Potential Coulometry Research Articles

Understanding the behavior of phenylurazole-tyrosine-click electrochemical reaction using hybrid electroanalytical techniques

In this work, the electrochemical behavior of 4-phenylurazole (Ph-Ur) was studied and the latter was used as a molecular anchor for the electrochemical bioconjugation of tyrosine (Y). Cyclic voltammetry (CV) and controlled potential coulometry (CPC) allowed the in-situ generation of the PTAD (4-phenyl-3 H-1,2,4-triazole-3,5(4 H)-dione) species from phenylurazole on demand for tyrosine electrolabeling. The chemoselectivity of the reaction was studied with another amino acid (lysine, Lys) and no changes in Lys were observed. To evaluate the performance of tyrosine electrolabeling, coulometric analyses at controlled potentials were performed on solutions of phenylurazole and the phenylurazole-tyrosine mixture in different proportions (2:1, 1:1, and 1:2). The electrolysis of the phenylurazole-tyrosine mixture in the ratio (1:2) produced a charge of 2.07 C, very close to the theoretical value (1.93 C), with high reaction kinetics, a result obtained here for the first time. The products obtained were identified and characterized by liquid chromatography coupled to high-resolution electrospray ionization mass spectrometry (LC-HRMS and LC- HRMS2). Two products were formed from the click reactions, one of which was the majority. Another part of this work was to study the electrochemical degradation of the molecular anchor 4-phenylazole (Ph-Ur). Four stable degradation products of phenylurazole were identified (C7H9N2O, C6H8N, C6H8NO, C14H13N4O2) based on chromatographic profiles and mass spectrometry results. The charge generated during the electrolysis of phenylurazole (two-electron process) (2.85 C) is inconsistent with the theoretical or calculated charge (1.93 C), indicating that secondary/parasitic reactions occurred during the electrolysis of the latter. In conclusion, the electrochemically promoted click phenylurazole-tyrosine reactions give rise to click products with high reaction kinetics and yields in the (1:2) phenylurazole-tyrosine ratios, and the presence of side reactions is likely to affect the yield of the click phenylurazole-tyrosine reaction.

Increasing the Sensitivity of pH Glass Electrodes with Constant Potential Coulometry at Zero Current.

It has recently become possible to increase the sensitivity of ion-selective electrodes (ISEs) by imposing a constant cell potential, allowing one to record current spikes with a capacitor placed in series in the circuit. The approach requires a transient current to pass through the measurement cell, which unfortunately may introduce measurement errors and additionally excludes the use of high-impedance indicator electrodes, such as pH glass electrodes. We present here an electronic circuit that overcomes these limitations, where the cell is measured at zero current in combination with a voltage follower, and the current spike and capacitor charging occur entirely within the instrument. The approach avoids the need for a counter electrode, and one may use any electrode useful in potentiometry regardless of its impedance. The characteristics of the circuit were found to approach ideality when evaluated with either an external potential source or an Ag/AgCl electrode. The current may be linearized and extrapolated to further reduce the measurement time. The circuit is further tested with the most common yet very challenging electrode, the pH glass electrode. A precision of 64 μpH was obtained for 0.01 pH change up to 0.05 from a reference solution. Similar pH changes were also measured reliably further away from the reference solution (0.5-0.55) and resulted in a precision of 377 μpH. The limitations of this experimental setup were explored by performing pH calibrations within the measuring range of the probe.

Transfer of Sodium Ion across Interface between Na+-Selective Electrode Membrane and Aqueous Electrolyte Solution: Can We Use Nernst Equation If Current Flows through Electrode?

Electrochemical impedance and chronopotentiometric measurements with Na+-selective solvent polymeric (PVC) membranes containing a neutral ionophore and a cation exchanger revealed low-frequency resistance, which is ascribed to Na+ ion transfer across the interface between the membrane and aqueous solution. The attribution is based on the observed regular dependence of this resistance on the concentration of Na+ in solutions. The respective values of the exchange current densities were found to be significantly larger than the currents flowing through ion-selective electrodes (ISEs) during an analysis in non-zero-current mode. This fact suggests that the interfacial electrochemical equilibrium is not violated by the current flow and implies that the Nernst equation can be applied to interpret the data obtained in non-zero-current mode, e.g., constant potential coulometry.

