Standard Reference Material (SRM) 2378 fatty acids in frozen human serum. Certification of a clinical SRM based on endogenous supplementation of polyunsaturated fatty acids.

Dietary fatty acids can be both beneficial and detrimental to human health depending on the degree and type of saturation. Healthcare providers and research scientists monitor the fatty acid content of human plasma and serum as an indicator of health status and diet. In addition, both the Centers for Disease Control & Prevention (CDC) and the National Institutes of Health - Office of Dietary Supplements are interested in circulating fatty acids (FAs) because they may be predictive of coronary heart disease. The National Institute of Standards and Technology (NIST) provides a wide variety of reference materials (RMs) and Standard Reference Materials® (SRM®s) including blood, serum, plasma, and urine with values assigned for analytes of clinical interest. NIST SRM 2378 Fatty Acids in Frozen Human Serum was introduced in 2015 to help validate methods used for the analysis of FAs in serum, and consists of three different pools of serum acquired from (1) healthy donors who had taken fish oil dietary supplements (at least 1000 mg per day) for at least one month (level 1 material), (2) healthy donors who had taken flaxseed oil dietary supplements (at least 1000 mg per day) for at least one month (level 2 material), and (3) healthy donors eating "normal" diets who had not taken dietary supplements containing fish or plant oils (level 3 material). The use of dietary supplements by donors provided SRMs with natural endogenous ranges of FAs at concentrations observed in human populations. Results from analyses using two methods at NIST, including one involving a novel microwave-assisted acid hydrolysis procedure, and one at the CDC are presented here. These results and their respective uncertainties were combined to yield certified values with expanded uncertainties for 12 FAs and reference values with expanded uncertainties for an additional 18 FAs.

Unsupervised classification of petroleum Certified Reference Materials and other fuels by chemometric analysis of gas chromatography-mass spectrometry data.

As feedstocks transition from conventional oil to unconventional petroleum sources and biomass, it will be necessary to determine whether a particular fuel or fuel blend is suitable for use in engines. Certifying a fuel as safe for use is time-consuming and expensive and must be performed for each new fuel. In principle, suitability of a fuel should be completely determined by its chemical composition. This composition can be probed through use of detailed analytical techniques such as gas chromatography-mass spectroscopy (GC-MS). In traditional analysis, chromatograms would be used to determine the details of the composition. In the approach taken in this paper, the chromatogram is assumed to be entirely representative of the composition of a fuel, and is used directly as the input to an algorithm in order to develop a model that is predictive of a fuel's suitability. When a new fuel is proposed for service, its suitability for any application could then be ascertained by using this model to compare its chromatogram with those of the fuels already known to be suitable for that application. In this paper, we lay the mathematical and informatics groundwork for a predictive model of hydrocarbon properties. The objective of this work was to develop a reliable model for unsupervised classification of the hydrocarbons as a prelude to developing a predictive model of their engine-relevant physical and chemical properties. A set of hydrocarbons including biodiesel fuels, gasoline, highway and marine diesel fuels, and crude oils was collected and GC-MS profiles obtained. These profiles were then analyzed using multi-way principal components analysis (MPCA), principal factors analysis (PARAFAC), and a self-organizing map (SOM), which is a kind of artificial neural network. It was found that, while MPCA and PARAFAC were able to recover descriptive models of the fuels, their linear nature obscured some of the finer physical details due to the widely varying composition of the fuels. The SOM was able to find a descriptive classification model which has the potential for practical recognition and perhaps prediction of fuel properties.

Development of two fine particulate matter standard reference materials (<4 µm and <10 µm) for the determination of organic and inorganic constituents.

Two new Standard Reference Materials (SRMs), SRM 2786 Fine Particulate Matter (<4 µm) and SRM 2787 Fine Particulate Matter (<10 µm) have been developed in support of the US Environmental Protection Agency's National Ambient Air Quality Standards for particulate matter (PM). These materials have been characterized for the mass fractions of selected polycyclic aromatic hydrocarbons (PAHs), nitrated PAHs, brominated diphenyl ether (BDE) congeners, hexabromocyclododecane (HBCD) isomers, sugars, polychlorinated dibenzo-p-dioxin (PCDD) and dibenzofuran (PCDF) congeners, and inorganic constituents, as well as particle-size characteristics. These materials are the first Certified Reference Materials available to support measurements of both organic and inorganic constituents in fine PM. In addition, values for PAHs are available for RM 8785 Air Particulate Matter on Filter Media. As such, these SRMs will be useful as quality control samples for ensuring compatibility of results among PM monitoring studies and will fill a void to assess the accuracy of analytical methods used in these studies. Graphical Abstract Removal of PM from filter for the preparation of SRM 2786 Fine Particulate Matter.

