High Analytical Precision Research Articles

Abundant 2480 Ma Detrital Zircons in ∼1740 Ma Vishnu Schist in Northwestern Arizona: Derivation From the Matachewan Large Igneous Province?

Detrital zircon grains in the ∼1740–1750 Ma Vishnu Schist and similar rock units in northwestern Arizona consist of up to 30% grains dated by U-Pb isotopic analysis at 2470–2490 Ma. These zircon grains are distributed over ∼40,000 km2 and define an age peak at 2480.0 ± 27.3 Ma (2SE). These grains have yielded unusually consistent 207Pb/206Pb dates, with generally smaller analytical uncertainty and greater concordance to ideal U-Pb evolution than grains of other ages. A weighted mean age of 2480 ± 0.9 Ma (2SE) for this zircon population reflects consistent analytical results and high analytical precision but not the accuracy of the age. The source of these zircons has not been identified. To better characterize the unidentified source, we analyzed 45 of these grains for trace and rare-earth elements by laser-ablation mass spectrometry and scanned 16 grains with an electron microprobe to identify mineral inclusions. Mass spectrometer determinations of Sc/Yb and Nb/Sc support derivation from an oceanic-island igneous source. Electron microprobe scans revealed quartz in 5 of 16 grains, indicating a felsic source. The low variability in 207Pb/206Pb dates and a generally linear relationship between U and Th support zircon derivation from a single igneous unit or closely related set of units without xenocrystic zircons. A literature search for other zircon populations with similar age and U/Th ratios identified ∼2480 Ma zircons in a Mesoproterozoic(?) metapsammite and conglomerate in southwestern Montana. This sandstone was deposited near the margin of the Wyoming craton and contains almost entirely 2400–3600 Ma zircons, unlike zircon grains in Vishnu Schist which include a large population of 1730–1900 Ma zircons. From this relationship we infer that the 2480 Ma zircons in both areas were derived from a source in the Wyoming craton. We conclude that the 2480 Ma Vishnu zircons were derived from a felsic batholith that formed above and from hotspot magma related to the ∼2450–2480 Ma Matachewan Large Igneous Province, that this batholith formed by mixing between a mantle-derived hotspot magma and assimilated Archean continental crust, and that the source rock was emplaced during initial rifting between the Wyoming craton and the Superior province.

Understanding the variability of the electrophysiologic laryngeal adductor reflex

ObjectiveThe laryngeal adductor reflex (LAR) is vital for airway protection and can be electrophysiologically obtained under intravenous general anesthesia (IGA). This makes the electrophysiologic LAR (eLAR) an important tool for monitoring of the vagus nerves and relevant brainstem circuitry during high-risk surgeries. We investigated the intra-class variability of normal and expected abnormal eLAR. MethodsRepeated measures of contralateral R1 (cR1) were performed under IGA in 58 patients. Data on presence/absence of cR2 and potential confounders were also collected. Review of neuroimaging, pathology and clinical exam, allowed classification into normal and expected abnormal eLAR groups. Using univariate and multivariate analysis we studied the variability of cR1 parameters and their differences between the two groups. ResultsIn both groups, cR1 latencies had coefficients of variation of <2%. In the abnormal group, cR1 had longer latencies, required higher activation currents and was more frequently desynchronized and unsustained; cR2 was more frequently absent. ConclusionscR1 latencies show high analytical precision for measurements. Delayed onset, difficult to elicit, desynchronized and unsustained cR1, and absence of cR2 signal an abnormal eLAR. SignificanceUnderstanding the variability and behavior of normal and abnormal eLAR under IGA can aid in the interpretation of its changes during monitoring.

