Long-term diffusion experiment at Mont Terri: first results from field and laboratory data

The diffusion of radionuclides is an important safety aspect for nuclear waste disposal in argillaceous host rocks. A long-term diffusion experiment, termed DI-A, is being carried out at the Mont Terri Rock Laboratory in the Opalinus Clay formation. The aim of this experiment is the understanding of the migration and sorption behaviour of cationic and anionic species in consolidated clays. This study reports on the experimental layout and the first results obtained from the DI-A experiment, which include the investigation of HTO, ²²Na⁺, Cs⁺, and I⁻ migration during a period of 1 year by analysing these tracers in the water circulating in the borehole. In addition, results obtained from through-diffusion experiments on small-sized samples with HTO, I⁻, and ³⁶Cl⁻ are presented.The decrease of tracer concentrations in the borehole is fastest for Cs⁺, followed by ²²Na⁺, HTO, and finally I⁻. The chemical composition of the artificial pore water in the borehole shows very little variation with time, thus indicating almost no chemical disturbance around the borehole.Through-diffusion experiments in the laboratory that were performed parallel to the bedding plane with two different methods yielded effective diffusion coefficients for HTO of 4–5×10⁻¹¹ m² s⁻¹ and significantly lower ones for anions Cl⁻ and I⁻ (0.7–1.6×10⁻¹¹ m² s⁻¹). The results indicate the importance of anion exclusion effects arising from the negatively charged clay surfaces. Furthermore, they demonstrate the anisotropic diffusion properties of the clay formation with significantly increased diffusion rates parallel to bedding relative to the perpendicular direction.The tracer data of the in situ experiment were successfully described with 2D diffusion models using diffusion and sorption parameters obtained from the above mentioned and other laboratory studies. The modelling results indicate that HTO and I⁻ diffused with no retardation. The retardation of Na⁺ and Cs⁺ could be described by empirical sorption expressions from previously derived batch sorption (Cs⁺) or diffusion (Na⁺) experiments.Overall, the obtained results demonstrate the feasibility of the technical concept to study the diffusion of non-sorbing and sorbing tracers in consolidated clays.     

Spatial variability of transport parameters in the Boom Clay

Several transport parameters (as hydraulic conductivity K, apparent diffusion coefficient D_p and diffusion accessible porosity η of HTO and iodide) have been intensively measured in the laboratory on high-quality cores taken at the Mol-1 borehole of the Mol site, in Belgium. The borehole was cored in 1997 from about 145 to 325 m depth, including the whole thickness of the Boom Formation, a Tertiary clay situated between 186 and 288 m depth (ground level), and part of the surrounding layers.The hydraulic conductivity measurements confirm the low permeability of the Boom Clay. An upper 90-m-thick clay layer within this formation can be considered as homogeneous with respect to the hydraulic conductivity. The vertical hydraulic conductivity K_v (i.e. K perpendicular to the bedding) is in the order of magnitude of 10⁻¹² m s⁻¹ and the average is 2.3×10⁻¹² m s⁻¹. This layer comprises from top to bottom the “Transition Zone”, the Putte Member, the Terhagen Member and the top of the Belsele-Waas Member of the Boom Formation. The 12 m at the base of the Formation, which corresponds to the lower part of the Belsele-Waas Member is characterised by larger K_v values (ranging between 10⁻¹¹ and 9×10⁻¹¹ m s⁻¹).The same thick clay layer can also be considered as homogeneous, regarding the values of the apparent diffusion coefficient and the diffusion accessible porosity η of tritiated water (HTO) and iodide. The average value of the diffusion accessible porosity is 0.37±0.03 for HTO and 0.16±0.02 for iodide. The apparent diffusion coefficient varies from 1.1×10⁻¹⁰ to 5.5×10⁻¹⁰ m² s⁻¹ for HTO and from 9.1×10⁻¹¹ to 5.2×10⁻¹⁰ m² s⁻¹ for iodide.     

