The Analytical Chemistry Division is terminating the production of individually certified neutral density filter Standard Reference Materials^� (SRMs^�) for chemical spectrophotometry, which has yielded over 3500 sets of neutral density filters since its inception in 1970. The action recognizes the availability of fit-for-purpose traceable certified reference materials (CRMs) from the commercial sector.� End users are encouraged to purchase CRMs from the NIST-Traceable Reference Material� (NTRM�) producer or from secondary suppliers whose documentation is consistent with the NIST traceability policy or who are accredited to Guide 17025 or Guide 34 of the International Standards Organization (ISO).

Sales of SRM 930e, SRM 1930, and SRM 2930 neutral density glass visible filters will cease when existing stocks are depleted.� Production of SRM 2031a, metal-on-fused-silica neutral density filters for the UV and visible, will be curtailed to terminate sales on schedule with the glass filters.

The NIST ACD will continue to offer recertification of existing SRM filters.� (Secondary suppliers may also recertify expired NIST SRMs as traceable CRMs.) ACD recertification measurements will soon feature traceability to the regular transmittance scale maintained by the NIST Optical Technology Division (OTD) for the NIST Calibration Program.� A single ultimate US scale of regular spectral transmittance will then be supported by NIST for physical and chemical metrology.

June 2004

New Standard to Help Diagnose Heart Attacks
Michael Welch, Analytical Chemistry Division

Diagnosing heart attacks will become a more precise science thanks to the first of a new series of clinical standards just issued by the National Institute of Standards and Technology (NIST). Standard Reference Material (SRM) 2921 (human cardiac troponin complex) will help manufacturers develop and calibrate assays that measure specific protein concentrations in patient blood samples to determine whether a heart attack has occurred.

The SRM is a solution containing certified concentrations of three related proteins, including cardiac troponin I, purified from human heart tissue from cadavers. Users can calibrate their assays by analyzing the SRM and comparing the results to the NIST-certified value for troponin I. The standard is expected to help reduce variations in clinical test results from as much as 50-fold on the same sample to just twofold. “It’s a big first step toward getting the system under control,” says Michael Welch, leader of the NIST development team.

NIST already produces more than 60 SRMs for the clinical diagnostics community, but this is the first one designed to help measure concentrations of large, protein-based health status markers. Troponin I is difficult to measure because it can exist in low concentrations and in different chemical forms, sometimes attached to other related proteins. NIST is developing additional standards and methods for measuring other health status indicators of this type, including hormones used to assess thyroid function, and other markers for heart attack risk such as homocysteine and C-reactive protein.

SRM 2921 is intended to help U.S. makers of in vitro diagnostic (IVD) medical devices sell their products in Europe. A European Union directive requires that such devices be calibrated with standards that are traceable to internationally recognized certified reference materials or procedures. SRM 2921 has been nominated for inclusion on the international list of higher order reference materials. The list currently contains approximately 150 entries for 96 health status markers; NIST SRMs provide traceability for 72 of these.

May 2004

Loggerhead sea turtles may be getting sick because of environmental exposure to toxic organic chemicals, such as polychlorinated biphenyls (or PCBs) and pesticides, according to a new study led by Duke University, with collaboration from the National Institute of Standards and Technology (NIST), and other organizations.

Released on April 21 in the online edition of Environmental Health Perspectives, the study found that turtles with higher concentrations of contaminants had poorer health. The authors note that the correlations suggest, though do not prove, a cause-and-effect link.

The new study is the first to investigate sea turtle health effects linked to a class of chemicals called organochlorines that are known to sicken other wildlife. Scientists took blood and fat samples from 48 live juvenile turtles captured in North Carolina waters and carried out clinical health assessments. Duke then worked with NIST researchers to measure the samples for concentrations of 80 different PCB and pesticide compounds. The research team found significant correlations for a wide variety of biological functions, suggesting, for example, changes in the immune system, possible liver damage, and possible alterations in protein and carbohydrate regulation.

The data may help scientists understand and address population declines in sea turtles, all species of which are threatened or endangered.

The NIST work was performed at the Hollings Marine Laboratory in Charleston, S.C., in which NIST is a partner. Researchers from the New England Aquarium and North Carolina State University also collaborated on the sea turtle research. Funding was provided by the Morris Animal Foundation, Disney Wildlife Conservation Fund, Oak Foundation, and Duke University Marine Biomedical Center.