Electrocatalytic Nitrite Reduction in Neutral Water with Ni(II) and Co(II) Macrocycle Complexes: Catalytic Evaluation and Mechanistic Elucidation

AbstractNitrite anions, of anthropogenic origin, in the environment disrupt the nitrogen cycle making the electrocatalytic reduction of nitrite a significant objective. Homogeneous Ni(II) and Co(II) complexes bearing a macrocyclic supporting ligand consisting of a tridentate redox active bis(imino)pyridine moiety coupled with a tertiary amine donor site are effective and selective for the electrocatalytic reduction of nitrite to ammonium ion and hydroxylamine in buffered (pH 7) aqueous solutions. Controlled potential coulometry at potentials from −0.98 to −1.05 V vs Ag/AgCl in 4‐morpholinepropanesulfonic acid (MOPS) buffer yielded ammonium as the major product with Faradaic efficiencies ranging from 76–90 %. A foot‐of‐the‐wave analysis yielded calculated turn‐over frequencies of 61 s−1and 28 s−1 for the Ni and Co complexes, respectively. The Ni complex displayed a higher selectivity for NH4+/NH2OH than the Co analog. A computational examination of the catalytic mechanism of the Ni complex was used to support and elucidate the proposed chemical steps, provide some energetic details of the electron and proton transfers, and present a rationale for the selectivity of this reduction.

Hydrogen evolution at Ni foam electrodes and Ni-Sn coated Ni foam electrodes

The hydrogen evolution reaction (HER) was investigated in 1.0 M KOH at 25 °C at Ni foams with different pore sizes (450–1200 µm), and at the Ni-Sn/Ni foam electrodes, where Ni-Sn alloys were electrodeposited from the pyrophosphate-glycine bath using controlled potential coulometry (CPC) technique. The cross-section analysis revealed that rough Ni-Sn alloy covers complete available inner and outer foam surface, while investigated coating composition varied from 62 to 80 at% Ni (20–38 at% Sn). Comparing the HER polarization curves, the overpotential at j = −200 mA cm−2 was 427 mV lower for Ni-Sn samples than for bare Ni foams, while Tafel slopes changed from − 120 mV dec−1 at bare Ni foams to − 50 mV dec−1 for Ni-Sn/Ni foam samples. The lowest overpotential at − 100 mA cm−2 achieved is as low as − 77 mV. These cathodes could be promising 3D materials for industrial water electrolysis in zero-gap membrane flow cells.

Ultrasensitive sensing of pH and fluoride with enhanced constant potential coulometry at membrane electrodes

Minute potential changes at membrane electrodes may be translated to easily detectable current spikes if the cell potential is held constant and the change is imposed onto a capacitive element placed in series. While this results in a very important increase in measurement precision, the current transient passing through the sensing membrane contributes to measurement uncertainty and may not be applicable to all sensing materials. This limitation is overcome by treating the ion-selective electrode as reference electrode, which allows one to avoid current passing through the ion-selective membrane. The potential stability of the Ag/AgCl element upon passage of current was confirmed to be excellent, as expected for an ideally non-polarizable electrode. This greatly increases the reproducibility and precision of the method. The approach also allows one to use the LaF3 crystal-based fluoride sensitive membrane, for which passage of current transients gives deleterious effects. An electronic circuit was built to automate the control of the capacitive element. An improvement of precision (from 829 to 177 μpH) and a reduction of signal drift (from 1.89% of total charge to 0.38%) was demonstrated with membrane-based pH electrodes while fluoride sensing was achieved for the first time with constant potential coulometry at high reproducibility and precision (RSD of just 0.026% activity change).

Electrochemistry and Mass Transport of Ytterbium(III) in Bis(trifluoromethylsulfonyl)imide-Based Room-Temperature Ionic Liquids: Effects of Temperature, Viscosity, and Electrode Materials

