Long-term Reproducibility Research Articles

Fast non-destructive measurement of intramuscular fat in Australian beef and lamb using nuclear magnetic resonance (NMR) technologies

Nuclear magnetic resonance (NMR) is an excellent technique for non-destructive analysis of meat because it has high accuracy, a linear response, and insignificant drift over time, which removes the need for recalibration. Furthermore, single-side NMR devices have open geometries that enable measurements of subsections of larger samples without taking sub-samples. Here we demonstrated long-term reproducibility in a benchtop device and the utility of a single-sided NMR device. We validated long-term reproducibility of NMR measurements of lamb intramuscular fat (IMF) in a commercial processor boning room years after the original model was created. It was hypothesised that the NMR IMF% model would retain precision and accuracy on independent validation. The root mean squared (RMS) error of prediction of lamb IMF was 0.79 %. The R2 between reference measurements, predicted IMF% was 0.74, the slope of the chemical IMF% vs NMR predictions was 0.989, and the bias was 0.53 % IMF. In the second example, we showed that IMF% measurements of high value beef striploins could be measured off a commercial processing belt and returned without damaging the product. It was hypothesised that a commercial prototype single-sided NMR system would predict IMF% in beef M. longissimus thoracis et lumborum. Here the RMS error of the correlation was 1.58 % IMF and R2 was 0.97. We believe the long-term stability, high accuracy, and nondestructive nature make unilateral NMR devices ideal for applications in the red meat industry where intramuscular fat contributes to product value.

Novel sensing signal mode constructed by dual responsive silence layer combined with catalytic hydrogen evolution

For electrochemical assays, to obtain sensing signals, the redox of the modified electrochemical signal substance to provide a detectable signal is commonly required. However, during the process of assembly and sensing, the loss of signal substance caused by multiple steps of modification, incubation, and washing would lead to non-negligible fluctuation of signal and lack of reproducibility. To overcome this issue, a novel sensing signal mode without electrochemical signal substance was developed. By introducing electrochemical catalytic hydrogen evolution into the sensing scheme, and taking the overpotential as the detectable signal, the sensing system was constructed in the absence of electrochemical signal substance. As a proof of concept, the sensor was used to quantify squamous cell carcinoma antigen, a model analyte, and exhibited an excellent analytical performance with a wide linear range from 0.100 ng mL−1 to 100 ng mL−1 and a low detection limit of 52.4 fg mL−1. As envisioned, the sensor exhibited excellent long-term stability and reproducibility due to the avoidance of signal substance. This method provided a new way for the design of electrochemical sensors.

Long-term Reproducibility Improvement of LIBS Quantitative Analysis Based on Multi-period Data Fusion Calibration Method

Long-term Reproducibility Improvement of LIBS Quantitative Analysis Based on Multi-period Data Fusion Calibration Method

Tailoring glassy carbon electrode surface with FeBiO3 for electrochemical detection of dinitrophenol isomers

ABSTRACT This study presents a simultaneous, rapid, and highly sensitive electrochemical detection of 2,4- and 2,5-dinitrophenol isomers using an iron bismuth oxide (FeBiO3)-modified glassy carbon electrode (GCE). The FeBiO3-modified GCE exhibited superior electrochemical performance over bare GCE, Bi2O3-modified GCE, and Fe2O3-modified GCE, as demonstrated by electrochemical impedance spectroscopy (EIS) with the potassium ferricyanide (Fe(CN6)3-/4-) standard. The synthesised electrocatalyst FeBiO3 exhibited strong absorption both in the visible and UV regions of the spectrum, attributed to band gap transitions and charge transfer transitions linked to its Bi2O3 and Fe2O3 components. The morphology and the structure of the FeBiO3 were characterised using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD), while Fourier transform infrared spectroscopy (FTIR) was employed to analyse the functional groups attached to the surface of FeBiO3. Cyclic voltammetry (CV) clearly demonstrated an increased current and improved peak resolution for the reduction of 2,4- and 2,5-dinitrophenols at the FeBiO3/GCE, compared to the bare GCE. The mechanism shows that the reduction of 2,4- and 2,5-dinitrophenols occurs through interactions with the surface oxygen functional groups of FeBiO3, resulting in the stepwise reduction of their NO2 groups to hydroxyamino compounds and then to nitrosophenols. Using square wave voltammetry (SWV), the reduction peak currents were significantly improved, enhancing detection sensitivity beyond that reported in previous works. A linear range from 1 µM to 1 mm for the dinitrophenol isomers was established, with detection limits of 0.07 µM for 2,4-dinitrophenol and 0.09 µM for 2,5-dinitrophenol. The FeBiO3/GCE electrode showed interferences with mono-nitrophenols and mono-/di-chlorophenols in solution but maintained excellent long-term stability and reproducibility, allowing it to effectively detect dinitrophenol isomers in drinking water, tap water, and wastewater samples.

