Assessing children's potential exposures to harmful metals in tire crumb rubber by accelerated photodegradation weathering.

Whether a tire crumb rubber (TCR) playground would expose children to potentially harmful chemicals such as heavy metals is an open question. The released metals available for pickup on the surface of TCR tiles was studied by accelerated 2-year aging of the TCRs in the NIST-SPHERE (National Institute of Standards and Technology Simulated Photodegradation via High Energy Radiant Exposure). The dermal contact was mimicked by a method of composite surface wiping from US Environmental Protection Agency throughout the weathering process. The surface release of ten most concerned harmful metals (Be, Cr, Cu, As, Se, Cd, Sb, Ba, Tl, Pb) was monitored through the course of aging. The cumulative release of Cu, As, Tl, and Sb reached potentially harmful levels at various times within 3 years, although only Cr was found at a harmful level on the surface of the tiles. Taking the cleansing effect of precipitation or periodic cleansing with rain into account, TCR playgrounds may still be safe for use.

Assessing Arsenic Species in Foods Using Regularized Linear Regression of the Arsenic K-edge X-ray Absorption Near Edge Structure.

The toxicity and bioavailability of arsenic is heavily dependent on its speciation. Therefore, robust and accurate methods are needed to determine arsenic speciation profiles for materials related to public health initiatives, such as food safety. Here, X-ray spectroscopies are attractive candidates as they provide in situ, nondestructive analyses of solid samples without perturbation to the arsenic species therein. This work provides a speciation analysis for three certified reference materials for the food chemistry community, whose assigned values may be used to assess the merit of the X-ray spectroscopy results. Furthermore, extracts of SRM 3232 Kelp Powder, which is value-assigned for arsenic species, are measured to provide further evidence of its efficacy. These analyses are performed on the results of As K-edge X-ray Absorption Near Edge Structure (XANES) measurements collected on each sample. Notably, such analyses have traditionally relied on linear combination fitting of a minimal subset of empirical standards selected by stepwise regression. This is known to be problematic for compounds with meaningfully collinear spectra and can yield overestimates of the accuracy of the analysis. Therefore, the least absolute shrinkage and selection operator (lasso) regression method is used to reduce the risk of overfitting and increase the interpretability of statistical inferences. As this is a biased statistical method, results and uncertainties are estimated using a bootstrap method accounting for the dominant sources of variability. Finally, this method does not separate model and data selection from regression analysis. Indeed, a survey of many spectral influences is presented including changes in the: state of methylation, state of protonation, oxidation state, coordination geometry, and sample phase. These compounds were all included in the model's training set, preventing model over-simplification and enabling high-throughput and robust analyses.

Analytical Methodologies for the Determination of Organoarsenicals in Edible Marine Species: A Review.

Setting regulatory limits for arsenic in food is complicated, owing to the enormous diversity of arsenic metabolism in humans, lack of knowledge about the toxicity of these chemicals, and lack of accurate arsenic speciation data on foodstuffs. Identification and quantification of the toxic arsenic compounds are imperative to understanding the risk associated with exposure to arsenic from dietary intake, which, in turn, underscores the need for speciation analysis of the food. Arsenic speciation in seafood is challenging, owing to its existence in myriads of chemical forms and oxidation states. Interconversions occurring between chemical forms, matrix complexity, lack of standards and certified reference materials, and lack of widely accepted measurement protocols present additional challenges. This review covers the current analytical techniques for diverse arsenic species. The requirement for high-quality arsenic speciation data that is essential for establishing legislation and setting regulatory limits for arsenic in food is explored.

Organoarsenicals in Seafood: Occurrence, Dietary Exposure, Toxicity, and Risk Assessment Considerations - A Review.