Organohalogen Contaminants and Vitamins in Northern Fur Seals (Callorhinus ursinus) Collected During Subsistence Hunts in Alaska.

During native subsistence hunts from 1987 to 2007, blubber and liver samples from 50 subadult male northern fur seals (Callorhinus ursinus) were collected on St. Paul Island, Alaska. Samples were analyzed for legacy persistent organic pollutants (POPs), recently phased-out/current-use POPs, and vitamins. The legacy POPs measured from blubber samples included polychlorinated biphenyl congeners, DDT (and its metabolites), chlorobenzenes, chlordanes, and mirex. Recently phased-out/current-use POPs included in the blubber analysis were the flame retardants, polybrominated diphenyl ethers, and hexabromocyclododecanes. The chemical surfactants, perfluorinated alkyl acids, and vitamins A and E were assessed in the liver samples. Overall, concentrations of legacy POPs are similar to levels seen in seal samples from other areas of the North Pacific Ocean and the Bering Sea. Statistically significant correlations were seen between compounds with similar functions (pesticides, flame retardants, vitamins). With sample collection spanning two decades, the temporal trends in the concentrations of POPs and vitamins were assessed. For these animals, the concentrations of the legacy POPs tend to decrease or stay the same with sampling year; however, the concentrations of the current-use POPs increased with sampling year. Vitamin concentrations tended to stay the same across the sampling years. With the population of northern fur seals from St. Paul Island on the decline, a detailed assessment of exposure to contaminants and the correlations with vitamins fills a critical gap for identifying potential population risk factors that might be associated with health effects.

Long-term stability and temporal trends of organic contaminants in four collections of mussel tissue frozen standard reference materials.

The stability of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and chlorinated pesticides in frozen mussel tissue Standard Reference Materials (SRMs) stored at -80 °C was assessed by analyzing samples of SRM 1974, SRM 1974a, and SRM 1974b Organics in Mussel Tissue (Mytilus edulis) periodically over 25 y, 20 y, and 12 y, respectively. The most recent analyses were performed during the certification of the fourth release of this material, SRM 1974c. Results indicate the concentrations of these persistent organic pollutants have not changed during storage at -80 °C. In addition, brominated diphenyl ethers (BDEs) were quantified in each of the materials during this study. The stability information is important for on-going monitoring studies collecting large quantities of samples for future analyses (i.e., formally established specimen banking programs). Since all four mussel tissue SRMs were prepared from mussels collected at the same site in Dorchester Bay, MA, USA, the results provide a temporal trend study for these contaminants over a 17 year period (1987 to 2004).

Development of urine standard reference materials for metabolites of organic chemicals including polycyclic aromatic hydrocarbons, phthalates, phenols, parabens, and volatile organic compounds.

Two new Standard Reference Materials (SRMs), SRM 3672 Organic Contaminants in Smokers' Urine (Frozen) and SRM 3673 Organic Contaminants in Non-Smokers' Urine (Frozen), have been developed in support of studies for assessment of human exposure to select organic environmental contaminants. Collaborations among three organizations resulted in certified values for 11 hydroxylated polycyclic aromatic hydrocarbons (OH-PAHs) and reference values for 11 phthalate metabolites, 8 environmental phenols and parabens, and 24 volatile organic compound (VOC) metabolites. Reference values are also available for creatinine and the free forms of caffeine, theobromine, ibuprofen, nicotine, cotinine, and 3-hydroxycotinine. These are the first urine Certified Reference Materials characterized for metabolites of organic environmental contaminants. Noteworthy, the mass fractions of the environmental organic contaminants in the two SRMs are within the ranges reported in population survey studies such as the National Health and Nutrition Examination Survey (NHANES) and the Canadian Health Measures Survey (CHMS). These SRMs will be useful as quality control samples for ensuring compatibility of results among population survey studies and will fill a void to assess the accuracy of analytical methods used in studies monitoring human exposure to these organic environmental contaminants.

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.

Determination of selected oxygenated polycyclic aromatic hydrocarbons (oxy-PAHs) in diesel and air particulate matter standard reference materials (SRMs).

