable chromatographic peak heights of the two main tocopherols, γ and α, with smaller amounts of δ and β. The four tocopherol isoforms were determined by three independent liquid chromatography methods with absorbance and fluorescence detection. Various chromatographic and detection modes are used for assignment of certified values because biases inherent to one method should not be present in the other, and the existence of bias can therefore be identified.

Development of ballistics identification—from image comparison to topography measurement in surface metrology

Fired bullets and ejected cartridge cases have unique ballistics signatures left by the firearm. By analyzing the ballistics signatures, forensic examiners can trace these bullets and cartridge cases to the firearm used in a crime scene. Current automated ballistics identification systems are primarily based on image comparisons using optical microscopy. The correlation accuracy depends on image quality which is largely affected by lighting conditions. Because ballistics signatures are geometrical micro-topographies by nature, direct measurement and correlation of the surface topography is being investigated for ballistics identification. A Two-dimensional and Three-dimensional Topography Measurement and Correlation System was developed at the National Institute of Standards and Technology for certification of Standard Reference Material 2460/2461 bullets and cartridge cases. Based on this system, a prototype system for bullet signature measurement and correlation has been developed for bullet signature identifications, and has demonstrated superior correlation results.

Laudatio for Dr. Richard M. Lindstrom

Dr. Richard M. Lindstrom was born in Ashland, Wisconsin, USA. He received his B.S. (Honors) from the University of Wisconsin, Madison, in 1963, and Ph.D. in 1970 from the University of California, San Diego. His Ph.D. dissertation ‘‘Radionuclides in Meteorites and in the Lunar Surface’’ was one of the first theses to be based on the Apollo 11 lunar samples. He then went to the Tata Institute of Fundamental Research in Bombay as a postdoctoral fellow, and a year later moved to Brookhaven National Laboratory. Dr. Lindstrom joined the National Bureau of Standards (NBS, now NIST) in 1972 to develop a lowbackground counting laboratory. In 1974 he moved to the Inorganic Chemical Metrology Group, concentrating on accurate methods of elemental analysis using a variety of nuclear techniques. Dr. Lindstrom pioneered the development of promptgamma activation analysis (PGAA) and its application to the elemental characterization of substances and certification of Standard Reference Materials (SRMs). He also led a team of specialists to develop the world’s first cold-neutron PGAA system at NIST, and participated in establishing PGAA facilities in Japan and Hungary. With other scientists, Dr. Lindstrom used PGAA to detect neutron standing waves for the first time, and also measured the 200microbarn thermal neutron cross section of Pb, with implications for nucleosynthesis and nuclear models. Dr. Lindstrom has contributed significantly to understanding of several fundamental aspects of gamma-ray spectrometry, namely dead time and pileup effects, lossfree counting methods, and methods for determining of peak areas. He developed an interactive computer program called SUM, originally written to address the incorrect calculation of peak area uncertainty in a commercial gamma spectrometry packages, but which also provides improved accuracy in cases where a photopeak is very large, very small, or non-Gaussian. Dr. Lindstrom has contributed to improved nuclear data, and thus improved accuracy of NAA measurements. He provided a more precise value for half-life of As and several other nuclides. As a direct result of his work, the nuclear data evaluation community has changed its algorithms for combining published values. He was one of the first to identify every feature in the background of a gamma-ray detector. He operates a state-of-the-art lowbackground counting facility, and has recently installed a low-background detector more than 500 m underground. S. Glover (&) University of Cincinnati, Cincinnati, USA e-mail: seg3@cdc.gov

Certification of standard reference materials containing bitter orange

A suite of three dietary supplement standard reference materials (SRMs) containing bitter orange has been developed, and the levels of five alkaloids and caffeine have been measured by multiple analytical methods. Synephrine, octopamine, tyramine, N-methyltyramine, hordenine, total alkaloids, and caffeine were determined by as many as six analytical methods, with measurements performed at the National Institute of Standards and Technology and at two collaborating laboratories. The methods offer substantial independence, with two types of extractions, two separation methods, and four detection methods. Excellent agreement was obtained among the measurements, with data reproducibility for most methods and analytes better than 5% relative standard deviation. The bitter-orange-containing dietary supplement SRMs are intended primarily for use as measurement controls and for use in the development and validation of analytical methods.

