Stripping Voltammetry Research Articles

Development of electrochemical Zn2+ sensors for rapid voltammetric detection of glucose-stimulated insulin release from pancreatic β-cells

Diabetes is a chronic disease characterized by elevated blood glucose levels resulting from absent or ineffective insulin release from pancreatic β-cells. β-cell function is routinely assessed in vitro using static or dynamic glucose-stimulated insulin secretion (GSIS) assays followed by insulin quantification via time-consuming, costly enzyme-linked immunosorbent assays (ELISA). In this study, we developed a highly sensitive electrochemical sensor for zinc (Zn2+), an ion co-released with insulin, as a rapid and low-cost method for measuring dynamic insulin release. Different modifications to glassy carbon electrodes (GCE) were evaluated to develop a sensor that detects physiological Zn2+ concentrations while operating within a biological Krebs Ringer Buffer (KRB) medium (pH 7.2). Electrodeposition of bismuth and indium improved Zn2+ sensitivity and limit of detection (LOD), and a Nafion coating improved selectivity. Using anodic stripping voltammetry (ASV) with a pre-concentration time of 6 min, we achieved a LOD of 2.3 μg/L over the wide linear range of 2.5–500 μg/L Zn2+. Sensor performance improved with 10-min pre-concentration, resulting in increased sensitivity, lower LOD (0.18 μg/L), and a bilinear response over the range of 0.25–10 μg/L Zn2+. We further characterized the physicochemical properties of the Zn2+ sensor using scanning electron microscopy (SEM), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). Finally, we demonstrated the sensor's capability to measure Zn2+ release from glucose-stimulated INS-1 β-cells and primary mouse islets. Our results exhibited a high correlation with secreted insulin and validated the sensor's potential as a rapid alternative to conventional two-step GSIS plus ELISA methods.

Ultra-sensitive detection of methylparathion using palladium nanoparticles embedded reduced graphene oxide redox nanoreactors

The environment-friendly and energy-efficient monodispersed carbon-based nanosystems for environment monitoring are always in colossal demand. The present work has come up with a novel reverse microemulsification route which is inherently safer, energy-efficient and toxicant free approach for synthesis of monodisperse palladium nanoparticles embedded RGO based nanoreactors (Pd@NrGO/GCE). In present system, Pd@NrGO/GCE are acting as nanoreactors by providing large surface areas for electrocatalysis of methylparathion and allowing the study of redox attributes at faster rates. The successful characterization was done using X-ray diffraction studies, Raman spectroscopy, field emission scanning electron microscopy, small angle X-ray scattering and high resolution transmission electron microscopy analysis. The electroanalytical response in the square wave anodic stripping voltammetry has been generated by the adsorption of MP followed by subsequent redox catalysis by Pd@NrGO/GCE. The homogeneous film fabrication was enabled by smooth spherical nanostructures imparting higher surface areas with small particle size. The sensor performance towards oxidation of MP poses wide linearity and a low limit of detection of 1.067 ngml−1 with successful application to real time analysis.

A Planar Disk Electrode Chip Based on MWCNT/CS/Pb2+ Ionophore IV Nanomaterial Membrane for Trace Level Pb2+ Detection.

Unlike conventional lead ion (Pb2+) detecting methods, electrochemical methods have the attractive advantages of rapid response, good portability and high sensitivity. In this paper, a planar disk electrode modified by multiwalled carbon nanotube (MWCNTs)/chitosan (CS)/lead (Pb2+) ionophore IV nanomaterial and its matched system are proposed. This system presented a good linear relationship between the concentration of Pb2+ ions and the peak current in differential pulse stripping voltammetry (DPSV), under optimized conditions of -0.8 V deposition potential, 5.5 pH value, 240 s deposition time, performed sensitive detection of Pb2+ within sensitivity of 1.811 μA · μg-1 and detection limit of 0.08 μg · L-1. Meanwhile, the results of the system in detecting lead ions in real seawater samples are highly similar to that of inductively coupled plasma emission spectrometer (ICP-MS), which proved a practicability for the system in detection of trace-level Pb2+.

