The Measurement of Membrane Potential and NO3 Activity in Root Cells Using Ion-Selective Microelectrodes

Remobilisation of nitrate in plants, especially in vacuole of plant, is mostly related to the qua- lity of agricultural products and the high nitrogen use efficiency in plants. Ion-selective microelectrodes offer a non-destructive and non-interruptive method to measure NO 3 gradients and electric potential differences across both the plasma membrane and tonoplast. Thus, a double-barrelled microelectrode backfilled with a membrane sensor for NO 3 embedded in poly vinyl chloride (PVC) can record the NO 3 activity in cytoplasm and vacuole of a cell. This paper presented how to make this kind of microelectrode and how to do the intracellular measurements on intact plants. Our result showed that nitrate activity was about 2.7 mmol L 1 in cytoplasm while 70 mmol L 1 in vacuole, which implicated that vacuole was a pool of nitrate in plants.

Direct Determination of Potassium-Sodium Activity Ratio in Soil Suspension with Two Ion-Selective Electrodes

A K+-selective electrode and a Na+-selective electrode were used to construct a measuring cell without liquid-junction for the determination of the ion activity ratio of K+ to Na+ in soil suspensions. The measured cell potential was not affected by the total electrolyte concentration when the total cation concentration was 10-1-10-3 mol L-1 and the concentration ratio CK+ / CNa+. was 10:1 to 1:50. When the concentration ratios were equal to 1and the total electrolyte concentrations were 10-2 and 10-3 mol L-1, the ion activity ratio measurement would not be affected by pH in the pH range of 3.5 to 11.5 and 4.4 to 11 respectively. Ions other than H+ have no remarkable influence on the measurement. The ion activity ratio of K+ to Na+ measured directly in soil suspension agree well with those in centrifuged supernant solution. The relative deviation was within 4%. From the measured ion activity ratio, the difference of the bonding energies of K+ and Na+ ions was calculated.

Preparation of CeO_2 Nanoparticles and Its Application to Ion-selective Electrodes Based on Acetyl Cellulose

CeO2 nanoparticles with an average diameter of about 30 nm were prepared by sol-gel method at lower temperature. The gel, transformed from the aqueous solution of metal nitrate and citric acid, can be combusted completely at lower temperature. The redox behavior and the crystallization process of the dried gel were studied by thermogravimetric analysis and infrared spectroscopy. The synthesized powders were characterized by X-ray powder diffraction and transmission electron microscopy. In addition, rare earth elements ion-selective electrodes based on acetyl cellulose were prepared using ultra fine cerium oxide powders.

Highly Efficient Power Conversion from Salinity Gradients with Ion-Selective Polymeric Nanopores

A polymeric nanopore membrane with selective ionic transport has been proposed as a potential device to convert the chemical potential energy in salinity gradients to electrical power. However, its energy conversion efficiency and power density are often limited due to the challenge in reliably controlling the size of the nanopores with the conventional chemical etching method. Here we report that without chemical etching, polyimide （PI） membranes irradiated with GeV heavy ions have negatively charged nanopores, showing nearly perfect selectivity for cations over anions, and they can generate electrical power from salinity gradients. We further demonstrate that the power generation efficiency of the PI membrane approaches the theoretical limit, and the maximum power density reaches 130m W/m2 with a modified etching method, outperforming the previous energy conversion device that was made of polymeric nanopore membranes.

Potentiometric Urea Biosensor Based on Ion-Selective Electrode by Different Immobilization Procedures

Enzyme was immobilized on an ammonium ion-selective electrode by different methods.An ion-selective electrode is not completely ion-specific,and interfering ions react with the ion-selective electrode membrane,altering the measured potential.Therefore,the characteristics of the effect of other ions on ammonium ion-selective electrode-based urea biosensors are considered.Based on the experimental results,the urea biosensor based on entrapment had a high response voltage of around 189 mV and fast response time of around 16 sec.Moreover,selectivity of the urea biosensor in different interfering ions was considered to elucidate the characteristics of ammonium ion-selective electrode-based biosensors.

Construction and Application of a PVC Membrane Enoxacin Ion-selective Electrode Based on a Needle-shaped Inner Reference Electrode

A PVC membrane enoxacin ion-selective electrode based on a needle-shaped inner reference electrode was prepared. A Ag/AgCl wire was used as the substrate of this electrode. It was previously coated with a thin sheet of urea-formaldehyde resin containing Cl - ions to form a needle-shaped inner reference electrode, then the inner reference electrode was coated with a thin sheet of a PVC membrane containing an enoxacin tetraphenylborate ion-pair complex. The influences of various ion-pair complexes, concentrations of the active components in the membrane and the plasticizers on the performance of the electrode were studied by orthogonal design. The linear response range of the electrode was 7.9×10 -5 -1.0×10 -2 mol/L. The detection limit was 2.0×10 -5 mol/L. The slope was 30.4 mV/decade(25 ℃). The electrode can be used for the potentiometric determination of enoxacin tablets directly. The average recovery was 100.4%, and the RSD was 0.9%. The results agreed with those determined by the method in Chinese Pharmacopoeia.