Effect of Valence State on ICP-OES Value Assignment of SRM 3103a Arsenic Spectrometric Solution

The certification of Standard Reference Material (SRM is a registered trademark of NIST) 3103a As Spectrometric Solution is based on the gravimetric preparation value that is verified by inductively coupled plasma optical emission spectrometry (ICP-OES) measurements. A disagreement between the gravimetric and the spectrometric values for a batch of As calibration solutions led to the discovery that the solutions contained a mixture of trivalent and pentavalent As species and that the pentavalent species was approximately 8% more sensitive than the trivalent species with ICP-OES determination. The kinetics of the reaction between As metal and nitric acid were studied, and the results were applied to develop a procedure that would consistently produce single-species pentavalent As standards, which eliminates As speciation as a source of measurement bias in the SRM certification process.

Effect of NaCl and HCl concentrations on primary pH measurement for the certification of standard materials

pH is an important parameter to control the production of food, medicine, petrochemical products and others. Thus, standard reference materials used to calibrate pH meters are necessary to guarantee reliability of the measurements. The Chemical Metrology Division (Dquim) of the National Metrology Institute of Brazil (Inmetro) has as one of its missions the certification of standard reference materials. In the case of pH, it will be done by the pH primary measurement system of Inmetro, in operation at Dquim since 2003. The buffer solution of nominal pH value equal to 6.865 will be the first to be certified. The study of some measurement parameters has already been accomplished, and will lead to the improvement of the primary pH measurement. In this paper, the effect of NaCl and HCl concentrations on the primary pH measurement is discussed, based on the results obtained by Inmetro in the regional comparison SIM 8.11P.

Certification of standard reference material 970, ascorbic acid in serum, and analysis of associated interlaboratory bias in the measurement process.

The accurate and reproducible measurement of ascorbic acid is essential in delineating the role of ascorbic acid as a diagnostic tool for human disease and for the comparison of data acquired by different laboratories. A stabilized pair of standards of ascorbic acid in human serum, which is compatible with most analytical methods, have been prepared. The certification was based on the gravimetric addition of ascorbic acid to metaphosphoric acid-stabilized, ascorbic acid-depleted serum and NIST liquid chromatography-electrochemical measurements. The NIST results were analyzed statistically for homogeneity, and the expanded uncertainty of each SRM was calculated using all of the NIST data. An interlaboratory comparison exercise was also performed. These materials, Standard Reference Material (SRM) 970 Ascorbic Acid in Serum, Level I and Level II, are homogeneous and are certified to contain (10.07 +/- 0.21) and (30.57 +/- 0.28) mmol ascorbic acid/L of solution (expanded uncertainty), respectively. In the interlaboratory comparison (n = 17), the relative SDs for the two materials were 22% and 19%. Two lots of serum, each containing different amounts of ascorbic acid stabilized in metaphosphoric acid, have been prepared and characterized. Many laboratories provide inaccurate results.

The development and certification of Standard Reference Materials (SRMs) to assess and ensure accurate measurement of Pb in the environment.

The National Institute of Standards and Technology (NIST) has had a major quality-assurance role in the federal effort to reduce lead poisoning of children in the United States through its mission of ensuring the accuracy of chemical measurements. NIST certifies reference materials (standard reference materials--SRMs) that are used to benchmark measurements by secondary and field methods of analysis--to ensure that decisions of great health and economic impact are soundly based on good measurement science. Over the past 10 years, in cooperation with the US Environmental Protection Agency (EPA), US Department of Housing and Urban Development (HUD), and the United States Geological Survey (USGS), NIST has prepared and certified SRMs for lead content in soil, indoor dust, and paint. The role of these materials in meeting regulatory and abatement needs is described and their certified values are summarized.

