Ion-selective Electrode Potentiometry Research Articles

Development of disposal SPCE pH sensor based on polypyrrole and cloth as conductive polymer

In fish farming, monitoring water quality is crucial for the health and growth of the fish. This field area needs a robust device to monitor the pH meter. In this research, a disposal pH sensor was developed from alternative materials that can offer a wider application area than the conventional glass sensor. Polypyrrole (PPy) membrane was applied to the carbon electrode and acted as a pH-sensitive material when combined with the counter electrode. The carbon electrode was made by printing the carbon paste into cotton-rayon cloth and electrodeposition processing to create a PPy layer on the electrode surface. Afterward, the working electrode was evaluated using cyclic voltammetry and ion-selective electrode potentiometry to optimize the performance. The experimental measurements show that the electrodeposition process at 4.5 A and 30 s creates PPy deposits with optimum sensor performance. pH response and stability tests have also been performed, as the results show that the pH sensor has met the requirement for Nernst effect and IUPAC standard. Finally, the sensor was validated using a reference pH meter to test the water sample acquired from local lake, river, and fishpond, where the result shows that the pH sensor gives accurate measurements.

Association of hypertension in pregnancy with serum electrolyte disorders in late pregnancy among Cameroonian women

Multiple electrolyte disorders, including sodium, potassium and calcium disorders, have been associated with hypertension in pregnancy. Most of these studies failed to evaluate the combined effect of low and high sodium, potassium, calcium and chloride ion concentrations on hypertension in pregnancy. This study evaluates the combined effect of these ion categories (low, normal, high) on hypertension in pregnancy. Biochemical ion assays and blood pressure measurements were carried out on 1074 apparently healthy pregnant women in late third trimester. Serum potassium, sodium, chloride, and ionised calcium were measured by ion-selective electrode potentiometry, while total plasma calcium was measured by absorption spectrophotometry. Hypertension in pregnancy was defined as systolic blood pressure ≥ 140 mmHg and/or diastolic blood pressure ≥ 90 mmHg. The prevalence of hyponatraemia, hypokalaemia, hypochloraemia, ionised hypocalcaemia and total hypocalcaemia in late pregnancy was 1.30 [0.78–2.18]%, 3.55 [2.60–4.84]%, 1.96 [1.28–2.97]%, 1.49 [0.92–2.21]% and 43.58 [40.64–46.56]%, respectively. Hypernatraemia, hyperkalaemia, hyperchloraemia, ionised hypercalcaemia and total hypercalcaemia were found in 1.49 [0.92–2.41]%, 2.34 [1.59–3.43]%, 4.38 [3.31–5.77]%, 39.94 [37.06–42.90]%, 2.79 [1.96–3.96]% of the participants, respectively. The prevalence of hypertension in pregnancy was 7.17 [5.77–8.87]%. When ion categories were considered in multiple logistic regression, only ionised and total calcium had significant associations with hypertension in pregnancy. Women with ionised hypercalcaemia had lower odds of hypertension in pregnancy (AOR = 0.50 [0.29–0.87], p-value = 0.015), and women with total hypocalcaemia had higher odds of hypertension in pregnancy (AOR = 1.99 [1.21–3.29], p-value = 0.007), compared to women with ionised and total normocalcaemia, respectively. Increasing kalaemia was associated significantly with higher odds of hypertension in pregnancy; however, kalaemia below and above the normal concentrations had no significant association with hypertension. Nonetheless, participants with kalaemia ≤ 3.98 mmol/L, had lower odds of hypertension in pregnancy compared with those with higher kalaemia (OR = 0.40 [0.24–0.66], p-value = 0.0003). Calcium disorders remain the most frequent electrolyte disorders in pregnancy. When normal cut-offs are considered for calcium and other ions, only ionised and total calcium influence the occurrence of hypertension in pregnancy. Kalaemia seems to affect hypertension in pregnancy but primarily within its normal concentrations. Serum electrolyte follow-up is indispensable for a proper pregnancy follow-up.

