Laurent Authier

Formation of reactive nitrogen species including peroxynitrite in physiological buffer exposed to cold atmospheric plasma

Cold Atmospheric Plasmas (CAPs) or Non Thermal Plasmas (NTPs) are increasingly used for biomedical applications. Herein, we studied the interactions of such CAPs, typically atmospheric ionization waves produced in a helium–nitrogen mixture (He/1% N2) with a commonly used physiological liquid in biology, e.g. Phosphate Buffered Saline solution (PBS) at pH 7.4. Optical Emission Spectroscopy (OES) of the plasma phase revealed the formation in the He/1% N2 CAP of nitric oxide NO and hydroxyl HO˙ derivatives which can lead to numerous Reactive Oxygen and Nitrogen Species (RONS) after dissolution in the exposed PBS. Chemical changes in solution were first assessed by conductimetry and pHmetry; these experiments showed that an evaporation of the solution occurred under gas exposition and was amplified by the CAPs, being mostly related to the interaction between the ionization wave and the gas flow. Further, UV-visible absorption spectroscopy was used to identify and quantify long-lived RONS, namely nitrite (NO2−), nitrate (NO3−), as well as a short-lived species, i.e. peroxynitrite anion (ONOO−). The production in physiological solution of ONOO− under CAP exposure is demonstrated for the first time, based on experiments at two pH conditions (7.4 and 12) and on the analysis of decomposition kinetics of this unstable species. The combination of complementary physico-chemical techniques allows to decipher the complex reactivity of CAPs from the plasma phase to the liquid phase.

Cadmium speciation assessed by voltammetry, ion exchange and geochemical calculation in soil solutions collected after soil rewetting

Analytical techniques and speciation models have been developed to characterize the speciation of Cd in soil solution. They provide an estimate of operationally defined species of Cd that need to be compared, especially for soil solutions highly concentrated in organic matter as are the solutions collected after soil rewetting. This work deals with the comparison between the speciation of Cd measured by anodic stripping voltammetry (ASV) and ion exchange and the speciation of Cd calculated using Visual MINTEQ. The aim of this study was to quantify and explain the differences in Cd speciation observed between the three approaches. Cd speciation was assessed in soil solutions collected 4, 8, 24, 48, 96 and 144h after the rewetting of an air-dried contaminated soil. To optimize the computed speciation of Cd, other physico-chemical parameters were followed (e.g. pH, ionic strength and the concentrations of major anions, major cations and dissolved organic carbon) and a brief characterisation of dissolved organic matter (DOM) was performed. The discrepancy between model predictions and analytical measurements highlighted the need for caution in the interpretation of geochemical speciated data for Cd. The major result of this study was that a characterization of DOM based on its specific UV-absorbance at 254 nm improved the accuracy of model predictions. Another finding is that labile Cd complexes, even organic, may have been included in the electrochemically labile fraction of Cd measured by ASV.

Comparison of two experimental speciation methods with a theoretical approach to monitor free and labile Cd fractions in soil solutions.

This work focused on the suitability of two techniques to monitor cadmium speciation in soil solutions collected during a 7-day incubation of a contaminated soil. Anodic stripping voltammetry (ASV) and ion exchange were performed on soil solutions collected daily and results were compared with calculations obtained with the speciation software Visual MINTEQ. The electrochemically labile Cd fraction was greater than the exchange-estimated free Cd fraction during the first 6 days, after which it decreased sharply during the last 2 days to reach values close to the exchange-estimated free Cd fraction. Further investigations showed that the increase in pH was mainly responsible for the reduction. However, calculations performed with Visual MINTEQ software clearly demonstrated that a change in the nature of organic matter and/or its complexing capacity also needed to be taken into consideration.

Improved synthesis of a protected 11-oxoestrone

An improved synthesis of 11-oxoestrone-3-acetate-17-ethyleneketal is reported. Adjustments are proposed for the oxidation of estrone by 2,3-dichloro-5,6-dicyano-1,4-benzoquinone into 9(11)-dehydroestrone. A complete hydroboration-oxidation of the resulting ketal, by means of borane-methylsulfide complex, gives the corresponding 11-hydroxy derivative. This latter compound is then acetylated for successful oxidation with pyridinium chlorochromate on alumina. The overall yield is 30%.

Free Zn2+ determination in natural freshwater of the Pyrenees: towards on-site measurements with AGNES

An on-site methodology has been developed for the direct determination of free Zn2+ with AGNES (Absence of Gradients and Nernstian Equilibrium Stripping) in freshwaters. This implementation includes: (i) the use of screen-printed electrodes, which provide good limits of detection and easy transportation and deployment; (ii) no need for sample purging; (iii) a calibration in a synthetic river solution that reproduces the speciation changes of the natural samples well and allows oxygen interference to be minimised; (iv) the addition of a background electrolyte up to 0.01 mol L–1 in both the calibration and freshwater samples; (v) chemical stripping chronopotentiometry as the quantification stage of AGNES. This procedure minimises the effects of working at low ionic strength and in the presence of dissolved oxygen. In the laboratory, the methodology was checked with different natural samples taken from rivers Garonne, Gave de Cauterets and Gave de Pau in the Pyrenees. Results appeared in good agreement with theoretical estimations computed from Visual Minteq. On-site measurements were performed for the first time with AGNES in the Gave de Cauterets in Soulom (France) and the results were corroborated with purged measurements performed in the laboratory.

Use of screen-printed microelectrodes working as generator/collector systems for the determination of the antioxidant capacity of phenolic compounds.

A new method using cheap homemade dual-electrodes has been developed to measure the antioxidant capacity of phenolic compounds. These micro-sized electrodes are elaborated by successive screen-printing of conductive ink and insulator layers and are then used as generator/collector sensors. Cyclic voltammetry and chronoamperometry with a bipotentiostat have been used to test and characterize these sensors. The antioxidant capacity values found by this new method are compared with a classical method (using a macro-sized electrode) to demonstrate its reliability.

Speciation of copper in agricultural soils contaminated by lead using screen-printed electrodes and square-wave anodic stripping voltammetry (SPE-SWASV)

An analytical strategy, involving carbon screen printed working electrodes (SPEs) modified with mercury combined with square wave anodic stripping voltammetry (SWASV), was optimized for the total and electrolabile copper concentration determination in the presence of lead. The accuracy of the method was checked by analyzing a solution of mineralized certified reference soil, the mineralization step allowing the quantity of metals to be assumed totally in electrolabile form in the solution of mineralized soil. The influence of the calibration modes and potential matrix effects was investigated. Under optimized conditions, the accuracy (i.e. trueness and repeatability) and robustness were verified. For that, the electrolabile copper concentration and the Relative Standard Deviation (RSD) were evaluated according to the change frequency of the SPE and the analyzed solution after each SPE-SWASV measurement in the solution of the mineralized soil. Additionally, analyses were performed by inductively coupled plasma mass spectrometry (ICP-MS) as a confirmation mean. From statistical tests in a 95% confidence interval, a copper recovery of 97% (regarding a certified value) and a RSD of 9% were found for the electrochemical method. Agricultural soils often contain lead in significant concentration, so analyses were also carried out on lead. This verified that there was no interaction between copper and lead on the measurement. Then, the developed method was applied for the first time in an original strategy consisting of the quantification of the total and the electrolabile amounts of copper and lead in agricultural soils in order to estimate the potential hazard brought by their mobilization from the soil. For that, soils were (i) mineralized to obtain the total metal amounts and (ii) leached to reach the electrolabile ones.