The use of microelectrodes with AGNES

Absence of gradients and nernstian equilibrium stripping (AGNES) is a new electroanalytical technique designed to determine free heavy metal ion concentrations in solutions. AGNES had been applied, up to date, with conventional equipment such as the hanging mercury drop electrode (HMDE). Due to their much smaller volume, microelectrodes can reach a given preconcentration factor within a much shorter deposition time, so their use for AGNES has been evaluated in this work. For the particular case of the mercury microelectrode deposited onto an Ir disk (radius around 5 lm), AGNES has been successfully used for speciation purposes in the system Pb + PDCA (pyridinedicarboxylic acid). However, due to a relatively large capacitive current, which decays slowly, the limit of quantification for such microelectrodes has only been reduced by one half with respect to that of the HMDE

Biophysical Environmental Chemistry: A New Frontier for Chemistry

The paper discusses the position and role of environmental chemistry among the other environmental disciplines. It discusses the various aspects of environmental chemistry and emphasizes the need for developing fundamental studies in biophysical environmental chemistry in order to better understand the functioning of environmental systems. These systems include a large number of various structures in the nanometer to meter range which play key roles on compound fluxes and consequently on the homeostasis of ecosystems and on their disturbance by anthropogenic activities. Both structures and fluxes are presently ill-known and new concepts and methods must be developed in this field. For chemistry, this is a challenging area where supramolecular structures and processes play dominant roles. It is also a challenging field for the development of environmental sciences since detailed and sound physico-chemical processes are needed in macroscopic modeling of compound circulation in ecosystems. In addition, teaching this discipline to chemistry students would allow them to confront complex, structured real systems. This paper also discusses the relationship between biophysical environmental chemistry and the other environmental disciplines within integrated multidisciplinary studies. The structure used at the Faculty of Sciences of the University of Geneva to favour a flexible but efficient integration is briefly described

Computing steady-state metal flux at microorganism and bioanalogical sensor interfaces in multiligand systems. A reaction layer approximation and its comparison with the rigorous solution

In complicated environmental or biological systems, the fluxes of chemical species at a consuming interface, like an organism or an analytical sensor, involve many coupled chemical and diffusion processes. Computation of such fluxes thus becomes difficult. The present paper describes an approximate approach, based on the so-called reaction layer concept, which enables one to obtain a simple analytical solution for the steady-state flux of a metal ion at a consuming interface, in the presence of many ligands, which are in excess with respect to the test metal ion. This model can be used for an unlimited number of ligands and complexes, without limit for the values of the association/dissociation rate constants or diffusion coefficients. This approximate solution is compared with a rigorous approach for the computation of the fluxes based on an extension of a previously published method (J. Galceran, J. Puy, J. Salvador, J. Cecília, F. Mas and J. L. Garcés, Phys. Chem. Chem. Phys., 2003, 5, 50915100). The comparison is performed for a very wide range of the key parameters: rate constants and diffusion coefficients, equilibrium constants and ligand concentrations. Their combined influence is studied in the whole domain of fully labile to non-labile complexes, via two combination parameters: the lability index, L, and the reaction layer thickness, μ. The results show that the approximate solution provides accurate results in most cases. However, for particular combinations of metal complexes with specific values of L or μ, significant differences between the approximate and rigorous solutions may occur. They are evaluated and discussed. These results are important for three reasons: (i) they enable the use of the approximate solution in a fully reliable manner, (ii) when present, the differences between approximate and rigorous solution are largely due to the coupling of chemical reactions, whose importance can thus be estimated, (iii) due to its simple mathematical expression, the individual contribution of each metal species to the overall flux can be computed

Changes in LA volume and diameter correlate with mechanisms of recurrence after paroxysmal AF ablation.

Papathanasiou et al point out that the two different methods of LA volume and diameter measurement in our recent publication could limit the significance of the correlations we reported with PV reconnection and non-PV foci as mechanisms of post AF ablation recurrence. While we acknowledge the lack of statistically significant correlations of smaller echo derived LA diameter with PV reconnection or of a larger angiographic LA volume with non-PV foci, the congruent confidence intervals of this correlation suggest a statistical trend. Non-uniform LA dimensional changes as an expression of structural remodelling may also be a possible explanation. Published data indicates that angiographic LA volumes consistently exhibit a positive bias compared to echocardiographic volumes but do provide intra-procedural measurements better correlating with gold standard techniques like CT or MRI. Finally we agree with Papathanasiou et al that dynamic changes in LA dimensions likely correlate with early and late mechanisms of recurrence and merit prospective studies

Analytical Techniques for the in situ Measurement and Speciation of Trace Compounds in Natural Waters