Oxygenated polycyclic aromatic hydrocarbons (oxy-PAHs) have recently received much attention in discussions regarding the negative impacts of particulate matter (PM) on human health and the environment. The National Institute of Standards and Technology provides several environmental matrix standard reference materials (SRMs) with certified and reference values for polycyclic aromatic hydrocarbons (PAHs) and nitrated PAHs. In this study, the concentrations of oxygenated PAHs are determined in three air PM SRMs (1649b, 1648a, and 2786) and three diesel PM SRMs (1650b, 2975, and 1975) using two independent gas chromatography-mass spectrometry methods. Concentrations of oxy-PAHs were at the milligrams per kilogram level with higher overall concentrations in diesel PM (up to 50 mg/kg for 9,10-anthraquinone). One of the highest oxy-PAH concentrations (up to 5 mg/kg) measured in the air particulate SRMs was for 7,12-benz[a]anthracenquinone. These results suggest that oxygenated PAHs should not be neglected in the analysis of PM as their concentrations can be as high as those of some PAHs and are one to two orders of magnitude higher than those for nitro-PAHs.

Development of botanical and fish oil standard reference materials for fatty acids.

As part of a collaboration with the National Institutes of Health's Office of Dietary Supplements and the Food and Drug Administration's Center for Drug Evaluation and Research, the National Institute of Standards and Technology has developed Standard Reference Material (SRM) 3274 Botanical Oils Containing Omega-3 and Omega-6 Fatty Acids and SRM 3275 Omega-3 and Omega-6 Fatty Acids in Fish Oil. SRM 3274 consists of one ampoule of each of four seed oils (3274-1 Borage (Borago officinalis), 3274-2 Evening Primrose (Oenothera biennis), 3274-3 Flax (Linium usitatissimum), and 3274-4 Perilla (Perilla frutescens)), and SRM 3275 consists of two ampoules of each of three fish oils (3275-1 a concentrate high in docosahexaenoic acid, 3275-2 an anchovy oil high in docosahexaenoic acid and eicosapentaenoic acid, and 3275-3 a concentrate containing 60% long-chain omega-3 fatty acids). Each oil has certified and reference mass fraction values for up to 20 fatty acids. The fatty acid mass fraction values are based on results from analyses using gas chromatography with flame ionization detection (GC-FID) and mass spectrometry (GC/MS). These SRMs will complement other reference materials currently available with mass fractions for similar analytes and are part of a series of SRMs being developed for dietary supplements.

Milk and serum standard reference materials for monitoring organic contaminants in human samples.

Four new Standard Reference Materials (SRMs) have been developed to assist in the quality assurance of chemical contaminant measurements required for human biomonitoring studies, SRM 1953 Organic Contaminants in Non-Fortified Human Milk, SRM 1954 Organic Contaminants in Fortified Human Milk, SRM 1957 Organic Contaminants in Non-Fortified Human Serum, and SRM 1958 Organic Contaminants in Fortified Human Serum. These materials were developed as part of a collaboration between the National Institute of Standards and Technology (NIST) and the Centers for Disease Control and Prevention (CDC) with both agencies contributing data used in the certification of mass fraction values for a wide range of organic contaminants including polychlorinated biphenyl (PCB) congeners, chlorinated pesticides, polybrominated diphenyl ether (PBDE) congeners, and polychlorinated dibenzo-p-dioxin (PCDD) and dibenzofuran (PCDF) congeners. The certified mass fractions of the organic contaminants in unfortified samples, SRM 1953 and SRM 1957, ranged from 12 ng/kg to 2200 ng/kg with the exception of 4,4'-DDE in SRM 1953 at 7400 ng/kg with expanded uncertainties generally <14 %. This agreement suggests that there were no significant biases existing among the multiple methods used for analysis.

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[a]anthracene, benzo[k]fluoranthene, benzo[e]pyrene, benzo[a]pyrene, benzo[ghi]perylene, and benzo[b]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.

Significant variation in the concentration of carcinogenic polycyclic aromatic hydrocarbons in yerba maté samples by brand, batch, and processing method.

Drinking maté, common in southern South America, may increase the risk of esophageal squamous cell carcinoma (ESCC). In 2006, we found high but variable polycyclic aromatic hydrocarbon (PAH) content in commercial yerba maté samples from eight Brazilian brands. The PAH content of new samples from the same brands, purchased in 2008, and four brands from a single manufacturer processed in different ways, obtained in 2010, were quantified to determine whether PAH concentration was still high, whether PAH content variation was brand specific, and whether processing method affects PAH content of commercial yerba maté. Concentrations of individual PAHs were quantified using gas chromatography/mass spectrometry with deuterated PAHs as internal standards. Median total PAH concentration was 1500 ng/g (range: 625-3710 ng/g) and 1090 ng/g (621-1990 ng/g) in 2008 and 2010 samples, respectively. Comparing 2006 and 2008 samples, some brands had high PAH concentrations in both years, while PAH concentration changed considerably in others. Benzo[a]pyrene concentrations ranged from 11.9 to 99.3 ng/g and 5.11 to 21.0 ng/g in 2008 and 2010 samples, respectively. The 2010 sample processed without touching smoke had the lowest benzo[a]pyrene content. These results support previous findings of very high total and carcinogenic PAH concentrations in yerba maté, perhaps contributing to the high incidence of ESCC in southern South America. The large PAH content variation by brand, batch, and processing method suggests it may be possible to reduce the content of carcinogenic PAHs in commercial yerba maté, making it a healthier beverage.