Cyclic staircase voltammetry, rotating disk electrode voltammetry, controlled potential coulometry, and electrochemical impedance spectroscopy were used to probe the electrochemistry and mass transport of Yb3+ in the six room temperature ionic liquids based on the bis(trifluoromethylsulfonyl)imide (Tf2N−) anion with, 1-(1-butyl)−3-methylimidazolium (BuMeIm+), 1-(1-butyl)−1-methylpyrrolidinium (BuMePyro+), 1-(1-butyl)pyridinium (BuPy+), 1-butyltrimethylammonium (BuMe3N+), 1-ethyl-3-methylimidazolium (EtMeIm+), and tri(1-butyl)methylammonium (Bu3MeN+) cations. These investigations were carried out at glassy carbon as well as polycrystalline gold, platinum, and tungsten electrodes. The heterogeneous electron transfer rate of the quasireversible Yb3+/2+ redox couple was found to depend strongly on the electrode materials with the fastest rate observed at gold and the slowest rate found at tungsten, but was independent of the physicochemical properties of the various ionic liquids, in particular, the absolute viscosity. However, the mass transport of Yb3+ was dependent on the viscosity, and the temperature dependence of the diffusion coefficients was well represented by a Vogel-Tammann-Fulcher type expression for glass-forming ionic liquids. Analysis of the diffusion coefficient data with the Stokes-Einstein equation indicated that the solvodynamic radius of the diffusing Yb3+ was constant and independent of the structure and properties of the ionic liquid cations. The solvodynamic radius of Yb3+ was estimated from the “stick model” for the Stokes-Einstein equation. Application of the Random Closest Packing (RCP) model for spheres in consideration of the solvodynamic radius of the diffusing Yb3+ and the ionic radii of Yb3+ and Tf2N−, indicated that the former must diffuse in association with ∼5–6 of the anions.

Electrochemical synthesis of new quinone-imines with assisted of 4-ethynylaniline and para-toluidine as nucleophile

Electrochemical oxidation of 3 and 4 substituted catechols in the presence of 4-ethynylaniline and para-toluidine as a nucleophile in acetonitrile/ sodium acetate 0.15 M (30/70) solution has been carried out in detail with employing the cyclic voltammetry and controlled potential coulometry methods. The results show that the o-benzoquinones derived from these catechols participate in Michael type reaction with these nucleophiles to form the corresponding new p-quinone imines. We derived some new p-quinone-imines derivatives with good yields based on the electrochemical oxidation in the controlled potential situation, without toxic reagents and solvents, at the carbon electrode, and in an undivided cell.

Elucidating Two Distinct Pathways for Electrocatalytic Hydrogen Production Using CoII Pincer Complexes.

Hydrogen gas is a sustainable energy source with water as the sole combustion product. As a result, efforts to catalyze H2 production are pertinent and widespread. The electrocatalytic H2 generating capabilities of two CoII complexes, [Co(κ3 -2,6-{Ph2 PNR}2 (NC5 H3 ))Br2 ] with R=H (I) or R=Me (II), were presented for a variety of proton sources including trifluoroacetic acid (TFA), acetic acid (AA), and trifluoroethanol (TFE). Cyclic voltammetry and controlled potential coulometry demonstrated that electrocatalysis from I and II occurred at two different potentials and are associated with different reduction processes. Density functional theory analysis provided insight into the identities of the catalyst and supported two distinct reaction pathways for electrocatalytic proton reduction. Specifically, stronger acids (e. g., AA, TFA) proceeded at -1.31 to -1.45 V through a MI /MIII pathway while sources with higher pKa values (e. g., TFE, H2 O) generated hydrogen at -2.4 V via M0 /MII ligand-assisted metal-centered reduction.

Light-driven ion extraction of polymeric membranes for on-demand Cu(II) sensing

The modulation of the ion-fluxes across a polymeric membrane is important for designing attractive methodologies. As an alternative to the commonly used dynamic electrochemistry approaches, light can be used as an external stimulus and provides a very convenient way to manipulate ions release and/or extraction into a polymeric membrane. Herein, we designed a solid-contact polymeric membrane ion-selective sensor that exhibits dynamic response by light irradiation at 375 nm. The electrode membrane contains a light-sensitive lipophilic salt (bis(4-tert-butylphenyl)iodonium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (R+-R-, BTDT-TFPB) instead of traditional ion exchanger. Under light illumination, the decomposition of the lipophilic cation makes the membrane with ion-exchange properties. The solid-contact ion-selective electrodes based on potentiometry and constant potential coulometry have been explored for direct ion sensing. Copper was selected as a mode analyte and can be determined at micromole levels. The proposed dynamic ion sensors show promise for on-demand ion sensing.

