Photoluminescence spectroscopy of anthrathiophenes and benzonaphthothiophenes in Shpol'skii matrixes.

The dispersion of harmful oil components into the ocean waters could pose long-term risks to flora and fauna. Due to the complexity of oil-contaminated sites, the unambiguous identification and quantitation of environmental pollutants often requires the sequence of high-performance liquid chromatography and gas chromatography-mass spectrometry. A classic example is the analysis of polycyclic aromatic hydrocarbons. This article tackles a different aspect of environmental analysis as it focuses on the Shpol'skii spectroscopy of polycyclic aromatic sulfur heterocycles, specifically those belonging to the subgroups often known as anthrathiophenes and benzonaphthothiophenes. Photoluminescence measurements were made with a commercial spectrofluorimeter equipped with a continuous wave excitation source for steady state measurements and a pulsed excitation source for time-resolved measurements in the phosphorescence time domain. To the extent of our literature search, this is the first report on the 4.2 K fluorescence and phosphorescence spectra of anthrathiophenes and benzonaphthothiophenes, and the 77 K and 4.2 K phosphorescence lifetimes of benzonaphthothiophenes. 77 K and 4.2 K analytical figures of merit revealed the possibility to detect the studied compounds at the parts-per-billion (ng mL-1) concentration levels. The spectral and lifetime data gathered in this article provides the required information to choose an appropriate photoluminescence technique for the analysis of four-ring polycyclic aromatic sulfur heterocycles in complex environmental extracts.

External Quality Assessment of 24,25-dihydroxyvitamin D3 (24,25(OH)2D3) assays.

The discovery that mutations of the CYP24A1 gene are a cause of idiopathic infantile hypercalcemia (IIH) has revived interest in measuring serum 24,25(OH)2D3. Several studies have also suggested that a high 25-hydroxyvitamin D3(25-OHD3):24,25(OH)2D3 ratio might provide additional diagnostic information in the investigation of vitamin D deficiency. Measurement of 24,25(OH)2D3 is necessarily restricted to laboratories with mass spectrometry methods although cross reactivity of the metabolite in immunoassays for 25-OHD is a potential cause of misleading results. The international External Quality Assessment (EQA) scheme for vitamin D metabolites (DEQAS) was set up in 1989. In 2013 DEQAS became an accuracy based EQA for 25-OHD with 'target values' assigned by the National Institute of Standards and Technology (NIST) Reference Measurement Procedure (RMP). A pilot scheme for serum 24,25(OH)2D3 was started in 2015 and participants were asked to measure the metabolite on each of the 5 samples sent out for 25-OHD. Inter-laboratory agreement was poor but this may reflect methodological differences, in particular different approaches to assay standardization. An important potential contribution to reducing variability among assays was the development by NIST of a 24,25(OH)2D3 RMP and its use in assigning values to SRMs 972a, 2973 and 2971, supported by the NIH Office of Dietary Supplements (ODS) as part of the Vitamin D Standardization Program (VDSP) effort.

Hydroxyvitamin D assays: An historical perspective from DEQAS.

Recent years have seen a substantial increase in demand for 25-hydroxyvitamin D (25-OHD) assays. DEQAS (the Vitamin D External Quality Assessment Scheme) has been monitoring the performance of these assays since 1989. The first DEQAS distribution was in June 1989 and results were submitted by 13 laboratories in the UK, two of which used HPLC/UV; the rest used ligand binding assays with a tritium tracer. Inter-laboratory CVs (ALTM) ranged from 29.3% (42.7nmol/L) to 53.7% (20.0nmol/L). Currently the scheme has participants in 56 countries using 30 methods or variants of methods. In January 2017, 918 participants returned results and inter-laboratory CVs (ALTM) ranged from 10.3% (73.1nmol/L) to 15.3% (29.4nmol/L). Over the last 27 years, there have been a number of significant milestones in assay development. The first major advance was the development of an iodinated 25-OHD tracer by Hollis and Napoli in 1992, subsequently used in an RIA kit marketed by DiaSorin. This and other commercial radioimmunoassays that followed brought 25-OHD assays within reach of many more non-specialist routine laboratories. With the introduction of fully automated non-isotopic assays without solvent extraction, measurement of 25-OHD became available to any clinical chemistry laboratory with an appropriate analytical platform. However, as the limitations of these non-extraction assays became apparent more laboratories started using LC-MS/MS methodology. Meanwhile the variable accuracy of 25-OHD methods has been addressed by the Vitamin D Standardization Program (VDSP) which encourages manufacturers to produce methods traceable to the reference measurement procedures (RMPs) of NIST, University of Ghent and the Centers for Disease Control and Prevention (CDC). DEQAS changed to an accuracy-based scheme in 2013 and now assesses assay accuracy against the NIST RMP. This review will use DEQAS results and statistics to chart the historical development in 25-OHD assay technology and highlight some of the problems encountered in obtaining reliable results for this most challenging of analytes.