May 2004

Diabetes is a serious disease affecting millions of Americans. If not properly diagnosed and treated, diabetes can cause serious organ damage, blindness, and ultimately death. This disease results from insufficient insulin production to regulate the levels of glucose in the blood, which can vary widely if unchecked. If a diabetic is diagnosed before serious damage occurs, proper monitoring and treatment can greatly reduce the serious consequences of the disease. Blood glucose is one of the markers for assessing diabetic status. For many of the fourteen million diagnosed diabetics in the U.S., measurement of blood glucose is a daily ritual. For non-diabetics, blood glucose measurements are a standard component of routine blood tests. Since important medical decisions are made based on the results of the blood glucose tests, it is critical that these tests be accurate.

NIST has provided the clinical diagnostics community with high purity neat materials and/or human body fluid-based Standard Reference Materials (SRMs) for more than twenty years. These SRMs are used by both the in vitro diagnostic (IVD) industry and clinical laboratories to assure the accuracy of routine methods used to monitor health status.

Recently, work has been completed on SRM 965a, Glucose in Frozen Human Serum. This SRM consists of four human serum materials with glucose concentrations that cover the range from severe hypoglycemia (35 mg/dL) to severe hyperglycemia (293 mg/dL). The previous lot, SRM 965, had three levels covering a much narrower concentration range. Value-assignment was accomplished using the NIST isotope dilution/gas chromatography/mass spectrometry-based method that is recognized worldwide as a higher order reference measurement procedure for glucose in blood. SRM 965a is the only serum-based certified reference material for glucose listed in the recently published Joint Committee on Traceability in Laboratory Medicine Database of higher order reference materials.

June 2004

A new set of neutral density glass Standard Reference Material® (SRM®) optical filters extends the present coverage of transmittance standards to accommodate the useful dynamic range of modern research grade visible spectrophotometers. With nominal transmittances of 0.1 %, 0.3 %, and 90 %, SRM 2930 complements pre-existing SRMs 930 (10 %, 20 %, and 30 %) and 1930 (1 %, 3 %, and 50 %). The extension of the range to low transmittance permits the qualification of instruments to determine higher chemical concentrations without the bias-prone step of dilution required otherwise. At the other end of the extended range, the new SRM supports the evaluation of uncertainties in concentration and/or absorption cross-section near the limit of detection for low concentrations or nearly transparent samples. Though SRM 2930 is available to all interested customers, the one-time production is particularly intended for use as a transfer standard by commercial producers of certified reference materials. Such secondary suppliers are encouraged to follow the NIST traceability policy to produce materials equivalent to the NIST neutral density SRM filters, whose production is ending with over 3000 sets in the field. Within NIST, retained sets of all three of these neutral density SRMs are employed as master transfer standards used by the Analytical Chemistry Division (ACD) to assert traceability over a range of three decades to the scale of regular transmittance for the United States as maintained by the Optical Technology Division (OTD) of the Physics Laboratory. ACD will continue to offer biennial recertification with traceability to the OTD scale to support existing customers.

June 2004

High-strength, silica fume concrete
was used to stiffen the Key Bank Tower
in Cleveland, Ohio.

SRM 2696 is the culmination of a five-year development project carried out by the SFA and NIST and financed in part by the Federal Highway Administration. The Silica Fume Standard Reference Material was developed in response to the increased usage of silica fume as an ingredient of High Performance Concrete (HPC). Silica fume is a byproduct of producing silicon metal and ferrosilicon alloys, and its chemical and physical properties make it a very reactive pozzolan. Concrete containing silica fume can have very high strength and durability. More and more silica fume is being recycled in this manner instead of being placed in landfills. Standard-writing organizations around the world are implementing specifications for chemical composition and physical properties of silica fume, which has created a need for a suitable certified reference material.

Each unit of SRM 2696 consists of a single, sealed bottle of approximately 70 grams of powder supplied with a Certificate of Analysis and a Material Safety Data Sheet (MSDS). SRM 2696 can be ordered directly from NIST through the secure, online SRM Order Request System: https://srmors.nist.gov/index.cfm. Copies of the Certificate and MSDS are also available (no purchase required) from the website or by telephone (301) 975-6776, fax (301) 926-4751, or email srminfo@nist.gov.

June 2004

Faced with a growing number of ignitable chemicals with similar characteristics, arson investigators have their hands full trying to tell residues of insecticide, for example, from those of gasoline. But identifying fuels used to set fires will be easier now, thanks to some help from the National Institute of Standards and Technology (NIST).