Determination of perfluorinated alkyl acid concentrations in biological standard reference materials.

Standard reference materials (SRMs) are homogeneous, well-characterized materials used to validate measurements and improve the quality of analytical data. The National Institute of Standards and Technology (NIST) has a wide range of SRMs that have mass fraction values assigned for legacy pollutants. These SRMs can also serve as test materials for method development, method validation, and measurement for contaminants of emerging concern. Because inter-laboratory comparison studies have revealed substantial variability of measurements of perfluoroalkyl acids (PFAAs), future analytical measurements will benefit from determination of consensus values for PFAAs in SRMs to provide a means to demonstrate method-specific performance. To that end, NIST, in collaboration with other groups, has been measuring concentrations of PFAAs in a variety of SRMs. Here we report levels of PFAAs and perfluorooctane sulfonamide (PFOSA) determined in four biological SRMs: fish tissue (SRM 1946 Lake Superior Fish Tissue, SRM 1947 Lake Michigan Fish Tissue), bovine liver (SRM 1577c), and mussel tissue (SRM 2974a). We also report concentrations for three in-house quality-control materials: beluga whale liver, pygmy sperm whale liver, and white-sided dolphin liver. Measurements in SRMs show an array of PFAAs, with perfluorooctane sulfonate (PFOS) being the most frequently detected. Reference and information values are reported for PFAAs measured in these biological SRMs.

Quantification of drugs of abuse in municipal wastewater via SPE and direct injection liquid chromatography mass spectrometry.

We present an isotopic-dilution direct injection reversed-phase liquid chromatography-tandem mass spectrometry method for the simultaneous determination of 23 drugs of abuse, drug metabolites, and human-use markers in municipal wastewater. The method places particular emphasis on cocaine; it includes 11 of its metabolites to facilitate assessment of routes of administration and to enhance the accuracy of estimates of cocaine consumption. Four opioids (6-acetylmorphine, morphine, hydrocodone, and oxycodone) are also included, along with five phenylamine drugs (amphetamine, methamphetamine, 3,4-methylenedioxy-methamphetamine, methylbenzodioxolyl-butanamine, and 3,4-methylenedioxy-N-ethylamphetamine) and two human-use markers (cotinine and creatinine). The method is sufficiently sensitive to directly quantify (without preconcentration) 18 analytes in wastewater at concentrations less than 50 ng/L. We also present a modified version of this method that incorporates solid-phase extraction to further enhance sensitivity. The method includes a confirmatory LC separation (selected by evaluating 13 unique chromatographic phases) that has been evaluated using National Institute of Standards and Technology Standard Reference Material 1511 Multi-Drugs of Abuse in Freeze-Dried Urine. Seven analytes (ecgonine methyl ester, ecgonine ethyl ester, anhydroecgonine methyl ester, m-hydroxybenzoylecgonine, p-hydroxybenzoyl-ecgonine, ecgonine, and anhydroecgonine) were detected for the first time in a wastewater sample.

Separation of 26 toxaphene congeners and measurement in air particulate matter SRMs compared to technical toxaphene SRM 3067.

Toxaphene is a complex technical mixture that has been found ubiquitously in the environment but has caused issues for analysis, especially of individual congeners. This paper reports the elution order of 26 major toxaphene congeners on three gas chromatographic columns. The three different stationary phases generally had similar elution orders for the toxaphene congeners, but fewer co-elutions occurred on a low-bleed, low-polarity column. These congeners (except for two that co-eluted and were not added to the calibration mixture) were examined in air particulate matter standard reference materials (SRMs), 1648a, 1649a, and 1649b as well as SRM 3067 toxaphene in methanol for assignment of reference values. SRM 3067 had mass fractions an order of magnitude greater than the air particulate SRMs, which ranged from 0.568 +/- 0.018 ng g(-1) dry mass (B9-2006 in SRM 1648a) to 12.9 +/- 0.20 ng g(-1) dry mass (B9-715 (P 58) in SRM 1649a). The three air particulate SRMs all had different mass fractions and proportions of congeners relative to the sum of the toxaphene congeners. SRM 3067 may be useful as a technical mixture toxaphene congener calibrant. SRMs 1648a and 1649b will serve as reference materials for the analysis of 21 (three congeners were not included due to values below the detection limit or a potential polychlorinated biphenyl co-elution) toxaphene congeners in atmospheric particulate samples.

