Titration Of Copper Research Articles

The use of thiazole derivative molecules as sensor materials: Potentiometric determination of Cu(II) ions

AbstractIn this study, poly(vinyl chloride) (PVC)–membrane potentiometric sensors for the determination of copper(II) ions were prepared using 2‐acetamido‐4‐(2‐hydroxyphenyl)thiazole (L1), 2‐amino‐4‐(trifluoromethyl)thiazole‐5‐carboxylic acid (L2) and ethyl 2‐amino‐4,5,6,7‐tetrahydrobenzo[d]thiazole‐6‐carboxylate (L3) ionophores. It was determined that the potentiometric performance characteristics of the sensors prepared with L1 were superior to the others. Based on these properties, the optimum membrane composition was determined as 3.0% ionophore (L1), 64.0% bis(2–ethylhexyl)adipate (DEHA), 32.0% PVC and 1.0% potassium tetrakis (p–chlorophenyl) borate (KTpClPB). The newly developed sensor had a low detection limit of 6.74 × 10−7 mol L−1 over a wide concentration range of 1.0 × 10−1–1.0 × 10−6 mol L−1. Compared with different metal ions, the sensor showed good selectivity to copper(II) ions, had a repeatable, stable and fast response time. The copper(II)–selective sensor could work in a wide range without being affected by pH changes (5.0–9.0). It was used as indicator electrode for the potentiometric titration of copper(II) ions with ethylenediaminetetraacetic acid (EDTA), and successfully applied for the determination of copper(II) ions content in different water samples.

Molecular Insights into a Novel Cu(I)-Sensitive ArsR/SmtB Family Repressor in Extremophile Acidithiobacillus caldus.

Acidithiobacillus caldus is a common bioleaching bacterium that is inevitably exposed to extreme copper stress in leachates. The ArsR/SmtB family of metalloregulatory repressors regulates homeostasis and resistance in bacteria by specifically responding to metals. Here, we characterized A. caldus Cu(I)-sensitive repressor (AcsR) and gained molecular insights into this new member of the ArsR/SmtB family. Transcriptional analysis indicated that the promoter (PIII) of acsR was highly active in Escherichia coli but inhibited upon AcsR binding to the PIII-acsR region. Size exclusion chromatography and circular dichroism spectra revealed that CuI-AcsR shared an identical assembly state with apo-AcsR, as a dimer with fewer α helices, more extended strands, and more β turns. Mutation of the cysteine site in AcsR did not affect its assembly state. Copper(I) titrations revealed that apo-AcsR bound two Cu(I) molecules per monomer in vitro with an average dissociation constant (KD) for bicinchoninic acid competition of 2.55 × 10-9 M. Site-directed mutation of putative Cu(I)-binding ligands in AcsR showed that replacing Cys64 with Ala reduces copper binding ability from two Cu(I) molecules per monomer to one, with an average KD of 6.05 × 10-9 M. Electrophoretic mobility shift assays revealed that apo-AcsR has high affinity for the 12-2-12 imperfect inverted repeats P2245 and P2270 in the acsR gene cluster and that Cu-loaded AcsR had lower affinity for DNA fragments than apo-AcsR. We developed a hypothetical working model of AcsR to better understand Cu resistance mechanisms in A. caldus. IMPORTANCE Copper (Cu) resistance among various microorganisms is attracting interest. The chemolithoautotrophic bacterium A. caldus, which can tolerate extreme copper stress (≥10 g/L Cu ions), is typically used to bioleach chalcopyrite (CuFeS2). Understanding of Cu resistance in A. caldus is limited due to scant investigation and the absence of efficient gene manipulation tools. Here, we characterized a new member of the ArsR/SmtB family of prokaryotic metalloregulatory transcriptional proteins that repress operons linked to stress-inducing concentrations of heavy metal ions. This protein can bind two Cu(I) molecules per monomer and negatively regulate its gene cluster. Members of the ArsR/SmtB family have not been investigated in A. caldus until now. The discovery of this novel protein enriches understanding of Cu homeostasis in A. caldus.