The development and implementation of quality assurance programs to support nutritional measurements.

The National Institute of Standards and Technology administers quality assurance programs devoted to improving measurements of nutrients and related metabolites in foods, dietary supplements, and serum and plasma samples. These programs have been developed in collaboration with the National Institutes of Health to assist measurement communities in their efforts to achieve accurate results that are comparable among different laboratories and over time. Targeted analytes include micronutrients, botanical markers, nutritional elements, contaminants, fatty acids, and vitamin D metabolites.

Development and certification of green tea-containing standard reference materials.

A suite of three green tea-containing Standard Reference Materials (SRMs) has been issued by the National Institute of Standards and Technology (NIST): SRM 3254 Camellia sinensis (Green Tea) Leaves, SRM 3255 Camellia sinensis (Green Tea) Extract, and SRM 3256 Green Tea-Containing Solid Oral Dosage Form. The materials are characterized for catechins, xanthine alkaloids, theanine, and toxic elements. As many as five methods were used in assigning certified and reference values to the constituents, with measurements carried out at NIST and at collaborating laboratories. The materials are intended for use in the development and validation of new analytical methods, and for use as control materials as a component in the support of claims of metrological traceability.

Certification of vitamins and carotenoids in SRM 3280 multivitamin/multielement tablets.

A new multivitamin/multielement dietary supplement Standard Reference Material (SRM) has been issued by the National Institute of Standards and Technology (NIST), with certified and reference concentration values for 13 vitamins, 24 elements, and 2 carotenoids. The constituents have been measured by multiple analytical methods with data contributed by NIST and by collaborating laboratories. This effort included the first use of isotope dilution mass spectrometry for value assignment of both fat-soluble vitamins (FSVs) and water-soluble vitamins (WSVs). Excellent agreement was obtained among the methods, with relative expanded uncertainties for the certified concentration values typically ranging from <2% to 15% for vitamins.

Certification of standard reference materials containing bitter orange.

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

Determination of HBCD, PBDEs and MeO-BDEs in California sea lions (Zalophus californianus) stranded between 1993 and 2003.

Blubber samples from male California sea lions (Zalphophus californianus) stranded between 1993 and 2003 were analyzed for 27 polybrominated diphenyl ether (PBDE) congeners, three isomers of hexabromocyclododecane (HBCD) and 14 methoxylated polybrominated diphenyl ether (MeO-BDE) congeners. Total PBDEs ranged from 450 ng/g to 4740 ng/g wet mass and total HBCD ranged from < 0.3 ng/g to 12 ng/g wet mass. The concentration of HBCD increased from 0.7 ng/g to12.0 ng/g wet mass in sea lion blubber between 1993 and 2003. However, no significant temporal trend was observed for any of the other brominated compounds over this 10 year period. Only one of the 14 MeO-BDE congeners was detected in the blubber samples, 6-methoxy-2,2',4,4'-tetrabromodiphenyl ether (6-MeO-BDE 47), and concentrations ranged from < 0.2 ng/g to 12 ng/g wet mass. A bromo-, chloro-heterocyclic compound, 1,1'-dimethyl-tetrabromo-dichloro-2,2'-bipyrrole (DBP-Br4Cl2), previously reported in marine species along the Pacific coast, was also identified in the sea lion blubber. DBP-Br4Cl2 ranged from 44 ng/g wet mass to 660 ng/g wet mass and was present at concentrations rivaling the dominant PBDE congener, BDE 47 (2,2',4,4'-tetrabromodiphenyl ether). Concentrations of DBP-Br4Cl2 were positively correlated with 6-MeO-BDE 47 (r = 0.7; p < 0.05). Both of these compounds have been identified in marine algae and sponges, and studies suggest they are both produced from natural sources. This study demonstrates that brominated compounds from both anthropogenic and biogenic sources can accumulate to similar levels in marine mammals. In addition, HBCD concentrations appear to be increasing in California sea lion populations, whereas PBDE concentrations, between 1993 and 2003, were highly variable.

Elemental composition of liver and kidney tissues of rough-toothed dolphins (Steno bredanensis).