A strategy for As(III) determination based on ultrafine gold nanoparticles decorated on magnetic graphene oxide

In this work, a new dendrimer modified magnetic graphene oxide (GO) was used as a substrate for electrodeposition of Au nanoparticles. The modified magnetic electrode was employed for sensitive measuring of As(III) ion as a well-established human carcinogen. The prepared electrochemical device exhibits excellent activity towards As(III) detection using the square wave anodic stripping voltammetry (SWASV) protocol. At optimum conditions (deposition potential at −0.5 V for 100 s in 0.1 M acetate buffer with pH 5.0), a linear range from 1.0 to 125.0 μgL−1 with a low detection limit (calculated by S/N = 3) of 0.47 μg L−1 was obtained. In addition to the simplicity and sensitivity of the proposed sensor, its high selectivity against some major interfering agents, such as Cu(II) and Hg(II) makes it an appreciable sensing tool for the screening of As(III). In addition, the sensor revealed satisfactory results for detection of As(III) in different water samples, and the accuracy of obtained data were confirmed by inductively coupled plasma atomic emission spectroscopy (ICP-AES) setup. Accounting for the high sensitivity, remarkable selectivity and good reproducibility, the established electrochemical strategy has great potential for analysis of As(III) in environmental matrices.

A new sustainable approach using a composite material based on dimethylglyoxime and graphite immobilized on a 3D printed support for selective nickel detection

In this work, the development of a low-cost electrochemical device (U$ 0.02 per electrode) from the immobilization of a composite material (CM) based on graphite powder, dimethylglyoxime (DMG) and nail polish, on a 3D printed acrylonitrile butadiene styrene (ABS) support was proposed for direct, sensitive and selective determination of Ni(II) by square-wave cathodic adsorptive stripping voltammetry (SWCAdSV) in a reduction potential of −1.15 V (vs Ag|AgCl|KCl(sat)). The CM was properly characterized by X-ray diffraction (XRD) and Raman spectroscopy, additionally, the electrode surface of the proposed device (3Ds-CM/DMG) was morphologically characterized through images obtained by scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The electrode was applied as a proof of concept for monitoring Ni(II) levels in spiked tap water and synthetic urine samples. Under optimal analysis conditions, the developed method showed a good linear working range with concentrations ranging from 5 to 100 µg L−1, detectability (limit of detection) of 1.693 µg L−1, and excellent precision with relative standard deviation (RSD) of 2.9%. The doped samples at three concentration levels presented recovery values from 93.8 to 103.1%, using as a sample preparation step a simple dilution in supporting electrolyte. Furthermore, the results were analytically validated by statistical comparison with results obtained by flame atomic absorption spectrometry (F AAS). Finally, the electrodes showed RSD of 6.1% for construction reproducibility, which allows inferring that the proposed electrode proves to be a promising analytical tool with wide applicability.

Adsorptive Stripping Voltammetry for Determination of Vanadium: A Review.

The main purpose of this review is to present methods of adsorptive stripping voltammetry that can be used to determine trace amounts of VO2(+) in various types of samples. The detection limits achieved using different working electrodes are presented. The factors influencing the obtained signal, including the selection of the complexing agent and the selection of the working electrode, are shown. For some methods, in order to increase the range of applied concentrations in which vanadium can be detected, a catalytic effect is introduced to adsorptive stripping voltammetry. The influence of the foreign ions and organic matter contained in natural samples on the vanadium signal is analyzed. This paper presents methods of elimination associated with the presence of surfactants in the samples. The methods of adsorptive stripping voltammetry for the simultaneous determination of vanadium with other metal ions are also characterized below. Finally, the practical use of the developed procedures, mainly for the analysis of food and environmental samples, is summarized in a tabular version.

Platinum Group Element distribution in water and marine biota from two impacted estuarine environments (Douro and Ave estuaries, Portugal)

Platinum Group Elements (PGEs) are contaminants of emerging environmental concern considering their continuous increasing use and subsequent release in the environment. While recent field studies provided PGE levels in seawater, scarce knowledge still exists regarding PGE contamination in marine organisms, especially for rhodium (Rh). Water, macroalgae and mussels were sampled along two representative urbanized estuarine systems and adjacent coastal areas (Douro and Ave estuaries, Portugal). Rhodium and platinum (Pt) concentrations were quantified through both stripping voltammetry and mass spectrometry in collected samples. Spatial mapping of PGE contamination was, to a certain extent, correlated with proxies of urban effluents. The use of Pt/Rh ratios reflected the dominant influence of PGE traffic emissions along the Douro and inputs from various sources (including industries) on the Ave Estuary. Macroalgae and mussels PGE concentrations reflected urban pressure, amplifying environmental signals, and supporting their relevant use as bioindicators of PGE contamination in estuarine/coastal systems.