Fluoride content of common legume beans consumed in Ethiopia

ABSTRACT. The most widely used legume beans food in Ethiopia are fava beans (Vicia faba), green gram (Vigna radiata), white lupin (Lupinus albus), and three types of kidney beans (Phaseolus vulgaris). These legume crops are grown in various regions of Ethiopia and can absorb significant amounts of fluoride from air, water, and soil. This study examined the fluoride content of legume beans collected from four different regions of Ethiopia by ion selective electrode potentiometry. Fluoride concentrations in this study were found to range from 1.9 to 22.8 mg/kg. Fava bean sample from Asella was found to contain higher fluoride (22.8 mg/kg) than in the fava beans from other sites and other beans from any site. Fluoride levels (13.0 mg/kg) in kidney bean from Migira was in the middle of the range while the fluoride levels (2.5 mg/kg) in the white lupin and green gram (1.9 mg/kg) were found in the lower end of the range. This study indicates that daily consumption of 100 g of fava and kidney beans may results in health problem while that of green gram and white lupin are safe for human health (will not exceed 3 mg/day set by Food and Nutrition Board of USA).
 KEY WORDS: Fava bean, Green gram, Kidney beans, White lupin, Food, Fluoride
 Bull. Chem. Soc. Ethiop. 2023, 37(6), 1325-1336. DOI: https://dx.doi.org/10.4314/bcse.v37i6.3

Self-Calibrated Ion-Selective Electrodes.

Ion-selective electrode (ISE) potentiometry is reliable only if on-site calibration using a standard solution is performed before ion measurements. The complex device and operation required for calibration hinder the implementation of ISEs in decentralized sensing. Reported herein is a new type of ISE that is calibrated by a built-in component of the sensor without requiring any fluid handling processes. The indicator and reference electrodes are connected by a thin ionic conductor such as an aqueous phase containing the measuring ions in a capillary tube. This connection establishes a baseline electromotive force (EMF) that incorporates phase boundary potentials across multiple interfaces of the electrochemical cell and serves as a one-point calibration. Unlike conventional ISEs that rely on one EMF reading for each measurement, the proposed sensor utilizes a sample-induced EMF change relative to the baseline for each ion measurement. The variability in relative EMF is found to be <2.0 mV for multiple full potentiometric sensors consisting of plasticizer-based K+ ISEs and hydrogel-based Ag/AgCl reference electrodes. This value is significantly smaller than the variability of absolute EMF readouts in similar sensors without the self-calibration design. Moreover, when the ion-conducting calibration bridge has a low concentration of primary ions, low ion mobility, and/or a small contact area with the indicator and reference phases, it does not compromise the Nernstian response slope toward the analyte ions in the sample and therefore does not need to be removed for sample testing. The accuracy of the single-use self-calibrated K+ sensor in testing undiluted human blood samples is validated using a commercial blood gas analyzer as the reference method. Although this study focuses on disposable sensors consisting of tubes, the fluidics-free self-calibration strategy may be adapted to other sensor configurations such as planar sensors.

Multi-Techniques for Iodine Determination and Dose Uniformity Assays in Iodized Mineral Dietary Supplements

The determination of iodine in iodized mineral dietary supplements is considered a challenge, especially in view of the variety in the sample composition and the analyte concentration. Thus, in this work, microwave-induced combustion (MIC) was combined with ion chromatography (IC) and ion-selective electrode potentiometry (ISE) for iodine determination and dose uniformity assays in mineral dietary supplements. Sample masses up to 800 mg were efficiently digested and only a diluted alkaline solution (200 mmol L-1 NH4OH) was necessary to absorb the analyte for further determination step. The final digest was fully compatible with multi-technique detection usually available in routine analysis laboratories. Recoveries ranging from 94% to 106% was achieved and relative standard deviations for repeatability and intermediate precision were always lower than 8%. Limits of quantification were 4 µg g-1 and 10 µg g-1, respectively, by using IC and ISE. The analytical method was applied for iodine determination in mineral dietary supplements from four brands with different iodine dosages (from 100 to 1250 μg g-1, according to the manufacturers) and for uniformity assay evaluation using individual tablets/capsules of mineral dietary supplements. Non-compliance regarding label information for some samples was reported, drawing the attention of supervisory institutions. The analytical strategies presented in the present study can be successfully used in routine analysis of the quality control of mineral dietary supplements.