Diet, especially seafood, is the main source of arsenic exposure for humans. The total arsenic content of a diet offers inadequate information for assessment of the toxicological consequences of arsenic intake, which has impeded progress in the establishment of regulatory limits for arsenic in food. Toxicity assessments are mainly based on inorganic arsenic, a well-characterized carcinogen, and arsenobetaine, the main organoarsenical in seafood. Scarcity of toxicity data for organoarsenicals, and the predominance of arsenobetaine as an organic arsenic species in seafood, has led to the assumption of their nontoxicity. Recent toxicokinetic studies show that some organoarsenicals are bioaccessible and cytotoxic with demonstrated toxicities like that of pernicious trivalent inorganic arsenic, underpinning the need for speciation analysis. The need to investigate and compare the bioavailability, metabolic transformation, and elimination from the body of organoarsenicals to the well-established physiological consequences of inorganic arsenic and arsenobetaine exposure is apparent. This review provides an overview of the occurrence and assessment of human exposure to arsenic toxicity associated with the consumption of seafood.

Determination of total arsenic and hydrophilic arsenic species in seafood.

Marine organisms are vital sources of staple and functional food but are also the major dietary route of human exposure to total arsenic. We surveyed the total arsenic content and the mass fractions of hydrophilic arsenic species from five different marine food types cutting across the food chain from microalgae, macroalgae, bivalve clam, crustaceans and finfish. Total arsenic was determined using inductively coupled plasma-mass spectrometry (ICP-MS) while arsenic speciation analysis was performed using high-performance liquid chromatography (HPLC) coupled to ICP-MS as the detector. The total arsenic contents ranged from 133 ± 11 ng/g to 26,630 ± 520 ng/g. The mass fractions of inorganic arsenic (iAs), arsenobetaine (AsB), dimethylarsinic acid (DMA), and the four commonly occurring arsenosugars (AsSugars) are reported. Extractable hydrophilic arsenic species accounted for 10 % (aquacultured shrimp) to 95 % (kelp) of the total arsenic. DMA was established to be a byproduct of the decomposition of AsSugars in acid extracts of samples known to contain these species.

Sensitive Immunoassay Detection of Plasmodium Lactate Dehydrogenase by Inductively Coupled Plasma Mass Spectrometry.

Rapid, reliable, and sensitive detection of Plasmodium infection is central to malaria control and elimination. Many Malaria Rapid Diagnostic Tests (RDTs) developed for this purpose depend upon immunoassays that can be improved by advances in bound antibody sensor technology. In a previous study, immuno-polymerase chain reaction (PCR) was shown to provide highly sensitive detection of Plasmodium falciparum lactate dehydrogenase (PfLDH) in monoclonal antibody (mAb) sandwich assays. Here, we show comparably high immunoassay sensitivity by inductively coupled plasma mass spectrometry (ICP-MS) detection of gold nanoparticles (AuNPs). Following capture of PfLDH with the primary mAb and binding of the AuNP-labeled detection mAb, ICP-MS signals from the AuNPs provided quantitative measures of recombinant PfLDH test dilutions and P. falciparum-infected erythrocytes. A detection limit of 1.5 pg/mL was achieved with the PfLDH protein. Parasitemia in cultures of P. falciparum-infected erythrocytes could be detected to a lower limit of 1.6 parasite/µl (p/µl) for early ring-stage forms and 0.3 p/µl for mixed stages including mature trophozoites and schizont-stages. These results show that ICP-MS detection of AuNPs can support highly sensitive and accurate detection of Plasmodium infection.

Development of a kelp powder (Thallus laminariae) Standard Reference Material.

A Standard Reference Material (SRM) of seaweed, SRM 3232 Kelp Powder (Thallus laminariae) has been developed to support food and dietary supplement measurements in compliance with the Food Safety Modernization Act (FSMA) and the Dietary Supplement Health and Education Act of 1994 (DSHEA). The material was characterized for nutritional minerals, arsenic species, isomers of vitamin K1, proximates, and toxic elements. Kelp is a rich source of vitamins and minerals, and it is an excellent source of dietary iodine. Kelp also contains a large amount of arsenic, which is toxic as inorganic species but much less so as organic species. To capture the dietary profile of kelp, certified values were issued for As, Ca, Cd, Cr, Cu, Fe, Hg, I, K, Mg, Mn, Mo, Na, Pb, and Zn. Reference values for proximates were assigned. For the first time, a certified value for iodine, reference values for isomers of vitamin K1, and reference values for arsenic species including arsenosugars were assigned in a seaweed. SRM 3232 fills a gap in Certified Reference Materials (CRMs) needed for quality assurance and method validation in the compositional measurements of kelp and similar seaweeds used as food and as dietary supplements. Graphical Absract Arsenic species and isomers of vitamin K1 were determined in the development of SRM 3232 Kelp Powder (Thallus laminariae).