Low-temperature thermionic emission from nitrogen-doped nanocrystalline diamond films on n-type Si grown by MPCVD

Temperature-dependent emission current–voltage measurements were carried out for nitrogen (N)-doped nanocrystalline diamond (NCD) films grown on n-type Si substrates by microwave plasma-assisted chemical vapor deposition (MP-CVD). Low threshold temperature (~ 260 °C) and low threshold electric field (~ 5 × 10^− 5 V/µm) were observed. Both the temperature dependence and the electric field dependence have shown that the obtained emission current was based on electron thermionic emission from N-doped NCD films. We have also studied the relation between nitrogen concentration and the saturation emission current. The saturation current obtained was as high as 1.4 mA at 5.6 × 10^− 3 V/µm at 670 °C when the nitrogen concentration was 2.4 × 10²⁰ cm^− 3. Low value of effective work function (1.99 eV) and relatively high value of Richardson constant (~ 70) were estimated by well fitting to Richardson–Dushman equation. The results of smaller φ and larger A′ suggest that N-doped NCD has great possibility of being a highly efficient thermionic emitter material.     

Oxygen diffusion into polystyrene–bentonite films

A simple fluorescence technique is proposed for the measurement of the diffusion coefficient of oxygen into polystyrene–clay composite films. The composite films were prepared from the mixture of surfactant-free pyrene (P)-labeled polystyrene latexes (PS) and modified bentonite (MNaLB) at various compositions at room temperature. These films were annealed at 200 °C above the glass transition (T_g) temperature of polystyrene for 10 min. Oxygen diffusion into the films was monitored with steady state fluorescence (SSF) measurements. Measurements were performed at room temperature for different film compositions (0, 5, 10, 20, 30, 50 and 60 mass% modified bentonite) films to evaluate the effect of MNaLB content on oxygen diffusion. The diffusion coefficient, D of oxygen was determined by the fluorescence quenching method by assuming Fickian transport and increased from 7.4 × 10^− 10 to 26.9 × 10^− 10 cm² s^− 1 with increasing MNaLB content. This increase in D value was explained by formation of microvoids in the film. These voids are large enough to contribute to the penetration of oxygen molecules through the films. The montmorillonite content did not affect the quenching rate constant, k_q and mutual diffusion coefficient, D_m values.     

Diffusion coefficients and accessible porosity for HTO and Cl in compacted FEBEX bentonite

The transport properties of a Spanish bentonite (FEBEX bentonite) were studied. The behaviour of the conservative anionic species ³⁶Cl⁻ is compared with HTO (neutral and conservative tracer, tritiated water). Apparent and effective diffusion coefficients, as well as the accessible porosity, were determined in a wide range of clay dry densities. Effective diffusion coefficients for HTO and ³⁶Cl⁻ were measured in through-diffusion experiments. Apparent diffusion coefficients were measured for HTO with in-diffusion (ID) experiments.A very important parameter for describing the transport of radionuclides is the accessible porosity, which is often difficult to determine, especially at high clay densities, for the anions. Therefore, it is very important to use different methods to compare the results obtained in order to understand the limitations of each technique and finally provide reliable results. Furthermore, the use of different techniques and the independent determination of each transport parameter can be used to validate the results.Apparent and effective diffusion coefficients for both HTO and Cl⁻ showed an exponential decrease when the dry density increased, with the decrease being more pronounced in the case of Cl⁻. The accessible porosity for HTO is equal to the total porosity. The accessible porosity for chloride is only a small fraction of total porosity (2–3% at a dry density of 1.65 g/cm³, when the total porosity is about 40%).     

Electrodeposition of silver from the system AgNO3—ethyleneglycol—water. Effect of temperature ( −30°C) on the smoothness of silver deposits

The electrodeposition of silver from a nitrate bath can be improved by lowering the temperature and by the addition of ethyleneglycol as anti-freeze. When the bath temperature is lowered below 0°C, the dendritic silver deposition is suppressed and a smooth surface is obtained; at −30°C a very finegrained deposit results. The dendritic growth is supposedly prohibited partly by the lowering of temperature and to a less extent by the adsorption of ethyleneglycol at the surface both of which might enhance the activation overvoltage of silver deposition. From the polarisation measurement in, 0·25 M AgNO₃ electrolytes, the exchange current density of Ag deposition was evaluated as 1·70 × 10⁻² A/cm²(25°C) and with 50 vol. per cent ethyleneglycol, 9·72 × 10⁻⁴ A/cm² (25°C) and 1·22 × 10⁻⁵ A/cm² (−32°C). Adsorption of ethyleneglycol on Ag cathode was discussed by differential capacitance change.     

