6 research outputs found
Pressurized Liquid Extraction of Diesel and Air Particulate Standard Reference Materials: Effect of Extraction Temperature and Pressure
Four particulate matter Standard Reference Materials
(SRMs) available from the National Institute of Standards and Technology
(NIST) were used to evaluate the effect of solvent, number of static
cycles and static times, pressure, and temperature when using pressurized
liquid extraction (PLE) for the extraction of polycyclic aromatic
hydrocarbons (PAHs) and nitrated-PAHs. The four materials used in
the study were SRM 1648a Urban Particulate Matter, SRM 1649b Urban
Dust, SRM 1650b Diesel Particulate Matter, and SRM 2975 Diesel Particulate
Matter (Industrial Forklift). The results from the study indicate
that the choice of solvent, dichloromethane compared to toluene and
toluene/methanol mixtures, had little effect on the extraction efficiency.
With three to five extraction cycles, increasing the extraction time
for each cycle from 5 to 30 min had no significant effect on the extraction
efficiency. The differences in extraction efficiency were not significant
(with over 95% of the differences being <10%) when the pressure
was increased from 13.8 to 20.7 MPa. The largest increase in extraction
efficiency occurred for selected PAHs when the temperature of extraction
was increased from 100 to 200 °C. At 200 °C naphthalene,
biphenyl, fluorene, dibenzothiophene, and anthracene show substantially
higher mass fractions (>30%) than when extracted at 100 °C
in all the SRMs studied. For SRM 2975, large increases (>100%)
are also observed for some other PAHs including benz[<i>a</i>]anthracene, benzo[<i>k</i>]fluoranthene, benzo[<i>e</i>]pyrene, benzo[<i>a</i>]pyrene, benzo[<i>ghi</i>]perylene, and benzo[<i>b</i>]chrysene when
extracted at the higher temperatures; however, similar trends were
not observed for the other diesel particulate sample, SRM 1650b. The
results are discussed in relation to the use of the SRMs for evaluating
analytical methods
The influence of the aromatic character in the gas chromatography elution order: the case of polycyclic aromatic hydrocarbons
<p>A link between the aromatic character of polycyclic aromatic hydrocarbons (PAHs) and gas chromatography (GC) elution order in columns with a polysiloxane backbone in the stationary phase is reported for the first time. The aromatic character was calculated using a method that combines the π-Sextet Rule and the Pauling Ring Bond Orders to allow the establishment of the location and migration of aromatic sextets in PAH structures. One GC column with a polysiloxane-like backbone (Rxi-PAH) and three GC columns with a polysiloxane backbone (DB-5, SE-52 and LC-50) were used for the analysis. According to the results of this study, within an isomer group, PAHs that contain a lower number of rings affected by the aromatic sextets tend to elute earlier than PAHs that contain a higher number of rings affected by the aromatic sextets. The PAHs that follow the calculated elution order are 88% in the Rxi-PAH column, 88% in the DB-5 column, 93% in the SE-52 column and 85% in the LC-50 column. It is expected that future analyses with other aromatic compounds in GC columns with a polysiloxane backbone in the stationary phase will follow a GC elution order that agrees with the aromatic character of the molecules.</p
Development and Certification of a Standard Reference Material for Vitamin D Metabolites in Human Serum
The National Institute of Standards and Technology (NIST),
in collaboration
with the National Institutes of Health’s Office of Dietary
Supplements (NIH-ODS), has developed a Standard Reference Material
(SRM) for the determination of 25-hydroxyvitamin D [25(OH)D] in serum.
SRM 972 Vitamin D in Human Serum consists of four serum pools with
different levels of vitamin D metabolites and has certified and reference
values for 25(OH)D<sub>2</sub>, 25(OH)D<sub>3</sub>, and 3-epi-25(OH)D<sub>3</sub>. Value assignment of this SRM was accomplished using a combination
of three isotope-dilution mass spectrometry approaches, with measurements
performed at NIST and at the Centers for Disease Control and Prevention
(CDC). Chromatographic resolution of the 3-epimer of 25(OH)D<sub>3</sub> proved to be essential for accurate determination of the metabolites
Development of a Cigarette Tobacco Filler Standard Reference Material
A new tobacco filler
Standard Reference Material (SRM) has been
issued by the National Institute of Standards and Technology (NIST)
in September 2016 with certified and reference mass fraction values
for nicotine, <i>N</i>-nitrosonornicotine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone,
and volatiles. The constituents have been determined by multiple analytical
methods with measurements at NIST and at the Centers for Disease Control
and Prevention, and with confirmatory measurements by commercial laboratories.
This effort highlights the development of the first SRM for reduced
nicotine and reduced tobacco-specific nitrosamines with certified
values for composition
Development of an Improved Standard Reference Material for Vitamin D Metabolites in Human Serum
The
National Institute of Standards and Technology (NIST) has developed
Standard Reference Material (SRM) 972a Vitamin D Metabolites in Frozen
Human Serum as a replacement for SRM 972, which is no longer available.
SRM 972a was developed in collaboration with the National Institutes
of Health’s Office of Dietary Supplements. In contrast to the
previous reference material, three of the four levels of SRM 972a
are composed of unmodified human serum. This SRM has certified and
reference values for the following 25-hydroxyvitamin D [25(OH)D] species:
25(OH)D<sub>2</sub>, 25(OH)D<sub>3</sub>, and 3-<i>epi</i>-25(OH)D<sub>3</sub>. The value assignment and certification process
included three isotope-dilution mass spectrometry approaches, with
measurements performed at NIST and at the Centers for Disease Control
and Prevention (CDC). The value assignment methods employed have been
modified from those utilized for the previous SRM, and all three approaches
now incorporate chromatographic resolution of the stereoisomers, 25(OH)D<sub>3</sub> and 3-<i>epi</i>-25(OH)D<sub>3</sub>
Development of a Standard Reference Material for Metabolomics Research
The
National Institute of Standards and Technology (NIST), in collaboration
with the National Institutes of Health (NIH), has developed a Standard
Reference Material (SRM) to support technology development in metabolomics
research. SRM 1950 Metabolites in Human Plasma is intended to have
metabolite concentrations that are representative of those found in
adult human plasma. The plasma used in the preparation of SRM 1950
was collected from both male and female donors, and donor ethnicity
targets were selected based upon the ethnic makeup of the U.S. population.
Metabolomics research is diverse in terms of both instrumentation
and scientific goals. This SRM was designed to apply broadly to the
field, not toward specific applications. Therefore, concentrations
of approximately 100 analytes, including amino acids, fatty acids,
trace elements, vitamins, hormones, selenoproteins, clinical markers,
and perfluorinated compounds (PFCs), were determined. Value assignment
measurements were performed by NIST and the Centers for Disease Control
and Prevention (CDC). SRM 1950 is the first reference material developed
specifically for metabolomics research