Long-Term Reproducibility of BMD-Measurements with Clinical QCT Using Simultaneous and Asynchronous Calibration Methods and Different Measurement and Reconstruction Protocols.

Osteoporosis is underdiagnosed and undertreated. To improve timely fracture risk assessment optimized densitometry methods are required such as opportunistic spinal quantitative computed tomography (QCT). However, it is unclear how to best calibrate these scans and correct for potential scanner drift of QCT when used for monitoring bone mineral density (BMD) changes. We compared gold standard simultaneous calibration with asynchronous calibration methods, assessing mid-term (12weeks) and long-term (1.5years) reproducibility of BMD measurements. Cortical and trabecular compartments of the European Spine Phantom were studied with ten different protocols including low dose and high resolution (HR)-modes. Based on weekly phantom data, we compared simultaneous calibration to asynchronous single (termed global) or monthly calibration. The accuracy was better for trabecular measurements than for cortical measurements for all calibration methods. Reproducibility was excellent for all methods and slightly better for asynchronous than for simultaneous calibration both for trabecular and cortical bone. For HR protocols, reproducibility was better than for low dose measurements. In trabecular compartments averaged HR-BMD remained stable for global (- 0.1%/year, ns) but not for simultaneous calibration (- 1.5%/year, p < 0.001). No significant drifts could be detected for averaged low dose BMD (- 0.9 to + 0.8%/year) for either calibration method. Our data suggest that with regard to precision and accuracy measurements with asynchronous calibration are suitable for vertebral BMD assessment (no contrast agents) in clinical practice. Regular (e.g., monthly) stability tests using a calibration phantom could assure long term stability of at least 1year.

LSPR Sensitivity of Ag-X NRs Core-Shell (X=Au, Al, TiO2, ZnO, SiO2): A Boundary Element Method Simulation Study

Abstract Silver nanorods (Ag NRs) have garnered significant attention in sensor applications due to their exceptional sensitivity to localized surface plasmon resonance (LSPR), facilitating the detection of minute changes in the surrounding environment. However, the inherent instability of silver in various environmental conditions poses a considerable challenge to the long-term reliability and reproducibility of Ag NR-based sensors. Core-shell structure Ag NRs by coating with Au, Al, TiO2, ZnO, and SiO2 layers reduce instability. These coatings act as protective barriers, shielding the underlying Ag NRs from environmental factors while preserving their LSPR properties. In this study, we employ the Boundary Element Method (BEM) simulation to investigate the sensitivity of coating Ag NRs with different materials (Au, Al, TiO2, ZnO, and SiO2) in enhancing both their stability and sensitivity for LSPR-based sensing applications.

γ- WO3 decorated MXene: An advanced nanomaterial for room temperature operable enhanced ammonia sensor

The proliferation of Internet of Things (IoT) applications necessitates the deployment of high-performance ammonia (NH3) sensors. In recent studies, Ti3C2Tx, a novel two-dimensional (2D) material, has been extensively investigated for its potential as a room temperature NH3 sensor. However, pristine MXene-based sensors have exhibited deficiencies in long-term stability and reproducibility. In response, an MXene/γ-WO3 composite has been synthesized using an ultra-sonication method to address these challenges. The resulting composite sensor has demonstrated remarkable performance, attributable to, increased active sites from defects induced by WO3, and the presence of a p-n heterojunction. Notably, electron transfer from WO3 to Ti3C2Tx has been identified as a critical contributing factor to the enhanced characteristics of these nanohybrids, as evidenced by observed alterations in binding energies for the Ti 2p and W 4f core levels. These findings have expanded our understanding of the electrical interactions in Ti3C2/WO3 and their potential applications in diverse domains. The pristine MXene sensor exhibited a response of 59.39% at 300 ppm at room temperature, while the composite MXene/γ-WO3 displayed a response of 92.3%. Additionally, the response recovery time was recorded at 22seconds and 9seconds, respectively. The chemiresistive ammonia sensor's performance was evaluated across a range of concentrations (25–300 ppm) and relative humidity levels (11–94% RH). The composite sensor has demonstrated reproducibility and long-term stability, coupled with high sensitivity to NH3. This manuscript aims to highlight the enhanced ammonia sensing properties and selectivity of MXene/γ-WO3 composite materials.