EpsRAc is a copper-sensing MarR family transcriptional repressor from Acidithiobacillus caldus.

The MarR family, as multiple antibiotic resistance regulators, is associated with the resistance of organisms to unfavorable conditions. MarR family extracellular polymeric substances (EPS)-associated transcriptional regulator (EpsRAc) was closely associated with copper resistance in Acidithiobacillus caldus (A. caldus). Transcriptional analysis showed high activity of the epsR promoter (PI) in Escherichia coli and differential response to metal ions. The copper content and UV absorption spectrum of the co-purified protein did not increase, but a stoichiometry of 0.667mol Cu(I) per EpsRAc monomer was observed in vitro in copper titration experiments, suggesting that Cu(II) acts with low affinity in binding to the EpsRAc protein. Electrophoretic mobility shift assays (EMSA) demonstrated that EpsRAc could bind to its own promoter in vitro, and the binding region was the palindrome sequence TGTTCATCGTGTGTGAGCACACA. EpsRAc negatively regulated its own gene expression, whereas Cu(II) mitigates this negative effect. EpsRAc did not bind to other neighboring gene promoters. Finally, we developed a working model to illustrate the regulatory mechanism of A. caldus in response to extreme copper stress. KEY POINTS: • Identification of a MarR family EPS-associated transcriptional regulator, named EpsRAc. • Cu(I) can bind to the EpsRAc protein with low affinity. • EpsRAc negatively regulates the expression of epsR, and Cu(II) can alleviate this negative regulation.

INFRARED SPECTRAL AND MAGNETIC PROPERTIES OF BASIC COPPER(II) NITRATE PRODUCED BY SLOW TITRATION METHOD

The main purposes for this work are to formulate and characterize the infrared (IR) and magnetic moment of the compounds resulted from the slow titration of copper(II) nitrate with sodium hydroxide and in the reverse procedures in an aqueous solution. The titration is carried out with various concentrations and at a constant temperature, ⁓ 19 oC, and monitored using pH meter with the rate of the titration⁓ 1 mL per minute. The corresponding data of change in mole ratio of Cu2+/OH- against pH reveals that the end point of the titration occurs at pH about 8, leading to stoichiometry formula, 3Cu(NO3)2.5Cu(OH)2, but Cu(NO3)2.5Cu(OH)2 in the reverse procedure (OH-/Cu2+). The pale blue for the former but deep blue compounds were isolated and then characterized IR spectroscopy and magnetic moment. Both compounds containing nitrate ion are evident from the corresponding IR spectra, and their magnetic moment values which were found in the range of 1.7-1.9 BM, are to be normal for copper(II) salt corresponding to one unpaired electron in the electronic configuration.

Investigating trace metal precipitation in highly concentrated cell culture media with Pourbaix diagrams.

Commercial production of therapeutic proteins using mammalian cells requires complex process solutions, and consistency of these process solutions is critical to maintaining product titer and quality between batches. Inconsistencies between process solutions prepared at bench and commercial scale may be due to differences in mixing time, temperature, and pH which can lead to precipitation and subsequent removal via filtration of critical solution components such as trace metals. Pourbaix diagrams provide a useful tool to model the solubility of trace metals and were applied to troubleshoot the scale-up of nutrient feed preparation after inconsistencies in product titer were observed between bench- and manufacturing-scale batches. Pourbaix diagrams modeled the solubility of key metals in solution at various stages of the nutrient feed preparation and identified copper precipitation as the likely root cause of inconsistent medium stability at commercial scale. Copper precipitation increased proportionally with temperature in bench-scale preparations of nutrient feed and temperature was identified as the root cause of copper precipitation at the commercial scale. Additionally, cell culture copper titration studies performed in bench-scale bioreactors linked copper-deficient mammalian cell culture to inconsistent titers at the commercial scale. Pourbaix diagrams can predict when trace metals are at risk of precipitating and can be used to mitigate risk during the scale-up of complex medium preparations.