Chloride Oxidation as an Alternative to the Oxygen-Evolution Reaction on HxWO3 Photoelectrodes

A comparison of photoelectrochemical oxygen-evolution reaction (OER) and chloride oxidation is performed on semiconducting HxWO3 thin films. Over a 3 h controlled potential coulometry (CPC) experim...

Electrochemical oxidation of urazoles in the presence of Meldrum’s acid derivatives: Synthesis of new urazole species, experimental and computational study

• Electrochemistry is an environmentally friendly strategy have been applied for synthesis of new urazoles. • Urazoles are five-membered heterocyclic compounds, which serve different uses in biological activities. • Mechanism and thermodynamic study of electrochemical oxidation of urazoles in the presence of Meldrum’s acid derivatives have been performed. In this work, the electrochemical oxidation of 4-phenylurazole (1) and 4-(4-aminophenyl) urazole (2) in the presence of some Meldrum’s acid derivatives as nucleophiles was studied. Some new urazole derivatives were synthesized in water–ethanol (70:30 v/v) solutions via anodic oxidation of the urazoles ( 1 and 2 ). Because the electrochemical oxidation mechanisms of different electrophiles in the presence of Meldrum’s acids are different, the computational analysis was performed to analyze the mechanism of reactions. Cyclic voltammetry, controlled potential coulometry and spectroscopic methods were applied to obtain experimental results, and the theoretical results were calculated at DFT (B3LYP/6-311G (d,p)) level of theory. In this research, firstly, the effect of the Δ G tot on the oxidation potential was investigated, and it was found that the potential of the electrochemical oxidation of some urazole species is dependent on their Δ G tot . Secondly, the dependence of the electrochemical oxidation mechanism to Δ G tot for the urazole species ( 1 and 2 ) was studied. The results of this study showed why the mechanisms of the electrochemical oxidation of the studied species ( 1 and 2 ) in the presence of all three Meldrum’s acid derivatives are EC .

Green-Electrochemical Synthesis of Novel Catechol Derivative Based on O-Quinone Nucleophilic Addition

In this work, a green-electrochemical synthesis was applied on oxidation of catechol (1) to o -benzoquinone (2) using cyclic voltammetry and controlled potential coulometry. Encouraging results were obtained and has been investigated in the presence of semicarbazide ( 3 ) as a nucleophile in an ethanol/phosphate buffer mixture (pH 7.0). The results showed that novel heterocyclic compound, triazinone, functionalized with hydroxyl and amide groups have been synthesised. The effect of pH, number of cycles, and scan rate were studied to attain a good yield and a high purity of products. The results indicate that the generated o -quinone ( 2 ) participates in a Michael addition reaction with nucleophilic hydrazide via EC mechanism to form the new triazinone adduct. After purification, the products have been characterized by IR, UV-Visible, 1 H and 13 C NMR methods. The green-electrochemical synthesis approach produced novel organics with excellent purities and yields while being environmentally friendly and free of hazardous reagents.

A technique for uranium and plutonium determination using coulometric potentiostatic facility UPK-19 for analysis of mixed-oxide fuel

The content of uranium and plutonium is the main characteristic of mixed uranium-plutonium oxide fuel, which is strictly controlled and has a very narrow range of the permissible values. We focused on developing a technique for measuring mass fractions of uranium and plutonium by controlled potential coulometry using a coulometric unit UPK-19 in set with a R-40Kh potentiostat-galvanostat. Under conditions of sealed enclosures, a special design of the support stand which minimized the effect of fluctuations in ambient conditions on the signal stability was developed. Optimal conditions for coulometric determination of plutonium and uranium mass fractions were specified. The sulfuric acid solution with a molar concentration of 0.5 mol/dm3 was used as a medium. Lead ions were introduced into the background electrolyte to decrease the minimum voltage of hydrogen reduction to –190 mV. The addition of aluminum nitride reduced the effect of fluoride ions participating as a catalyst in dissolving MOX fuel samples, and the interfering effect of nitrite ions was eliminated by introducing a sulfamic acid solution into the cell. The total content of uranium and plutonium was determined by evaluation of the amount of electricity consumed at the stage of uranium and plutonium co-oxidation. Plutonium content was measured at the potentials, at which uranium remains in the stable state, which makes it possible to subtract the contribution of plutonium oxidation current from the total oxidation current. The error characteristics of the developed measurement technique were evaluated using the standard sample method and the real MOX fuel pellets. The error limits match the requirements set out in the specifications for MOX fuel. The technique for measuring mass fractions of uranium and plutonium in uranium-plutonium oxide nuclear fuel was certified. The relative measurement error of the mass fraction of plutonium and uranium was ±0.0070 and ±0.0095, respectively. The relative error of the ratio of the plutonium mass fraction to the sum of mass fractions of uranium and plutonium was ±0.0085.