Biosensor Based on ZIF-67-HRP and MWCNTs Nanocomposite Modified Glass Carbon Electrode for the Detection of Luteolin in Vegetables.

Luteolin has various pharmacological properties, including anti-inflammatory, antioxidant, and antitumor characteristics. Due to its potential value in drugs and functional foods, it is important to develop an efficient method for detecting luteolin. In this work, the poor selectivity of existing luteolin nonenzymatic sensors was solved by translating the enzyme-catalyzed reaction from bulk solution to the surface of a horseradish peroxidase (HRP) modified electrode through an electrocatalytic oxidation process. Here, we modified the surface of a glassy carbon electrode (GCE) with metal-organic frameworks (MOFs; ZIF-67 here, abbreviated as ZIF), functional nanomaterials, and HRP and finally covered it with Nafion (NF). In this case, luteolin acts as a hydrogen donor, and the electrode acts as a hydrogen acceptor; the oxidation reaction occurs on the electrode surface. The use of ZIF-67 ensured the conformational stability of HRP to ensure the selectivity and anti-interference property, and SDS-dispersed multiwalled carbon nanotubes (MWCNTs) enhanced the electrode conductivity. The use of NF avoids shedding of the electrode material during the testing process. A UV-vis spectrophotometer was used to study the selectivity of luteolin by HRP and the compatibility between HRP and ZIF. The materials were characterized and analyzed by scanning electron microscopy and transmission electron microscopy. Due to the synergistic effect of these nanomaterials, the linear range of NF/ZIF-HRP/MWCNTs-SDS/GCE was 1.0 × 10-2 to 6.0 μM, with detection limits of 25.3 nM (S/N = 3). The biosensor showed long-term stability and reproducibility, with a relative standard deviation of 4.2% for the peak current (n = 5). Finally, the biosensor was successfully used to detect luteolin in carrots, celery, and cauliflower.

Electrochemical sensor based on mesoporous g-C3N4/N-CNO/gold nanoparticles for measuring oxycodone

Oxycodone, often used as an analgesic, is a potent opioid. While its effectiveness has been proven in the control of moderate to acute pain, excessive use of oxycodone imposes heart failure, heart palpitations, reduction of red blood cells, bone pain, and even death. Therefore, monitoring the oxycodone concentration in blood is vital for emergency care. For this purpose, a novel electrochemical sensor was designed based on a glassy carbon electrode modified with mesoporous g-C3N4 (M-C3N4), carbon nano-onions doped with nitrogen (N-CNO), and gold nanoparticles. At first, the SEM and XRD techniques were employed to characterize prepared M-C3N4 and N-CNO samples. The electro-oxidation behavior of the oxycodone was evaluated by cyclic and differential pulse voltammetric methods. Based on the influence of the potential scanning rate and solution pH on the voltammetric response of oxycodone oxidation, a redox mechanism was proposed. A 16 nM detection limit was acquired for the oxycodone analysis with a linear response in the 0.05–150 µM range. This sensor showed a remarkable ability for oxycodone detection in plasma samples. The long-term stability, superior selectivity, and reproducibility of this sensor prove its ability to measure oxycodone accurately and precisely in authentic spices.