A 3D phytic acid cross-linked high-porous conductive hydrogel integrating g-C3N4 for electrochemical multiplex sensing of heavy metal ions

It is a great challenge to develop an effective super-sensitive capture method for multiplex heavy metal ions (HMIs), because HMIs is extremely toxic to public health and the environment, what's more their contamination is usually multiplex ions pollution. In this work, a 3D high-porous conductive polymer hydrogel was designed and prepared with high-stable and easy mass production, which is very favorable for the industrialization. The polymer hydrogel (g–C3N4–P(Ani-Py)-PAAM) was formed from the mixture of aniline pyrrole copolymer and acrylamide cross-linked with phytic acid as dopant and cross-linker and integrated with g-C3N4. The 3D networked high-porous hydrogel not only exhibits excellent electrical conductivity, but also provides a large surface area for increasing the number of immobilized ions. Importantly, the 3D high-porous conductive polymer hydrogel was applied successfully in electrochemical multiplex sensing of HIMs. The prepared sensor used differential pulse anodic stripping voltammetry exhibited high sensitivities, low detection limit and wide detection ranges for Cd2+, Pb2+, Hg2+ and Cu2+, respectively. Moreover, the sensor showed a high accuracy in lake water test. The preparation and application of the hydrogel in electrochemical sensor provided an availability strategy to capture and detect the various HMIs by electrochemistry in solution and has great commercial application prospect.

Simultaneous Sensing of Cd(II), Pb(II), and Cu(II) Using Gold Nanoparticle-Modified APTES-Functionalized Indium Tin Oxide Electrode: Effect of APTES Concentration.

In this work, indium tin oxide (ITO) electrodes were functionalized with varying 3-aminopropyltriethoxysilane (APTES) concentration percentages (0.5, 0.75, 1.0, and 2.0 wt %) to obtain the optimum conditions for the assembly of the as-synthesized gold nanoparticles (AuNPs). The AuNP coverage, wettability, and electrochemical performance of the modified electrodes were evaluated. The AuNP/0.75% APTES-ITO-modified electrode exhibited uniform coverage of AuNPs and high electrochemical performance for the simultaneous detection of Cd(II), Pb(II), and Cu(II) ions. Under the optimum conditions, the AuNP/0.75% APTES-ITO-modified electrode showed a linear detection range of 5-120 ppb and limit of detection of 0.73, 0.90, and 0.49 ppb for the simultaneous detection of Cd(II), Pb(II), and Cu(II) ions, respectively, via square wave anodic stripping voltammetry. The modified electrode demonstrated good anti-interference toward other heavy metal ions, good reproducibility, and suitability for application in environmental sample analysis.

Selective determination of cadmium and lead ions in different food samples by poly (riboflavin)/carbon black-modified glassy carbon electrode

In this research, a poly (riboflavin)/carbon black-modified glassy carbon electrode (PRF/CB/GCE) is introduced as a novel electrochemical sensor toward Cd2+ and Pb2+ simultaneous measurement in presence of bismuth ions, applying differential pulse anodic stripping voltammetry (DPASV). Regarding the optimized conditions, the linear ranges were achieved from 0.5 to 600 nM for Cd2+ and Pb2+. The detection limit (LOD) was found to be 0.16 nM for Cd2+ and 0.13 nM for Pb2+. In order to perform the technique in real application, the proposed electrode was used to simultaneously detect ions in rice, honey, and vegetable samples with satisfactory recoveries – indicating that the sensor possesses good practicability to determine Cd2+ and Pb2+. Moreover, an atomic absorption spectrometry (AAS) was used in order to detect the concentration of ions as a reference technique in rice, honey, and vegetable samples.