Development of a fifteen component hydrocarbon gas standard reference material at 5 nmol/mol in nitrogen

Primary gravimetric gas cylinder standards containing fifteen alkane, alkene and aromatic hydrocarbons (C2–C10) were prepared. A procedure previously developed to prepare gas cylinder standards for volatile organic compounds at the 5 nmol/mol (ppb) level was used. The set of primary hydrocarbon gas standards prepared by this procedure were intercompared by using gas chromatography with a hydrogen flame ionization detector (GC-FID). The linear regression analysis showed excellent agreement among the standards for each compound. Similar mixtures containing many of these hydrocarbons have been evaluated over time and have shown stability of the concentrations in aluminum gas cylinders for three years. This research resulted in the production and certification of Standard Reference Material (SRM) 1800, which contains fifteen hydrocarbons in nitrogen at a nominal concentration of 5 nmol/mol for each analyte. A batch of twenty-four cylinders containing the mixture was prepared at NIST following previously demonstrated protocols for their preparation. Each cylinder was analyzed against one cylinder from the batch, designated as the “lot control”, for each of the fifteen hydrocarbons. The data showed that the batch was homogeneous, from 0.2 to 0.7% depending on the compound, and stable for each hydrocarbon in the mixture resulting in certification and issuance of SRM 1800.

Certification of standard reference material (SRM) 1941a, organics in marine sediment

SRM 1941a, Organics in Marine Sediment, has been recently issued with certified concentrations for 23 polycyclic aromatic hydrocarbons, 21 polychlorinated biphenyl congeners, 6 chlorinated pesticides, and sulfur. Noncertified concentrations have been also reported for additional PAHs, PCB congeners, and chlorinated pesticides and for percent total organic carbon (TOC), aliphatic hydrocarbons, and trace elements. SRM 1941a is the most extensively characterized natural matrix SRM issued by the National Institute of Standards and Technology (NIST).

The contribution of neutron activation analysis for the certification of standard reference materials

The contribution of neutron activation analysis for the certification of standard reference materials

Isotope dilution mass spectrometry

In the past isotope dilution mass spectrometry (IDMS) has usually been applied using the formation of positive thermal ions of metals. Especially in calibrating other analytical methods and for the certification of standard reference materials this type of IDMS became a routine method. Today, the progress in this field lies in the determination of ultra trace amounts of elements, e.g. of heavy metals in Antarctic ice and in aerosols in remote areas down to the sub-pg g −1 and sub-pg m −3 levels respectively, in the analysis of uranium and thorium at concentrations of a few pg g −1 in sputter targets for the production of micro- electronic devices or in the determination of sub-picogram amounts of 230Th in corals for geochemical age determinations and of 226Ra in rock samples. During the last few years negative thermal ionization IDMS has become a frequently used method. The determination of very small amounts of selenium and technetium as well as of other transition metals such as vanadium, chromium, molybdenum and tungsten are important examples in this field. Also the measurement of silicon in connection with a re-determination of Avogadro's number and osmium analyses for geological age determinations by the Re/Os method are of special interest. Inductively-coupled plasma mass spectrometry is increasingly being used for multi-element analyses by the isotope dilution technique. Determinations of heavy metals in samples of marine origin are representative examples for this type of multi-element analysis by IDMS. Gas chromatography-mass spectrometry systems have also been successfully applied after chelation of metals (for example Pt determination in clinical samples) or for the determination of volatile element species in the environment, e.g. dimethyl sulfide. However, IDMS—specially at low concentration levels in the environment—seems likely to be one of the most powerful analytical methods for speciation in the future. This has been shown, up to now, for species of iodine, selenium and some heavy metals in aquatic systems.

Determination of copper in white-metal bearing alloys

A method is proposed for the determination of copper in white-metal bearing alloys by direct controlled-potential electrolysis with a tantalum cathode at −0.32 V vs. SCE in a sulphate/bisulphate buffered electrolyte (pH 2) with fluoroboric acid and sodium tartrate as masking agents. Only Bi(III) interferes. Any co-deposited Bi can be corrected for by its spectrophotometric determination with Semi-Xylenol Orange after preconcentration with La(III) as carrier, from an ammoniacal solution containing the redissolved deposit. Any residual Cu(II) in the electrolyte is determined by spectrophotometry with 2,9-dimethyl-1, 10-phenanthroline. The standard deviation of this method has been found to be 0.03 mg ( n = 12) and its relative standard deviation from 0.03 to 0.17%. It has been successfully used for referee analysis and certification of standard reference materials.