Evaluating the long-term stability of a predefined palatal region for tooth movement analysis

ObjectivesWe conducted a three-dimensional (3D) analysis of orthodontic tooth movement (TM) using digital dental models (DMs), focusing on the palatal region of interest (PROI), aiming to evaluate the long-term stability of the PROI, validate the 3D TM analysis with PROI registration, and compare it with conventional lateral cephalometric analyses. MethodsTwenty adult patients treated with a multibracket appliance were evaluated at their first visit (T0) and at least 5 years later (T1) using DMs and lateral cephalograms (LCs). The long-term stability of PROI was assessed by calculating the point cloud distances between DM-T0 and DM-T1. TM analysis using DM with PROI registration for the maxillary central incisors was assessed through linear and angular measurements in the sagittal view and subsequently compared with the LCs. ResultsThe average point cloud distance of the PROI between DM-T0 and DM-T1 was 0.21 mm (standard deviation, 0.13 mm). TM analysis using DMs demonstrated excellent reproducibility for both linear and angular measurements (intra-rater correlation coefficient, > 0.99). The 95 % limits of agreement between the DM and LC measurements were < 5.14° for angular change, 3.53 mm for horizontal displacement, and 0.98 mm for vertical displacement. No significant differences were observed in the angular and linear measurements when the TM was compared using the DMs and LCs. ConclusionsThe PROI remained stable for over 5 years, supporting the reproducibility and accuracy of TM assessment using PROI registration in orthodontic clinical practice. Clinical significanceDM analysis lacks the risks associated with X-ray exposure and can be easily performed in daily clinical practice, indicating its potential for future clinical applications. These findings further support the use of DM with PROI registration for TM analysis in orthodontic clinical practice, emphasizing its long-term stability and reproducibility.

Electrochemical sensing platform using reduced graphene oxide and Sn MOF-derived hollow cubic composites for sensitive detection of catechol in environmental water samples

Catechol, a polyphenolic molecule and significant organic chemical intermediate, is a highly dangerous environmental contaminant due to its unpredictable nature and potential harm to both humans and the environment. This study presents the development of Sn MOF@rGO-650, identified as a hollow cube by SEM and TEM, created by carbonizing rGO on the surface of Sn MOF after in situ encapsulation. The Sn MOF@rGO-650 modified glassy carbon electrode was successfully constructed for the electrochemical detection of catechol. Under optimal conditions, the sensor exhibited a detection limit of 33 nM, a linear range of 0.20 μM–28 μM, and good long-term stability and reproducibility. This work proves for the first time that Sn MOF@rGO-650 composites can effectively detect catechol in real environmental water samples, achieving recoveries between 95.7 % and 104.8 %, and is validated in UV spectroscopy, which highlights its potential for practical applications.

Prospective longitudinal cohort study of quantitative muscle magnetic resonance imaging in a healthy control population.

Quantitative muscle magnetic resonance imaging (qMRI) is a valuable methodology for assessing muscular injuries and neuromuscular disorders. Notably, muscle diffusion tensor imaging (DTI) gives insights into muscle microstructural and macrostructural characteristics. However, the long-term reproducibility and robustness of these measurements remain relatively unexplored. The purpose of this prospective longitudinal cohort study was to assess the long-term robustness and range of variation of qMRI parameters, especially DTI metrics, in the lower extremity muscles of healthy controls under real-life conditions. Twelve volunteers (seven females, age 44.1 ± 12.1 years, body mass index 23.3 ± 2.0 kg/m2) underwent five leg muscle MRI sessions every 20 ± 4 weeks over a total period of 1.5 years. A multiecho gradient-echo Dixon-based sequence, a multiecho spin-echo T2-mapping sequence, and a spin-echo echo planar imaging diffusion-weighted sequence were acquired bilaterally with a Philips 3-T Achieva MR System using a 16-channel torso coil. Fifteen leg muscles were segmented in both lower extremities. qMRI parameters, including fat fraction (FF), water T2 relaxation time, and the diffusion metrics fractional anisotropy (FA) and mean diffusivity (MD), were evaluated. Coefficients of variance (wsCV) and intraclass correlation coefficients (ICCs) were calculated to assess the reproducibility of qMRI parameters. The standard error of measurement (SEM) and the minimal detectable change (MDC) were calculated to determine the range of variation. All tests were applied to all muscles and, subsequently, to each muscle separately. wsCV showed good reproducibility (≤ 10%) for all qMRI parameters in all muscles. The ICCs revealed excellent agreement between time points (FF = 0.980, water T2 = 0.941, FA = 0.952, MD = 0.948). Random measurement errors assessed by SEM and the MDC were low (< 12%). In conclusion, in this study, we showed that qMRI parameters in healthy volunteers living normal lives are stable over 18 months, thereby defining a benchmark for the expected range of variation over time.