A major research component of the analytical activities of the Analytical and Biophysical Environmental Chemistry group of the University of Geneva (CABE) is focused on the development of chemical sensors and mini or microanalytical systems for in situ measurements of trace compounds in aquatic environmental systems, including surface waters, sediments or water treatment plants. In this field, new concepts are required in order to determine not only the total concentration of environmental analytes but also the concentrations and physicochemical properties of their environmentally relevant chemical forms (chemical speciation). New selective analytical systems integrating reliable and rugged sensors with simple separation principles must be imagined to perform in situ (at depth), real-time, automatic measurements. Microtechnology is a key factor in such developments. New analytical methods must also be developed to characterize the nature and properties of the major natural, often colloidal or polymeric, complexing agents. In this context, the scientific approach of CABE is explained

Predicting progression of aortic stenosis by measuring serum calcification propensity

BACKGROUND: The aim of this prospective, double‐blinded study in patients with aortic sclerosis was to determine whether a new calcification propensity measure in the serum could predict disease progression. METHODS: We included 129 consecutive patients with aortic sclerosis as assessed during a routine clinical echocardiographic exam. Clinical, echocardiographic, and serum laboratory parameters were collected, including a new blood test providing an overall measure of calcification propensity by monitoring the maturation time of calciprotein particles (T50 test). The echocardiographic exam was repeated after 1 year. Multiple regression analysis was performed to identify independent predictors of the annual increase of peak transvalvular Doppler velocity (∆vmax). Furthermore, the accuracy of the T50 test to detect patients with the most marked stenosis progression was assessed by receiver operating characteristic (ROC)‐analysis. RESULTS: Mean age was 75 ± 9 years, 79% were men. The T50 was 271 ± 58 min. Overall, there was no significant stenosis progression between baseline and follow‐up (∆vmax 3.8 ± 29.8 cm/s, p = ns). The T50 test was not found to be an independent linear predictor in multivariate testing. By ROC‐analysis, however, a T50‐value ≤ 242 min was able to significantly detect a ∆vmax above the 90th percentile (∆vmax ≥ 43 cm/s, AUC = 0.67, p = .04, Sensitivity = 69%, Specificity = 70%). CONCLUSIONS: The T50 test showed a modest but significant ability to identify a pronounced aortic stenosis progression in patients with aortic sclerosis. The test could not be established as an independent linear predictor of disease progression, possibly due to the low valvular disease burden and short follow‐up interval

Sigmoid isostiffness-lines: An in-vitro model for the assessment of aortic stenosis severity.

Introduction The aortic valve opening area (AVA), used to quantify aortic stenosis severity, depends on the transvalvular flow rate (Q). The currently accepted clinical echocardiographic method assumes a linear relation between AVA and Q. We studied whether a sigmoid model better describes this relation and determined "isostiffness-lines" across a wide flow spectrum, thus allowing building a nomogram for the non-invasive estimation of valve stiffness. Methods Both AVA and instantaneous Q (Qinst) were measured at 10 different mean cardiac outputs of porcine aortic valves mounted in a pulsatile flow loop. The valves' cusps were chemically stiffened to obtain three stiffness grades and the procedure was repeated for each grade. The relative stiffness was defined as the ratio between LV work at grade with the added stiffness and at native stiffness grade. corresponding to the selected of the highest 3 and 5 cardiac output values was predicted in K-fold cross-validation using sequentially a linear and a sigmoid model. The accuracy of each model was assessed with the Akaike information criterion (AIC). Results The sigmoid model predicted more accurately (AIC for prediction of AVA with of the 3 highest cardiac output values: -1,743 vs. -1,048; 5 highest cardiac output values: -1,471 vs. -878) than the linear model. Conclusion This study suggests that the relation between AVA and Q can be better described by a sigmoid than a linear model. This construction of "isostiffness-lines" may be a useful method for the assessment of aortic stenosis in clinical echocardiography

Metal speciation dynamics in colloidal ligand dispersions. Part 3: Lability features of steady-state systems

A lability criterion is developed for dynamic metal binding by colloidal ligands with convective diffusion as the dominant mode of mass transport. Scanned stripping chronopotentiometric measurements of Pb(II) and Cd(II) binding by carboxylated latex core-shell particles were in good agreement with the predicted values. The dynamic features of metal ion binding by these particles illustrate that the conventional approach of assuming a smeared-out homogeneous ligand distribution overestimates the lability of a colloidal ligand system. Due to the nature of the spatial distribution of the binding sites, the change in lability of a metal species with changing ligand concentration depends on whether the ligand concentration is varied via manipulation of the pH (degree of protonation) or via the particle concentration. In the former case the local ligand density varies, whereas in the latter case it is constant. This feature provides a useful diagnostic tool for the presence of geometrically constrained binding sites