Voltammetric Analysis of Phytochelatin Complexation in Ternary Metal Mixtures Supported by Multivariate Analysis and ESI‐MS

The competitive binding of Cu²⁺, Cd²⁺ and Pb²⁺ in ternary mixtures by the phytochelatins PC₂ and PC₅ (PC_n; (γGlu‐Cys)_n‐Gly, n=2 and 5) are examined by voltammetry, which allows one to follow the displacements of the voltammetric signals induced by the competitive binding among the metal ions towards PC₂ or PC₅ complexation, and direct injection positive‐mode Electrospray Ionization Mass Spectrometry (ESI‐MS), in order to obtain the stoichiometries of the complexes. Voltammetric data are analyzed by Gaussian Peak Adjustment (GPA), which is a recently developed multivariate analysis method for nonlinear electrochemical data. Different complexes have been detected or deduced their presence, depending on the experimental conditions. Ternary complexes CuCdPC_n and CdPbPC_n were detected for both PC₂ and PC₅, while the ternary CuPbPC_n complex was only detected for PC₂. Some of the complexes have been only detected by ESI‐MS because in some cases voltammetry data could not be totally resolved, even by using GPA. The quaternary CdPbCuPC_n complex has been detected for PC₅, but for PC₂ data are not so conclusive. In summary, the signal evolution for mixed CdCuPC_n complexes is quite different. These observations could be a reflection of an antagonistic effect for the case of PC₂ and a synergetic one for PC₅.     

Gas-phase microreactors as a powerful tool for kinetic investigations

The purpose of this review was to show the versatility of gas-phase microreactors for the determination of kinetics of chemical systems. Precise kinetic models were demonstrated for two industrially relevant cases: (a) the continuous selective catalytic NO reduction by hydrocarbons in the excess oxygen at 150–550°C and (b) the catalytic production of ethylene oxide, one of the most important intermediates in the world.     

Coulometric Response of H+-Selective Solid-Contact Ion-Selective Electrodes and Its Application in Flexible Sensors†

The analytical performance of H⁺-selective solid-contact ion-selective electrodes (SCISEs) based on solid contact polyaniline doped with chloride (PANI(Cl)) and poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonate) (PEDOT(PSS)) was characterized by a developed coulometric signal transduction method. PEDOT(PSS) solid contact is covered by PVC based H⁺-selective membrane. The obtained coulometric signal demonstrates that the cumulated charge can be amplified by increasing the capacitance of solid contact. SCISEs covered with spin-coated membrane behave faster amperometric response than electrodes with drop-cast membrane. In contrast to earlier works, the amperometric response and impedance spectrum demonstrates H⁺ transfer through SCISEs is independent from the thickness of membrane. The exceptional behavior of PANI(Cl) H⁺-SCISEs shows that the capacitance estimated from impedance spectrum at low frequency 10 mHz and coulometric signal of PANI(Cl) based SCISEs is influenced by the applied potentials, whereas PEDOT(PSS) solid contact is independent from the chosen applied potentials. Furthermore, preliminary investigations of coulometric signal transduction on flexible pH sensor implies its potential applications in wearable sensors for sweat ion concentration detection.