Law enforcement agencies, insurance fraud investigators and forensic services are expected to use Standard Reference Material (SRM) 2285, NIST's first standard intended to aid arson investigations. The new SRM is a liquid containing 15 compounds from common accelerants in various certified concentrations. It will be used to calibrate instruments that help analysts classify fire scene residues into six categories of fuels.

The hydrocarbon compounds are separated and identified based on how long it takes for them to pass through an instrument called a gas chromatograph. The retention time depends partly on a compound's volatility, or how fast it changes from liquid to vapor, and partly on experimental conditions such as temperature. Users analyze the SRM, analyze the residue from the crime scene and compare the retention time patterns to help identify the components used at the fire.

The instruments' readouts indicate both the presence and concentration of the various components; these patterns may indicate a particular fuel source. In helping investigators accurately identify the components and thus the original fuel used to set a fire, the SRM may help improve the 2 percent national conviction rate for arson cases. SRM 2285 also may be useful in the petroleum industry and environmental science.

SRM 2285, Arson Test Mixture in Methylene Chloride, contains 15 compounds, including even chain aliphatic hydrocarbons from hexane to tetracosane, toluene, p-xylene, o- and m-ethyltoluene, and 1,2,4- trimethylbenzene, and it is intended primarily for use in the calibration of chromatographic instrumentation used for the classification of an ignitable liquid residue. The classification of the ignitable liquid residues is primarily based on the carbon number of the various hydrocarbons, as well as the presence of various aromatic marker compounds. Gas chromatographic (GC) analysis
of volatile mixtures relies upon accurate retention time data to provide qualitative identification of compounds.This is particularly important with hydrocarbon materials, whose mass spectra are often quite similar in structure and appearance. Therefore, a certified standard of homologous alkanes is critical for calibrating the retention time scale of chromatographic columns.

This SRM will benefit local, state, and federal law enforcement agencies; private sector laboratories serving as insurance fraud investigators; and forensic science services abroad. It is also anticipated that the petroleum industry will be served by this standard in their analysis of crude and refined petroleum products. In addition, SRM 2285 will be useful for the environmental analysis of hydrocarbons in various matrices.

A unit of SRM 2285 consists of five 2 mL ampoules, each containing approximately 1.2 mL of solution. The certified concentrations of the individual components range from 1.0 mg/g to 1.4 mg/g. The concentrations are also expressed as percent volume fraction on the Certificate of Analysis for information. In addition, two gas chromatograms appear on the Certificate of Analysis, one from analysis of SRM 2285 on a relatively nonpolar GC stationary phase and one from analysis on a moderately polar stationary phase, showing the shift in the retention order between the aliphatic and aromatic components.

SRM 2285 Ordering Information

March 2004

Hydrogen is one of the chief contributors to brittleness in metals, its control in manufacturing processes is crucial. Rapid, measurement methods used in industrial are calibrated with working standard materials. NIST is producing a new series of titanium alloy SRMs certified for hydrogen concentrations. The process exploits the reversibility of the reaction Ti + H2 = TiH2, in which the equilibrium lies far to the right (with hydrogen tightly bound as hydride) at room temperature and far to the left (with hydrogen as gas) at high temperature. Reaction is rapid at 500�C. These SRMs are produced by degassing a widely used titanium alloy (containing 6 % aluminum and 4 % vanadium) at 700 �C in a high vacuum, then adding a measured quantity of hydrogen gas to the system. The hydrogen content of the degassed metal and the final products are further characterized by prompt-gamma activation analysis (PGAA) at the NIST Center for Neutron Research.

The first SRM (2453, with a nominal mass fraction of 100 mg/kg hydrogen) has been prepared by this method and is now available for purchase. Two additional materials, SRMs 2452 and 2454, nominally 50 mg/kg and 200 mg/kg respectively, are in the final stages of certification. This series will be available to check the linearity of instrument calibration, and provide check samples at levels significantly above and below the critical level of about 100 mg/kg. Selection of the concentrations was made in consultation with the ASTM E-01 task group.

The aerospace industry and, increasingly, the automotive and consumer goods industries employ titanium alloys because of their excellent combination of high strength, light weight, and good high-temperature properties.

These SRMs will help ensure that fabricated titanium components in fact have these desired properties. SRM 2453 consists of 5 g of chips, each approximately 15 mg in mass, contained in an amber glass bottle.