Controlled Potential Coulometry for the accurate determination of plutonium in the presence of uranium: The role of sulfate complexation

Controlled Potential Coulometry (CPC) is generally regarded as one of the most accurate analytical methods available for the quantification of plutonium (Pu) in acidic aqueous solutions. With a growing use of mixed oxide nuclear fuel, there has been an interest in the technique’s applicability to the analysis of Pu in the presence of uranium (U). Expanding on previous studies, the work presented herein demonstrates the highly accurate CPC analysis of Pu in mixed solutions (Pu + U) containing large quantities of U (U:Pu up to 100:1) as well as establishing the role played by sulfate anions during the analyses.By combining experimental results with speciation simulations, it is shown that the introduction of U in mixed Pu + U solutions is accompanied by increases in sulfate ions in the nitric acid medium which complex unequally with the different Pu cations in solution. The anions’ stronger affinity of for Pu(IV) rather than Pu(III) causes a decrease in the formal potential of the Pu(IV)/Pu(III) redox couple, directly affecting the degree of completion of the electrochemical reactions performed during CPC. A correction factor, f, is applied to account for the degree of completion of the analysis’ electrochemical steps and compensate for the effects of complexation. Thereby, a level of accuracy comparable to that achieved during the analysis of pure Pu solutions, is attained.Ultimately, a series of recommendations are put forward such that it becomes possible to maintain CPC’s good analytical performance for the measurement of Pu content in mixed Pu + U solutions.

Accurate determination of plutonium by Controlled Potential Coulometry: uncertainty evaluation by the Monte Carlo Method approach

The accurate determination of plutonium (Pu) mass fraction in nuclear materials is essential to nuclear matter accountancy and international safeguard programs. Controlled-Potential Coulometry (CPC) is one of the best available analytical methods to perform such measurements. The implementation of CPC at the Nuclear Matter Metrological Laboratory of the French Atomic Energy Commission is described as well as the evaluation of measurement uncertainty using two approaches: the guide to the expression of uncertainty in measurement, and the Monte Carlo Method. The uncertainty values determined are compared to the international target values published by the International Atomic Energy Agency.

Nekoliko monoslojeva elektrohemijski istaloženog iridijuma na podlozi od Ti2AlC kao katalizatori za izdvajanje vodonika u rastvoru sumporne kiseline

The hydrogen evolution reaction (HER) was investigated at sub-monolayers of iridium electrodeposited on Ti2AlC substrate. The lowest amount of electrodeposited iridium was 3 close-packed (111) monolayers (3 ML), while the highest one was 22 ML (3, 5, 10, 15 and 22 ML). The lowest and the highest amounts of iridium were electrodeposited by linear sweep voltammetry (LSV), while the other three samples were electrodeposited by controlled potential coulometry, from the solution containing 1 mM, or 3 mM K3IrCl6 + 0.5 M Na2SO4 (pH 6.2) at 70 °C. The HER was investigated by polarization and electrochemical impedance spectroscopy (EIS) measurements. Polarization curves for iridium sub-monolayers equal, or higher than 6 ML showed low Tafel slope of -14 to -16 mV dec-1 up to about -0.1 A cm-2, while at higher current densities the Tafel slopes increased, varying between -40 and -72 mV dec-1. The highest value of exchange current density (jo) was obtained for 6 ML of electrodeposited iridium, being -27.89 A g-1. The overpotential at j = -0.3 A cm-2 could be determined for samples containing 15 ML and 22 ML of iridium, being 82 mV.

Green Synthesis and Electrochemical Properties of Mono- and Dimers Derived from Phenylaminoisoquinolinequinones.