Point-of-care test for rapid assessment of blood lithium levels in women with bipolar disorder during perinatal period

IntroductionDetermination of lithium levels in serum has become a standard of care due to its narrow therapeutic rang, thus an immediate test for determination of blood lithium may contribute to minimize toxicit, to avoid relapse and to ensure treatment adherence. This is particularly relevant during pregnancy and early postpartum because pharmaokinetic changes in renal physiology.ObjectivesThe aim of this study is verify Medimate point-of-care method performance and systematically compare it with the routine laboratory measurement of lithium.MethodsThis cross-sectional method comparison study was conductec in the Unit of Perinatal Mental Health in the Hospital Clinic of Barcelona. Pearson and Bland-Altman analyses were performed to assess the accuracy, precision and correlation between the capillary electrophoresis technology (Medimate MiniLab) and the ion selective electrode (ISE) potentiometry method (AVL 9180).ResultsTwenty-five women with bipolar disorder in treatment with lithium during perinatal period were enrolled, corresponding to 75 blood specimens for analyses. Correlation (r), mean difference (bias), and 95% limit of agreement (LOA) of the point-of-care method [r=0.917; bias 0.0021 (95% LOA; 0.440, 0.619) mEq/L], showed that difference between ISE method and capillary electrophoresis technology was not statistically significant.ConclusionsConsidering the practicality, the microchip capillary electrophoresis technology provides a simple and highly affordable way of measuring lithium levels in a single drop of blood outside the clinical laboratory. The Medimate point-of-care system (POC) appears well adapted for the rapid and specific detection of lithium as an alternative to the current ISE procedure.DisclosureNo significant relationships.

Ionised and total hypocalcaemia in pregnancy: An analysis of prevalence and risk factors in a resource-limited setting, Cameroon.

Hypocalcaemia remains a prevalent laboratory finding in pregnancy, capable of inducing adverse maternofoetal outcomes. This study compares the prevalence of hypocalcaemia in apparently healthy pregnant women from the ionised, and total calcaemia viewpoints and further identifies factors associated with total crude and ionised hypocalcaemia in pregnancy. A hospital-based cross-sectional study was conducted between November 2020 and September 2021, targeting apparently healthy pregnant women received in late pregnancy in four maternities in the Nkongsamba Health District, Cameroon. Blood samples were collected and analysed for serum ionised calcium concentrations and pH (by ion-selective electrode potentiometry), and for total calcium and albumin concentration (by atomic absorption spectrophotometry). Sociodemographic, obstetric and nutritional data were collected using an interviewer-administered questionnaire. The average age of the 1074 participants included in the study was 28.20±6.08 years. The prevalence of total crude and total albumin-corrected hypocalcaemia in this study was 61.64 [58.69-64.50]% and 56.70 [53.72-59.64]%, respectively (p-value = 0.000). The prevalence of ionised hypocalcaemia was very low (2.89 [2.04-4.07]%) compared with the prevalence of total hypocalcaemia (p-value = 0.000). Monthly income below 100.000FCFA (179 USD) (AOR = 0.73, p-value = 0.024), taking more than 2 meals daily (AOR = 0.68, p-value = 0.006) and taking desserts (AOR = 0.73, p-value = 0.046) reduced the odds of total crude hypocalcaemia, while having banana/plantain and tubers as the content of their most consumed meal significantly increased the odds of total crude hypocalcaemia (AOR = 1.37, p-value = 0.012). Single women (AOR = 2.54, p-value = 0.021), with a higher education (AOR = 3.27, p-value = 0.017), who initiated antenatal care before 4 months (AOR = 2.47, p-value = 0.029), had their odds of ionised hypocalcaemia significantly increased. On the other hand, women below 30 years (AOR = 0.44, p-value = 0.039), with occupations other than housewife (AOR = 0.34, p-value = 0.027), and women who took desserts between meals (AOR = 0.45, p-value = 0.034) had their odds of ionised hypocalcaemia significantly reduced. Taking calcium supplements simultaneously with other supplements also significantly reduced the odds of total hypocalcaemia in pregnancy (OR = 0.69, p-value = 0.027). Ionised hypocalcaemia in pregnancy is a rare finding. Only 2.89% of all apparently healthy pregnant women have ionised hypocalcaemia in late pregnancy, while 56.70% have total hypocalcaemia. Factors like the daily number of meals, taking of desserts, the content of the most consumed meal and monthly revenue significantly affect the prevalence of total hypocalcaemia in pregnancy. On the other hand, factors like age above 30 years, having a higher education, being single, having initiated antenatal care before 4 months of pregnancy, being a housewife and not taking desserts between meals have a significantly positive association with ionised hypocalcaemia.