Electrochemical detection of lead and cadmium ions in water by sensors based on modified track-etched membranes

Electrochemical sensors based on PET track-etched membranes (TeMs) were prepared by photograft polymerization of 2-hydroxyethylmethacrylate (HEMA) and subsequent formation of interpolyelectrolyte complexes with poly(allylamine) (PAlAm). The functionalized TeMs were characterized by scanning electron microscopy (SEM), FTIR spectroscopy, gas permeability and colorimetric assay. Parameters of graft polymerization such as monomer concentration, time of irradiation, solvent and others were estimated and optimized. Cd(II) and Pb(II) ions were detected by using square wave anodic stripping voltammetry (SW-ASV). Additional modification of the modified membranes with 4-mercaptophenylboronic acid (MPBA) led to increasing of stability of the sensors. The linear range for the detection of Cd(II) and Pb(II) ions using the modified electrode was 50 µg - 4.25 mg/L and 10 µg – 4.25 mg/L. Moreover, the obtained results of SW-ASV demonstrated that the enhancement in the electrochemical signals was achieved with PET TeMs-g-PHEMA-PAlAm\MPBA compared to that of a bare PET TeMs-g-PHEMA. Selectivity test showed that alkali and alkaline earth metal ions, except for magnesium (up to 1 mg/l), do not particularly interfere with the determination of lead and cadmium in the analyte. Sensing of Pb and Cd ions in river water demonstrate us that prepared sensors can be used in real conditions with sufficient accuracy and reproducibility of the results.

Ultra-thin silver nanowires’ synthesis in pore-confined space of mesoporous silica thin film

In the present work, we report a synthesis procedure for the preparation of vertically aligned mesoporous silica thin films containing long, nanometer-scale thin silver nanowires inside pores. The inter-channel nanowires had a fine crystalline structure and a diameter of no more than 2 nm. Despite the diameter being the edge of the theoretical possibility of synthesis, the nanowires were stable enough to be observed by transmission electron microscope and could be clearly observed. For the synthesis, we applied the idea of silica nanoreactors, and the procedure consists of two steps: fabrication of an initial organically-functionalized silica thin film containing silver ions distributed regularly inside vertically aligned pores and following thermal decomposition resulting in the decomposition of the organic anchoring groups and the formation of metallic crystalline nanowires from released silver atoms. Both the final nanocomposite and the initial material were studied by means of transition electron microscopy and electrochemical techniques: linear scan and differential pulse anodic stripping voltammetry. The crystallinity of silver nanowires inside silica mesopores was proved by electron diffraction. The spatial confinement realized by silica nanochannels facilitated the stabilization of relatively small and ultra-thin nanowires and the formation of a hexagonal P63/mmc silver crystalline structure instead of the more common Fm3m cubic.

Study of different types of copper electrodes for anodic stripping voltammetric detection of trace metal ions

Copper electrodes exhibit interesting characteristics for application in electrochemical stripping analysis and represent another alternative to their mercury counterparts. In this work, we studied different types of copper-based electrodes for anodic stripping voltammetric detection of trace metal ions. We investigated copper film (CuFE), and bulk copper electrodes, such as in-situ and ex-situ prepared CuFEs using glassy carbon and screen-printed carbon supporting electrodes, a bulk copper disk and screen-printed copper electrode, and a copper wire as the simplest, inexpensive, and readily available analog. For studying their electroanalytical performances, low concentrations (μg L−1) of Cd(II) and Pb(II) were used as model ions. We examined and optimized several key parameters affecting the preparation and functioning of copper electrodes, such as the composition of the measurement solution, copper concentration for in-situ and ex-situ preparation of CuFE, deposition potential, deposition time, etc. Most of the tested copper electrodes showed favorable stripping voltammetric performances, particularly the CuFE ex-situ prepared on a glassy carbon electrode and the CuFE in-situ prepared on a screen-printed carbon substrate. Notably, a copper wire revealed an excellent electroanalytical operation with a limit of detection of 0.6 μg L−1 for Pb(II) and 1.8 μg L−1 for Cd(II). The practical applicability of a copper electrode was tested by measuring a real tap water sample.

