2004
Analytical Chemistry Division Archive News |
Transition in the ACD Optical Filters Program
John Travis,
Analytical Chemistry Division
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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
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Computer model
of the complex crystal structure of the human protein cardiac
troponin.
Graphic
Courtesy Protein Data Bank
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New
Standard to Help Diagnose Heart Attacks
Michael
Welch, Analytical Chemistry Division
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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. Its 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
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Sea
Turtle Health Linked to Contaminants
Jennifer Keller, Analytical
Chemistry Division
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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
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New
Standard Reference Material Developed to Improve the
Accuracy of Blood Glucose Determinations
Michael
Welch, Analytical Chemistry Division
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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
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Extended
Transmittance Coverage for Visible Molecular
Absorption Spectrophotometry
John
Travis, Analytical Chemistry Division
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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
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NIST
and the Silica Fume Association Announce the Availability of
Standard Reference Material® 2696 Silica Fume
John
Sieber, Analytical Chemistry Division
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High-strength,
silica fume concrete
was used
to stiffen the Key Bank Tower
in Cleveland, Ohio.
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May
21st, 2004 - The National Institute of Standards and Technology (NIST)
in cooperation with the Silica Fume Association (SFA) is pleased to
announce the release of a new Standard Reference Material, SRM®
2696 Silica Fume. SRM 2696 is primarily intended for use in evaluating
chemical and instrumental methods of analysis of silica fume used
in conjunction with product specifications. Certified values are now
established for silicon expressed as SiO2 and six other chemical constituents
plus reference values for five chemical constituents and the physical
measurement parameter Specific Surface Area determined using nitrogen
absorption. All values are products of extensive testing by NIST and
collaborating laboratories from manufacturers, distributors, state
departments of transportation, universities, and commercial testing
laboratories.
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
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Standard
Helps ID Fuels Used in Arson
Michele
Schantz , Analytical Chemistry Division
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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
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NIST
SRM 2453: Hydrogen in Titanium Alloy
Richard
Lindstrom, Analytical Chemistry
Division
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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
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NIST
SRM 2242: Relative Intensity Correction Standard for
Raman Spectroscopy: 532 nm Excitation
Steven
Choquette, Analytical Chemistry Division
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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
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New
Standard on the Menu, Certified Slurried Spinach
Katherine
Sharpless, Analytical Chemistry Division
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Slurried
Spinach 2385, a new NIST Standard Reference Material, can be used
by food manufacturers to help ensure the accuracy of nutritional
labels.
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Popeye
was right: spinach is good for you. The National Institute of Standards
and Technology (NIST) now has certified exactly whats in it.
Standard
Reference Material (SRM) 2385 consists of small jars of slurried
spinachpure spinach thats 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 antioxidantsboth
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
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NIST
SRM 2036 Near Infrared Wavelength/Wavenumber Reflection Standard
Steven
Choquette, Analytical Chemistry Division
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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 NISTs
existing SRMs 2035/2065 NIR transmission wavelength standards. These
SRMs 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
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NIST
SRM 3230
Iodine-129 Isotopic Standard (Low Level)
NIST
SRM 3231
Iodine-129 Isotopic Standard (High Level)
Stephen
Long, Analytical Chemistry Division
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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
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NIST
SRMS 3000s EPA: Organic Compounds Related to Water Analysis
Michele
Schantz, Analytical Chemistry Division
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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
Contact: acd_webmaster@nist.gov
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