On December 14, 1997, 62 rough-toothed dolphins (Steno bredanensis) stranded on Cape San Blas, on the Florida coast of the Gulf of Mexico. Approximately 30 animals died either on the beach or in rehabilitation facilities. Two were successfully rehabilitated and released. Liver, kidney, blubber, and muscle tissues were collected from 15 animals that died on the beach. Portions of the liver and kidney from each dolphin were analyzed using instrumental neutron activation analysis and inductively coupled plasma mass spectrometry to determine mass fractions of 37 elements. Levels of several electrolytes (Na, Cl, K, Br, Rb, I, Cs) and of the essential trace elements Fe, Cu, and Zn in both tissues were similar to those found in other Odontoceti. Mass fractions of Ca ranged from 60 mg/kg to 1,200 mg/kg (wet mass basis), indicating significant inhomogeneity in the kidney tissues of several animals. Necropsy reports noted that the kidneys of many of these animals contained fibrous nodules. The measured Ca inhomogeneity may be due to mineralization of the fibrous kidney tissue. Hepatic levels of Hg and Se were at the high end of the ranges generally found in livers of other Odontoceti and were slightly higher in animals with fibrous kidneys than in the others. Mass fractions of Se, Ag, and Hg in liver tissues increased with the size and age of the animals indicating accumulation of these elements in the liver with age. Results also indicate that Se and Hg accumulate in rough-toothed dolphin kidney. Accumulation of these elements with age has been reported commonly for marine mammals and other species.

A Critical Evaluation of Interlaboratory Data on Total, Elemental, and Isotopic Carbon in the Carbonaceous Particle Reference Material, NIST SRM 1649a.

Because of increased interest in the marine and atmospheric sciences in elemental carbon (EC), or black carbon (BC) or soot carbon (SC), and because of the difficulties in analyzing or even defining this pervasive component of particulate carbon, it has become quite important to have appropriate reference materials for intercomparison and quality control. The NIST "urban dust" Standard Reference Material(®) SRM 1649a is useful in this respect, in part because it comprises a considerable array of inorganic and organic species, and because it exhibits a large degree of ((14)C) isotopic heterogeneity, with biomass carbon source contributions ranging from about 2 % (essentially fossil aliphatic fraction) to about 32 % (polar fraction). A primary purpose of this report is to provide documentation for the new isotopic and chemical particulate carbon data for the most recent (31 Jan. 2001) SRM 1649a Certificate of Analysis. Supporting this is a critical review of underlying international intercomparison data and methodologies, provided by 18 teams of analytical experts from 11 institutions. Key results of the intercomparison are: (1) a new, Certified Value for total carbon (TC) in SRM 1649a; (2) (14)C Reference Values for total carbon and a number of organic species, including for the first time 8 individual PAHs; and (3) elemental carbon (EC) Information Values derived from 13 analytical methods applied to this component. Results for elemental carbon, which comprised a special focus of the intercomparison, were quite diverse, reflecting the confounding of methodological-matrix artifacts, and methods that tended to probe more or less refractory regions of this universal, but ill-defined product of incomplete combustion. Availability of both chemical and (14)C speciation data for SRM 1649a holds great promise for improved analytical insight through comparative analysis (e.g., fossil/biomass partition in EC compared to PAH), and through application of the principle of isotopic mass balance.

Determination of polychlorinated dibenzo-p-dioxin and dibenzofuran congeners in air particulate and marine sediment standard reference materials (SRMs).

Due to the limited number of environmental matrix certified reference materials (CRMs) with assigned values for natural levels of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), an interlaboratory study was undertaken by the National Institute of Standards and Technology (NIST) and Environment Canada to establish reference concentration values for selected PCDD/Fs in two well-characterized NIST Standard Reference Materials (SRMs): SRM 1649a (Urban Dust) and SRM 1944 (New York/New Jersey Waterway Sediment). Results from 14 laboratories were used to provide reference values for the seventeen 2, 3, 7, 8-substituted PCDD/F congeners, the totals for individual tetra- through hepta-substituted PCDD/F homologues, and the total amount of tetra- through hepta-substituted PCDD/Fs. The mass fractions for the individual 2, 3, 7, 8-substituted congeners range from approximately 0.01 microg/kg to 7 microg/kg dry mass.

Certification of the methylmercury content in SRM 2977 mussel tissue (organic contaminants and trace elements) and SRM 1566b oyster tissue.