Molecular Insights into the Copper-Sensitive Operon Repressor in Acidithiobacillus caldus.

The copper-sensitive operon repressor (CsoR) family, which is the main Cu(I)-sensing family, is widely distributed and regulates regulons involved in detoxification in response to extreme copper stress (a general range of ≥3 g/liter copper ions). Here, we identified CsoR in hyper-copper-resistant Acidithiobacillus caldus (CsoRAc), an organism used in the bioleaching process of copper ores. CsoRAc possesses highly conserved Cu(I) ligands and structures within the CsoR family members. Transcriptional analysis assays indicated that the promoter (PIII) of csoR was active but weakly responsive to copper in Escherichia coli. Copper titration assays gave a stoichiometry of 0.8 mol Cu(I) per apo-CsoRAc monomer in vitro combined with atomic absorption spectroscopy analysis. CuI-CsoRAc and apo-CsoRAc share essentially identical secondary structures and assembly states, as demonstrated by circular dichroism spectra and size exclusion chromatography profiles. The average dissociation constants (KD = 2.26 × 10-18 M and 0.53 × 10-15 M) and Cu(I) binding affinity of apo-CsoRAc were estimated by bathocuproine disulfonate (BCS) and bicinchoninic acid (BCA) competition assays, respectively. Site-directed mutations of conserved Cu(I) ligands in CsoRAc did not significantly alter the secondary structure or assembly state. Competition assays showed that mutants had the same order of magnitude of Cu(I) binding affinity as apo-CsoRAc. Moreover, apo-CsoRAc could bind to the DNA fragment P08430 in vitro, although with low affinity. Finally, a working model was developed to illustrate putative copper resistance mechanisms in A. caldus. IMPORTANCE Research on copper resistance among various species has attracted considerable interest. However, due to the lack of effective and reproducible genetic tools, few studies regarding copper resistance have been reported for A. caldus. Here, we characterized a major Cu(I)-sensing family protein, CsoRAc, which binds Cu(I) with an attomolar affinity higher than that of the Cu(I)-specific chelator bathocuproine disulfonate. In particular, CsoR family proteins were identified only in A. caldus, rather than A. ferrooxidans and A. thiooxidans, which are both used for bioleaching. Meanwhile, A. caldus harbored more copper resistance determinants and a relatively full-scale regulatory system involved in copper homeostasis. These observations suggested that A. caldus may play an essential role in the application of engineered strains with higher copper resistance in the near future.

Synthesis of Kraton/Polyaniline Ionomer Composite Membrane as Cu (II) Ion Selective Membrane Electrode

Background: Kraton/polyaniline ionomer is synthesized and further characterized by electrochemical studies to check the redox properties of the material. Ion exchange capacity, proton conductivity, and selectivity of the synthesized membrane were determined. And found that the membrane was selective for Cu (II) ions. Methods: The dry Kraton membranes were weighed and kept in 25 mL of 10 % prepared aniline solution in a conical flask for 5, 10, 15, and 20 minutes below 10 0C for socking. The prepared solution of 30 mL of 0.1 M potassium peroxydisulfate was added in a conical flask at constant stirring below 10 0C for half an hour. Finally, the aluminum foil-covered conical flask was kept in the refrigerator for 24 h and modified Kraton membranes were weighed again before carrying out further studies. Results: The membrane was characterized by some physicochemical methods like SEM, TGA, T-IR, IEC, proton conductivity and selectivity sorption studies. An ionomeric membrane of Kraton polymer was developed as reported earlier. Kraton membrane showed the IEC of 1.9 meq·g-1. The FTIR spectrum of Kraton/PANI film reveals that weight loss up to 400°C may be found because of the thermal degradation of composite substances. Conclusion: Ion-selective potentiometric was carried out using the self-prepared ion-selective membrane electrode. The membrane was prepared by solution casting method. The membrane was characterized by some physicochemical methods like SEM, TGA, T-IR, IEC, proton conductivity and selectivity sorption studies. On the basis of selectivity studies, the composite material was found selective for Cu (II) ion. A copper ISME was successfully fabricated using the solution casting method. The ISME possessed good selectivity, linearity, working pH range, and response time which was also used as an indicator electrode for the titration of copper using EDTA.