In the search for new quinoid compounds endowed with potential anticancer activity, the synthesis of novel heterodimers containing the cytotoxic 7-phenylaminoisoquinolinequinone and 2-phenylaminonaphthoquinone pharmacophores, connected through methylene and ethylene spacers, is reported. The heterodimers were prepared from their respective isoquinoline and naphthoquinones and 4,4′-diaminodiphenyl alkenes. The access to the target heterodimers and their corresponding monomers was performed both through oxidative amination reactions assisted by ultrasound and CeCl3·7H2O catalysis “in water”. This eco-friendly procedure was successfully extended to the one-pot synthesis of homodimers derived from the 7-phenylaminoisoquinolinequinone pharmacophore. The electrochemical properties of the monomers and dimers were determined by cyclic and square wave voltammetry. The number of electrons transferred during the oxidation process, associated to the redox potential EI1/2, was determined by controlled potential coulometry.

Utilizing Charge Effects and Minimizing Intramolecular Proton Rearrangement to Improve the Overpotential of a Thiosemicarbazonato Zinc HER Catalyst.

The zinc(II) complex of diacetyl-2-(4-methyl-3-thiosemicarbazone)-3-(2-hydrazonepyridine), ZnL1 (1), was prepared and evaluated as a precatalyst for the hydrogen evolution reaction (HER) under homogeneous conditions in acetonitrile. Complex 1 is protonated on the noncoordinating nitrogen of the hydrazonepyridine moiety to yield the active catalyst Zn(HL1)OAc (2) upon addition of acetic acid. Addition of methyl iodide to 1 yields the corresponding methylated derivative ZnL2I (3). In solution, partial dissociation of the coordinated iodide yields the cationic derivative 3'. Complexes 1-3 were characterized by 1H NMR, FT-IR, and UV-visible spectroscopies. The solid-state structures of 2 and 3 were determined by single crystal X-ray diffraction. HER studies conducted in acetonitrile with acetic acid as the proton source yield a turnover frequency (TOF) of 7700 s-1 for solutions of 1 at an overpotential of 1.27 V and a TOF of 6700 s-1 for solutions of 3 at an overpotential of 0.56 V. For both complexes, the required potential for catalysis, Ecat/2, is larger than the thermodynamic reduction potential, E1/2, indicative of a kinetic barrier attributed to intramolecular proton rearrangement. The effect is larger for solutions of 1 (+440 mV) than for solutions of 3 (+160 mV). Controlled potential coulometry studies were used to determine faradaic efficiencies of 71 and 89% for solutions of 1 and 3, respectively. For both catalysts, extensive cycling of potential under catalytic conditions results in the deposition of a film on the glassy carbon electrode surface that is active as an HER catalyst. Analysis of the film of 3 by X-ray photoelectron spectroscopy indicates the complex remains intact upon deposition. A proposed ligand-centered HER mechanism with 1 as a precatalyst to 2 is supported computationally using density functional theory (DFT). All catalytic intermediates in the mechanism were structurally and energetically characterized with the DFT/B3LYP/6-311g(d,p) in solution phase using a polarizable continuum model (PCM). The thermodynamic feasibility of the mechanism is supported by calculation of equilibrium constants or reduction potentials for each proposed step.

Measurement of As(III) with in situ subtraction of background and interferent signals by double potential step-anodic stripping coulometry

Water quality monitoring for heavy metal contaminants is currently performed using instrumental techniques that rely on random “grab sampling” where samples are collected on-site and then transported to a central laboratory for analysis. Alternatively, there are some portable instruments which are suitable for monitoring heavy metals in the field. However, both approaches require a trained technician and provide only a snapshot of the water quality at a particular time and place. Far preferable would be a measurement approach that might enable 24/7, on-demand monitoring in real time, and in this work we describe progress on a novel electrochemical sensor system that might make such applications feasible. Specifically, we report advances in a new technique termed anodic stripping coulometry (ASC) in which the charge associated with the deposition and stripping of the contents of a fixed-volume, thin-layer sample cell is used to provide, viaFaraday’s law, an absolute determination of metal content. As(III) was chosen as the target analyte, and a double potential step (DPS) procedure for in situ background correction has been developed, which does not require the use of a separate blank solution. With the DPS-ASC approach, response for As(III) is linear between 10 0–1,000 ppb with a detection limit at the 75 ppb level. Accurate results were obtained both for lab samples containing high levels of other metals, such as Cu(II), Cd(II), Pb(II), and Zn(II), and for river water samples spiked with As(III). While further work remains to be done, this represents important progress in the development of ASC-based sensors suitable for calibration-free, on-site heavy metal monitoring networks.