The methylmercury content in two new marine bivalve mollusk tissue Standard Reference Materials (SRMs) has been certified using results of analyses from the National Institute of Standards and Technology (NIST) and two other laboratories. The certified concentrations of methylmercury were established based on the results from four and six different (independent) analytical methods, respectively, for SRM 1566b Oyster Tissue (13.2 +/- 0.7 microg/kg) and SRM 2977 Mussel Tissue (organic contaminants and trace elements) (36.2 +/- 1.7 microg/kg). The certified concentration of methylmercury in SRM 1566b is among the lowest in any certified reference material (CRM).

Determination of non-ortho polychlorinated biphenyls in environmental Standard Reference Materials.

The concentrations of three non-ortho ("coplanar") polychlorinated biphenyls, 3,3',4,4'-tetrachlorobiphenyl (IUPAC PCB 77), 3,3',4,4',5-pentachlorobiphenyl (IUPAC PCB 126), and 3,3',4,4',5,5'-hexachlorobiphenyl (IUPAC PCB 169), were determined in five NIST Standard Reference Materials (SRMs) of environmental and biological interest. The measured levels were approximately between (0.2 to 1.3) ng/g in SRM 1588a (Organics in Cod Liver Oil), (0.3 to 9) ng/g in SRM 1944 (New York/New Jersey Waterway Sediment), (0.2 to 0.4) ng/g in SRM 1945 (Organics in Whale Blubber), (1 to 18) ng/g in SRM 2974 (Organics in Freeze-dried Mussel Tissue [Mytilus edulis]), and (0.1 to 0.4) ng/g in candidate SRM 1946 (Lake Superior Fish Tissue). PCB 169 was present at < 0.1 ng/g in SRMs 1944 and 2974.

Preparation of Standard Reference Material 2383 (Baby Food Composite) and use of an interlaboratory comparison exercise for value assignment of its nutrient concentrations.

The preparation of the recently released Standard Reference Material (SRM) 2383 Baby Food Composite and the process used for value assignment of nutrient concentrations are reported. SRM 2383 can be used as a control material when assigning values to in-house control materials and when validating analytical methods for measuring proximates, vitamins, and minerals in baby food and similar matrixes. The SRM was prepared as a commercial baby food would be prepared, with the same ingredients. The Certificate of Analysis for SRM 2383 provides assigned values for concentrations of proximates, vitamins, and minerals for which product labeling is required by the Nutrition Labeling and Education Act of 1990. These assigned values were based on measurements by the National Institute of Standards and Technology (NIST) and/or collaborating laboratories. Assignment of analyte concentrations based solely on analyses by collaborating laboratories is described in this paper. Certified values are provided for retinol, tocopherols, and several carotenoids including total beta-carotene; the certification of and methodology used for measurement of these analytes is discussed in a companion paper (this issue, page 288). Reference values are provided for solids, ash, fat, nitrogen, protein, carbohydrate, calories, vitamin B1, vitamin B2, vitamin B6, niacin, biotin, calcium, phosphorus, magnesium, manganese, iron, zinc, copper, sodium, potassium, and chloride. Reference values for additional carotenoids are reported in the companion paper (this issue, page 288). Information values are provided for iodine, selenium, molybdenum, vitamin D, vitamin B12, folic acid, pantothenic acid, choline, inositol, sugars, total dietary fiber, and 3 classes of fats.

Quality assurance in analysis of cryogenically stored liver tissue specimens from the NIST National Biomonitoring Specimen Bank (NBSB).

Portions of liver tissue specimens originally stored in the National Biomonitoring Specimen Bank (NBSB) and analyzed between 1980 and 1987 were re-analyzed in 1997 using instrumental neutron activation analysis (INAA) for the determination of 17 trace elements. Duplicate portions of each specimen had been stored at two different temperatures. The first was stored in a liquid nitrogen vapor-cooled freezer at -150 degrees C, standard NBSB storage conditions, and the other in an electric freezer maintained at -80 degrees C. Two portions of seven livers from each storage temperature were re-analyzed for this work. Results showed no changes in trace element content as a function of storage temperature, within the uncertainty of the method used. Results from these analyses agreed with results of initial analyses for most analytes in most sub-samples. Of the exceptions, five were due, in part, to an incorrect basis mass for the initial sub-specimen of one tissue, five with variable Zn results were attributed to difficulties in peak fitting for this element during INAA data processing, and the remaining were isolated differences discussed in this paper. Results of this work indicate that specimen storage and processing protocols are adequate to prevent noticeable contamination of specimens with trace elements, with the exception of Cr. Variability in Cr content was observed for the liver tissues which may have been caused by Cr contamination of the samples by the Teflon mill. Analyses of portions of Standard Reference Material (SRM) 1566a Oyster Tissue (certified in 1989) and SRM 1577a Bovine Liver (certified in 1982) were also included in this study for the purpose of quality control and to assess the stability of these freeze-dried powders that were stored at room temperature. No changes were observed in these materials.