SRM 2453 Ordering Information

March 2004

This Standard Reference Material (SRM) is a certified spectroscopic standard for the correction of the relative intensity of Raman spectra obtained with instruments employing 532 nm laser excitation. SRM 2242 consists of an optical glass that emits a broadband luminescence spectrum when excited with 532 nm laser radiation. The relative spectral intensity of the glass luminescence has been determined through the use of a white-light, uniform-source, integrating sphere that has been calibrated for its irradiance at NIST. The shape of the luminescence spectrum of this glass is described by a polynomial expression that relates the relative spectral intensity to the wavenumber (cm-1) expressed as the Raman shift from the excitation wavelength of 532 nm. This polynomial, together with a measurement of the luminescence spectrum of the standard, can be used to determine the spectral intensityresponse correction that is unique to each Raman system. The resulting instrumentintensity- response correction may then be used to obtain Raman spectra that are instrument independent. This SRM is the second in a series of SRM�s (2241, 2242) that will provide relative intensity correction for Raman spectrometers employing lasers commonly used for Raman spectroscopy. This SRM is intended for use in measurements over the range of 20 �C to 25 �C and with Raman systems that employ laser excitation at 532.

SRM 2242 is a manganesedoped (0.15 wt % MnO2) borate matrix glass. Each unit of this SRM consists of a glass slide that is approximately 10.7 mm in width x 30.4 mm in length x 2.0 mm in thickness, with one surface optically polished and the opposite surface ground to a frosted finish using a 400 grit polish. The frosted surface of the slide is characterized by a surface average roughness (root-mean-square) in the range of 1.30 ..m to 1.49 ..m, as determined by stylus profilometry. The slide is held in a 12.5 mm square cuvette-style optical mount. This mount is designed for the typical 12.5 mm sampling accessories widely used in chemical spectroscopy, i.e., absorbance, fluorescence, etc. This mount can easily be placed on its side for use on a microscope stage.

The mount holds the glass slide, frosted side up, in place with a clip. The glass slide extends approximately 0.3 mm above the sides of the mount to allow its use with close focus objectives.

SRM 2242 Ordering Information

March 2004

Popeye was right: spinach is good for you. The National Institute of Standards and Technology (NIST) now has certified exactly what’s in it.

Standard Reference Material (SRM) 2385 consists of small jars of slurried spinach—pure spinach that’s been blanched, pureed and passed through filter screens. The concentrations of vitamins and other constituents have been measured and certified, so that the food industry can use the SRM to validate analytical methods and provide accurate nutritional information for its products. An analytical method is evaluated by using it to measure constituents in the SRM and then comparing the results to the NIST-certified values.

Slurried Spinach 2385, a new NIST Standard Reference Material, can be used by food manufacturers to help ensure the accuracy of nutritional labels.
The NIST values confirm that spinach is rich in antioxidants—both beta-carotene and lutein. Although the actual amounts look small (the antioxidants constitute 0.0019 percent and 0.0033 percent of the spinach by mass, respectively), spinach contains far more of the two combined than most other fruits or vegetables.

Antioxidants help fight formation of free radicals, highly reactive molecules that can damage DNA and are implicated in the development of certain diseases. Beta-carotene converts to vitamin A in the body and is needed for healthy vision, skin and hair. Lutein is a pigment found in the retina and may help guard against eye diseases such as age-related macular degeneration. Among its other attributes, spinach also contains 1.55 percent dietary fiber by weight.

The new SRM was developed at the request of the food industry and with the help of more than 10 food manufacturers. NIST now supplies 37 different food SRMs to the industry, one or more for each of the nine sectors of the Association of Analytical Communities’ food triangle, which categorizes food based on its fat, carbohydrate or protein content. The food triangle helps to assure the availability of validated analytical methods for all types of foods.

January 2004

NIST SRM 2036 Near Infrared Wavelength/Wavenumber Reflection Standard
Steven Choquette, Analytical Chemistry Division

Standard Reference Material (SRM) 2036 is a certified transfer standard intended for the verification and calibration of the wavelength or wavenumber scales of Near-Infrared (NIR) spectrometers operating in transflectance or diffuse reflectance mode. Typically these spectrometers will use either fiber optic probes or integrating sphere accessories. SRM 2036 is a reflection standard designed to compliment NIST’s existing SRMs 2035/2065 NIR transmission wavelength standards. These SRM’s are rare earth oxide (REO) doped glasses containing of samarium, ytterbium, holmium, and neodymium.

