Calibration and metrology research

Abstract

A new, multi-electrode, liquid sampling glow discharge ionization source for mass spectrometry is described. This ion source consists of multiple (2-4) counter (anode) electrodes in comparison to prior single counterelectrode designs of this type. In the
experiments presented here, these ion sources have been interfaced with ThermoScientific Exactive Orbitrap instruments and Advion Expression Compact Mass Spectrometer instruments. Advantages and analytical performance improvements are
described. These include ability to use higher plasma currents, resulting in a more robust and energetic plasma exhibiting higher sensitivity, lower spectral background, ppt detection limits, and 2-3x faster washout times. A low-cost, 3D printed version of a dual
counter electrode design is also described. The ion source can further be utilized in either atomic (elemental/isotopic) or molecular (molecular ion, fragmentation) ionization modes.

Reference

Hoegg, E., Williams, T., Bills, J., R., M., & Koppenaal, D. (2020). A multi-electrode glow discharge ionization source for atomic and molecular mass spectrometry. Journal of Analytical Atomic Spectrometry. Retrieved 2021, from https://pubs.rsc.org/nl-be/content/getauthorversionpdf/D0JA00142B.

Abstract

Flexible electronic gas sensors working at room temperature have acquired enormous attention in recent years due to their suitability to be integrated into various wearable electronic products. In this investigation, we have demonstrated a H₂ gas sensor using less platinum bimetallic nickel–platinum nanocatalyst-functionalized carbon nanofibers (CNFs@Ni–Pt) fabricated on a flexible platform. The flexible CNF@Ni–Pt sensor showed only a negligible decrease in response during mechanical stress under flat (21%) and bent (17%) states after several bending cycles owing to the high aspect ratio of the carbon nanofiber network, which helps us to indulge a long bending path.

Moreover, the flexible CNF@Ni–Pt sensor showed superior sensor response (50%) toward H₂ with outstanding selectivity toward other interfering gases. In addition, hydrogen adsorption kinetic studies performed on flexible CNF@Ni–Pt sensors indicated comparable theoretically calculated (0.42) and experimental (0.49) rate constant values. In situ Raman spectroscopy analysis aided in unraveling the H₂ interaction with the catalytically active Ni–Pt sites anchoring on the surface of CNFs, and a plausible sensing mechanism could be predicted. Flexible, less platinum CNF@Ni–Pt sensors can find wider applications in the fields of flexible electronics, biomedical, and environmental monitoring.

Reference

Nair, K. G., Vishnuraj, R., & Pullithadathil, B. (2021). Highly sensitive, flexible H₂ gas sensors based on less platinum bimetallic Ni–Pt nanocatalyst-functionalized carbon nanofibers. ACS Applied Electronic Materials, 3(4), 1621–1633. https://doi.org/10.1021/acsaelm.0c01103

Abstract

Technological advances have motivated researchers to transition from traditional gas chromatography/isotope ratio mass spectrometry to rapid, high-throughput, laser-based instrumentation for N₂O isotopic research. However, calibrating laser-based instruments to yield accurate and precise isotope ratios has been an ongoing challenge. To streamline the N₂O isotope research pipeline, we developed the calibration protocol for laser-based analyzers described here. While our approach is targeted at laboratory soil incubations, we anticipate that it will be broadly applicable for diverse types of stable isotope research. We prepared standards diluted from USGS52 and from a commercial cylinder to develop a calibration curve spanning from 0.3 to 300 ppm N₂O. To calibrate over this broad range, we binned each isotopocule (N₂O, N¹⁵NO, ¹⁵NNO, and NN¹⁸O) into low, medium, and high concentration ranges and then used mathematically similar polynomial functions to calibrate the isotopocules within each concentration range. We also assessed the temporal stability of the instrument and the capacity for our calibration approach to work with isotopically enriched gas samples.

Our calibration approach yielded generally accurate and precise data when isotopocules were calibrated in concentration ranges, and the measurements appeared to be temporally stable. For all isotopocules at natural abundance, the residual percentage error was smallest in the medium N₂O range. There was more noise in the corrected isotopomers and isotopologue at natural abundance in samples with the lowest and highest N₂O concentrations. Corrected isotopomer results from isotopically enriched samples were very precise. Developing our calibration strategy involved learning several key lessons: (1) calibrate isotopocules in distinct concentration ranges, (2) use mathematically similar models to calibrate the isotopocules in each range, (3) calibrated N₂O concentrations and δ values tend to be most accurate and precise in the medium N₂O range, and (4) we encourage users to take advantage of isotopic enrichment to capitalize on laser-based instrument strengths.

Reference

Stuchiner, E. R., Weller, Z. D., & Fischer, J. C. (2020). An approach for calibrating laser‐based N₂O isotopic analyzers for soil biogeochemistry research. Rapid Communications in Mass Spectrometry, 35(3). https://doi.org/10.1002/rcm.8978

Abstract

Many natural and engineering flows transport more than one scalar. Moreover, to study the scalar mixing therein, knowledge of the velocity field is also essential. For this reason, the present work describes the development of a three-wire thermal-anemometry-based probe to simultaneously measure velocity, helium concentration, and temperature in turbulent flows. It is first demonstrated, both theoretically and experimentally, that the temperature measured by a cold-wire thermometer is effectively insensitive to helium concentration. Then, building on recent work by Hewes and Mydlarski (2021 Meas. Sci. Technol. 32 105305), which pertains to the design of interference probes (i.e. thermal-anemometry-based probes used to measure velocity and gas concentration), a novel temperature compensation technique is proposed to extend their use to non-isothermal flows. The performance of the compensation technique is validated in turbulent coaxial jets by combining the cold-wire thermometer and interference probe to form a three-wire probe. Given that the three-wire probe can be employed to obtain simultaneous measurements of velocity and multiple scalars, it can therefore be used investigate phenomena such as multi-scalar mixing, including differential diffusion.

Reference

Hewes, A., & Mydlarski, L. (2021). Simultaneous measurements of velocity, gas concentration, and temperature by way of thermal-anemometry-based probes. Measurement Science and Technology, 33(1). Retrieved 2021, from https://iopscience.iop.org/article/10.1088/1361-6501/ac2ca5/meta.

Abstract

Detection of NO₂ plays an important role in various safety applications. However, sensitive and reversible sensing of NO₂ remains a challenge. Here we demonstrate the use of poly(3,4-ethylenedioxythiophene) (PEDOT) conducting polymer percolation networks for chemiresistive sensing of NO₂. By adjusting the electrochemical polymerisation and doping conditions of the polymer, we show control over the relative contributions of oxidised and over-oxidised PEDOT to the sensing behaviour. Reversible NO₂ sensors using only PEDOT as the sensor material are demonstrated. By operating the sensor near the electrical percolation threshold, a higher sensitivity is achieved compared to more traditional thin film based chemiresistive sensors. A limit of detection of 907 ± 102 ppb was achieved.

Sensor responses to 3 rounds of 8 ppm, 4 ppm, 2 ppm, and 1 ppm NO₂ of a PEDOT percolation network based sensor optimised to give a reversible sensor response (A). Average sensor responses in delta R/R_o x 100% for 3 exposures per concentration for the same sensor (B). The data for 8 ppm was not included in the trend line because the data for 8 ppm is a clear outlier, resulting in a larger change in the sensor response than expected.

Citation

Lefferts, M. J., Artmitage, B. I., Murugappan, K., & Castell, M. R. (2021). PEDOT percolation networks for reversible chemiresistive sensing of NO₂. Analytical Chemistry. https://doi.org/https://doi.org/10.1039/D1RA03648C