Fluoride levels in river water from the volcanic regions of Cauca (Colombia)

Fluoride concentrations of 0.5 mg/L in drinking water are considered useful for dental caries prevention. However, fluoride concentrations higher than 1.2 mg/L in water can pose a risk of dental fluorosis due to high exposure to fluoride. The objective is to determine the fluoride concentration in water from aqueducts of different Colombian municipalities of Cauca (Popayán, Coconuco, and Puracé) to assess the fluoride dietary intake from the consumption of this water. A total of 66 water samples have been taken from Popayán, Coconuco, and Puracé. Fluoride content was determined by fluoride ion-selective electrode (ISE) potentiometry. The fluoride concentrations recorded in Coconuco and Puracé water were ≤ 0.002 mg/L. The mean fluoride content recorded in the Popayán water was 0.42 mg/L, with its highest concentration in Cauca River water (0.83 mg/L). Considering the admissible intake values, the water from Popayán confers remarkable fluoride intakes, especially in children with high percentages of contribution to the admissible daily intake (46.7% to 7- to 12-month children and 41.5% to 1- to 3-year children). The fluoride content in the water of Coconuco and Puracé does not reach an optimal value (< 0.5 mg/L) for the protective effect against dental caries, while the water of the main Cauca River basin does reach the optimal value. Likewise, the intake of fluoride from the consumption of the analyzed water does not confer any health risk. However, the implementation of monitoring systems for fluoride levels is recommended in order to safeguard the consumer’s health.

Hypocalcaemia and calcium intake in pregnancy: A research protocol for critical analysis of risk factors, maternofoetal outcomes and evaluation of diagnostic methods in a third-category health facility, Cameroon.