STUDY OF CALCIUM ION-SELECTIVE ELECTRODE BASED ON A NEW NEUTRAL CARRIER

A calcium ion-setective eletrode based on a new neutral carrier was studied.The electrode gives a Nernstian response in the rang 5.9-1 Pa and the response is stable in a wide pH range.Logarithms of setectivity coefficents are -2.3 Li(+),-3.5 Na(+),-4.0 K(+),-3.7NH_4(+),-4.5 Mg(2+) and -4.4Zn(2+).

DEVELOPMENT OF DOUBLE-BARRELED CALCIUM ION-SELECTIVE MICROELECTRODE

A new PVC matrix membrane double-barreled calcium ion-selective microelectrode based on liquid ion exchanger has been designed and constructed.The tip diameter of about 2.5μm as well as lower selectivity coefficients for K+,Na and Mg2+are adequate for in-tracellular measurements of Ca activities.The inner wall of the selective channel was made to be hydrophobic by treatment withalkyl-alcohols.By means of this microelectrode some physiologicalphenomena related to Ca2+activities have been studied,and Caconcentrations in clinical microsamples have also been determined.

Studies of Adsorption of Cadmium Ions by Biowaste Adsorbent from Aqueous Solutions with Ion-Selective Electrodes and ICP-OES

Using environment-friendly and low-cost biowaste adsorbents as toxic metal ion removal substrates from aqueous solutions has a great economic advantage. This work evaluated pumpkin and potato peel biowastes for the adsorption of cadmium ions. The biowastes were treated with acid or base. Batch experiments were carried out by introducing a known concentration of metal ion solution into the biowaste sorbent at various pH levels. The pH and metal ion concentration was monitored with pH and cadmium ion-selective electrode continuously for two hours, and the final concentration for the metal ion after 24 hours was measured with the cadmium electrode and then confirmed with ICP-OES. L-type isotherms were obtained that fit to Freundlich model. Adsorption isotherms showed chemical adsorption and the kinetics following the second order model. Equilibrium adsorption capacity is higher than 29 mg/g at pH 5.6 when the initial concentration is 220 ppm. Dynamic cadmium adsorption capacity is 17 mg/g from aqueous solution when the feed solution is 220 ppm with pumpkin peel biowaste sorbent. The biowaste materials can be regenerated with acid washing.

A review on the synergism between corrosion and fatigue of magnesium alloys:Mechanisms and processes on the micro-scale

Understanding the interaction between cyclic stresses and corrosion of magnesium(Mg)and its alloys is increasingly in demand due to the continuous expansion of structural applications of these materials.This review is dedicated to exploring the corrosion-fatigue mechanisms of these materials,with an emphasis on microscale processes,and the possibility of expanding current knowledge on this topic using scanning electrochemical techniques.The interaction between fatigue and corrosion of Mg alloys is analyzed by considering the microstructural aspects(grain size,precipitates,deformation twins),as well as the formation of pits.Furthermore,in the case of coated alloys,the role of coating defects in these phenomena is also described.In this context,the feasibility of using scanning electrochemical microscopy(SECM),scanning vibrating electrode technique(SVET),scanning ion-selective electrode technique(SIET),localized electrochemical impedance spectroscopy(LEIS)and scanning Kelvin probe(SKP)methods to study the corrosion-fatigue interaction of Mg alloys is examined.A comprehensive review of the current literature in this field is presented,and the opportunities and limitations of consolidating the use of these techniques to study the microscale processes involved in Mg corrosion-fatigue are discussed.

A comparative study of four 20-membered N_2S_4-crown ethers as ionophores for polymeric membrane silver selective electrodes

Four 20-membered N_2S_4-monoazathiacrown ethers have been synthesized and explored as neutral ionophores for Ag^+-selective electrodes.Potentiometric responses reveal that the flexibility of the ligands has great effect on the selectivity and sensitivity to Ag^+ ions.The electrode based on ionophore 9,10,20,25-tetrahydro-5H,12H-tribenzo[b,n,r][1,7,10,16,4,13]tetrathiadiaza cycloicosine 6,13-(7H,14H)-dione(C) with 2-nitrophenyl octyl ether(o-NPOE) as solvent in a poly(vinyl chloride)(PVC) membrane matrix sho...