SI traceable determination of arsenic species in kelp (Thallus laminariae).

A dietary supplement, kelp contains a significant amount of arsenic that is mostly arsenosugars. The determination of arsenosugars is difficult due to a lack of arsenosugar calibration standard, because arsenosugar compounds are not commercially available. This work reports the determination of arsenicals in a kelp extract with traceability to the International System of Units (SI). The hydrophilic fraction of arsenicals was reproducibly extracted from a candidate Standard Reference Material (SRM) 3232 Kelp Powder (Thallus Laminariae) in development at the National Institute of Standards and Technology (NIST). Arsenosugars and dimethylarsinic acid (DMA) were separated into fractions using analytical liquid chromatography (LC) cation and anion columns. The arsenic in the fractions was determined using instrumental neutron activation analysis (INAA). Cation exchange separation was used for INAA determination of arsenosugar 3-[5'-deoxy-5'-(dimethylarsinoyl)-ß-ribofuranosyloxy]propylene glycol (As(328)) for the first time, while DMA, arsenosugars 3-[5'-deoxy-5'-(dimethylarsinoyl)-ß-ribofuranosyloxy]-2-hydroxypropyl 2,3-dihydroxypropyl hydrogen phosphate (As(482)), and 3-[5'-deoxy-5'-(dimethylarsinoyl)-ß-ribofuranosyloxy]-2-hydroxypropanesulfonic acid (As(392)) were determined following anion exchange separation. The contents of DMA, As(328), As(482), and As(392) were 0.41 mg kg-1 ± 0.09 mg kg-1, 1.10 mg kg-1 ± 0.25 mg kg-1, 5.23 mg kg-1 ± 0.46 mg kg-1, and 13.17 mg kg-1 ± 0.67 mg kg-1, respectively. Separately, components of arsenic species in the kelp extract including DMA, As(328), and inorganic arsenic were determined using LC-inductively coupled plasma mass spectrometry. Results of DMA and As(328) were 0.485 mg kg-1 ± 0.024 mg kg-1 and 1.14 mg kg-1 ± 0.03 mg kg-1, respectively, which were in good agreement with those determined by INAA in fractions of LC eluent. The most toxic species, AsIII and AsV were found to be < 0.07 mg kg-1 and 0.231 mg kg-1 ± 0.018 mg kg-1, respectively. Results were traceable to SI.

Separation, Sizing, and Quantitation of Engineered Nanoparticles in an Organism Model Using Inductively Coupled Plasma Mass Spectrometry and Image Analysis.

For environmental studies assessing uptake of orally ingested engineered nanoparticles (ENPs), a key step in ensuring accurate quantification of ingested ENPs is efficient separation of the organism from ENPs that are either nonspecifically adsorbed to the organism and/or suspended in the dispersion following exposure. Here, we measure the uptake of 30 and 60 nm gold nanoparticles (AuNPs) by the nematode, Caenorhabditis elegans, using a sucrose density gradient centrifugation protocol to remove noningested AuNPs. Both conventional inductively coupled plasma mass spectrometry (ICP-MS) and single particle (sp)ICP-MS are utilized to measure the total mass and size distribution, respectively, of ingested AuNPs. Scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS) imaging confirmed that traditional nematode washing procedures were ineffective at removing excess suspended and/or adsorbed AuNPs after exposure. Water rinsing procedures had AuNP removal efficiencies ranging from 57 to 97% and 22 to 83%, while the sucrose density gradient procedure had removal efficiencies of 100 and 93 to 98%, respectively, for the 30 and 60 nm AuNP exposure conditions. Quantification of total Au uptake was performed following acidic digestion of nonexposed and Au-exposed nematodes, whereas an alkaline digestion procedure was optimized for the liberation of ingested AuNPs for spICP-MS characterization. Size distributions and particle number concentrations were determined for AuNPs ingested by nematodes with corresponding confirmation of nematode uptake via high-pressure freezing/freeze substitution resin preparation and large-area SEM imaging. Methods for the separation and in vivo quantification of ENPs in multicellular organisms will facilitate robust studies of ENP uptake, biotransformation, and hazard assessment in the environment.

