Electrochemical method for the determination of arsenic 'in the field' using screen-printed grid electrodes

This project describes development and problem solving efforts to realise a viable portable sensor for arsenic, applicable to drinking water. The work is the first dedicated effort towards this goal, after the preliminary investigations previously conducted at Cranfield University (Cooper, 2004 and Noh, 2005). Using polymeric gold ink BQ331 (DuPont Microcircuit Materials, Bristol, UK) as working electrode on screen printed strips, the electrochemical procedure was studied. Due to the wealth of research on electrochemical and non electrochemical methods for arsenic determination, this project attempts to capitalise on the unique advantages of the screen-printed gold surface. In particular, the issues surrounding the performance of the sensor were evaluated by electrochemical and spectroscopic means (including infrared, nuclear magnetic resonance and X-ray photoelectron spectroscopy). A number of custom screen printed electrodes were prepared in house comparing sensor performance on compositional factors. An interference coming from silver interaction with chloride in the reference electrode was identified. As such, the design of the sensor needs to change to include either an immobilising layer, such as Nafion, over the silver, or to omit screen-printed silver altogether. The Nafion was presumed to work by excluding (or at least much reducing) the passage of negatively charged chloride ions to the silver surface preventing formation of soluble silver chloride complexes. The design of the sensor was considered in light of performance and sensitivity. The screen-printed electrodes were cut to facilitate a microband design lending favourable diffusive to capacitive current characteristics. With this design, As(III) detection was demonstrated comfortably at 5 ppb (in a copper tolerant 4 M HCl electrolyte) without electrode need for additional preparation procedures. This is below the World Health Organisation (WHO) guideline and United States Environmental Protection Agency (USEPA) regulation level of 10 ppb in drinking water. The electrode materials are already mass manufacturable at an estimated cost less than £ 0.5 per electrode. Themicroband design could, in principle, be applied to mercury and other metal ions. The procedure for As(V) either with chemical or electrochemical reduction and determination still needs to be assessed. However, the presented electrode system offers a viable alternative to the colorimetric test kits presently employed around the world for arsenic in drinking water. Also, the Nicholson Method (Nicholson, 1965a), used for characterising electron transfer kinetics at electrode surfaces, was extended for application to rough surfaces using a fractal parameter introduced by Nyikos and Pajkossy (1988). This work includes mathematical derivation and numerical evaluation and gives a number of predictions for electrochemical behaviour. These predictions could not be tested experimentally, as yet, since the physical conditions must be carefully controlled

On generalized Frame-Stewart numbers

For the multi-peg Tower of Hanoi problem with $k \geqslant 4$ pegs, so far the best solution is obtained by the Stewart's algorithm based on the the following recurrence relation: $\mathrm{S}\_k(n)=\min\_{1 \leqslant t \leqslant n} \left\{2 \cdot \mathrm{S}\_k(n-t) + \mathrm{S}\_{k-1}(t)\right\}$, $\mathrm{S}\_3(n) = 2^n -- 1$. In this paper, we generalize this recurrence relation to $\mathrm{G}\_k(n) = \min\_{1\leqslant t\leqslant n}\left\{ p\_k\cdot \mathrm{G}\_k(n-t) + q\_k\cdot \mathrm{G}\_{k-1}(t) \right\}$, $\mathrm{G}\_3(n) = p\_3\cdot \mathrm{G}\_3(n-1) + q\_3$, for two sequences of arbitrary positive integers $\left(p\_i\right)\_{i \geqslant 3}$ and $\left(q\_i\right)\_{i \geqslant 3}$ and we show that the sequence of differences $\left(\mathrm{G}\_k(n)- \mathrm{G}\_k(n-1)\right)\_{n \geqslant 1}$ consists of numbers of the form $\left(\prod\_{i=3}^{k}q\_i\right) \cdot \left(\prod\_{i=3}^{k}{p\_i}^{\alpha\_i}\right)$, with $\alpha\_i\geqslant 0$ for all $i$, arranged in nondecreasing order. We also apply this result to analyze recurrence relations for the Tower of Hanoi problems on several graphs.Comment: 13 pages ; 3 figure