Testing the reproducibility of in situ Lu[sbnd]Hf dating using Lu-rich garnet from the Tørdal pegmatites, southern Norway

In situ LuHf geochronology offers the potential for direct dating of garnet within petrographic context. However, the method requires matrix-matched standards to calibrate measured Lu/Hf ratios. In order to assess the accuracy of this calibration, as well as the reproducibility of the resulting LuHf dates, two Lu-rich (up to 1 wt% Lu) garnet samples from the Tørdal pegmatite field in southern Norway were analysed over six analytical sessions. Multi-session isochron LuHf dates of 930.3 ± 1.4 Ma (MSWD = 1.0, 164 analyses) and 930.3 ± 1.7 Ma (MSWD = 1.5; 125 analyses) were obtained, conform with previously published age constraints. The relative standard deviation of 0.1% between the analytical sessions indicates that the dates are highly reproducible. For each individual analytical session, age uncertainties of 0.3–0.6% were achieved by measuring high Lu count rates in analog detection mode. We further describe a calibration strategy that deals with LuHf datasets where Lu is measured in both pulse and analog detector mode. Given the high analytical precision and reproducibility, we suggest that the Tørdal garnets are suitable reference materials for future LA-ICP-MS/MS LuHf studies.

Non-invasive diagnostic test for lung cancer using biospectroscopy and variable selection techniques in saliva samples.

Lung cancer is one of the most commonly occurring malignant tumours worldwide. Although some reference methods such as X-ray, computed tomography or bronchoscope are widely used for clinical diagnosis of lung cancer, there is still a need to develop new methods for early detection of lung cancer. Especially needed are approaches that might be non-invasive and fast with high analytical precision and statistically reliable. Herein, we developed a swab "dip" test in saliva whereby swabs were analysed using attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy harnessed to principal component analysis-quadratic discriminant analysis (QDA) and variable selection techniques employing successive projections algorithm (SPA) and genetic algorithm (GA) for feature selection/extraction combined with QDA. A total of 1944 saliva samples (56 designated as lung-cancer positive and 1888 designed as controls) were obtained in a lung cancer-screening programme being undertaken in North-West England. GA-QDA models achieved, for the test set, sensitivity and specificity values of 100.0% and 99.1%, respectively. Three wavenumbers (1422 cm-1, 1546 cm-1 and 1578 cm-1) were identified using the GA-QDA model to distinguish between lung cancer and controls, including ring C-C stretching, CN adenine, Amide II [δ(NH), ν(CN)] and νs(COO-) (polysaccharides, pectin). These findings highlight the potential of using biospectroscopy associated with multivariate classification algorithms to discriminate between benign saliva samples and those with underlying lung cancer.

Profiling of circulating glial cells for accurate blood-based diagnosis of glial malignancies.

Here, we describe a blood test for the detection of glial malignancies (GLI-M) based on the identification of circulating glial cells (CGCs). The test is highly specific for GLI-M and can detect multiple grades (II-IV) and subtypes including gliomas, astrocytomas, oligodendrogliomas, oligoastrocytomas and glioblastomas, irrespective of gender and age. Analytical validation of the test was performed as per Clinical and Laboratory Standards Institute (CLSI) guidelines. Real-world performance characteristics of the test were evaluated in four clinical (observational) studies. The test has high analytical sensitivity (95%), specificity (100%) and precision (coefficient of variation [CV] = 13.7% for repeatability and CV = 23.5% for within laboratory precision, both at the detection threshold) and is not prone to interference from common drugs and serum factors. The ability of the test to detect and differentiate GLI-M from non-malignant brain tumours (NBT), brain metastases from primary epithelial malignancies (EPI-M) and healthy individual donors (HD) was evaluated in four clinical cohorts. Across these clinical studies, the test showed 99.35% sensitivity (95% confidence interval [CI]: 96.44%-99.98%) and 100% specificity (95% CI: 99.37%-100%). The performance characteristics of this test support its clinical utility for diagnostic triaging of individuals presenting with intracranial space-occupying lesions (ICSOL).

Quantitative Evaluation of CFTR Gene Expression: A Comparison between Relative Quantification by Real-Time PCR and Absolute Quantification by Droplet Digital PCR.

In the precision medicine era of cystic fibrosis (CF), therapeutic interventions, by the so-called modulators, target the cystic fibrosis transmembrane conductance regulator (CFTR) protein. The levels of targetable CFTR proteins are a main variable in the success of patient-specific therapy. In turn, the CFTR protein level depends, at least in part, on the level of CFTR mRNA. Many mechanisms can modulate the CFTR mRNA level, for example, transcriptional rate, stability of the mRNA, epigenetics, and pathogenic variants that can affect mRNA production and degradation. Independently from the causes of variable CFTR mRNA levels, their exact quantitative assessment is of great importance in CF. Methods with high analytical sensitivity, precision, and accuracy are mandatory for the quantitative evaluation aimed at the amelioration of the diagnostic, prognostic, and therapeutic aspects. This paper compares, for the first time, two CFTR gene expression quantification methods: a well-established method for the relative quantification of CFTR mRNA using a real-time PCR and an innovative method for its absolute quantification using a droplet digital PCR. No comprehensive methods for absolute CFTR quantification via droplet digital PCR have been published so far. The accurate quantification of CFTR expression at the mRNA level is a critical step for the personalized therapeutic approaches of CF.