Facile Synthesis and Characterization of 5-[(3-Methylthiophene-2-yl-methyleneamino)]-2-mercaptobenzimidazole and Its Potentiometric Sensor Application in a Polyvinyl Chloride Membrane for the Determination of Copper(II)

A novel Schiff base designated as 5-[(3-methylthiophene-2-yl-methyleneamino)]-2-mercaptobenzimidazole was synthesized and characterized. A polyvinyl chloride-membrane potentiometric copper(II)-selective sensor was prepared by using the synthesized 5-[(3-methylthiophene-2-yl-methyleneamino)]-2-mercaptobenzimidazole compound. The prepared polyvinyl chloride-membrane copper(II)-selective sensor exhibited very good selectivity and sensitive potentiometric response towards copper(II) ions compared to a wide variety of other cations. The sensor had a fast response time of <5 s, and showed a linear Nerstian behavior to copper(II) ions over a wide concentration range from 1.0 × 10−5 to 1.0 × 10−1 mol L−1 with a slope of 29.2 ± 0.7 and correlation coefficient of 0.9998. The prepared polyvinyl chloride-membrane copper(II)-selective sensor was used for 14 weeks without any significant change in its potentiometric response. The potentiometric response of the developed sensor was highly repeatable. Additionally, the developed sensor was used as an indicator electrode for the potentiometric titration of copper(II) ion with ethylenediaminetetraacetic acid. The sensor was also successfully applied to the direct determination of copper(II) ions in tap water, river water, and dam water samples.

Automatic Biamperometric Titration of Copper(II) by Iodide in Some Non-Aqueous Media

Automatic Biamperometric Titration of Copper(II) by Iodide in Some Non-Aqueous Media

Grafting of model primary amine compounds to cellulose nanowhiskers through periodate oxidation

This study demonstrates regioselective oxidation of cellulose nanowhiskers using 2.80–10.02 mmols of sodium periodate per 5 g of whiskers followed by grafting with methyl and butyl amines through a Schiff base reaction to obtain their amine derivatives in 80–90 % yield. We found a corresponding increase in carbonyl content (0.06–0.14 mmols/g) of the dialdehyde cellulose nanowhiskers with the increase in oxidant as measured by titrimetric analysis and this was further evidenced by FT-IR spectroscopy. Grafting of amine compounds to the oxidized cellulose nanowhiskers resulted in their amine derivatives, which are found to be partially soluble in DMSO. Therefore, the reduction reaction between amines and carbonyl groups was confirmed through 13C NMR spectra, which was also supported by copper titration, XPS, and FT-IR spectroscopy. Morphological integrity and crystallinity of the nanowhiskers was maintained after the chemical modification as studied by AFM and solid-state 13C NMR, respectively.

구리수은막 전극에을 사용한 이소니아자이드의 전위차 역적정

구리수은막 전극(CBMFE)으로 전위차 역적정함으로써 이소니아자이드(INH)를 정량하는 간단하고 빠른 방법이다. 순수한 형태와 투약형태에 대해서 1.0-10.0 mg 범위에서 정량 할 수 있도록 적정조건을 설정하였다. 방법의 정밀도와 정확도는 통계적인 방법으로 평가되었으며, 정제와 시럽속에 함유된 INH 정량법은 F-시험과 t-시험을 통하여 영국약전(BP) 방법과 비교하였다. A simple, rapid potentiometric back titration of Isoniazid (INH) in the presence of Rifampicin (RIF) in tablets and syrups is described. The method is based on the oxidation of INH by a known excess of copper (II) ion and the back titration of unreacted copper (II) ion potentiometrically with ascorbic acid using a lab-made Copper Based Mercury Film Electrode (CBMFE). The titration conditions have been optimized for the determination of 1.0-10.0 mg of INH in pure and dosage forms. The precision and accuracy of the method have been assessed by the application of lack-of-fit test and other statistical methods. Interference was not caused by RIF and other excipients present in dosage forms. Application of the method for INH assay in tablets and syrups was validated by comparison of the results of proposed method with that of the British Pharmacopoeia (BP) method using F- and t- statistical tests of significance.