Reduction electrochimique de la magnesium(II)-mesoporphyrine IX dimethylester et de la magnesium(II)-protoporphyrine IX dimethylester dans le N,N-dimethylformamide

Electroreduction of magnesium(II)mesoporphyrin IX dimethylester (MgMPDME) and magnesium(II)-protoporphyrin IX dimethylester has been investigated by polarography, coulometry at controlled potential and cyclic voltammetry in the solvent dimethylformamide. Both were electro-reduced in three discrete one-electron transfer steps. The third electroreduction step of Mg-MPDME involved a coupled chemical reaction. All six limiting currents were diffusion controlled. The polarographic diffusion coefficients of the two metalloporphyrins were the same, viz. 4.5 × 10⁻⁶ cm² s⁻¹ at 25°C. Electrochemical rate constants effective at relevant formal potentials were in the range between 0.02 and 0.08 cm s⁻¹. The corresponding six half-wave potentials have been determined with precision of 0.02 V.     

Kinetics and irreversibility of cesium and uranium sorption onto bentonite colloids in a deep granitic environment

Sorption of radionuclides onto a stable colloidal phase may significantly enhance their transport in groundwater. A key point, to be analysed to assess the relevance of colloids in the safety of a deep geological radioactive waste repository, is the irreversibility of the colloid/radionuclide bond.In this work, sorption and desorption kinetics of cesium and uranium(VI) onto bentonite colloids in a granitic reduced environment was studied by means of batch experiments, carried out in anoxic conditions under N₂ atmosphere. Sorption kinetics was followed during 18 weeks, and sorption isotherms were also carried out to get additional information on sorption mechanisms. The water used in all the experiments was an alkaline, low ionic strength (pH=9.5 and I=1×10⁻³M) granitic groundwater from the NAGRA's Grimsel Test Site (GTS), Switzerland, which also presents reduced Eh (−200 mV). In this water, bentonite colloids were shown to be stable during several months.Both cesium and uranium presented a nonlinear sorption behaviour in the range of concentration investigated. In kinetic experiments, the measured log Kd for Cs ([Cs]=1×10⁻⁷ M) was 3.94±0.15, and this value did not show significant variations with time. However, the adsorption of cesium on bentonite colloids involves two reactions, a rapid exchange on planar sites (hours) and a slower component (days) in which cesium diffuses to less available but highly selective sites. This slow process, that can be evidenced only when very low tracer concentrations are used (<1×10⁻⁹ M), is most probably responsible for the fixation of a fraction of the sorbed cesium, and for the partial sorption irreversibility shown in desorption tests. Kd values measured after several desorption experiments increased significantly with the age of the sorption complex. For example, for the sample with 1-day contact time, the second desorption Kd was 8600 ml/g whereas the 5 and 8 weeks contact time samples showed second desorption Kd 15 000 and 30 000 ml/g, respectively.The measured log Kd for U ([U(VI)]=4×10⁻⁷ M) varied from 2.91 to 3.21 (±0.15) during 18 weeks of the kinetic experiment. The main variation of Kd values took place in the first 4 weeks, and then a very slow increasing trend was observed, which could be probably attributed to a partial reduction of U(VI) to U(IV).In desorption tests with uranium, desorption K_ds were independent on the initial contact time. Nevertheless, a certain sorption/desorption hysteresis was observed, which is most probably due to the contribution of surface complexation reactions, at the edge sites of clay colloids, to uranium sorption. Hence, U sorption is not completely reversible.     

Electrochemical behavior of Ni(II)/Ni in a hydrophobic amide-type room-temperature ionic liquid

Electrochemical reaction of Ni(II)/Ni was investigated in a hydrophobic room-temperature ionic liquid, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (BMPTFSA) containing Ni(TFSA)₂ as a Ni source. The UV–vis spectra showed that Ni(II) in BMPTFSA is octahedrally coordinated with TFSA⁻ anions. The average activation energy for the diffusion coefficients of this Ni(II) complex was 26 kJ mol⁻¹, which was close to that for the viscosity. The diffusion coefficient of Ni(II) was estimated to be 9.3 × 10⁻⁸ cm² s⁻¹. Chronoamperometric measurements showed that the electrodeposition of Ni on a platinum substrate involved three-dimensional instantaneous nucleation under diffusion control at room-temperature. The electrodeposits obtained by galvanostatic electrolysis with the current density of −0.046 mA cm⁻² at 70 and 100 °C were identified as metallic Ni by XRD.     