Short- and long-term reproducibility of body surface gastric mapping using the Gastric Alimetry® system.

Many diagnostic tests for gastroduodenal symptoms, such as gastric emptying scintigraphy (GES), gastric emptying breath tests (GEBT), and electrogastrography (EGG) show variable intra-individual reproducibility over time. This study investigated the short- and long-term reproducibility of body surface gastric mapping (BSGM), a non-invasive test for assessing gastric function, in controls and patients with chronic gastroduodenal disorders. Participants completed three standardized BSGM tests using Gastric Alimetry® (Alimetry, New Zealand). The test encompassed a fasting baseline (30 min), a 482 kCal standard meal, and a 4 h postprandial recording. The first two tests were >6 months apart and the last occurred ~1 week after the second test, to evaluate long and short-term reproducibility. Fourteen patients with upper gastrointestinal symptoms and 14 healthy controls were recruited. There were no significant differences in any BSGM metrics between the tests at short and long term (all p > 0.180). Lin's concordance correlation coefficients (CCC) for the primary metrics were high, ranging from 0.58 to 0.96, with intra-individual coefficients of variance (CVintra) ranging from 0.2% to 1.9%. Reproducibility was higher, and intra-individual variation lower, than in previous studies of GES (CCC = 0.54-0.83, CVintra = 3%-77%), GEBT (CVintra = 8%-11%), and EGG (CVintra = 3%-78%). BSGM spectral metrics demonstrate high reproducibility and low intra-individual variation at both short and long term, with superior results to comparable tests. The high reproducibility of Gastric Alimetry supports its role as a diagnostic aid for gastric dysfunction and a reliable tool for evaluating treatment outcomes and disease progression over time.

Controllable synthesis of heterostructured CuO–ZnO microspheres for NO2 gas sensors

Nitrogen dioxide (NO2) sensors experience the drawback of requiring high operating temperatures because of the low charge transfer ability of gas-sensing materials. Herein, an advanced NO2 sensor resistant to interference is designed using the interfacial energy barriers of a hierarchical CuO/ZnO composite. With the benefits of abundant desirable defect features, and the amplification effect of heterojunctions, the sensor based on CuO/ZnO composite with 10% Cu(CH3COO)2·H2O (S2) shows outstanding performance in terms of faster response and recovery time (1.8-fold/1.1-fold), higher response (3.1-fold), and lower power consumption (140℃ decrease) compared to the pristine ZnO sensor. Furthermore, the composite sensor exhibits long-term stability and reproducibility, indicating the potential promise of CuO/ZnO heterojunctions in interference-resistant detection of low-concentration NO2 in real applications. This study not only provides a rational solution to designing advanced gas sensors by tuning the interfacial energy barriers of heterojunctions, but also provides a fundamental understanding of CuO structures in the gas-sensing field.

Assessing the Stability of Photon-Counting CT: Insights from a Two-Year Longitudinal Study.

Among the advancements in computed tomography (CT) technology, photon-counting computed tomography (PCCT) stands out as a significant innovation, providing superior spectral imaging capabilities while simultaneously reducing radiation exposure. Its long-term stability is important for clinical care, especially longitudinal studies, but is currently unknown. This study sets out to comprehensively analyze the long-term stability of a first-generation clinical PCCT scanner. Over a two-year period, from November 2021 to November 2023, we conducted weekly identical experiments utilizing the same multi-energy CT protocol. These experiments included various tissue-mimicking inserts to rigorously assess the stability of Hounsfield Units (HU) and image noise in Virtual Monochromatic Images (VMIs) and iodine density maps. Throughout this period, notable software and hardware modifications were meticulously recorded. Each week, VMIs and iodine density maps were reconstructed and analyzed to evaluate quantitative stability over time. Spectral results consistently demonstrated the quantitative stability of PCCT. VMIs exhibited stable HU values, such as variation in relative error for VMI 70 keV measuring 0.11% and 0.30% for single-source and dual-source modes, respectively. Similarly, noise levels remained stable with slight fluctuations linked to software changes for VMI 40 and 70 keV that corresponded to changes of 8 and 1 HU, respectively. Furthermore, iodine density quantification maintained stability and showed significant improvement with software and hardware changes, especially in dual-source mode with nominal errors decreasing from 1.44 to 0.03 mg/mL. This study provides the first long-term reproducibility assessment of quantitative PCCT imaging, highlighting its potential for the clinical arena. This study indicates its long-term utility in diagnostic radiology, especially for longitudinal studies.