The Studies of Conditions for Inducing Chirality to Cu(II) Complexes by Chiral Zn(II) and Ni(II) Complexes with Schiff Base

Recently, we have discovered that some chiral Schiff‐base nickel(II) complexes induced d‐d bands of CD spectra of some achiral copper(II) complexes. However, the novel phenomenon could be observed only a few systems of hybrid materials or limited conditions so far. In order to test conditions about copper(II) ions, we investigated model systems (1) metal‐dendrimer (Cu‐PAMAM; G4‐NH2 terminal) containing relatively small amount of copper(II) ions (4.5 equivalent to PAMAM) for modeling separated systems of achiral copper(II) complex from chiral Schiff‐base nickel(II) or zinc(II) complexes, Bis(N‐R‐1‐naphtylethyl‐3,5‐dichlorosalicydenaminato)nickel(II) or zinc(II) by polymer matrix. (2) equilibrium of copper(II) N‐ethylethylenediamine complexes to measure absorption spectra of d‐d band, pH, and electron conductivity during titration of copper(II) ions. The results showed that (1) 4.5Cu‐PAMAM could not be induced their d‐d bands by the chiral nickel(II) or zinc(II) complexes, which suggested that separation by polymers prevented from inducing CD peaks. (2) Although 36Cu‐PAMAM was known, uncoordinated copper(II) ions excess to ligands mainly attributed to increase electron conductivity by remained ions in methanol solutions, which was not associated with intermolecular interaction or dipole moments being effective for the induced CD mechanism by using molecular recognition between neutral molecules of metal complexes.

Visible Light Induced NO2 − Removal Over CuCrO2 Catalyst

The delafossite CuCrO2 is a promising candidate for the visible light driven catalysis. The NO2 − removal by photoelectrochemical process is studied under mild conditions, close to that encountered in the natural environment. CuCrO2 exhibits a long term chemical stability with a corrosion rate of 0.34 μmol m−2 year−1 in KCl (0.5 M). A forbidden band of 1.3 eV has been evaluated from the diffuse reflectance spectrum. The flat band potential (−0.07 V SCE) determined from the Mott–Schottky plot is close to the photocurrent onset potential (0 V SCE). Hence, the conduction band is positioned at −1.08 V SCE and thus lies below the NO2 − level leading to a feasible reduction upon visible illumination. The conversion occurs in less than ∼5 h with a quantum efficiency of ∼0.5%. The possibility of identifying the reaction products via the intensity–potential characteristics was explored by using standard solutions. The decrease of the conversion rate over time is attributed to the competitive water reduction. In absence of catalyst, NO2 − is oxidized to NO3 − in air equilibrated solution and the reaction follows a first order kinetic with a half life of 21 h, NO3 − has been identified by iodometry through copper titration.

Copper speciation by competing ligand exchange method using differential pulse anodic stripping voltammetry with ethylenediaminetetraacetic acid (EDTA) as competing ligand

A technique has been developed to study chemical speciation of copper in freshwaters by competing ligand exchange (CLE) method using anodic stripping voltammetry (ASV) in the differential pulse (DP) mode with ethylenediaminetetraacetic acid (EDTA) as a competing ligand. The voltammetric behavior of Cu(II)–EDTA complex has been investigated using DPASV. When DPASV is used at an appropriate deposition potential, the inert Cu(II)–EDTA complex becomes electroactive, and is reduced directly. Furthermore, at the same deposition potential, Cu(II)–fuvic acid and Cu(II)–humic acid complexes do not contribute significantly to the analytical signal, which makes EDTA a suitable competing ligand in the determination of copper speciation using CLE–ASV. This method has been applied to freshwater samples from Rideau Canal (Ottawa, ON, Canada). The analysis of the copper titration data of these freshwater samples has indicated the presence of a very strong copper-binding ligand with a conditional stability constant of approximately 10 20 and a corresponding very high concentration (above 100 nM) of the ligand.