Shape selectivity for constrained solutes in reversed-phase liquid chromatography.

In reversed-phase liquid chromatography (RPLC), the separation of compound mixtures of similar polarity can present a significant challenge for the analyst. Examples of such compounds include geometric isomers present in environmental samples (e.g., polycyclic aromatic hydrocarbons, polycyclic aromatic sulfur heterocycles, and polychlorinated biphenyl congeners) and compounds of biological significance (e.g., carotenoids and steroids). In general, compounds with rigid, well-defined molecular shape are best separated using a column with enhanced shape selectivity characteristics. This perspective presents an overview of column properties that influence shape selectivity for constrained solutes. Approaches to the characterization of stationary-phase structure are described, and the findings are correlated with chromatographic performance. Finally, retention models of shape discrimination are presented that are consistent with observed retention behavior. An appreciation for shape recognition effects in RPLC will facilitate method development for certain classes of difficult to resolve compounds.

Determination of polycyclic aromatic sulfur heterocycles in fossil fuel-related samples.

An analytical method is described for the separation, identification, and quantification of a number of polycyclic aromatic sulfur heterocycles (PASHs) in three fossil fuel-related samples including two Standard Reference Materials (SRMs), SRM 1597 (coal tar) and SRM 1582 (petroleum crude oil), and a decant oil. The compounds measured include the 3 possible naphtho[b]thiophenes; dibenzothiophene and selected methyl-, ethyl-, dimethyl-, and trimethyl-substituted isomers; the 3 possible benzo[b]naphthothiophenes; and the 30 methylbenzo[b]naphthothiophenes isomers. Because of the occurrence of polycyclic aromatic hydrocarbons and PASHs together with their large number of possible alkyl-substituted isomers, the analytical method described requires a number of prerequisites: effective sample cleanup, selective stationary phases, and selective methods of detection. The sample cleanup involves solid-phase extraction using aminopropylsilane cartridges with different solvent mixtures followed by normal-phase liquid chromatographic isolation of the PASHs based on the number of aromatic carbons. These aromatic ring fractions are then separated by capillary gas chromatography using two stationary phases with different selectivities, 5% phenyl-substituted methylpolysiloxane stationary phase and 50% phenyl-substituted methylpolysiloxane stationary phase, and analyzed with mass-selective detection and atomic emission detection. A liquid crystalline stationary phase was also used to separate the methylbenzo[b]naphthothiophene isomers in the crude oil sample. Advantages and limitations of each chromatographic and detection technique are discussed.

Comparison of supercritical fluid extraction and Soxhlet extraction for the determination of polychlorinated biphenyls in environmental matrix standard reference materials.

Supercritical fluid extraction (SFE) was compared to traditional Soxhlet extraction for the determination of polychlorinated biphenyl congeners in three standard reference materials: SRM 1941a (Organics in Marine Sediment), SRM 1944 (New York/New Jersey Waterway Sediment) and SRM 2974 [Organics in Mussel Tissue (Mytilus edulis) (Freeze-Dried)]. The concentrations determined using SFE compared well with the certified concentrations for the majority of the polychlorinated biphenyl congeners.

Coupled achiral/chiral column techniques in subcritical fluid chromatography for the separation of chiral and nonchiral compounds.

A multicolumn approach was developed to address the limited achiral selectivity of chiral stationary phases. Groups of structurally related compounds, including beta-blockers and 1,4-benzodiazepines, were separated using coupled achiral/chiral stationary phases under subcritical fluid conditions. The achiral selectivity of amino and cyano stationary phases was used to modify the resolution of compounds on a Chiralcel OD chiral stationary phase by combining the achiral and chiral columns in series. In the case of the benzodiazepines, separation of achiral compounds was performed concurrently with the enantioseparation of chiral molecules. The separation of components of a multidrug cough and cold medication was also demonstrated on a cyano column coupled with a Chiralpak AD chiral stationary phase. The use of modified carbon dioxide eluents eliminated the mobile phase incompatibility problems associated with column coupling in liquid chromatography and incorporated the high efficiency of sub- and supercritical fluid chromatography.