Flexible biodegradable electrochemical sensor of PBAT and CNDs composite for the detection of emerging pollutants

Herein we proposed the fabrication and optimization of a flexible electrochemical sensor composed of polymer poly(butylene adipate-co-terephthalate) (PBAT) and Carbon Nitrite Dots (CNDs). The materials stand out for being low-cost, flexible, biodegradable, and easily discarded after use. Characterization was performed by Cyclic Voltammetry (CV), Electrochemical Impedance Spectroscopy (EIS), contact angle, Raman spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), and Transmission Electron Microscopy (TEM). The sensor was used to simultaneously detect emerging pollutants such as cadmium and copper by Square Wave Anodic Stripping Voltammetry (SWV) technique. As result, a linear behavior in the concentration range of 0.1 to 1.0 mM for cadmium and copper showed excellent electrochemical activity with sensitivity of (3.79 ± 0.21) × 10−5 (mA cm−2) (M)−1 for cadmium and (2.06 ± 0.14) × 10−5 (mA cm−2) (M)−1 for copper. The LD and LQ values obtained for cadmium were 2.75 × 10−6 M and 9.16 × 10−6 M, and for copper were 7.09 × 10−6 M and 2.36 × 10−5 M, respectively. Therefore, the sensors obtained in this work have the advantage of simultaneously detecting emerging pollutants such as cadmium and copper, including real tap water samples.

Tuning Interfacial Chemistry to Direct the Electrosynthesis of Metal Oxide Semiconductors.

ConspectusMetal oxide semiconductors have many features that make them attractive for both fundamental and applied studies. For example, these compounds contain elements (e.g., Fe, Cu, Ti, etc.) that are derived from minerals rendering them earth-abundant and, most often, are also not toxic. Therefore, they have been examined for possible applicability in a very diverse range of technological applications including photovoltaic solar cells, charge storage devices, displays, smart windows, touch screens, etc. The fact that metal oxide semiconductors have both n- and p-type conductivity makes them amenable for use as hetero- or homojunctions in microelectronic devices and as photoelectrodes in solar water-splitting devices. This Account presents a review of collaborative research on the electrosynthesis of metal oxides from our respective groups against the backdrop of key developments on this topic. The many variants that interfacial chemical modification schemes offer are shown herein to lead to the targeted synthesis of a wide array of not only simple binary metal oxides but also more complex chemistries involving multinary compound semiconductors and alloys.This Account presents our perspective on how parallel developments in the understanding of and ability to manipulate electrode-electrolyte interfaces have correspondingly enabled the innovation of a broad array of electrosynthetic strategies. These coupled with the advent of versatile tools to probe interfacial processes (undoubtedly, a child of the nanotechnology "revolution") afford an operando examination of how effective the strategies are to secure the targeted metal oxide product as well as the mechanistic nuances. Flow electrosynthesis, for example, removes many of the complications accruing from the accumulation of interfering side products─veritably, this is an Achilles heel of the electrosynthesis approach. Coupling flow electrosynthesis with downstream analysis tools based on spectroscopic or electroanalytical probes opens up the possibility of immediate process feedback and optimization. The combination of electrosynthesis, stripping voltammetry, and electrochemical quartz crystal nanogravimetry (EQCN), either in a static or in a dynamic (flow) platform, is shown below to offer intriguing possibilities for metal oxide electrosynthesis. While many of the examples below are based on our current and recent research and in other laboratories, unlocking even more potential will hinge on future refinements and innovations that surely are around the corner.

Morphology and atomic configuration control of heavy metal attraction modified layer on screen-printed electrode to enhance electrochemical sensing performance

The sensitivity of screen-printed electrochemical (SPE) sensors is heavily dependent on the selection of appropriate modifiers that can optimize the chemical (functional ligands, surface charge, binding energy) and physical (morphological structure) properties of the sensor surface. This study aimed to investigate the impact of these chemical and physical factors on the sensitivity of modified SPEs for the detection of lead and cadmium. The study employed anodic stripping voltammetry to evaluate the sensing performance of SPEs modified with different modifiers, including cellulose acetate, chitosan, Nafion, nylon-6, and silver nanoparticles. Results showed that metal-attracting functional groups and surface charged electrode were the dominant factors affecting the sensitivity of SPEs in heavy metal sensing. Specifically, negatively charged electrode surfaces and metal-attracting -SO32- ligands, as found in Nafion-modified SPE, were identified as the key factors in improving sensor selectivity, rather than the rough physical morphology of the SPE, which was believed to provide more metal detection sites. This conclusion was supported by the combination analyses of electrochemical impedance spectroscopy, electrochemically active surface area and computational molecular binding energy of bare and modified SPEs. The findings of this study provide valuable insights for selecting appropriate SPE modifiers and designing sensor architectures for heavy metal detection.