Comparison for the simultaneous determination of 237Np and Pu isotopes between TEVA and TK200 resin

A reliable and stable method was developed to accurately analyze neptunium (237Np) and plutonium isotopes in environmental samples using 242Pu or 236Pu as a tracer. Key parameters, including the valence adjustment conditions and the stabilities of Pu and Np in the different resins, were investigated using TK200 and TEVA resin. It was found that Pu and Np could be efficiently extracted simultaneously using TK200 resin under the optimal loading conditions (6–12 M HNO3) with the addition of 0.01–0.12 M NaNO2 for valence adjustment. These isotopes were subsequently stripped out using a solution containing 0.1 M HCl, 0.05 M HF, and 0.01 M NH2OH·HCl. The separation efficiencies of Pu and Np were >93%, and the chemical yield ratio between Np and Pu was maintained steady at an average of 1.00 ± 0.03 (n > 50) under the optimal conditions. The analytical method was validated by analyzing environmental soil samples spiked with known amounts of 239Pu and 237Np standard solutions or certified reference materials. The measured values of 237Np, 239Pu, and 240Pu obtained by inductively coupled plasma tandem mass spectrometry were consistent with their International Atomic Energy Agency literature values within a 95% confidence interval. These results confirm the reliability and high analytical precision (<6%) of this developed method using Pu as a non-isotopic tracer for monitoring the chemical yield of 237Np. The developed method can also be used for environmental pollutant monitoring and for tracer studies of the 237Np and Pu isotopes.

Application of a porous graphitic carbon column to carbon and nitrogen isotope analysis of underivatized individual amino acids using high-performance liquid chromatography coupled with elemental analyzer/isotope ratio mass spectrometry.

Isolation of underivatized amino acids (AAs) using high-performance liquid chromatography (HPLC) is becoming a popular method for carbon (δ13 C) and nitrogen isotope (δ15 N) analyses of AAs because of the high analytical precision and for performing dual-isotope analysis. However, some AAs in natural samples, especially small, hydrophilic AAs, are not suitably separated using reversed-phase columns (e.g., C18) and ion-exchange columns (e.g., Primesep A). We developed a new method for HPLC using a porous graphitic carbon column for the separation of nine hydrophilic AAs. After purification, δ13 C and δ15 N values of AAs were determined using elemental analyzer/isotope ratio mass spectrometry (EA/IRMS). We demonstrated the application of this method by determining δ13 C and δ15 N values of individual hydrophilic AAs in a biological sample, the muscle of blue mackerel (Scomber australasicus). Chromatographically, the baseline separation of hydrophilic AAs was achieved in both the standard mixture and the biological sample. We confirmed that δ13 C and δ15 N values of AA standards remained unchanged during the whole experimental procedure. The δ13 C values of AAs in mackerel muscle are also in good agreement with the values obtained using another verified method for δ13 C analysis. The good separation performance of hydrophilic AAs and the reliability of δ13 C and δ15 N analyses of individual AAs using the porous graphite column offer a significant advantage over conventional settings. We suggest that, in the future, the HPLC × EA/IRMS method can be used for reliable δ13 C and δ15 N analyses of AAs in natural samples.

A magnetically enhanced RF discharge source for metastable krypton production.

We describe a high intensity metastable Kr source based on a helical resonator RF discharge. By adding an external B-field to the discharge source, the metastable Kr flux is enhanced. The effect of geometric configuration and magnetic field strength has been studied and optimized experimentally. Compared to the helical resonator discharge source without an external B-field, the new source showed an enhancement factor of 4-5 in producing metastable Kr beams. This improvement has a direct impact on the radio-krypton dating applications as it can increase the atom count rate, resulting in a higher analytical precision.

