Trace manganese detection via differential pulse cathodic stripping voltammetry using disposable electrodes: Additively manufactured nanographite electrochemical sensing platforms

Additive manufacturing is a promising technology for the rapid and economical fabrication of portable electroanalytical devices. In this paper we seek to determine how our bespoke additive manufacturing feedstocks act as the basis of an electrochemical sensing platform towards the sensing of manganese(ii) via differential pulse cathodic stripping voltammetry (DPCSV), despite the electrode comprising only 25 wt% nanographite and 75 wt% plastic (polylactic acid). The Additive Manufactured electrodes (AM-electrodes) are also critically compared to graphite screen-printed macroelectrodes (SPEs) and both are explored in model and real tap-water samples. Using optimized DPCSV conditions at pH 6.0, the analytical outputs using the AM-electrodes are as follows: limit of detection, 1.6 × 10-9 mol L-1 (0.09 μg L-1); analytical sensitivity, 3.4 μA V μmol-1 L; linear range, 9.1 × 10-9 mol L-1 to 2.7 × 10-6 mol L-1 (R2 = 0.998); and RSD 4.9% (N = 10 for 1 μmol L-1). These results are compared to screen-printed macroelectrodes (SPEs) giving comparable results providing confidence that AM-electrodes can provide the basis for useful electrochemical sensing platforms. The proposed electroanalytical method (both AM-electrodes and SPEs) is shown to be successfully applied for the determination of manganese(ii) in tap water samples and in the analysis of a certified material (drinking water). The proposed method is feasible to be applied for in-loco analyses due to the portability of sensing; in addition, the use of AM-printed electrodes is attractive due to their low cost

Accuracy versus precision in boosted top tagging with the ATLAS detector

Abstract The identification of top quark decays where the top quark has a large momentum transverse to the beam axis, known as top tagging, is a crucial component in many measurements of Standard Model processes and searches for beyond the Standard Model physics at the Large Hadron Collider. Machine learning techniques have improved the performance of top tagging algorithms, but the size of the systematic uncertainties for all proposed algorithms has not been systematically studied. This paper presents the performance of several machine learning based top tagging algorithms on a dataset constructed from simulated proton-proton collision events measured with the ATLAS detector at √ s = 13 TeV. The systematic uncertainties associated with these algorithms are estimated through an approximate procedure that is not meant to be used in a physics analysis, but is appropriate for the level of precision required for this study. The most performant algorithms are found to have the largest uncertainties, motivating the development of methods to reduce these uncertainties without compromising performance. To enable such efforts in the wider scientific community, the datasets used in this paper are made publicly available.</jats:p

Electrochemistry inside microdroplets of kerosene: Electroanalysis of (methylcyclopentadienyl) manganese(I) tricarbonyl(I)

A novel electrochemical technique for the determination of (methycyclopentadienyl) manganese(I) tricarbonyl in kerosene is presented. The protocol involves creating an ensemble of microdroplets via spraying a fine mist of the sample under investigation onto an electrode substrate which is then immersed into an immiscible supported phase of either water or acetonitrile which can be used to voltammetrically interrogate the species of interest. In particular the kerosene | acetonitrile interface allows the study of the electrochemical oxidation of (methycyclopentadienyl) manganese(I) tricarbonyl, MMT which normally occurs at large overpotentials (E1/2 = + 1.22 V vs. saturated calomel electrode). Proof-of-concept is shown for kerosene droplets containing MMT suggesting a generic methodology for the electrochemical determination of analytes in voltammetrically otherwise inaccessible media such as petroleum and oils. © 2006 Wiley-VCH Verlag GmbH and Co. KGaA

The electrochemistry of tetraphenyl porphyrin iron(III) within immobilized droplets supported on platinum electrodes