Characterization of Cu 2+-binding modes in the prion protein by visible circular dichroism and multivariate curve resolution

Visible circular dichroism (CD) spectra from the copper(II) titration of the metal-binding region of the prion protein, residues 57–98, were analyzed using the self-modeling curve resolution method multivariate curve resolution–alternating least squares (MCR-ALS). MCR-ALS is a set of mathematical tools for estimating pure component spectra and composition profiles from mixture spectra. Model-free solutions (e.g., soft models) are produced under the assumption that pure component profiles should be nonnegative and unimodal. Optionally, equality constraints can be used when the concentration or spectrum of one or more species is known. MCR-ALS is well suited to complex biochemical systems such as the prion protein which binds multiple copper ions and thus gives rise to titration data consisting of several pure component spectra with overlapped or superimposed absorption bands. Our study reveals the number of binding modes used in the uptake of Cu 2+ by the full metal-binding region of the prion protein and their relative concentration profiles throughout the titration. The presence of a non-CD active binding mode can also be inferred. We show that MCR-ALS analysis can be initialized using empirically generated or mathematically generated pure component spectra. The use of small model peptides allows us to correlate specific Cu 2+-binding structures to the pure component spectra.

Copper speciation in estuarine waters by forward and reverse titrations

The chemical speciation of copper in the estuarine waters of the Vigo Ria was determined by titrations with salicylaldoxime (reverse copper titrations) and with copper (forward titrations). The forward titrations quantified the concentrations of ligands present in excess whereas the reverse titrations demonstrated the presence of low concentrations of very strong binding ligands, approximately matching the copper concentration. The data obtained by the reverse titrations indicated that copper was about 10× stronger bound than data based on the usual forward titrations. The copper concentration in these ria waters was low at 5 nM with a minor mid-estuarine maximum of 8 nM. These copper levels are amongst the lowest reported for estuarine waters and therefore represent uncontaminated waters. The concentration of inorganic copper was very low across the ria at ∼ 10–100 fM, except at Bouzas harbour (salinity 35.5) where it was raised to ∼ 1 pM due to copper contamination, in waters affected by the port facilities, to total levels of 15 to 20 nM copper, exceeding the concentration of the very strong ligand detected by the reverse titrations.

PH dependent copper binding properties of a Cu A azurin variant with both bridging cysteines replaced with serines

A double mutant of Cu A azurin was prepared in which both bridging cysteine thiolate ligands of the binuclear Cu A center were replaced by serine. The copper binding properties of this protein were investigated, and shown to be pH dependent. At lower pH (5.2 ± 0.1), the protein binds one copper per protein molecule as demonstrated by electrospray ionization mass spectrometry. Copper titrations resulted in electronic absorptions at 730 nm (peak) and ca. 330 nm (shoulder) in the UV–Vis spectrum. EPR data show a four line pattern with hyperfine A ∥ = 150 G and g ∥ and g ⊥ values 2.32 and 2.03, characteristic of a type II (T2) copper. Superhyperfines to two nitrogen atoms were also observed. At higher pH (8.5 ± 0.1), the protein binds upto two copper atoms per protein molecule, and copper titrations exhibit a blue transition at 595 nm in the UV–Vis spectrum. The EPR data are consistent with two monomeric sites very similar to one another having hyperfines A ∥ = 182 and 150 G, g ∥ = 2.24 and 2.22 and a similar g ⊥ value of 2.01. These results indicate that both bridging cysteines play a critical role in the Cu A center, and replacing them with serines is not enough to maintain the symmetrical diamond core structure or the characteristic electronic and functional properties of the Cu A center.