Adsorption and binding of the transgenic plant proteins, human serum albumin, β-glucuronidase, and Cry3Bb1, on montmorillonite and kaolinite: Microbial utilization and enzymatic activity of free and clay-bound proteins

Human serum albumin (HSA), β-glucuronidase (GUS), and the Cry3Bb1 protein from Bacillus thuringiensis subsp. kumamotoensis are expressed by genetically-modified plants. Commercial samples of these proteins adsorbed and bound rapidly on the clay minerals, kaolinite (K) and montmorillonite (M). Adsorption increased as the concentration of protein increased and then reached a plateau. The greatest amount of adsorption and binding occurred with the Cry3Bb1 protein, of which there was no desorption: 6.7 ±0.21 μg adsorbed and bound μg^− 1 of M; 2.1 ± 0.39 μg adsorbed and bound μg^− 1 of K. With GUS, 2.2 ± 0.29 μg adsorbed and 1.7 ±0.21 μg bound μg^− 1 of M; 1.5 ± 0.28 μg adsorbed and 1.0 ± 0.03 μg bound μg^− 1 of K. HSA was adsorbed and bound the least: 1.2 ±0.04 μg adsorbed and 0.8 ± 0.05 μg bound μg^− 1 of M; 0.4 ± 0.05 μg adsorbed and 0.4 ± 0.03 μg bound μg^− 1 of K. However, X-ray diffraction analyses indicated that only HSA intercalated M, and none of the proteins intercalated K, a nonswelling clay. When bound, the proteins were not utilized for growth by mixed cultures of soil microorganisms, whereas the cultures readily utilized the free (i.e., not adsorbed or bound) proteins as sources of carbon and energy. The enzymatic activity of GUS was significantly enhanced when bound on the clay minerals. These results indicated that recombinant proteins expressed by transgenic plants could persist and function in soil after release in root exudates and from decaying plant residues as the result of the protection provided against biodegradation by binding on clay minerals.     

PTFE-F-PbO2 电极在H2SO4溶液中的析氧行为

F-PbO2 electrode and polytetrafluoroethylene （PTFE） doped F-PbO2 electrode （PTFE-F-PbO2） were prepared on a plexiglas sheet substrate by a series of procedure including chemical and electrochemical depositions. The electrochemical activities of these two electrodes for oxygen evolution （OE） reaction were examined by electrochemical tests. In comparison with F-PbO2, PTFE-F-PbO2 electrode exhibited larger active surface area and higher oxygen vacancy deficiency, which resulted in its higher electrocatalytic activity for OE. In addition, both exchange current density and activation energy of the electrodes for OE were calculated in terms of active surface area. The values of exchange current density and activation energy in 0.5 mol·L^-1 H2SO4 aqueous solution were 1.125×10^ -3 mA·cm^-2 and 18.62 kJ·mol^-1 for PTFE-F-PbO2, and 8.384×10^-4 mA·cm^- 2 and 28.98 kJ·mol^-1 for F-PbO2, respectively. Because these values are calculated on the basis of the active surface areas of the electrodes, the enhanced activity of PTFE-F-PbO2 can be attributed to an increase in oxygen vacancy deficiency of PbO2 due to doping by PTFE. The influence of PTFE adulteration on the activity of PbO2 film electrode for OE was investigated in detail in this study.     

Temperature effects on iodine adsorption on organo-clay minerals: I. Influence of pretreatment and adsorption temperature

The sorptive capability of clay minerals for anionic radionuclides can be improved substantially by exchanging the natural inorganic interlayer cations with certain organic cations. After screening a variety of possible candidates, four organic cations were selected and combined with three clay minerals, providing 12 organo-cation/clay mineral combinations. The samples were tested for anion adsorption in batch experiments with radioiodide in a concentration range of 10⁻² to 10⁻⁹ mol l⁻¹ and exhibited high adsorption in bidistilled water as well as in synthetic groundwater. Results for two clay minerals—a smectite and a vermiculite—and four organic cations are given in this paper.Tests were also performed with temperature pretreated material. An increase of the pretreatment temperature from 20 to 40, 60, 80 and 100 °C did not result in a remarkable effect on iodide adsorption, except for the 1,12-dipyridiniododecan/vermiculite combination.In batch experiments with equilibrium temperatures of 20–60 °C, iodide adsorption decreased slightly with increasing temperature. Only 1,12-dipyridiniododecan in combination with smectite and vermiculite showed a somewhat lower iodide adsorption at higher temperatures.     