Hypocalcaemia in pregnancy remains a major health issue, particularly in the developing world where daily calcium intakes are suboptimal. This electrolyte imbalance can lead to severe maternofoetal and childhood consequences. Calcium supplementation, amongst others, contributes significantly to meeting calcium demands in pregnancy. With ionised calcaemia as the gold standard for diagnosis, total calcaemia and albumin-corrected calcaemia in other pathological states have been found to overestimate the burden of hypocalcaemia. The main objectives of this study are to describe the blood calcium level (total, albumin corrected, and ionised calcaemia) and associated maternofoetal outcomes while identifying determinants of calcium supplementation and ionised hypocalcaemia. This study will also evaluate the sensitivity and specificity of albumin corrected calcaemia as a diagnostic tool for hypocalcaemia (ionised calcaemia as the gold standard) among pregnant women in the Nkongsamba Regional Hospital, Cameroon. Our study will target a total of 1067 term pregnant women who shall be included consecutively into the study as they arrive the maternity of the Nkongsamba Regional Hospital for their last antenatal care visit. Data shall be collected using a semi-structured interview-administered questionnaire and blood samples collected for total plasma calcium, albumin and serum ionized calcium assays. Additional data will be collected at birth (maternal and foetal variables; foetal outcomes evaluated as secondary outcomes). Total calcaemia and albuminemia shall be measured by atomic absorption spectrophotometry, while ionised calcaemia will be measured by ion-selective electrode potentiometry(using MSLEA15-H electrolyte analyzer) per standard BIOLABO and MSLEA15 protocols, respectively. Data will be analysed using the statistical softwares epi-Info version 7.2.2.16 and STATA version 16. This study will present a more precise estimate of the burden of hypocalcaemia in late pregnancy as well as identify and analyse the different factors associated with calcium supplementation and ionised hypocalcaemia among term pregnant women in a developing world setting. Maternofoetal outcomes associated with hypocalcaemia will be determined as well as the sensitivity and specificity of total and albumin-corrected calcaemia in diagnosing hypocalcaemia. Our findings will contribute significantly to designing or strengthening interventions to control this electrolyte imbalance.

Experimentally Designed Sensor for Direct Determination of the Environmentally Hazardous Compound and Occupational Exposure Biomarker (p-aminophenol) in Different Sampling Matrices

p-Aminophenol (PAP) is a potentially toxic and mutagenic compound used and/or emitted in industrial, pharmaceutical and agriculture fields. Ion-selective electrode potentiometry (ISE) introduces an effective tool for real-time, portable and direct analysis to overcome lengthy sample preparation, treatment and derivatization steps. The current work aims to develop a portable ISE-potentiometric sensor for direct assay of PAP in industrial, environmental and biological matrices. Sensor assembly included a glassy carbon electrode upon which membrane cocktails were drop-casted. Optimization was carried out using a custom experimental design for the comprehensive evaluation of the main effects of the critical quantitative (percentage of ion-exchanger, PVC to plasticizer ratio and membrane thickness) and qualitative (ionophore type) factors on the sensor performance (Nernstian slope, LOD, LOQ, correlation coefficient). The optimized sensor included 1.20% ion exchanger, PVC: plasticizer ratio 1:4 and calix-[8]-arene as ionophore in 0.07 mm thick PVC membrane. The sensor proved a near-Nernstian slope of 61.9 mV decade−1 within a linear range of 2.99 × 10−5−1 × 10−2 M, a LOD of 2.86 × 10−5 M and rapid response time (1–5 s). The developed method was validated for PAP assay in urine, plasma, water, soil, hair dyes and in paracetamol marketed formulations. Eventually, the developed sensor can have multifarious applications in environmental, clinical and industrial fields.

Comparing Copper Serum Level and Cognitive Functioning in Patients With Schizophrenia and Healthy Controls.

Introduction:The altered serum profiles of several trace elements have been reported in Schizophrenia (SCZ). This study was designed to elucidate whether the serum levels of Copper (Cu) and Magnesium (Mg), the two essential trace elements which contribute to neurotransmitter transmission, are altered in patients with SCZ. We also investigated whether there is an interrelation between cognitive functioning and the serum levels of Cu and Mg.Methods:Sixty patients with SCZ and 30 healthy controls participated in this study. The patient group was divided into the following: i) early patients (n=35, ≤5 years of illness initiation), and ii) chronic patients (n=25, ≥5 years of illness duration). The serum levels of Cu and Mg were measured by atomic absorption spectroscopy and ion-selective electrode potentiometry, respectively. To assess cognitive abilities, a Persian adaptation of the Brief Assessment of Cognition in Schizophrenia (BACS) was administered.Results:The present research results revealed significantly higher Cu serum levels in both patient groups [early patients (M=94.6), chronic patients (M=97.5)], compared to the controls (M=71.0) (P<0.001); however, no significant difference was observed among the study groups for Mg [patients with the recent onset (M=2.0), chronic patients (M=2.0), and controls (M=1.9)] P=0.1. While the serum Cu profile of healthy individuals revealed a negative correlation with working memory (r=−0.42, P=0.02), and executive functioning (r=−0.40, P=0.03), no significant correlation was observed between Cu serum levels of patients and BACS cognitive domains.Conclusion:findings suggested that the high Cu serum concentration might impact the cognitive decline in healthy individuals; however, no significant correlation was observed in the Patients; i.e. most likely because cognition is severely impaired in SCZ. Additional studies examining trace elements in drug-naïve patients with SCZ are required.