Optimizing Zr-doped MC-ICP-MS sample-standard bracketing to simultaneously determine 87Sr/86Sr and δ88Sr for high sample-throughput

In recent years, the increasing demand for extensive strontium (Sr) datasets across various scientific fields has prompted the development of fast, precise, and reliable protocols. These protocols aim to achieve high sample-throughput without compromising data quality. A novel method termed the zirconium (Zr) doped sample-standard bracketing (SSB) has been recently introduced for isotope measurements using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS). This method allows for simultaneous acquisition of 87Sr/86Sr and δ88Sr data without the need for sample spiking. However, the reliability of this method in handling large datasets and ensuring long-term reproducibility requires additional documentation. A comprehensive examination of the reliability of Sr isotope data over two years involves the implementation of systematic tests on reference materials from the National Institute of standards and technology (NIST) with the standard reference material (SRM) numbers: 1400, 1515, 987, 2910b, 1486, as well as a Hawaiian volcano observatory basalt (BHVO-1). The results of this study lead to the definition of a set of quality control parameters. The developed protocol applies various controls to ensure precise matching of Sr and Zr concentrations for both the samples and the bracketing standard (NIST SRM 987), along with the identification of instrumental biases. The outlined quality control ensures the reproducibility of the results (87Sr/86Sr = 0.710247 ± 0.000026, 2SD, n = 557; and δ88Sr = 0.001 ± 0.053 ‰, 2SD, n = 537 for NIST SRM 987), proving invaluable for archaeological, geological, and ecological studies requiring the fast acquisition of extensive datasets (n > 100) to create isotopic baselines.

Catechin detection in tea samples based on catechin-induced conformational changes in papain

Catechin, the major ingredient in tea that affects its taste, varies based on the tea variety, climate, and extraction techniques. Although several techniques have been developed to determine catechin levels, an easy-to-use method is still lacking. Herein, the catechin levels were determined using papain for the first time. After incubating papain with catechin, the precipitate was discarded, and the remaining catechin-enzyme complex in the supernatant was determined by UV–visible absorption spectroscopy. Upon catechin binding papain’s main absorption band (at 280 nm) was altered, reflecting conformation changes in their aromatic amino acids. It was supported by the kinetic measurements determined with N-α-benzoyl-arginine-p-nitroanilide (BAPNA) as a substrate. Complex formation between catechin and papain markedly affects the enzyme activity, resulting in the diminishes of the yellow-colored product observed at 410 nm in a concentration-dependent manner. Under the optimum conditions, the analytical curve was linear in the concentration range 0.10 – 0.80 mg/mL (r2 = 0.9893) with a detection limit of 0.44 mg/mL. This developed biosensor demonstrated long-term stability (90 days) and reproducibility with a relative standard deviation below 10%. This usefulness of papain’s conformation changes was further demonstrated in the analysis of tea infusion samples, and the recoveries are in the acceptable range (79.1–81.2%).

Extraction, purification, and clumped isotope analysis of methane (Δ13CDH3 and Δ12CD2H2) from sources and the atmosphere

Abstract. Measurements of the clumped isotope anomalies (Δ13CDH3 and Δ12CD2H2) of methane have shown potential for constraining methane sources and sinks. At Utrecht University, we use the Thermo Scientific Ultra high-resolution isotope-ratio mass spectrometer to measure the clumped isotopic composition of methane emitted from various sources and directly from the atmosphere. We have developed an extraction system with three sections for extracting and purifying methane from high (&gt; 1 %), medium (0.1 % to 1 %), and low-concentration (&lt; 0.1 %) samples, including atmospheric air (∼ 2 ppm = 0.0002 %). Depending on the methane concentration, a quantity of sample gas is processed that delivers 3 ± 1 mL of pure methane, which is the quantity typically needed for one clumped isotope measurement. For atmospheric air with a methane mole fraction of 2 ppm, we currently process up to 1100 L of air. The analysis is performed on pure methane, using a dual-inlet setup. The complete measurement time for all isotope signatures is about 20 h for one sample. The mean internal precision values of sample measurements are 0.3 ± 0.1 ‰ for Δ13CDH3 and 2.4 ± 0.8 ‰ for Δ12CD2H2. The long-term reproducibility, obtained from repeated measurements of a constant target gas, over almost 3 years, is around 0.15 ‰ for Δ13CDH3 and 1.2 ‰ for Δ12CD2H2. The measured clumping anomalies are calibrated via the Δ13CDH3 and Δ12CD2H2 values of the reference CH4 used for the dual-inlet measurements. These were determined through isotope equilibration experiments at temperatures between 50 and 450 °C. We describe in detail the optimized sampling, extraction, purification, and measurement technique followed in our laboratory to measure the clumping anomalies of methane precisely and accurately. This paper highlights the extraction and one of the first global measurements of the clumping anomalies of atmospheric methane.