Surface Degradation and Nanoparticle Release of a Commercial Nanosilica/Polyurethane Coating Under UV Exposure.

Many coatings properties such as mechanical, electrical, and ultra violet (UV) resistance are greatly enhanced by the addition of nanoparticles, which can potentially increase the use of nanocoatings for many outdoor applications. However, because polymers used in all coatings are susceptible to degradation by weathering, nanoparticles in a coating may be brought to the surface and released into the environment during the life cycle of a nanocoating. Therefore, the goal of this study is to investigate the process and mechanism of surface degradation and potential particle release from a commercial nanosilica/polyurethane coating under accelerated UV exposure. Recent research at the National Institute of Standards and Technology (NIST) has shown that the matrix in an epoxy nanocomposite undergoes photodegradation during exposure to UV radiation, resulting in surface accumulation of nanoparticles and subsequent release from the composite. In this study, specimens of a commercial polyurethane (PU) coating, to which a 5 mass % surface treated silica nanoparticles solution was added, were exposed to well-controlled, accelerated UV environments. The nanocoating surface morphological changes and surface accumulation of nanoparticles as a function of UV exposure were measured, along with chemical change and mass loss using a variety of techniques. Particles from the surface of the coating were collected using a simulated rain process developed at NIST, and the collected runoff specimens were measured using inductively coupled plasma-optical emission spectroscopy (ICP-OES) to determine the amount of silicon released from the nanocoatings. The results demonstrated that the added silica nanoparticle solution decreased the photodegradation rate (i.e., stabilization) of the commercial PU nanocoating. Although the degradation was slower than the previous nanosilica epoxy model system, the degradation of the PU matrix resulted in accumulation of silica nanoparticles on the nanocoating surface and release to the environment by simulated rain. These experimental data are valuable for developing models to predict the long-term release of nanosilica from commercial PU nanocoatings used outdoors and, therefore, are essential for assessing the health and environmental risks during the service life of exterior PU nanocoatings.

An approach for identification and determination of arsenic species in the extract of kelp.

The National Institute of Standards and Technology is developing a kelp powder standard reference material (SRM) in support of dietary supplement measurements. Edible seaweeds such as kelp and laver consumed as diet or dietary supplement contain tens of mg/kg arsenic. The speciation information of arsenic in the seaweed should be provided because the total arsenic alone does not fully address the safety issue of the dietary supplement as the value assignment is originally intended. The inability to avail all arsenic species for value assignment measurements prevented the certification of arsenic species in the candidate SRM; however, approximately 70 % of total arsenic extracted with a 1:1 volume fraction of methanol:water mixture allowed arsenic speciation values to be assigned to a procedure-defined extract, which may be used for method validation in research to improve upon current extraction and measurement practices. Arsenic species in kelp and laver were identified using electrospray ionization ion trap time of flight mass spectrometry (ESI-IT-TOF). Arsenosugars As(328), As(482), and As(392) were found in the kelp candidate SRM while As(328) and As(482) were found in GBW 08521, a certified reference material (CRM) of laver produced by the National Institute of Metrology of China (NIM). A discovery that the digests of kelp and laver contained only dimethylarsinic acid led to the conclusion that the seaweeds did not contain detectible levels of arsenobetaine, arsenocholine or trimethylarsine oxide that could overlap with the peaks of arsenosugars in the separation. The mean ± s of (5.68 ± 0.28) mg/kg and (13.43 ± 0.31) mg/kg found for As(482) and As(392) in kelp, respectively, using instrumental neutron activation analysis (INAA) demonstrated that value assignment measurement of arsenosugars was possible without arsenosugar calibration standards.

RSK promotes G2/M transition through activating phosphorylation of Cdc25A and Cdc25B.

