Mark A. Chappell

This study investigates the geochemical characteristics of rare earth elements (REEs) in highland karstic bauxite deposits located in the Sierra de Bahoruco, Pedernales Province, Dominican Republic. These deposits, formed through intense weathering of volcanic material, represent a potentially valuable REE resource for the nation. Surface and subsurface soil samples were analyzed using portable X-ray fluorescence (pXRF) and a NixPro 2 color sensor validated with inductively coupled plasma optical emission spectrometry (ICP-OES). We employed compositional data analysis (CoDA) and machine learning models to estimate total REE concentrations, demonstrating that pXRF and the color sensor, when properly calibrated, are effective tools for remote geochemical exploration. The results reveal that REE concentrations increase with depth and elevation, with light REEs (LREEs) dominating the profiles. The correlation of REE concentrations with morphological soil development suggests that higher-altitude areas are enriched in REEs due to progressive weathering processes. The study also shows a strong relationship between REE concentrations and environmental factors such as latitude and elevation. While pXRF provided reliable estimates of total REE concentrations, to our surprise, the NixPro2 color sensor proved similarly accurate. The research emphasizes the practical value of the x-ray and color sensors for remote exploration, provided that a well-explored, robust calibration is performed to account for site-specific variability. These findings contribute to understanding the geochemical distribution of REEs in karstic bauxite deposits and highlight the potential for further exploration in remote, high-altitude regions. Future research should explore using these and other portable sensors, singly or combined, to predict REE speciation, for expediting information related to the environmentally sustainable extractability and potential economic feasibility of resources in expeditionary locations.

Many diagnostic assays require temperature-controlled sample storage and shipment to ensure accuracy. Here we present, the Labcorp TrueTherm, designed for thermal-controlled shipment of small volume blood samples. The reusable TrueTherm combines a stainless steel vacuum bottle with a custom internal cold pack and insulating stopper. Users refrigerate the cold pack to protect against warm or cold temperature excursions. The whole system is relatively compact, measuring about 10in (25cm) in length, 3 inches (8cm) in diameter, and 2.5 pounds (1kg) in weight. In order to evaluate thermal performance, the TrueTherm system was exposed to both ISTA-7D summer and winter conditions and internal temperature was recorded for 96hrs. Subsequently, venous blood samples were collected from n = 40 subjects, and immediately aliquoted into BD SST (Serum separator) Microtainers®. For each subject, sub-samples were subjected to centrifugal separation (provided by the Labcorp TrueSpin^TM battery-powered centrifuge), serum removal, and 24hr insulated shipping on ice packs compared to a variety of 72hr cross-country shipping conditions with and without centrifugal separation and with and without insulated packaging (including TrueTherm) during August 2022. TrueTherm maintained temperature between 2 and 20C for 72hrs under simulated summer and winter conditions. Under actual cross-country summer commercial shipping conditions, both centrifugal separation and thermal control via TrueTherm expanded the number of valid analytes compared to unprotected whole blood (see Table 1). The results suggest that TrueTherm is an effective system for protecting small blood samples from thermal extremes during extended shipping. Portable thermal moderation was complimentary with portable centrifugal separation to maximize stability of common analytes. Analyte stability at day 3 following cross-country shipping. Bias in n = 40 aggregated results compared to baseline values was evaluated against CLIA limits. (+) indicates an acceptable bias, (-) indicates a non-acceptable bias, and (±) indicates a borderline acceptable bias.