The importance of high precision in the evaluation of U-Pb zircon age spectra

We present high-precision isotope dilution-thermal ionization mass spectrometry (ID-TIMS) U-Pb zircon data from the Carboniferous Punteglias granodiorite from the Central Alpine basement in the Aar massif in Switzerland. These analyses yield complex age spectra consisting of both concordant and normally discordant dates, which form a linear array indicative of mixing of two age components within individual zircon crystals. While the upper intercept age reflects zircon growth during Variscan magmatism, the lower intercept of 24 ± 11 Ma is coincident with the Alpine orogeny. There is poor evidence from cathodo-luminescence imagery that magmatic zircon may have younger overgrowths, therefore, we pretreated an aliquot of zircon with physical abrasion followed by chemical abrasion to remove any potential later zircon overgrowths, and to directly date the initial magmatic domains of the zircon. This pretreatment significantly reduced age dispersion and yielded an age of 335.479 ± 0.041 Ma for the crystallization of zircon in the Punteglias granodiorite. Due to the effectiveness of this pretreatment, we interpret that the magmatic zircon was overgrown with younger domains during the Alpine orogeny. Detangling the observed complications in the Punteglias granodiorite zircons was largely possible due to the particularly high analytical precision of the ID-TIMS U-Pb dates that made it possible to detect discordance between the 206Pb/238U and 207Pb/235U systems. Lower-precision U-Pb ID-TIMS dates would not allow identification of such a two-component mixture and lead to analytically concordant points spreading over 105 to 106 years, and potentially leading to erroneous scientific interpretation. As an example, we model two hypothetical situations of simple mixing of two age components in the U-Pb concordia space to demonstrate the effect of precision on the ability to accurately interpret geological models from complicated age spectra. Combining these new high-precision data and modeling results highlights the importance of choosing the optimal, physical and/or chemical sample pre-treatment and the challenge of accurately interpreting complicated U-Pb data in terms of crystallization age.

High Precision And Resolution Chlorine Isotopic Analysis Of Apatite Using NanoSIMS

This paper reports a high analytical precision method for measuring the Cl isotopic composition of apatite using a CAMECA NanoSIMS 50L with Faraday Cup detectors (FC). Six apatite standard samples were used for calibration. Three sets of focused Cs+ beams with currents of ~400 pA (~Φ 700 nm), 1 nA (~Φ 1μm), and 2 nA (~Φ 1.5 μm) were used with different raster sizes (4 × 4 μm2, 8 × 8 μm2, and 10 × 10 μm2, respectively). We performed depth effect experiments with three primary beam settings to optimize the instrument configuration. While using a primary beam of 2 nA with a raster size of ~10 μm, the external precision of each session varied from 0.06 to 0.48 ‰ (1SD) depending on the Cl concentration of the measured apatite. For standards with a Cl content higher than 0.5 %, the external precision was mostly higher than 0.2 ‰. Using 1 nA and 0.4 nA with spatial resolutions of ~8 μm and 5 μm, the external precision for standards with Cl contents &gt;1 % ranged from 0.12 to 0.2 ‰ and 0.10 to 0.33 ‰, respectively. This technique enables high-precision measurements of chlorine isotopes with high spatial resolutions and can be applied to small apatite minerals in extraterrestrial samples.

A semi-automated instrument for cellular oxidative potential evaluation (SCOPE) of water-soluble extracts of ambient particulate matter

Abstract. Several automated instruments exist to measure the acellular oxidative potential (OP) of ambient particulate matter (PM). However, cellular OP of the ambient PM is still measured manually, which severely limits the comparison between two types of assays. Cellular assays could provide a more comprehensive assessment of the PM-induced oxidative stress, as they incorporate more biological processes involved in the PM-catalyzed reactive oxygen species (ROS) generation. Considering this need, we developed a semi-automated instrument, the first of its kind, for measuring the cellular OP based on a macrophage ROS assay using rat alveolar macrophages. The instrument named SCOPE – semi-automated instrument for cellular oxidative potential evaluation – uses dichlorofluorescein diacetate (DCFH-DA) as a probe to detect the OP of PM samples extracted in water. SCOPE is capable of analyzing a batch of six samples (including one negative and one positive control) in 5 h and is equipped to operate continuously for 24 h with minimal manual intervention after every batch of analysis, i.e., after every 5 h. SCOPE has a high analytical precision as assessed from both positive controls and ambient PM samples (coefficient of variation (CoV)&lt;17 %). The results obtained from the instrument were in good agreement with manual measurements using tert-butyl hydroperoxide (t-BOOH) as the positive control (slope =0.83 for automated vs. manual, R2=0.99) and ambient samples (slope =0.83, R2=0.71). We further demonstrated the ability of SCOPE to analyze a large number of both ambient and laboratory samples and developed a dataset on the intrinsic cellular OP of several compounds, such as metals, quinones, polycyclic aromatic hydrocarbons (PAHs) and inorganic salts, commonly known to be present in ambient PM. This dataset is potentially useful in future studies to apportion the contribution of key chemical species in the overall cellular OP of ambient PM.