Polycyclic aromatic hydrocarbons (PAHs) in a coal tar standard reference material--SRM 1597a updated.

SRM 1597 Complex Mixture of Polycyclic Aromatic Hydrocarbons from Coal Tar, originally issued in 1987, was recently reanalyzed and reissued as SRM 1597a with 34 certified, 46 reference, and 12 information concentrations (as mass fractions) for polycyclic aromatic hydrocarbons (PAHs) and polycyclic aromatic sulfur heterocycles (PASHs) including methyl-substituted PAHs and PASHs. The certified and reference concentrations (as mass fractions) were based on results of analyses of the coal tar material using multiple analytical techniques including gas chromatography/mass spectrometry on four different stationary phases and reversed-phase liquid chromatography. SRM 1597a is currently the most extensively characterized SRM for PAHs and PASHs.

Marine mammal blubber reference and control materials for use in the determination of halogenated organic compounds and fatty acids.

The National Institute of Standards and Technology (NIST) has a diverse collection of control materials derived from marine mammal blubber, fat, and serum. Standard Reference Material (SRM) 1945 Organics in Whale Blubber was recertified for polychlorinated biphenyl (PCB) congeners, organochlorine pesticides, and polybrominated diphenyl ether (PBDE) congeners. SRM 1945 has also been assigned mass fraction values for compounds not frequently determined in marine samples including toxaphene congeners, coplanar PCBs, and methoxylated PBDE congeners which are natural products. NIST also has assigned mass fraction values, as a result of interlaboratory comparison exercises, for PCB congeners, organochlorine pesticides, PBDE congeners, and fatty acids in six homogenate materials produced from marine mammal blubber or serum. The materials are available from NIST upon request; however, the supply is very limited for some of the materials. The materials include those obtained from pilot whale blubber (Homogenates III and IV), Blainville's beaked whale blubber (Homogenate VII), polar bear fat (Homogenate VI), and California sea lion serum (Marine Mammal Control Material-1 Serum) and blubber (Homogenate V).

Determination of perfluorinated alkyl acid concentrations in human serum and milk standard reference materials.

Standard Reference Materials (SRMs) are certified reference materials produced by the National Institute of Standards and Technology that are homogeneous materials well characterized with values for specified properties, such as environmental contaminant concentrations. They can be used to validate measurement methods and are critical in improving data quality. Disagreements in perfluorinated alkyl acid (PFAA) concentrations measured in environmental matrices during past interlaboratory comparisons emphasized the need for SRMs with values assigned for PFAAs. We performed a new interlaboratory comparison among six laboratories and provided, for the first time, value assignment of PFAAs in SRMs. Concentrations for perfluorooctane sulfonate (PFOS), perfluorooctanoate (PFOA), and other PFAAs in two human serum and two human milk SRMs are reported. PFAA concentration measurements agreed for serum SRM 1957 using different analytical methods in six laboratories and for milk SRM 1954 in three laboratories. The interlaboratory relative standard deviation for PFOS in SRM 1957 was 7%, which is an improvement over past interlaboratory studies. Matrix interferences are discussed, as well as temporal trends and the percentage of branched vs. linear isomers. The concentrations in these SRMs are similar to the present-day average concentrations measured in human serum and milk, resulting in representative and useful control materials for PFAA human monitoring studies.

Preparation and characterization of standard reference material 1849 infant/adult nutritional formula.

Standard Reference Material (SRM) 1849 Infant/Adult Nutritional Formula has been issued by the National Institute of Standards and Technology (NIST) as a replacement for SRM 1846 Infant Formula, issued in 1996. Extraction characteristics of SRM 1846 have changed over time, as have NIST's analytical capabilities. While certified mass fraction values were provided for five constituents in SRM 1846 (four vitamins plus iodine), certified mass fraction values for 43 constituents are provided in SRM 1849 (fatty acids, elements, and vitamins) and reference mass fraction values are provided for an additional 43 constituents including amino acids and nucleotides, making it the most extensively characterized food-matrix SRM available from NIST.