Recent advances in modified boron-doped diamond electrodes: A review

This review presents recent developments in the modification of boron-doped diamond electrodes (BDDEs) and their application in biosensing, electroanalysis, electrosynthesis, fuel cell construction, and CO2 reduction. The various modification procedures are also described. In addition to the outstanding properties of unmodified BDDEs, they have recently become a highly functional substrate for various modifications. The modifications of BDDEs by metals or metal oxides were aimed at increasing the surface area and promoting electron transfer kinetics or electrocatalytic activity for CO2 reduction, sensing of oxygen, or stripping voltammetry. Modification by polymers such as Nafion, polypyrrole, or polyaniline was used mostly to fine-tune the specificity of voltammetric analyses and interference suppression. DNA, enzymes, or other biomolecules were used to obtain specific sensing capabilities. These chemical modifications are critically compared to the other strategies used for BDDEs, including varied boron doping levels, the ratio of sp2 to sp3 carbon, and BDDE surface pre-treatment.

Simultaneous Heavy Metal Determination in Mussels by Anodic Stripping Voltammetry (ASV) Using Thick Film Modified Graphite Electrodes

Heavy metals are potent polluters of marine ecosystems. Consumption of contaminated seafood may lead to adverse health effects. In this work, thick film modified graphite sensors are used as working electrodes for the simultaneous determination of copper, lead, cadmium and zinc in mussel tissue from the Sea of Japan. The samples were prepared by HNO3 wet mineralization and analyzed in pH 4 acetate buffer by anodic stripping voltammetry. The analytical signal was studied as a function of accumulation potential, accumulation time, and sweep rate to determine the optimal electrolysis conditions. Standard addition method was used to evaluate the heavy metal concentrations to minimize matrix effects. The developed procedure is rapid, inexpensive, and reproducible, and has high selectivity and low limits of detection for the analytes. The relative standard deviations for the concentrations of Cu, Pb, Cd, and Zn are 13%, 21%, 7.7%, and 15%, respectively. The accuracy was confirmed by comparing the results with those obtained by inductively coupled plasma – optical emission spectrometry (ICP-OES) and inductively coupled plasma – mass spectrometry (ICP-MS).

Voltammetric sensing of Cd(II) at ZIF-8/GO modified electrode: Optimization and field measurements

In this work, a metal-organic framework/graphene oxide (MOF(ZIF-8)/GO) nanocomposite was utilized for the electroanalysis of trace level of Cd(II) after modification of a cheap graphite rod electrode (GRE). After closed circuit process on the modified electrode, the differential pulse anodic stripping voltammetry (DPASV) technique was used for measuring of Cd(II). In optimal conditions, the sensor showed a linear dependence of current with concentration range 0.1–30 ppb for Cd(II). Moreover, limit of detection 0.03 ppb were obtained. Besides good selectivity, the sensor also indicated good reproducibility (below 5%). Moreover, the sensor showed satisfactory sensing performance in river, dam and wastewater samples with recovery ranging from 97.2% to 102.4%. Additionally, possible interfering cations were examined, but no significant interference was found. For the detection of trace Cd(II) in real matrices, this sensor illustrated other good merits like high stability, rapidity and simplicity.

A new tool for the determination of humic substances in natural waters: Pulsed voltammetry approach

Humic substances (HS) in natural waters can be determined with a new, simple and sensitive method based on their influence on the background current in a differential pulse - adsorptive cathodic stripping voltammetry. The proposed method, termed PB-HS (pulsed background - humic substances) is discussed in detail, including its application in natural samples from the Krka River estuary. The method was additionally compared with absorbance measurements as well as with the typical electrochemical HS quantification in natural waters based on HS complexation with molybdenum (Mo). A good correlation between methods was observed, with PB-HS showing slightly better sensitivity to humic compounds than classical spectrophotometry. Higher HS concentrations measured with the Mo-method may be due to the enhanced hydrophobicity reached at pH 2 that is required by the method. Advantages of the proposed PB-HS method, compared to existing voltammetric methods for HS quantification, are that it does not require any reagent addition (except buffer) and that it can be used at the natural pH of water as well as in a wide salinity range, which is crucial for its application in estuarine waters.