Performance of the NGX High‐Resolution Multiple Collector Noble Gas Mass Spectrometer

AbstractThis paper describes the design, setup, and performance of a new analytical system installed at Lancaster University, UK, to determine noble gas isotopes in gas samples using an NGX high‐resolution multiple collector noble gas mass spectrometer. The fixed position Faraday cups are configured to simultaneously measure all nine Xe isotopes whilst permitting all other noble gases, such as He, to be analyzed in peak jumping mode. The stability, sensitivity, and reproducibility of the measurements using this new noble gas analytical system were examined by repeating runs of atmospheric air. Reproducibility of the measurements obtained from 90 and 73 air standard runs are 4.2% and 0.4% for 3He/4He and 21Ne/20Ne, respectively. There is no significant difference in the 40Ar/36Ar ratio measurements with various 40Ar abundances, suggesting good sensitivity and pressure linearity of the NGX instrument. The standard errors for 124Xe/130Xe, 126Xe/130Xe, 128Xe/130Xe, 129Xe/130Xe, 131Xe/130Xe, 132Xe/130Xe, 134Xe/130Xe and 136Xe/130Xe in 46 air measurements are 0.782%, 0.804%, 0.053%, 0.029%, 0.029%, 0.029%, 0.030%, and 0.031%, respectively. In contrast, the corresponding reference values from Basford et al. (1973) are 0.342%, 0.505%, 0.148%, 0.139%, 0.153%, 0.076%, 0.156%, and 0.138%, respectively. This suggests that multicollection measurements of Xe isotopes on Faraday cups using the NGX have higher precision than the previous results except for 124Xe and 126Xe, where low abundances affect the measurement precision. Compared to traditional peak jumping single‐collector mass spectrometers, the NGX has significantly decreased analytical time in Xe analysis by allowing simultaneous measurements of all isotopes. As a consequence, high analytical precision can be achieved.

Simultaneous Quantification of the Concentration and Carbon Isotopologue Distribution of Polar Metabolites in a Single Analysis by Gas Chromatography and Mass Spectrometry.

13C-isotope tracing is a frequently employed approach to study metabolic pathway activity. When combined with the subsequent quantification of absolute metabolite concentrations, this enables detailed characterization of the metabolome in biological specimens and facilitates computational time-resolved flux quantification. Classically, a 13C-isotopically labeled sample is required to quantify 13C-isotope enrichments and a second unlabeled sample for the quantification of metabolite concentrations. The rationale for a second unlabeled sample is that the current methods for metabolite quantification rely mostly on isotope dilution mass spectrometry (IDMS) and thus isotopically labeled internal standards are added to the unlabeled sample. This excludes the absolute quantification of metabolite concentrations in 13C-isotopically labeled samples. To address this issue, we have developed and validated a new strategy using an unlabeled internal standard to simultaneously quantify metabolite concentrations and 13C-isotope enrichments in a single 13C-labeled sample based on gas chromatography–mass spectrometry (GC/MS). The method was optimized for amino acids and citric acid cycle intermediates and was shown to have high analytical precision and accuracy. Metabolite concentrations could be quantified in small tissue samples (≥20 mg). Also, we applied the method on 13C-isotopically labeled mammalian cells treated with and without a metabolic inhibitor. We proved that we can quantify absolute metabolite concentrations and 13C-isotope enrichments in a single 13C-isotopically labeled sample.