In addition, SRM 2036 is physically contacted with a piece of sintered polytetrafluoroethylene (PTFE). The combination of the REO glass with a nearly ideal diffuse reflector provides seven reflection-absorption bands that are useful for wavelength calibration in the NIR spectral region. These NIR bands range from approximately 15% R to 40 % R. SRM 2036 is certified for the 10% band fraction
centroid of seven bands in the spectral region from 10, 300 cm-1 to 5130 cm-1 (vacuum wavenumber) at 8 cm-1 constant wavenumber resolution. Because the bands of SRM 2036 are sufficiently broad, the band locations are invariant, within the stated uncertainties, for wavenumber resolutions between 4 cm-1 and 64 cm-1 resolution.

These values will be useful for the verification of the wavenumber scale of NIR Fourier Transform spectrometers. The same seven bands are certified for the 10% band fraction centroid location spanning the spectral region from 975 nm to 1946 nm (air wavelength) for spectral slit widths of 3 nm, 5nm and 10 nm. These values will be useful for scanning grating spectrometers with single element detectors as well as dispersive spectrometers employing diode array detection. In addition, information values are provided for 13 additional reflection bands in the uv-visible portion of the spectrum ranging from 334 nm to 805 nm, as several commercial scanning spectrometers have useable ranges from 400 nm to 2500 nm.

A unit of SRM 2036 consists of the optical filter-PTFE assembly mounted in an optical holder, contained in a wooden box.

November 2003

NIST SRM 3231
Iodine-129 Isotopic Standard (High Level)
Stephen Long, Analytical Chemistry Division

Nuclear fission activities and fuel reprocessing have significantly elevated the levels of 129I in the terrestrial ecosystem. Although measurements of this isotope in human thyroid tissue have indicated an increase over pre-nuclear background levels, they are currently not considered to be of radiological significance. Environmental 129I measurements are important for assessing future impact on human health and to gain further knowledge of 129I distribution and environmental behavior.

These SRMs are intended for use in instrument calibrations and for quality assurance of mass spectrometry measurements of 129I. This long-lived radionuclide (half-life 1.57 x 107 yr.) is a significant indicator of fission activity. Accelerator mass spectrometry (AMS) has been used success-fully to measure 129I / 127I ratios to global background levels
(< 1 x 10-12 found in iodine reagents, for instance).

Negative thermal ionization mass spectrometry (NTIMS) and, more recently inductively coupled plasma mass spectrometry (ICP-MS) have been shown to have excellent absolute detection limits and these techniques do have an established place in monitoring waste and potential discharges from reprocessing activities. SRM 3230, which is a "low level" standard and SRM 3231, a "high level" standard, were produced gravimetrically using well-characterized sources of 129I and high-purity natural iodine, and verified by AMS in collaboration with the PRIME Laboratory, Purdue University, IN.
A unit of SRM 3230 / SRM 3231 consists of five amber borosilicate glass ampoules containing approximately 5 mL of iodine solution. Each unit contains two ampoules each of two different 129I / 127I ratios, together with one ampoule of blank iodine solution which contains no added 129I. The certified values for SRMs 3230 and 3231 are provided in Table 1.

TABLE 1. CERTIFIED VALUES FOR SRM 3230 AND SRM 3231

SRM 3230 (Low Level)                                      Certified Value
129I / 127I Isotope Ratio, Level I            4.920 x 10-10 ± 0.062 x 10-10
129I / 127I Isotope Ratio, Level II           0.985 x 10-12 ± 0.012 x 10-12

SRM 3231 (High Level)                                     Certified Value
129I / 127I Isotope Ratio, Level I             0.981 x 10-6 ± 0.012 x 10-6
129I / 127I Isotope Ratio, Level II            0.982 x 10-8 ± 0.012 x 10-8

November 2003

NIST announces the release of SRMs certified for organic compounds related to water analysis. These SRMs are intended primarily for the calibration of instrumentation and validation of methods for volatile or semi-volatile organic compound determinations. Because of its miscibility with water, each SRM can also be used to fortify aqueous samples with known amounts of the organic compound. These SRMs were developed by the NIST Analytical Chemistry Division (ACD) primarily to support the Chemical Calibration Providers of the Proficiency Testing Program with support by the U.S. Environmental Protection Agency (EPA). Watch for updates on additional SRMs for water analysis.

November 2003

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Date created: May 5, 2004
Last updated: May 17, 2006
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