Functionalizing Carbon Substrates with a Covalently Attached Cobalt Redox Buffer for Calibration-Free Solid-Contact Ion-Selective Electrodes.

With a view to potentiometric sensing with minimal calibration requirements and high long-term stability, colloid-imprinted mesoporous (CIM) carbon was functionalized by the covalent attachment of a cobalt redox buffer and used as a new solid contact for ion-selective electrodes (ISEs). The CIM carbon surface was first modified by electroless grafting of a terpyridine ligand (Tpy-ph) using diazonium chemistry, followed by stepwise binding of Co(II) and an additional Tpy ligand to the grafted ligand, forming a bis(terpyridine) Co(II) complex, CIM-ph-Tpy-Co(II)-Tpy. Half a molar equivalent of ferrocenium tetrakis(3-chlorophenyl)borate was then used to partially oxidize the Co(II) complex. Electrodes prepared with this surface-attached CIM-ph-Tpy-Co(III/II)-Tpy redox buffer as a solid contact were tested as K+ sensors in combination with valinomycin as the ionophore and Dow 3140 silicone or plasticized poly(vinyl chloride) (PVC) as the matrixes for the ion-selective membrane (ISM). This solid contact is characterized by a redox capacitance of 3.26 F/g, ensuring a well-defined interfacial potential that underpins the transduction mechanism. By use of a redox couple as an internal reference element to control the phase boundary potential at the interface of the ISM and the CIM carbon solid contact, solid-contact ion-selective electrodes (SC-ISEs) with a standard deviation of E° as low as 0.3 mV for plasticized PVC ISMs and 3.5 mV for Dow 3140 silicone ISMs were obtained. Over 100 h, these SC-ISEs exhibit an emf drift of 20 μV/h for plasticized PVC ISMs and 62 μV/h for silicone ISMs. The differences in long-term stability and reproducibility between electrodes with ISMs comprising either a plasticized PVC or silicone matrix offer valuable insights into the effect of the polymeric matrix on sensor performance.

Determination of Trace Cd(II) in Water and Cosmetics based on Au/GO/CuO Nanocomposite Functionalized Electrochemical Sensor

Cadmium (Cd(II)) is highly toxic to environmental, and while many approaches have been developed to measure cumulative Cd(II) concentration over time, online monitoring of spatiotemporal changes remains challenging. To address this, an electrochemical sensor for determination of ultra-trace Cd(II) was developed, based on gold/graphene oxide/copper oxide (Au/GO/CuO) nanomaterials modifying glassy carbon electrode. CuO nanoparticles were prepared by a green synthesis method using plant extract, and the Au nanoparticles were deposited on the GO/CuO nanosubstrates by an in situ electrochemical method. The prepared nanocomposites were characterized by field-emission scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The CuO nanoparticles are layered flower-like with an average particle size of 200–500 nm. Au/GO/CuO nanocomposites with high specific surface area and excellent electronic transmission capability enhanced the electrochemical signal of the sensor. Owing to the synergistic effect of Au/GO/CuO, the sensor exhibited good performance to Cd(II) in the ultra-wide range of 5 × 10−11–5 × 10−7 M with a detection limit of 2 × 10−11 M. The sensor was successfully quantified for determining Cd(II) with desirable recovery, displaying outstanding long-term stability, high sensitivity, and reproducibility. After validating its accuracy, this sensor was successfully used for detection of Cd(II) in water and cosmetic samples.