Highly Selective and Sensitive Membrane Sensors for Copper(II) Ion Based on a New Benzo‐Substituted Macrocyclic Diamide 6,7,8,9,10‐Hexahydro‐2H‐1,13,4,7,10‐benzodioxatriazacyclopentadecine‐3,11(4H,12H)‐dione

AbstractNovel PVC membrane (PME) and coated graphite (CGE) Cu2+‐selective electrodes based on 5,6,7,8,9,10‐hexahydro‐2H‐1,13,4,7,10‐benzodioxatriazacyclopentadecine‐3,11(4H,12H)‐dione are prepared. The electrodes reveal a Nernstian behavior over wide Cu2+ ion concentration ranges (1.0×10−7–1.0×10−1 M for PME and 1.0×10−8–1.0×10−1 M for CGE) with very low limits of detection (7.8×10−8 M for PME and 9.1×10−9 M for CGE). The potentiometric responses are independent of the pH of the test solutions in the pH range 2.7–6.2. The proposed electrodes possess very good selectivities for Cu2+ over a wide variety of the cations including alkali, alkaline earth, transitions and heavy metal ions. The practical utility of the proposed electrodes have been demonstrated by their use in the study of interactions between copper ions and human growth hormone (hGH) in biological systems, potentiometric titration of copper with EDTA and determination of copper content of a sheep blood serum sample and some other real samples.

Triiodide Ion‐Selective Electrode Based on Charge‐Transfer Complex of 4,7,13,16,21,24‐Hexaoxa‐1,10‐diazabicyclo‐[8.8.8]hexacosane

AbstractTwo new highly selective triiodide electrodes have been prepared using charge‐transfer complex of iodine with cryptand 222 as an electroactive ionophore and nitrophenyl octyl ether as a plasticizing agent. The electrodes showed Nernstian response to triiodide ions over a concentration range from 1.0 × 10−;2 — 7.9 × 10−;7 M and from 1.0 × 10−;2 — 1 × 10−;6 M with detection limits of 6.3 × 10−;7 and 7.9 × 10−;7 M for cryptand and its charge‐transfer complex with iodine, respectively. The response times (t95%) of the sensors were 10 and 5 s. The membrane could be used for more than 1 month without any divergence in potentials. The proposed sensors exhibited very high selectivity for triiodide ion over other anions, and could be used in a wide pH range ˜2–10. These electrodes were successfully applied as an indicator electrode in potentiometric titration of copper in ore samples.

The use of Nafion-coated thin mercury film electrodes for the determination of the dissolved copper speciation in estuarine water

Differential pulse anodic stripping voltammetry (DPASV) using a Nafion-coated thin mercury film electrode (NCTMFE) was implemented to determine the dissolved copper speciation in saline estuarine waters containing high concentrations of dissolved organic matter (DOM). The study used model ligands and estuarine water from San Francisco Bay, California, USA to demonstrate that the NCTMFE is more effective at distinguishing between electrochemically inert and labile copper species when compared to the conventional thin mercury film electrode (TMFE). Copper titration results verify that the NCTMFE better deals with high concentrations of DOM by creating a size-exclusion barrier that prevents DOM from interacting with the mercury electrode when performing copper speciation measurements. Pseudovoltammograms were used to illustrate that copper complexes found in natural waters were more apt to be electrochemically inert at the NCTMFE relative to the TMFE when subjected to high negative overpotentials. Copper speciation results using the NCTMFE from samples collected in San Francisco Bay estimated that >99.9% of all copper was bound to strong copper-binding ligands. These L 1-class ligands exceeded the concentration of total dissolved copper in all samples tested and control the equilibrium of ambient [Cu 2+] in the San Francisco Bay estuary.