A comparison of diamonds irradiated by high fluence neutrons or electrons, before and after annealing

Neutron- and electron-irradiated type Ia “black” diamonds were analyzed: three near colorless type Ia diamonds were treated in a nuclear reactor with a dose of 1.8 × 10¹⁷ neutrons/cm² and three equivalent samples were irradiated in an electron accelerator with a dose of approximately 0.5 GGy 10 MeV electrons. The diamonds were then annealed and analyzed after the different steps of the treatment. The samples turned from near colorless to very dark green to opaque black upon irradiation and deep greenish yellow to deep orangy brown upon annealing (Fig. 1). The amount of brown color developed during the treatment was found to relate to the type of irradiation used and likely to the total dose of irradiation. The absorption and photoluminescence features as well as the color changes that were observed were found to be unusual and characteristic for diamonds treated with such high irradiation doses. Certain spectral features such as the 644/649 nm, the 724/734/738 nm, the 920 nm and the 967 nm absorptions were only detected in the neutron-irradiated diamonds while others such as the 6165 cm^− 1 and the 805 nm absorptions were only found in the spectra of the electron-irradiated stones.In addition to these treatment experiments some neutron-irradiated very dark green (appearing black) diamonds were heated from 300 to 1100 °C in increments of 50 °C to get a precise idea of the temperature at which color changes occur and the various absorption peaks form. All diamonds turned yellowish to orangy brown after annealing above 700 °C and most of them exhibited unusually strong H1b and/or H1c absorptions after annealing at > 900 °C.     

Electrochemical behaviour of N-acetyl-l-cysteine on gold electrode—A tentative reaction mechanism

The electrochemical behaviour of N-acetyl-l-cysteine (NAC) has been investigated by linear and cyclic voltammetry on gold electrode at room temperature. The results showed two oxidation peaks under acid and neutral conditions and only one in basic medium. For each oxidation, as many electron was exchanged as proton. The influence of both the concentration and the potential scan rate on the peak currents highlighted a diffusion-controlled phenomenon for the first peak and an adsorption-limited reaction rate for the second one. The diffusion coefficient of NAC in solution and the surface concentration of the adsorbed species at pH 3 and 7 were close to 2 × 10⁻⁴ to 2 × 10⁻⁵ cm² s⁻¹ and 6 × 10⁻⁹ to 6 × 10⁻¹⁰ mol cm⁻², respectively. Film transfer experiments resulted in an irreversible adsorption of NAC on gold electrode, and the formation of a self-assembled monolayer (SAM).     

An efficient light-harvesting ruthenium dye for solar cell application

A novel, heteroleptic ruthenium dye comprising a vinyl group between the carboxylate and bipyridine segments as well as extended π-conjugation of the ancillary ligand, employing alkyl-bithiophene, was synthesized. The dye displayed a remarkably high absorption coefficient of 2.51 × 10⁴ M⁻¹ cm⁻¹ (at 562 nm) for its metal-to-ligand charge transfer band. The photo-to-current conversion efficiency of the corresponding dye-sensitized solar cell was 9.12% under AM 1.5 (100 mW/cm²) irradiation. Furthermore, owing to both the very strong metal-to-ligand charge transfer band and the large number of dye molecules adsorbed on the TiO₂ electrode, the conversion efficiency of the dye-sensitized cell was >7.5% at a light intensity ≤198 mW cm⁻².     

Gasification of charcoal using supercritical CO2 at high pressures

A novel one-shell high temperature and high pressure semi-continuous reactor has been developed for the study of the Boudouard reaction at temperatures up to 820 °C and pressures up to 32.5 MPa. Semicontinuous gasification of charcoal using supercritical CO₂ has been achieved at conversions up to 90.8% (w/w) at LSHV between 20 and 30 h⁻¹ after 5–9 h. A gasification model is proposed and validated. Effective rates of gasification (1.32 ± 0.12) × 10⁻⁶ to (6.10 ± 2.03) × 10⁻⁵ s⁻¹ were obtained. The results indicated that this method is technically feasible for the on-line production of high pressures streams of CO/CO₂ in the lab for carrying out further chemistries, avoiding the use of CO high pressure bottles.     