Activation of the mitogen-activated protein kinase (MAPK) cascade in mammalian cell lines positively regulates the G2/M transition. The molecular mechanism underlying this biological phenomenon remains poorly understood. Ribosomal S6 kinase (RSK) is a key downstream element of the MAPK cascade. Our previous studies established roles of RSK2 in Cdc25C activation during progesterone-induced meiotic maturation of Xenopus oocytes. In this study we demonstrate that both recombinant RSK and endogenous RSK in Xenopus egg extracts phosphorylate all three isoforms of human Cdc25 at a conserved motif near the catalytic domain. In human HEK293 and PC-3mm2 cell lines, RSK preferentially phosphorylates Cdc25A and Cdc25B in mitotic cells. Phosphorylation of the RSK sites in these Cdc25 isoforms increases their M-phase-inducing activities. Inhibition of RSK-mediated phosphorylation of Cdc25 inhibits G2/M transition. Moreover, RSK is likely to be more active in mitotic cells than in interphase cells, as evidenced by the phosphorylation status of T359/S363 in RSK. Together, these findings indicate that RSK promotes G2/M transition in mammalian cells through activating phosphorylation of Cdc25A and Cdc25B.

Fast and accurate determination of K, Ca, and Mg in human serum by sector field ICP-MS.

Electrolytes in serum are important biomarkers for skeletal and cellular health. The levels of electrolytes are monitored by measuring the Ca, Mg, K, and Na in blood serum. Many reference methods have been developed for the determination of Ca, Mg, and K in clinical measurements; however, isotope dilution thermal ionization mass spectrometry (ID-TIMS) has traditionally been the primary reference method serving as an anchor for traceability and accuracy to these secondary reference methods. The sample matrix must be separated before ID-TIMS measurements, which is a slow and tedious process that hindered the adoption of the technique in routine clinical measurements. We have developed a fast and accurate method for the determination of Ca, Mg, and K in serum by taking advantage of the higher mass resolution capability of the modern sector field inductively coupled plasma mass spectrometry (SF-ICP-MS). Each serum sample was spiked with a mixture containing enriched (44)Ca, (26)Mg, and (41)K, and the (42)Ca(+):(44)Ca(+), (24)Mg(+):(26)Mg(+), and (39)K(+):(41)K(+) ratios were measured. The Ca and Mg ratios were measured in medium resolution mode (m/Δm ≈ 4 500), and the K ratio in high resolution mode (m/Δm ≈ 10 000). Residual (40)Ar(1)H(+) interference was still observed but the deleterious effects of the interference were minimized by measuring the sample at K > 100 ng g(-1). The interferences of Sr(++) at the two Ca isotopes were less than 0.25 % of the analyte signal, and they were corrected with the (88)Sr(+) intensity by using the Sr(++):Sr(+) ratio. The sample preparation involved only simple dilutions, and the measurement using this sample preparation approach is known as dilution-and-shoot (DNS). The DNS approach was validated with samples prepared via the traditional acid digestion approach followed by ID-SF-ICP-MS measurement. DNS and digested samples of SRM 956c were measured with ID-SF-ICP-MS for quality assurance, and the results (mean ± expanded uncertainty in mg dL(-1) unit) for Ca (DNS = 10.14 ± 0.13, digested = 10.11 ± 0.10), Mg (DNS = 2.093 ± 0.008, digested = 2.098 ± 0.007), and K (DNS = 15.48 ± 0.11, digested = 15.50 ± 0.28) were in good agreement with the certified values (Ca = 10.17 ± 0.06, Mg = 2.084 ± 0.023, K = 15.55 ± 0.13). Major sources of uncertainty are sample measurement, spike calibration, and instrument factor including mass discrimination of the spectrometer and the detector deadtime.

Salivary antigen-5/CAP family members are Cu2+-dependent antioxidant enzymes that scavenge O2₋. and inhibit collagen-induced platelet aggregation and neutrophil oxidative burst.