Formation of CaUO2(CO3)32- and Ca2UO2(CO3)3(aq) complexes at variable temperatures (10-70 °C).

The ternary complexation of calcium uranyl tricarbonate species, CaUO2(CO3)32- and Ca2UO2(CO3)3(aq), which are the predominant U(vi) complexes in groundwater and seawater, was investigated at variable temperatures from 10 to 70 °C. Time-resolved laser fluorescence spectroscopy (TRLFS), calcium ion-selective electrode potentiometry, and ultraviolet/visible (UV/Vis) absorption spectroscopy were complementarily employed to determine the formation constants (log Kx13, x = 1 and 2 for mono- and dicalcium complexes, respectively). at infinite dilution (zero ionic strength) was determined by correction using specific ion interaction theory (SIT), and an increasing tendency of with temperature was observed. In addition, the molar enthalpy of complexation (ΔrHm) was measured by calorimetry at 25 °C. Based on thermodynamic data obtained in this work, the approximation models were examined for the prediction of the temperature effect on the complexation, and the constant enthalpy approximation with the chemical complexation reaction modified to an isoelectric reaction showed a satisfactory prediction of in the temperature range of 10-70 °C. Finally, the results of U(vi) speciation in groundwater indicated that the dominance of calcium uranyl tricarbonate complexes would be weakened at elevated temperatures by the strongly enhanced hydrolysis of U(vi).

Determination of fluorine in copper concentrate via high-resolution graphite furnace molecular absorption spectrometry and direct solid sample analysis – Comparison of three target molecules

The chemical composition of complex inorganic materials, such as copper concentrate, may influence the economics of their further processing because most smelters, and particularly the producers of high-purity electrolyte copper, have strict limitations for the permissible concentration of impurities. These components might be harmful to the quality of the products, impair the production process and be hazardous to the environment. The goal of the present work is the development of a method for the determination of fluorine in copper concentrate using high-resolution graphite furnace molecular absorption spectrometry and direct solid sample analysis. The molecular absorption of the diatomic molecule CaF was measured at 606.440nm. The molecule CaF was generated by the addition of 200µg Ca as the molecule-forming reagent; the optimized pyrolysis and vaporization temperatures were 900°C and 2400°C, respectively. The characteristic mass and limit of detection were 0.5ng and 3ng, respectively. Calibration curves were established using aqueous standard solutions containing the major components Cu, Fe, S and the minor component Ag in optimized concentrations. The accuracy of the method was verified using certified reference materials. Fourteen copper concentrate samples from Chile and Australia were analyzed to confirm the applicability of the method to real samples; the concentration of fluorine ranged from 34 to 5676mgkg−1. The samples were also analyzed independently at Analytik Jena by different operators, using the same equipment, but different target molecules, InF and GaF, and different operating conditions; but with a few exceptions, the results agreed quite well. The results obtained at Analytik Jena using the GaF molecule and our results obtained with CaF, with one exception, were also in agreement with the values informed by the supplier of the samples, which were obtained using ion selective electrode potentiometry after alkaline fusion. A comparison will also be made for the three target molecules and the three independently developed methods for the determination of fluorine, although all three methods used direct solid sample analysis.