Detection of EGFR Mutations in Plasma cfDNA and Paired CTCs of NSCLC Patients before and after Osimertinib Therapy Using Crystal Digital PCR.

Simple SummaryLiquid biopsy is a useful tool during longitudinal monitoring of NSCLC patients and requires highly sensitive and reliable technologies for accurate detection of genomic alterations. We evaluated and used crystal digital PCR to detect and quantify EGFR mutations in plasma cfDNA and paired CTCs of NSCLC patients before treatment with osimertinib and at progression of disease.Circulating tumor DNA (ctDNA) analysis has clinical utility in EGFR mutant NSCLC. Circulating tumor cells (CTCs) consist a unique source of information at the cellular level. Digital PCR (dPCR) is a valuable tool for accurate and valid analysis of gene mutations in liquid biopsy analysis. In the present study we detected EGFR mutations in ctDNA and paired CTCs under osimertinib therapy at two time points using crystal dPCR and the naica® system (Stilla Technologies). We quantified mutation allele frequencies (MAF) of EGFR mutations in 91 plasma cfDNA samples of 48 EGFR mutant NSCLC patients and in 64 matched CTC-derived genomic DNA samples, and the FDA-cleared cobas® EGFR mutation test in 80 identical plasma samples. Direct comparison between crystal dPCR and the cobas EGFR assay revealed a high concordance for all EGFR mutations. Our comparison of crystal dPCR results in ctDNA with the corresponding primary tissue has shown a strong correlation. EGFR mutations analysis in paired CTC-derived gDNA revealed a high heterogeneity. Crystal dPCR offers the unique advantages of high analytical sensitivity, precision, and accuracy for detecting and quantifying multiple EGFR mutations in plasma cfDNA and CTCs of NSCLC patients.

(Invited) Potential Applications of Nano-Electrochemistry in Point-of-Care Sensing Devices

Using low noise electronics and micro-electrodes we can now electrochemically detect and count single, nanometer-scale objects in solution.1,2 This talk will cover recent discoveries in the field of single entity electrochemistry showing that electro-inactive species, including proteins, DNA, and even cells, can be detected individually using unmodified electrodes.3–5 Despite these advances, however, limitations persist. The location upon which the individual analyte adsorbs onto the electrode surface influences the magnitude of the electrochemical signal it produces.6,7 Consequently, the electronic output does not reflect the true physical properties of the biological entity, thus inhibiting the analytical resolution desired for applications.In response, we have shown that coupling the electrochemical reaction to a homogeneous, rate-limiting chemical reaction ameliorates this problem, improving the precision of single-entity electrochemical blocking measurements. Using both finite element simulations and experimental statistical analysis we provide guidance for the sizing of redox-inactive materials with high analytical precision under a range of conditions, including variations in electrode size and analyte concentration. The presented nanoscale electrocatalytic approach could offer a novel means of achieving cost-effective, rapid, real-time detection of nanometer-scale “insulators” in complex media, an advance that could be of significant relevance to point-of-care medical diagnostics.

Determination of 17O Anomaly in Atmospheric Aerosol Nitrate

通过改造稳定同位素比质谱仪外设设备、优化系统参数、优化细菌反硝化方法等方法，建立了一种高灵敏度高精度的大气气溶胶硝酸盐氧同位素异常值快速测定方法。本方法的检出限为0.4 μg N，在最佳进样量为0.8 μg N时，测定精度可达到0.19‰。 A novel method for rapid determination of oxygen isotope anomaly (Δ 17 O) in atmospheric aerosol samples was developed. With this method, the measurement was completed in 15 min with a relatively high analytical precision and a low determination limit. To achieve an analytical precision of 0.6‰, this method required a minimum nitrate content of 29 nmol (0.4 μg N). The analytical precision was optimum with a nitrate content of 57 nmol (0.8 μg N). The nitrate in atmospheric aerosol samples was converted to nitrous oxide by optimized bacterial denitrification process within 4 hs. After that, a thermal decomposition of nitrous oxide in sample gas was carried out in a gold tube at 800 °C after separation and purification, followed by gas chromatographic separation and isotope analysis of oxygen. The experiment results showed that the analytical precision of Δ 17 O in this method could reach 0.19‰ with a sample content of 57 nmol NO 3 − , and the analytical precision of δ 15 N could reach 0.15‰. This method was not only suitable for oxygen isotope anomaly determination in atmospheric aerosol samples, but also for the other atmospheric environmental samples such as rain and snow samples with low concentrations. This research establishes a rapid determination method which can determinate the 17 O anomaly in atmospheric aerosol samples by transforming the peripheral equipment of stable isotope ratio mass spectrometer, optimizing the system parameters and the bacterial anti-nitrification method. This method requires a minimum of 0.4 μg N, and analytical precision could reach 0.19 ‰ at a sample content of 0.8 μg N.

