Quantification of persistent organic pollutants in dietary supplements using stir bar sorptive extraction coupled with GC-MS/MS and isotope dilution mass spectrometry

ABSTRACT

In this work, we describe a method developed to quantify persistent organic pollutants (POPs) including polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs) in dietary supplement samples using stir-bar sorptive extraction (SBSE)-GC-MS/MS-isotope dilution mass spectrometry (IDMS). This method enables accurate, precise, and sensitive quantification of POPs in plant-extract based dietary supplement products commercially available in the United States. When compared with calibration curves, IDMS provided more accurate and precise measurements. The mean error of measurements using this method was 7.24% with a mean RSD of 8.26%. The application of GC-MS/MS enabled approximately two-order-of-magnitude lower limit of quantifications compared with GC-MS. 12 commercially available plant-extract based dietary supplement samples were analysed using this method. PAHs including naphthalene, acenaphthene, fluorene, phenanthrene, fluoranthene, pyrene, chrysene, and benzo[a]pyrene were detected in most of the products and had average concentrations over 1 ng/g. OCPs were detected less frequently than PAHs in these products, and none of the OCPs had mean concentrations over 1 ng/g. The mean toxin concentration of each product was calculated, and the highest value was 3.20 ng/g. These results were compared with existing guidelines and none of the analytes in the samples were found to be above the daily allowable limits.     

Determination of 14 polycyclic aromatic hydrocarbons in mainstream smoke from domestic cigarettes

Polycyclic aromatic hydrocarbons (PAHs) are a class of environmental pollutants created primarily from incomplete combustion of various organic materials including tobacco. Cigarette smoke is a complex mixture of various classes of compounds, including numerous PAHs, in both the mainstream and the sidestream smoke fractions. We measured the levels of 14 PAHs in mainstream smoke from unfiltered custom cigarettes made from individual tobacco types and 30 brands of domestic blended cigarettes using standardized smoking conditions, extraction from the Cambridge filter pads, and gas chromatography/mass spectrometry. Differences in smoke PAHs from cigarettes with selected tobacco blends were identified and illustrate how blend composition contributes to the overall mainstream smoke PAH profile. The PAH levels varied among the different commercial cigarette brands, with the amount of total mainstream smoke PAHs ranging from 1 to 1.6 microg per cigarette. Under machine smoking conditions, the mainstream smoke from domestic cigarettes had individual PAHs ranging from benzo[k]fluoranthene at levels below 10 ng/cigarette to naphthalene at levels of around 500 ng/cigarette. Low delivery cigarettes smoked with blocked filter vent holes dramatically increased the mainstream smoke PAH deliveries with respect to their unblocked counterparts. Inhalation of PAHs and other harmful chemicals from cigarette smoke are unique as they represent a routine voluntary exposure to common environmental pollutants.     

Particle concentrations and effectiveness of free-standing air filters in bedrooms of children with asthma in Detroit,Michigan

Asthma can be exacerbated by environmental factors including airborne particulate matter (PM) and environmental tobacco smoke (ETS). We report on a study designed to characterize PM levels and the effectiveness of filters on pollutant exposures of children with asthma. 126 households with an asthmatic child in Detroit, Michigan, were recruited and randomized into control or treatment groups. Both groups received asthma education; the latter also received a free-standing high efficiency air filter placed in the child’s bedroom. Information regarding the home, emission sources, and occupant activities was obtained using surveys administered to the child’s caregiver and a household inspection. Over a one week period, we measured PM, carbon dioxide (CO₂), environmental tobacco smoke (ETS) tracers, and air exchange rates (AERs). Filters were installed at midweek. Before filter installation, PM concentrations averaged 28 μg m⁻³, number concentrations averaged 70,777 and 1471 L⁻¹ in 0.3–1.0 and 1–5 μm size ranges, respectively, and the median CO₂ concentration was 1018 ppm. ETS tracers were detected in 23 of 38 homes where smoking was unrestricted and occupants included smokers and, when detected, PM concentrations were elevated by an average of 15 μg m⁻³. Filter use reduced PM concentrations by an average of 69–80%. Simulation models representing location conditions show that filter air flow, room volume and AERs are the key parameters affecting PM removal, however, filters can achieve substantial removal in even "worst" case applications. While PM levels in homes with asthmatic children can be high, levels can be dramatically reduced using filters.     