Acute Hypotensive, Diuretic and Antioxidant Activities Induced by Urtica circularis

Aims: The aim of this study was to investigate the possible hypotensive and diuretic effects of ethanolic extract of Urtica circularis (Hicken) Soraru (Urticaceae) using preclinical methods. Place and Duration of Study: Department of Pharmacology, School of Pharmacy and Biochemistry, Universidad de Buenos Aires, from July 2015 to January 2016. Methodology: Effect on blood pressure and heart rate on anaesthetized normotensive and hypertensive rats were measured using Statham Gould P23ID pressure transducer coupled to a Grass 79D polygraph. Rats were placed in metabolic cages in order to collect urine. Urinary volume was measured and sodium and potassium concentration was estimated from each urine sample using indirect ion-selective electrode potentiometry. The vasorelaxant activity of major compound was studied using isolated aortic rings. Antioxidant activity was estimated measuring 2,2 diphenyl 2 picryl hydrazyl hydrate radical scavenging activity. Results: The intravenous administration of the extract of U. circularis (0.1‐30 mg/kg) in

Chemical speciation of uranium(VI) in marine environments: complexation of calcium and magnesium ions with [(UO2 )(CO3 )3 ](4-) and the effect on the extraction of uranium from seawater.

The interactions of Ca(2+) and Mg(2+) with [UO2 (CO3 )3 ](4-) were studied by calcium ion selective electrode potentiometry and spectrophotometry. The stability constants of ternary Ca-UO2 -CO3 and Mg-UO2 -CO3 complexes were determined with calcium ion selective electrode potentiometry and optical absorption spectrophotometry, respectively. The enthalpies of complexation for two successive complexes, [CaUO2 (CO3 )3 ](2-) and [Ca2 UO2 (CO3 )3 ](aq), were determined for the first time by microcalorimetry. The data help to revise the speciation of uranium(VI) species under seawater conditions. In contrast to the previously accepted assumption that the highly negatively charged [UO2 (CO3 )3 ](4-) is the dominant species, the revised speciation indicates that the dominant aqueous uranium(VI) species under seawater conditions is the neutral [Ca2 UO2 (CO3 )3 ](aq). The results have a significant impact on the strategies for developing efficient sorption processes to extract uranium from seawater.

A Potentiometric Study of the Association of Copper(II) and Sulfate Ions in Aqueous Solution at 25 °C

A study of the association between copper(II) and sulfate ions in aqueous solution has been made using copper ion-selective electrode potentiometry at constant ionic strengths (I) of 0.05, 0.1, 0.25, 0.5, 1.0, 3.0 and 5.0 mol·L−1 in NaClO4 media at 25 °C. Only one complex was detected, corresponding to the equilibrium: \( {\text{Cu}}^{ 2+ } ({\text{aq}}) + {\text{SO}}_{4}^{2 - } ({\text{aq}}) \rightleftarrows {\text{CuSO}}_{4}^{0} ({\text{aq}}). \) No higher order complexes were detected even at sulfate/copper(II) concentration ratios of up to 1,000. The present potentiometric values of log10K1(I) are shown to be consistently higher than those obtained by UV–Vis spectrophotometry because of the failure of the latter technique to detect all of the solvent-separated ion pairs present. Extrapolation of log10K1(I) to infinite dilution using an extended Guggenheim equation yielded a standard state value of log10\( K_{1} \{ {\text{CuSO}}_{4}^{0} ({\text{aq}})\} = 2.32 \pm 0.09 \), which is in excellent agreement with a recent IUPAC-recommended value.