Electrochemical Detection of Individual Catalytic and Redox-Inactive Materials

Using low noise electronics and micro-electrodes we can now detect single analytes in solution, one at a time.1,2 In this talk, we will briefly cover recent discoveries in the field of single entity electrochemistry and show that both electroactive and electro-inactive materials can be detected using complementary approaches.3,4 However, some strong limitations in this field persist. In the case of electroactive entities, in order to detect the single entity above the electrochemical noise level, a careful choice of the analyte that differs in its physical properties from the electrode is needed. Here, we show that an active particle-active electrode composed of the same material can provide mechanistic insight into electrochemical reactions.5 Current transients obtained during hydrogen evolution allow simultaneous measurement of the Pt catalyst over different length scales, size dependency suggests H atom intercalation as a catalytic deactivation mechanism.In the case of redox-inactive materials, a different analytical problem exists. The location of the adsorbed individual material at the electrode surface influences the magnitude of the electrochemical signal being blocked during a steady-state flux of a redox probe towards the electrode.6,7 Our recent discovery shows that coupling the electrochemical reaction to a homogeneous rate-limiting chemical reaction offers a platform for high precision measurements. Using both finite element simulations and experimental statistical analysis we provide guiding rules for sizing redox-inactive materials with high analytical precision under various conditions such as analyte and electrode size and analyte concentration.

A new analytical protocol for high precision U–Th–Pb chemical dating of xenotime from the TTG gneisses of the Bundelkhand Craton, central India, using CAMECA SXFive Electron Probe Micro Analyzer

Xenotime is a significant accessory mineral which is being extensively used for precise U–Th–Pb geochronology by Electron Microprobe Analysis (EPMA). This paper presents a protocol for high analytical precision (<3% uncertainties on the measured ages) developed for the accurate estimation of U–Th and Pb content in xenotime using SXFive EPMA at the Department of Geology, Banaras Hindu University, by deploying five spectrometers attached with TAP, LIF, LPET, LTAP and PET crystals. The protocol is applied to the xenotime grains of tonalite-trondhjemite-granodiorite-gneiss (TTG) rocks from the geochronologically well-constrained terrain of the Bundelkhand Craton, central India. The obtained xenotime age 2929±23 Ma of TTGs is in agreement with the earlier published Neoarchaen 2697±3 Ma Pb–Pb zircon ages from the same area which validates the authenticity of the analytical method developed at the BHU-EPMA facility.

Comparative performance of two commercial sample-to-result systems for hepatitis C virus quantitation and genotyping

ABSTRACT Objectives Accurate assays for hepatitis C virus (HCV) quantitation and genotyping are important for the management of HCV infection. In this study, we evaluated the performance of cobas HCV and cobas HCV GT assays (Roche) for HCV quantitation and genotyping on the cobas 4800 System. Methods We compared the performance of the cobas HCV assays with another commercial system (Abbott m2000) using a panel of well-characterized patient samples and proficiency testing samples. Results The limit-of-detection of the cobas HCV assay in our center was higher (15 IU/mL) than the manufacturer claim (9.2 IU/mL). The assay showed high analytical specificity, accuracy, precision, and linearity. Performance was congruent with the RealTime HCV assay (Abbott). For genotyping, the cobas HCV GT assay only showed moderate agreement with the RealTime HCV Genotype II assay (kappa = 0.550). The cobas assay outperformed the RealTime assay for typing HCV genotypes 1b and 6 (p = 0.033). Conclusion Our results confirm that the cobas 4800 System is a reliable platform for HCV quantitation and genotyping. The cobas HCV GT assay is a good choice for genotype 1b/6 endemic areas in east Asia, clearly outperforming the RealTime HCV Genotype II assay.