Mechanisms of Central Hypogonadism

Reproductive function depends upon an operational hypothalamo–pituitary–gonadal (HPG) axis. Due to its role in determining survival versus reproductive strategies, the HPG axis is vulnerable to a diverse plethora of signals that ultimately manifest with Central Hypogonadism (CH) in all its many guises. Acquired CH can result from any pituitary or hypothalamic lesion, including its treatment (such as surgical resection and/or radiotherapy). The HPG axis is particularly sensitive to the suppressive effects of hyperprolactinaemia that can occur for many reasons, including prolactinomas, and as a side effect of certain drug therapies. Physiologically, prolactin (combined with the suppressive effects of autonomic neural signals from suckling) plays a key role in suppressing the gonadal axis and establishing temporary CH during lactation. Leptin is a further key endocrine regulator of the HPG axis. During starvation, hypoleptinaemia (from diminished fat stores) results in activation of hypothalamic agouti-related peptide neurons that have a dual purpose to enhance appetite (important for survival) and concomitantly suppresses GnRH neurons via effects on neural kisspeptin release. Obesity is associated with hyperleptinaemia and leptin resistance that may also suppress the HPG axis. The suppressibility of the HPG axis also leaves it vulnerable to the effects of external signals that include morphine, anabolic-androgenic steroids, physical trauma and stress, all of which are relatively common causes of CH. Finally, the HPG axis is susceptible to congenital malformations, with reports of mutations within >50 genes that manifest with congenital CH, including Kallmann Syndrome associated with hyposmia or anosmia (reduction or loss of the sense of smell due to the closely associated migration of GnRH with olfactory neurons during embryogenesis). Analogous to the HPG axis itself, patients with CH are often vulnerable, and their clinical management requires both sensitivity and empathy.     

Application of a novel automatic disintegration apparatus for the development and evaluation of a direct compression rapidly disintegrating tablet

An automatic disintegration tester was developed and used to explore disintegration mechanism and times of rapidly disintegrating tablets. DT50, the time required for a tablet to decrease in its thickness by half, allowed an unbiased determination of disintegration time. Calcium silicate concentration, Explotab? concentration, DiPac?/Xylitab? ratio as fillers, and compression pressure were evaluated using a central composite model design analysis for their DT50, tensile strength, and friability. Tablets that could reasonably be handled (friability <10%) could be produced. The expansion coefficient (n) and the exponential rate constant (k) for disintegrating tablets, originally measured by Caramella et al. using force kinetics, could be determined from axial displacement data measured directly without the need to assume that disintegration force generation was indicative of changes in tablet volume. The n values of tablets containing calcium silicate, Ditab? and/or Xylitab?, magnesium stearate, and Explotab? suggested that the amount of Explotab? was not a significant factor in determining the disintegration mechanism; however, the type of disintegrant used did alter the n value. Primojel? and Explotab?, which are in the same class of disintegrants, exhibited similar DT50, n, and k. Polyplasdone? XL exhibited a much higher n, while yielding faster DT50, suggesting that its performance is more dependent on facilitating the interfacial separation of particles. AcDiSol? showed no apparent moisture sensitivity in regards to disintegration efficiency. The use of the novel apparatus proved to be useful in measuring disintegration efficiency of rapidly disintegrating tablets and in providing valuable information on the disintegration phenomena.     

Characterization of Staphylococcus aureus isolates from retail chicken carcasses and pet workers in Northwest Arkansas

Staphylococcus aureus can be carried on the skin and nasal passages of humans and animals as a commensal. A case of human methicillin-resistant S. aureus infection resulting from contact with pork has been reported. Poultry carcasses are sold at retail with the skin intact, but pork and beef typically are not. Thus, the risk of methicillin-resistant S. aureus human infection from whole raw poultry carcasses may be greater than that of exposure from pork or beef. The objective of this study was to isolate and characterize S. aureus from whole retail poultry carcasses and compare the isolates to S. aureus isolates from humans. A total of 25 S. aureus isolates were collected from 222 whole poultry carcasses. The isolates were characterized phenotypically with antibiotic resistance disc diffusion assays and genotypically using multilocus sequence typing. A total of 17 S. aureus isolates obtained from healthy humans were included and characterized in the same way as the poultry isolates. Staphylococcus spp. were recovered from all poultry carcasses. Only 25 poultry carcasses (11.2%) were contaminated with S. aureus. Of these 25 isolates, 36% were resistant to at least one of the antibiotics tested and 20% were resistant to two or more antibiotics tested. However, 100% of the human isolates were resistant to at least one of the antibiotics and 94% were resistant to two or more antibiotics. The results of the multilocus sequence typing indicate that most of the isolates grouped according to source. These results indicate a low prevalence of S. aureus present in poultry, and the isolates were not phenotypically similar to human isolates. The low number of S. aureus isolates from this study indicates that chicken carcasses would appear to not be a significant source of this bacterium.     