Comparison kinetics studies of Cu(II) adsorption by multi-walled carbon nanotubes in homo and heterogeneous systems: Effect of nano-SiO2

The adsorption kinetics of Cu(II) in homogeneous systems of CNTs and heterogeneous systems of CNTs and nano-SiO2 were investigated using ion selective electrode potentiometry. Particular attention was paid on the role of nano-SiO2 in the adsorption kinetics of Cu(II) by CNTs. It was found that the Cu(II) adsorption by CNTs and CNTs–SiO2 mixture was well described by pseudo-second-order kinetics. In homogeneous systems, the equilibrium time of Cu(II) adsorption decreases and the pseudo-second-order rate constant (k2) increases with increasing CNTs concentrations. Comparing the different types of CNTs, hydroxy CNTs (CNTs-OH), with higher k2 values, adsorb Cu(II) ion much faster than carboxyl CNTs (CNTs-COOH). This may be ascribed to their different adsorption mechanisms. The electrostatic attraction is the primary mechanism of Cu(II) adsorption by CNTs-OH, while Cu(II) adsorbed on CNT-COOH through complexing with the carboxyl groups on the surface of CNTs besides electrostatic attraction. In heterogeneous systems of CNTs and nano-SiO2, the Cu(II) adsorption reaches equilibrium much faster than in homogeneous systems of CNTs, indicating nano-SiO2 accelerates the Cu(II) adsorption. This acceleration effect is possibly related to the adsorption mechanism (electrostatic attraction) and higher BET surface area of nano-SiO2. FTIR and XPS spectra demonstrate the binding of nano-SiO2 and CNTs, and CNTs and Cu(II). The present results highlight the significant influence of nano-SiO2 on the Cu(II) adsorption by CNTs. Hence, it is critical to consider these effects in modeling and predicting the adsorption kinetics of metals by CNTs in heterogeneous systems.

Cadmium (II)-selective electrode based on palm shell activated carbon modified with task-specific ionic liquid: kinetics and analytical applications

In this study, palm shell activated carbon modified with task-specific ionic liquid was used as a novel electrode component for the potentiometric determination of cadmium ions in water samples. The proposed potentiometric sensor has good operating characteristics, including relatively high selectivity towards the Cd (II) ion, a Nernstian response to Cd (II) ions in a working concentration range of 1.0 × 10−9–1.0 × 10−2 M, with a reasonable detection limit of 1 × 10−10 M and a slope of 30.90 ± 1.0 mV/decade. No significant changes in electrode potential were observed when the pH was varied over the range of 4–9. A direct technique based on the use of ion-selective electrode potentiometry has been developed in our laboratory for the study of reaction kinetics and kinetic methods of analysis by continuous monitoring of the rate of production or consumption of an ion. The apparent adsorption rate constant was estimated assuming pseudo-second-order kinetics. Additionally, the proposed electrode has been successfully used for the determination of the cadmium content in real samples without a significant interaction from other cationic or anionic species.

Remediation of Soil Contamination with Heavy Metals by Using Zeolite and Humic Acid Additives

- Soil remediation at contaminated sites very often needs customized approach, because of the different content of pollutants. Various technologies from simple soil excavation and transporting to hazardous waste landfills to different kinds of remediation by vitrification and the use of additives can be used for the treatment of soil. A series of remediation experiments using zeolites and humic acids were applied to soil contaminated with copper. Remediation can be performed with easily available additive materials of natural origin found near the place of application, in order to diminish the leaching of contaminants. Soils contaminated and spiked with copper were mixed with additives, and ion selective electrode potentiometry was used in order to establish the stability constants of humic-metal complexes. Thus the study provides an opportunity to gain information on the fate of copper variously mixed with potential remediation agents zeolites and humic acids - as additives to contaminated soils.

Analytical determination of apparent stability constants using a copper ion selective electrode

Copper(II) complexes of di-, tri- and tetra peptides with previously published protonation constants were re-investigated using pH and copper ion selective electrode (ISE) potentiometry in conjunction with a modified version of HYPERQUAD computer program. The purpose was to demonstrate the suitability of the ISE approach for the determination of apparent stability constants for copper(II) complexes with ligands for which proton stability constants were not available. The interactions of Cu 2+ with oligopeptides were also analysed using surface enhanced laser desorption/ionisation time-of-flight mass spectrometry (SELDI-ToF-MS). The results provide an insight into the metal complex species formed, their apparent stabilities under selected conditions and the effect of the relative positions of certain amino acids within the peptide sequence.