The function of the antigen-5/CAP family of proteins found in the salivary gland of bloodsucking animals has remained elusive for decades. Antigen-5 members from the hematophagous insects Dipetalogaster maxima (DMAV) and Triatoma infestans (TIAV) were expressed and discovered to attenuate platelet aggregation, ATP secretion, and thromboxane A2 generation by low doses of collagen (<1 µg/ml) but no other agonists. DMAV did not interact with collagen, glycoprotein VI, or integrin α2ß1. This inhibitory profile resembles the effects of antioxidants Cu,Zn-superoxide dismutase (Cu,Zn-SOD) in platelet function. Accordingly, DMAV was found to inhibit cytochrome c reduction by O2[Symbol: see text] generated by the xanthine/xanthine oxidase, implying that it exhibits antioxidant activity. Moreover, our results demonstrate that DMAV blunts the luminescence signal of O2[Symbol: see text] generated by phorbol 12-myristate 13-acetate-stimulated neutrophils. Mechanistically, inductively coupled plasma mass spectrometry and fluorescence spectroscopy revealed that DMAV, like Cu,Zn-SOD, interacts with Cu(2+), which provides redox potential for catalytic removal of O2[Symbol: see text]. Notably, surface plasmon resonance experiments (BIAcore) determined that DMAV binds sulfated glycosaminoglycans (e.g. heparin, KD ~100 nmol/liter), as reported for extracellular SOD. Finally, fractions of the salivary gland of D. maxima with native DMAV contain Cu(2+) and display metal-dependent antioxidant properties. Antigen-5/CAP emerges as novel family of Cu(2+)-dependent antioxidant enzymes that inhibit neutrophil oxidative burst and negatively modulate platelet aggregation by a unique salivary mechanism.

Real-time size discrimination and elemental analysis of gold nanoparticles using ES-DMA coupled to ICP-MS.

We report the development of a hyphenated instrument with the capacity to quantitatively characterize aqueous suspended gold nanoparticles (AuNPs) based on a combination of gas-phase size separation, particle counting, and elemental analysis. A customized electrospray-differential mobility analyzer (ES-DMA) was used to achieve real-time upstream size discrimination. A condensation particle counter and inductively coupled plasma mass spectrometer (ICP-MS) were employed as downstream detectors, providing information on number density and elemental composition, respectively, of aerosolized AuNPs versus the upstream size selected by ES-DMA. A gas-exchange device was designed and optimized to improve the conversion of air flow (from the electrospray) to argon flow required to sustain the ICP-MS plasma, the key compatibility issue for instrumental hyphenation. Our work provides the proof of concept and a working prototype for utilizing this construct to successfully measure (1) number- and mass-based distributions; (2) elemental compositions of nanoparticles classified by size, where the size classification and elemental analysis are performed within a single experiment; (3) particle concentrations in both solution (before size discrimination) and aerosol (after size discrimination) phases; and (4) the number of atoms per nanoparticle or the nanoparticle density.

Plk1 is upregulated in androgen-insensitive prostate cancer cells and its inhibition leads to necroptosis.

Castration-resistant prostate cancer (PCa) is refractory to hormone therapy and new strategies for treatment are urgently needed. We found that androgen-insensitive (AI) PCa cells, LNCaP-AI, are reprogrammed to upregulate the mitotic kinase Plk1 (Polo-like kinase 1) and other M-phase cell-cycle proteins, which may underlie AI PCa growth. In androgen-depleted media, LNCaP-AI cells showed exquisite sensitivity to growth inhibition by subnanomolar concentrations of a small molecule inhibitor of Plk1, BI2536, suggesting that these cells are dependent on Plk1 for growth. In contrast, the androgen-responsive parental LNCaP cells showed negligible responses to BI2536 treatment under the same condition. BI2536 treatment of LNCaP-AI cells resulted in an increase in cell death marker PARP-1 (polymerase-1) but did not activate caspase-3, an apoptosis marker, suggesting that the observed cell death was caspase-independent. BI2536-treated LNCaP-AI cells formed multinucleated giant cells that contain clusters of nuclear vesicles indicative of mitotic catastrophe. Live-cell time-lapse imaging revealed that BI2536-treated giant LNCaP-AI cells underwent necroptosis, as evidenced by 'explosive' cell death and partial reversal of cell death by a necroptosis inhibitor. Our studies suggest that LNCaP-AI cells underwent reprogramming in both their cell growth and cell death pathways, rendering them highly sensitive to Plk1 inhibition that induces necroptosis. Harnessing necroptosis through Plk1 inhibition may be explored for therapeutic intervention of castration-resistant PCa.

Certification of elements in and use of standard reference material 3280 multivitamin/multielement tablets.