Microband sensor for As(III) analysis: Reduced matrix interference

A portable sensor based on a microband design for arsenic detection in drinking water is presented. The work was focused to minimize interference encountered with a standard screen-printed electrodes featuring an onboard gold working electrode, carbon counter and silver−silver chloride pseudo-reference electrodes as composite coatings on plastic surface. The interference effect was identified as chloride ions interacting with the silver surface of the reference electrode and formation of soluble silver chloride complexes such as AgCl43−. By modification of the reference electrodes with Nafion membrane (5 % in alcohols), the interference was entirely eliminated. However, membrane coverage and uniformity can impact the electrodes reproducibility and performance. Hence, the sensor design was further considered and a microband format was produced lending favorable diffusive to capacitive current characteristics. Using the microband electrodes allowed As(III) detection with limit of detection of 0.8 ppb (in 4 M HCl electrolyte), inherently avoiding the problems of electrode fouling and maximizing analyte signal in river water samples. This is below the World Health Organization limit of 10 μg L−1 (ppb). The electrolyte system was chosen so as to avoid problems from other common metal ions, most notably Cu(II). The presented electrode system is cost effective and offers a viable alternative to the colorimetric test kits presently employed for arsenic analysis in drinking water

Leadership in politics and science within the Antarctic Treaty

For over 50 years the Antarctic has been governed through the Antarctic Treaty, an international agreement now between 49 nations of whom 28 Consultative Parties (CPs) undertake the management role. Ostensibly, these Parties have qualified for their position on scientific grounds, though diplomacy also plays a major role. This paper uses counts of policy papers and science publications to assess the political and scientific outputs of all CPs over the last 18 years. We show that a subset of the original 12 Treaty signatories, consisting of the seven claimant nations, the USA and Russia, not only set the political agenda for the continent but also provide most of the science, with those CPs producing the most science generally having the greatest political influence. None of the later signatories to the Treaty appear to play a major role in managing Antarctica compared with this group, with half of all CPs collectively producing only 7% of the policy papers. Although acceptance as a CP requires demonstration of a substantial scientific programme, the Treaty has no formal mechanism to review whether a CP continues to meet this criterion. As a first step to addressing this deficiency, we encourage the CPs collectively to resolve to hold regular international peer reviews of their individual science programmes and to make the results available to the other CPs

Embedding OER\u27s For The Development of Information Literacy in the Foreign Language Classroom

Despite a rapid growth of Open Educational Resource (OER) availability, Thoms and Thoms (2014) note that few empirical studies examine the impact of OERs on foreign language learning and teaching. This paper presents an action research study investigating the embedding of selected components of DigiLanguages, an OER for Digital Literacies (DLs) for Foreign Languages (FL) within a Bachelor of Arts (BA) in International Business and Languages at the Technological University Dublin. Digilanguages.ie is an open portal developed collaboratively by six tertiary education institutions in Ireland. Digital literacies for FL learning and teaching is a key strand in this resource. The study involved two groups of students, one majoring in French and one in Italian. One of the aims of the study was to pilot the portal and identify affordances and constraints of introducing and adapting this OER to the individual FL classroom. Of equal importance was to analyse the potential of the OER to introduce and/or change pedagogical practices in an area that remains largely under investigated, namely DLs for foreign language learning. The study informs future steps in how to use a particular OER to embed units of DLs into FL courses. It also provides insights on developing a new set of professional practices among language teachers

Measures of suicidality in perinatal women: A systematic review

BACKGROUND: Suicide is a leading cause of death for perinatal women. Identifying women at risk of suicide is critical. Research on the validity and/or reliability of measures assessing suicidality in perinatal women is limited. This review sought to: (1) identify; and (2) evaluate the psychometric properties of suicidality measures validated in perinatal populations. METHODS: Nine electronic databases were systematically searched from inception to January 2022. Additional articles were identified through citation tracking. Study quality was assessed using an adapted tool, and the psychometric properties of measures were reviewed and presented using a narrative synthesis. RESULTS: A total of 208 studies were included. Thirty-five studies reported psychometric data on ten suicidality measures. Fifteen studies reported both validity and reliability data, 12 reported more than one type of validity, seven validated more than one measure and four only reported reliability. Nearly all measures primarily screened for depression, with an item or subscale assessing suicidal ideation and/or behaviours. Three measures were specifically developed for perinatal women, but only two were validated in more than one study. The Postpartum Depression Screening Scale (PDSS), suicidal thoughts subscale, was validated most frequently. LIMITATIONS: Methodological differences and variability between the measures (e.g., suicidality construct assessed, number of items and administration) precluded direct comparisons. CONCLUSION: Further validation of suicidality measures is needed in perinatal women. Screening for perinatal suicidality often occurs in the context of depression. The development of a standalone measure specifically assessing suicidality in perinatal women may be warranted, particularly for use in maternity care settings