Ion Chromatography and the Certification of Standard Reference Materials

Ion Chromatography and the Certification of Standard Reference Materials

Preparation and certification of standard reference material 1507: 11-nor-.DELTA.9-tetrahydrocannabinol-9-carboxylic acid in freeze-dried urine

The National Institute of Standards and Technology (NIST) has prepared and certified SRM 1507, a freeze-dried urine fortified with 11-nor-delta 9-tetrahydrocannabinol-9-carboxylic acid (THC-9-COOH), the major urinary metabolite of marijuana. The certified concentration of 20 +/- 1 ng/mL for the analyte was obtained from the concordant results of analyses of the material by gas chromatography/mass spectrometry (GC/MS) and high-performance liquid chromatography with electrochemical detection (HPLC-EC). Solid-phase extraction was used to prepare the sample for GC/MS analyses, and liquid-liquid extraction was used for the HPLC-EC analyses. The multistep HPLC method was developed at NIST to circumvent interferences from urinary constituents. The results of a round robin test on this material among five Department of Defense laboratories involved in drug testing are reported.

The role of neutron activation analysis in the certification of NBS Standard Reference Materials

Neutron activation analysis (NAA) is used extensively at the National Bureau of Standards as one of the analytical techniques in the certification of Standard Reference Materials (SRMs). Characteristics of NAA which make it valuable in this role are: accuracy; multielemental capability; ability to assess homogeneity; high sensitivity for many elements, and essentially blank-free nature. Examples of recent SRM analyses illustrating these characteristics are described.

Five years activity in determining trace elements for the certification of standard reference materials by neutron activation analysis

A review of the experiences developed in the last five years of analytical work concerning the determination of trace element concentrations in reference materials by neutron activation analysis has been reported and discussed. Several elements such as Co, Sc, Mn, V, Fe, La, Sb, Zn, Th, have been determined by instrumental neutron activation analysis, while elements such as Hg, Se, As, Cu, Cd, I, required a selective radiochemical procedure. The results obtained are compared with the final certified values. For each matrix and/or group of matrices analytical problems and their solutions are illustrated.

The use of isotope dilution mass spectrometry for the certification of standard reference materials

Isotope dilution mass spectrometry (IDMS) has been used extensively at the U.S. National Bureau of Standards as an accurate method to determine trace element concentrations in natural materials. Thermal ionization mass spectrometry is a single element technique capable of high accuracy and precision, and has been used for “definitive” measurements of trace elements in sera with 95% confidence limits less than 0.25%. Spark source mass spectrometry is a complementary multielement, high-sensitivity technique that has been used to determine up to 20 elements in a sample, with typical accuracies of 2%–5%. Together with appropriate chemical separations, such as anion and cation exchange, chelate resins, electrodeposition, and chemical extraction, IDMS has been applied to elemental concentration measurements ranging over eight orders of magnitude, from decigrams/gram to picograms/gram. Many of these applications have been used for the certification of a broad spectrum of biological and environmental Standard Reference Materials, including lead in Trace Elements in Water (SRM 1643), 15 elements in Coal Fly Ash (SRM 1633a), uranium in Bovine Liver (SRM 1577a), and mercury in water (SRM 1642).

Preparation and Certification of Standard Reference Materials to be Used in the Determination of Retained Austenite in Steels

In the steel hardening process, steel is heated to a temperature where a face-centered-cubic solid phase called austenite is formed. After a stabilization period, the steel is quenched into a medium which transforms the austenite into a metastable, body-centered-tetragonal solid phase called martensite. On occasion the austenite is not entirely transformed into martensite and some austenite remains. This untransformed (retained) austenite is sometimes detrimental to the finished product, and often there are requirements as to the amount of retained austenite permitted In the finished product.X-ray diffraction procedures (XRD) are normally used to determine the amount of retained austenite and this paper describes the preparation and characterization of the Standard Reference Materials used to calibrate x-ray diffraction units.