Standard Reference Material 3280 Multivitamin/ Multielement Tablets was issued by the National Institute of Standards and Technology in 2009, and has certified and reference mass fraction values for 13 vitamins, 26 elements, and two carotenoids. Elements were measured using two or more analytical methods at NIST with additional data contributed by collaborating laboratories. This reference material is expected to serve a dual purpose: to provide quality assurance in support of a database of dietary supplement products and to provide a means for analysts, dietary supplement manufacturers, and researchers to assess the appropriateness and validity of their analytical methods and the accuracy of their results.

Characterization of perchlorate in a new frozen human urine standard reference material.

Perchlorate, an inorganic anion, has recently been recognized as an environmental contaminant by the US Environmental Protection Agency. Urine is the preferred matrix for assessment of human exposure to perchlorate. Although the measurement technique for perchlorate in urine was developed in 2005, the calibration and quality assurance aspects of the metrology infrastructure for perchlorate are still lacking in that there is no certified reference material (CRM) traceable to the International System of Units. To meet the quality assurance needs in biomonitoring measurements of perchlorate and the related anions that affect thyroid health, the National Institute of Standards and Technology (NIST), in collaboration with the Centers for Disease Control and Prevention (CDC), developed Standard Reference Material (SRM) 3668 Mercury, Perchlorate, and Iodide in Frozen Human Urine. SRM 3668 consists of perchlorate, nitrate, thiocyanate, iodine, and mercury in urine at two levels that represent the 50th and 95th percentiles, respectively, of the concentrations (with some adjustments) in the US population. It is the first CRM being certified for perchlorate. Measurements leading to the certification of perchlorate were made collaboratively at NIST and CDC using three methods based on liquid or ion chromatography tandem mass spectrometry. Potential sources of bias were analyzed, and results were compared for the three methods. Perchlorate in SRM 3668 Level I urine was certified to be 2.70 ± 0.21 µg L(-1), and for SRM 3668 Level II urine, the certified value is 13.47 ± 0.96 µg L(-1).

Quantification of ligand packing density on gold nanoparticles using ICP-OES.

In this study, a prototypical thiolated organic ligand, 3-mercaptopropionic acid (MPA), was conjugated on gold nanoparticles (AuNPs), and packing density was measured on an ensemble-averaged basis using inductively coupled plasma optical emission spectrometry. The effects of sample preparation, including centrifugation and digestion, as well as AuNP size and concentration, on recovery were investigated. For AuNPs with diameters of 5, 10, 30, 60, and 100 nm, calculated packing density is independent of size, averaging 7.8 nm(-2) and ranging from 6.7 to 9.0 nm(-2), and is comparable to reported values for MPA and similar short-chain ligands on AuNPs. These preliminary data provide fundamental information on the advantages and limitations of ICP-based analyses of conjugated AuNP systems. Moreover, they provide necessary information for the development of more broadly applicable methods for quantifying nanoparticle-ligand conjugates of critical importance to nanomedicine applications.

Preliminary evaluation of a microwave-assisted metal-labeling strategy for quantification of peptides via RPLC-ICP-MS and the method of standard additions.

NIST has performed preliminary research on applying a calibration methodology based on the method of standard additions to the quantification of peptides via reverse-phase liquid chromatography coupled to inductively coupled plasma mass spectrometry (RPLC-ICP-MS). A microwave-assisted lanthanide labeling procedure was developed and applied to derivatize peptides using the macrocyclic bifunctional chemical chelator DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid), which significantly improved the lanthanide labeling yield and reduced reaction times compared to benchtop labeling procedures. Biomolecular MS technologies of matrix-assisted laser desorption ionization (MALDI)-MS and electrospray ionization (ESI)-MS/MS were used in concert with ICP-MS to confirm the results of microwave labeling, sample cleanup and standard additions experiments for several test peptides. The calibration scheme is outlined in detail and contextualized against complementary high accuracy calibration strategies currently employed for ICP-MS detection of biomolecules. Standard additions experiments using native, non-isotopic peptide calibrants confirm the simplicity of the scheme and the potential of applying a blending (recombined sample and spike) procedure, facilitating calibration via co-elution of lanthanide labeled peptides. Ways to improve and fully leverage the analytical methodology are highlighted.