Background: The increased demand for decentralized blood sample collection presents numerous operational challenges for diagnostics providers. Sample degradation including sample hemolysis due to time, temperature, and handling between collection and laboratory analysis leads to limited test menus and unreliable results. Here we evaluate the light-weight, portable Labcorp TrueSpin™ for rapid point-of-care blood separation using commercially available microvolume blood collection tubes. The TrueSpin is a class I FDA registered device designed for layperson use. The centrifuge runs on AA batteries and separates a blood sample in five minutes. Methods: Here we show results of studies evaluating sample quality and analyte stability in serum samples collected into gel microtubes and processed using the TrueSpin. Hemolysis and residual red blood cell (RBC) concentration are compared between samples separated using the TrueSpin and conventional centrifugation. Additionally, we evaluate serum-based chemistry analyte stability in both separated and unseparated samples stored for three days refrigerated and unrefrigerated. Results: No significant difference was seen in hemolysis or residual RBC concentration in serum samples prepared by TrueSpin compared to the reference centrifuge method. Furthermore, we show that many common serum-based chemistry analytes have limited (<1 day) stability if uncentrifuged, but improve to ≥3-day stability following TrueSpin separation and refrigerated or room temperature storage (see Table 1). Conclusions: These findings suggest that the TrueSpin is a simple and effective solution for remote sample separation and may enable broader test menus and increased test result reliability for decentralized sample collection pursuits.

Soil heterogeneity is a major contributor to the uncertainty in near-surface biogeochemical modeling. We sought to overcome this limitation by exploring the development of a new classification analogy concept for transcribing the largely qualitative criteria in the pedomorphologically based, soil taxonomic classification systems to quantitative physicochemical descriptions. We collected soil horizons classified under the Alfisols taxonomic Order in the U.S. National Resource Conservation Service (NRCS) soil classification system and quantified their properties via physical and chemical characterizations. Using multivariate statistical modeling modified for compositional data analysis (CoDA), we developed quantitative analogies by partitioning the characterization data up into three different compositions: Water-extracted (WE), Mehlich-III extracted (ME), and particle-size distribution (PSD) compositions. Afterwards, statistical tests were performed to determine the level of discrimination at different taxonomic and location-specific designations. The analogies showed different abilities to discriminate among the samples. Overall, analogies made up from the WE composition more accurately classified the samples than the other compositions, particularly at the Great Group and thermal regime designations. This work points to the potential to quantitatively discriminate taxonomically different soil types characterized by varying compositional datasets.

Environmental context: Nanometre-sized silver particles promote unique chemical reactions on their surface. This work examines the ability of silver nanoparticles to collect and store unpaired electrons, called radicals, on their surface. This capability by silver nanoparticles could potentially serve to drive degradation reactions in the environment. Radicals drive important chemical reactions in the environment. These unpaired electron species can be generated by energetic inputs, such as electromagnetic radiation, or from ultrasonication processes, whereby oxygen radicals are generated in aqueous solution through a cavitation mechanism. Previous evidence has demonstrated the potential for radicals to be stored on the surface of metallic gold nanoparticles, thus suggesting a potential transference of radical species from the nanoparticle surface for catalytic reactions, particularly during preparations of nanoparticle suspensions through ultrasonication. This work investigates the potential for the nanosilver (nAg) particles to similarly scavenge radicals from solution. nAg suspensions were reacted with 0.3-mM solutions containing the stable nitroxy radicals 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO), 4-oxo-2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPONE) and 4-amino-2,2,6,6-tetramethylpiperidino-1-oxyl (TEMPAMINE) analysed by quantitative electron spin resonance (ESR) spectroscopy. In ambient air, the addition of a nAg suspension to the 0.3-mM solutions reduced the integrated ESR intensity of the stable radicals by 50–93 % depending on radical species and nAg concentration, which we attributed to the sorption of the radicals onto the nAg surface. In separate experiments, the ESR intensities were further decreased under an Ar atmosphere, suggesting potential competition from ambient OH• to the sorption of the stable radicals. To verify this, we observed substantial increases in the integrated ESR intensity when the systems previously equilibrated under Ar atmosphere were exposed to ambient air. These results demonstrated that nAg scavenged the stable radicals from solution and were exchangeable from the metallic conduction band with OH•. Our work represents the first evidence for this mechanism to be demonstrated for nAg.