Catalytic dissociation of hydrogen on a tantalum carbide filament in the HFCVD of diamond

New experimental results are presented which describe the behaviour of a carburised tantalum (TaC) filament in the HFCVD of a diamond film. An abrupt filament temperature drop is observed which is associated with the transition of the filament surface from poisoned to clean. By measuring the power increase needed to compensate for the temperature drop at a wide range of temperatures and corresponding CH₄ concentrations, and also considering the difference in radiative cooling of the filament, an energy balance is established. From this energy balance the production rate for H atoms by catalytic dissociation is obtained. It is found to increase from a level of about 3.8×10²⁰ cm⁻² s⁻¹ at 2200 °C to about 1.6×10²¹ cm⁻² s⁻¹ at 3000 °C. This increase, by a factor of 4.5, is somewhat lower than the increase in growth rate observed over the same temperature interval. The difference in these increase factors is interpreted as suggesting that thermal dissociation of H₂ plays a substantial role for H-atom production along with catalytic dissociation.     

Electrochemical studies on the binding of a carcinogenic anthraquinone dye, Purpurin (C.I. 58 205) with DNA

The interaction of the anthraquininoid dye, Purpurin (C.I. 58 205) with fish-sperm DNA was electrochemically investigated in 0.02 mol L⁻¹ pH 7.0 Britton–Robinson (B–R) buffer. After interaction with DNA, the irreversible oxidation peak of the dye decreased and underwent a positive shift of potential, suggesting intercalation between the dye and DNA, this being consistent with fluorescence quenching results. The binding constant (K) and binding site size (s) of the two species were 9.6 × 10⁶ L mol⁻¹ and 1.7 respectively, as determined using voltammetric titration, indicating that the dye was strongly bound to the DNA.     

Chemical aspects of uranium recovery from seawater by amidoximated electron-beam-grafted polypropylene membranes

The amidoximated macroporous membranes (AO membranes) were prepared by post irradiation grafting of acrylonitrile (AN) onto thermally bonded non-woven matrix of poly(propylene) sheet using electron beams. These precursor membranes were reacted with hydroxylamine to convert AN to AO groups, and conditioned by treating them with 2.5% KOH at 80°C for 1 h. The water uptake capacity in seawater, Na⁺-exchange capacity, and uranium loading capacity from seawater of AO membranes were found to be 200±10 wt.%, (3.1±0.2)×10⁻⁴ mol/g, and (1.60±0.18)×10⁻³ mol/g, respectively. The expected functional group density based on the degree of AN grafting (125 wt.%) and its subsequent conversion to AO groups (80%) was found to be 7.8×10⁻³ mol/g. The comparison of the expected functional group density and uranium uptake capacity seems to suggest that UO₂²⁺ forms a complex with AO groups in 1:4 proportion. The uranium could be quantitatively desorbed (>90%) from the AO membrane in Na₂CO₃ and mineral acids like HCl in the equilibration times of 60 min and 40 min, respectively. Alkaline conditioning was found to be necessary for reuse of the membrane equilibrated with acid. However, AO membranes equilibrated with Na₂CO₃ could be reused without any conditioning for uranium sorption.     

Novel coated graphite electrode for the selective determination of Gd(III) in rocks and waste water samples

A novel gadolinium selective coated graphite electrode based on 2,6-bis-[1-{N-cyanopropyl,N-(2-methylpridyl)}aminoethyl]pyridine [P] is described. The best performance was exhibited by the electrode having membrane composition P:NaTPB:PVC:NPOE as 8:4:30:58 (%, w/w). The electrode demonstrates excellent potentiometric characteristics towards gadolinium ion over several interfering ions. The electrode exhibited a Nernstian response to Gd³⁺ ion over a wide concentration range 2.8 × 10⁻⁷ to 5.0 × 10⁻² M with a detection limit (6.3 ± 0.1) × 10⁻⁸ M and slope 19.6 ± 0.1 mV decade⁻¹ of a_Gd³⁺. Furthermore, it showed a fast response time (12 s) and can be used for 2.5 months without significant divergence in its characteristics. Noticeably, the electrode can tolerate the concentration of different surfactants up to 1.0 × 10⁻⁴ M and can be used successfully in 30% (v/v) ethanol media and 10% (v/v) methanol and acetonitrile water mixture. The useful pH range of this sensor is 2.0 to 8.0. It is sufficiently selective and can be used for the determination of Gd³⁺ ions in waste water and rock samples. It also serves as a good indicator in the potentiometric titration of GdCl₃ with EDTA.