For the first time, the voltammetry of an ensemble of immobilized benzonitrile microdroplets containing 5,10,15,20-tetraphenyl-21H,23H-porphine iron (III) chloride, TPPFeCl immobilized at platinum electrodes immersed in various aqueous electrolytes has been explored. The reduction of TPPFeCl was observed with the voltammetric response seen to be highly dependent on the nature of ions in the surrounding aqueous phase. Unlike voltammetry in purely homogeneous solution the nature of the aqueous electrolyte can influence the voltammetry in the droplet phase. The electrochemical reduction of TPPFeCl contained within tetrabutylammonium chloride (TBACl) supported benzonitrile (PhCN) microdroplets immersed into an aqueous solution of TBACl was first studied. During TPPFeCl reduction the resulting [TPPFeCl]- species is stabilized due to the excess of chloride anions inside the oil droplet. Voltammograms of homogeneous solutions of PhCN supported with TBACl show similar chemically reversible process which is also attributed to the stable [TPPFeCl]- species. This anion stabilization was not observed when the oil droplets were supported with tetrabutylammonium perchlorate (TBAP) or when the PhCN solution bathing the microdroplet ensemble was supported with TBAP resulting in a chemically irreversible process. The voltammetry of unsupported droplets immobilized on a platinum electrode immersed in different aqueous electrolytes was also explored and the fate of the [TPPFeCl]- species formed considered during the reduction sweep. Similarities and difference to voltammetry in purely homogeneous media are noted and the use of droplet voltammetry provides complimentary information. © 2006 Wiley-VCH Verlag GmbH and Co. KGaA

Chronopotentiometric stripping analysis using gold electrodes, an efficient technique for mercury quantification in natural waters

This paper proposes a simple methodology for mercury quantification in natural water by stripping chronopotentiometry at constant current, using gold (film) electrodes constructed from recordable CDs in stationary cell. The proposed method allows the direct measurement of labile mercury in natural waters. To quantify total mercury, a robust and low cost UV irradiation system was developed for the degradation of organic constituents of water. The proposed system presents such advantages as excellent sensitivity, low cost, versatility, and smaller dimensions (portability for on-field applications) when compared with other techniques (ICP, GFAAS, fluorimetry) traditionally utilized for mercury quantification. A large linear region of responses was observed, situated over the range 0.02 - 200 &mu; g L-1. Various experimental parameters were optimized and the system allowed quantifications in natural samples, with detection limit of 8 ng L-1 and excellent reproducibility (RSD of 1.4% for 48 repetitive measurements using a 10 &mu; g L-1 mercury solution). Different metal ions were evaluated, including copper, as possible interferences on stripping mercury signals. Applications of the new method were demonstrated for the analysis of certified and groundwater samples spiked with a known amount of mercury and for the quantification of methylmercury in synthetic oceanic water, originally utilized for fishes contamination experiment

Fast ultrasound-assisted treatment of urine samples for chronopotentiometric stripping determination of mercury at gold film electrodes

This work describes an efficient, fast, and reliable analytical methodology for mercury determination in urine samples using stripping chronopotentiometry at gold film electrodes. The samples were sonicated in the presence of concentrated HCl and H2O2 for 15 min in order to disrupt the organic ligands and release the mercury. Thirty samples can be treated over the optimized region of the ultrasonic bath. This sample preparation was enough to allow the accurate stripping chronopotentiometric determination of mercury in the treated samples. No background currents and no passivation of the gold film electrode due to the sample matrix were verified. The samples were also analyzed by cold vapour atomic absorption spectrometry (CV-AAS) and good agreement between the results was verified. The analysis of NIST SRM 2670 (Toxic Metals in Freeze-Dried Urine) also validated the proposed electroanalytical method. Finally, this method was applied for mercury evaluation in urine of workers exposed to hospital waste incinerators. (c) 2006 Elsevier B.V. All rights reserved

Immunostimulation in crustaceans: does it really protect against infection?

There is a growing need to control, prevent or minimise the devastating effects of disease in crustacean culture without recourse to toxic chemicals or antibiotics. In keeping with approaches to disease control in fish and higher mammals, interest is developing in compounds that confer protection and/or enhance immune reactivity to likely pathogens in shellfish (sometimes, erroneously, referred to as ‘shellfish vaccines’). The agents currently under scrutiny for crustaceans include glucans, lipopolysaccharides and killed bacterial cells. They are thought to act as ‘immunostimulants’ because of their known effects on the crustacean immune system in vitro. A number papers are now appearing in the literature claiming to demonstrate their positive impact on immunity and disease resistance. This review article considers the problem of disease and its control in crustacean farming, describing the types of immunostimulatory compounds claimed to have positive effects and evaluating their merit in enhancing immune capability in cultured species. Analysis of the validity of the results of many of the published studies raises questions about the value of these compounds for cost-effective control of infection in aquaculture, especially for long lasting protection in both adults and juveniles. This review further discusses the potential risks to the wellbeing of the stock animals from repeated use of these agents and makes the case for rigorous testing of putative stimulants, at the gene, protein and functional levels, as well as for the need to consider alternative strategies and approaches to disease control