Molecular Engineering of Cyclic Azobenzene-Peptide Hybrid Ligands for the Purification of Human Blood Factor VIII via Photo-Affinity Chromatography

The use of benign stimuli to control the binding and release of labile biologics for their isolation from complex feedstocks is a key goal of modern biopharmaceutical technology. This study introduces cyclic azobenzene-peptide (CAP) ligands for the rapid and discrete photo-responsive capture and release of blood coagulation factor VIII (FVIII). A predictive method—based on amino acid sequence and molecular architecture of CAPs—is developed to correlate the conformation of cis/trans-CAP photo-isomers to FVIII binding and release. Combined in silico - in vitro analysis of FVIII:peptide interactions guide the design of a rational approach to optimize isomerization kinetics and biorecognition of CAPs. A photoaffinity adsorbent, prepared by conjugating selected CAP G-cyclo_AZOB[Lys-YYKHLYN-Lys]-G on translucent chromatographic beads, features high binding capacity (>6 mg of FVIII per mL of resin) and rapid photo-isomerization kinetics (τ < 30 s) when exposed to 420–450 nm light at the intensity of 0.1 W cm⁻². The adsorbent purifies FVIII from a recombinant harvest using a single mobile phase, affording high product yield (>90%), purity (>95%), and blood clotting activity. The CAPs introduced in this report demonstrate a novel route integrating gentle operational conditions in a rapid and efficient bioprocess for the purification of life-saving biotherapeutics.     

Data-Driven Approach to Tailoring Mechanical Properties of a Soft Material

Data-driven, machine learning (ML)-assisted approaches have been used to study structure-property relationships at the atomic scale, which have greatly accelerated the screening process and new material discovery. However, such approaches are not easily applicable to modulating material properties of a soft material in a laboratory with specific ingredients. Moreover, it is desirable to relate material properties directly to the experimental recipes. Herein, a data-driven approach to tailoring mechanical properties of a soft material is demonstrated using ML-assisted predictions of mechanical properties based on experimental synthetic recipes. Polyurethane (PU) elastomer is used as a model soft material to demonstrate the approach and experimentally varied mechanical properties of the PU elastomer by modulating the mixing ratio between components of the elastomer. Twenty-five experimental conditions are selected based on the design of experiment and use those data points to train a linear regression model. The resulting model takes desired mechanical properties as input and returns synthetic recipes of a soft material, which is subsequently validated by experiments. Lastly, the prediction accuracies of different machine learning algorithms is compared. It is believed that the approach is widely applicable to other material systems to establish experimental conditions and material property relationships for soft materials.     

Enhancing Organic Semiconductor Molecular Packing Using Perovskite Interfaces to Improve Singlet Fission

Singlet fission, a process by which one singlet exciton is converted into two lower energy triplet excitons, is sensitive to the degree of electronic coupling within a molecular packing structure. Variations in molecular packing can be detrimental to triplet formation and triplet–triplet separation, ultimately affecting the harvesting of triplets for electricity in organic photovoltaic devices. Here, six phase-pure molecular packing structures of 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene) with varying optoelectronic properties are isolated using 2D lead halide perovskites as tunable, crystalline surfaces for crystallization. Transient absorption spectroscopy reveals that while triplet formation is fast (<100 fs) regardless of template structure, the increased ordering in perovskite-templated samples speeds up triplet–triplet separation and recombination, providing evidence that the benefits of phase-purity offset minor variations in molecular packing. Molecular dynamics modeling of the interface reveals that perovskite-templating allows for closer packing of TIPS-pentacene molecules for all perovskite templates. With an extensive number of organic molecule-perovskite pairings, this work provides a methodology to use ordered, periodic surfaces to elucidate structure–property relationships of small organic molecules in order to adjust structural or optoelectronic responses, such as molecular packing and singlet fission.