Adsorption of Potassium and Calcium Ions by Variable Charge Soils

Interactions of potassium and calcium ions with four typical variable charge soils in South China were examined by measuring pK-0.5pCa value with a potassium ion-selective electrode and a calcium ion-selective electrode,and pK value with a potassium ion-selective electrode.The results showed that adsorption of potassium and calcium ions increased with soil suspension pH,and the tendency of the pK-0.5pCa value changing with pH differed with respect to pH range and potassium to calcium ratio.Adsorption of equal amount of calcium and potassium ions led to release of an identical number of protons,suggesting similar adsorption characteristics of these two ions when adsorbed by variable charge soils.Compared with red soil,latosol and lateritic red soil had higher adsorption selectivities for calcium ion.The red soil had a greater affinity for potassium ion than that for calcium ion at low concentration,which seems to result from its possession of 2:1 type minerals,such as vermiculite and mica with a high affinity for potassium ion.The results indicated that adsorption of potassium and calcium ions by the variable charge soils was chiefly caused by the electrostatic attraction between the cations and the soil surfaces.Moreover,it was found that sulfate could affect the adsorption by changing soil surface properties and by forming ion-pair.

Adsorption Kinetics of Pb^(2+) and Cu^(2+) on Variable Charge Soils and Minerals: Ⅲ. Adsorption Kinetics of Pb^(2+) Within 30 Minutes

The adsorption kinetics of Pb^2+ on different soils and minerals with variable charges was studied by the two ion-selective electrode technique at different pH and concentrations.The results showed that more than 95% of adsorption on all the samples occurred during the first 5 minutes.All adsorption time-dependent data could fit the surface second-order equation very well.The values of Xm were goethite>kaolinite,and latosol>red soil at the same initial reaction concentration.The values of k were kaolinite>>goethite,and latosol>red soil at the same reaction pH and initial concentration.The higher the suspension pH,the faster the adsorption occurred.The meaning of Xm got by the two ion-selective electrode technique(one kind of batch technique) was different from that by the miscible displacement technique in that the former was only the equilibrium adsorption amount at a definite concentration and pH,but the latter was almost equal to the adsorption capacity at a definite pH with much less influence of concentration.One Pb^2+ was supposed to occupy two adsorption sites as the adsorption mechanism is concerned.

Potentiometric detection of polyions based on functionalized magnetic nanopaiticles

A novel potentiometric detection strategy based on functionalized magnetic nanoparticles has been developed for rapid and sensitive sensing of polyions.Highly dispersed magnetic nanoparticles coated with ion exchanger and plasticizer could promote an in situ cooperative ion-pairing interaction between the ion exchanger and the polyion analyte in sample solution by dramatically reducing the mass-transfer distance.With applying a magnetic field,the nanoparticles can be attached to the surface of ion exchanger free polymeric membrane.The observed potential signals are related to the polyion concentrations.The proposed polymeric membrane electrode exhibits a linear relationship between the greatest potential response slope（dE/dt） and the logarithm of protamine concentration in the range of 0.05-5μg/mL with a lower detection limit of 0.033μg/mL.

Kinetic Characteristics of Nitrate Uptake by Wheat and Rape and Their Determination

15-day old seedlings of wheat and rape were grown in a series of solutions with different concentrations of KNO3 for a definite period of time. The changes in NO3- concentration of the solutions were determined by the double ion-selective electrode method, and then the amount of NO3- taken up by the plants was estimated and values of Km and Imax of the Michealis-Menten equation were calculated. Results show that both the method and conditions of determination affected the values of Km and Imax. For example, the Km value was appreciably reduced when the volume of culture solution was increased or when the duration of nutrient uptake was shortened; the Km value obtained with short-term depletion method was higher than that obtained with long-term one. Similar Variations were found for the values of Imax. There was a considerable difference in the characteristics of uptake kinetics between wheat and rape when determined under the same conditions of determination. The isotherm of NO3- uptake by wheat could be separated into saturated and unsaturated parts, and when the concentration of NO3- exceeded 180 uuuuuuuuuuuuM, the relationship between the rate of NO3- uptake and NO3- concentration tended to be linear. However, the isotherm of NO3- uptake by rape was found to fit the Michealis-Menten equation and no linear relationship could be found.

Physiological Responses of Two Wheat Cultivars to Nitrogen Starvation

Plants need to be efficient in nutrient management, especially when they face the temporal nutrient defficiencies. Understanding how crops respond to nitrogen （N） starvation would help in the selection of crop cultivars more tolerant to N deficiency. In the present work, the physiological responses of two wheat cultivars, Yannong 19 （YN） and Qinmai 11 （QM）, to N starvation conditions were investigated. The two cultivars differed in biomass and N rearrangement between shoots and roots during N starvation. QM allocated more N to roots and exhibited higher root/shoot biomass ratio than YN. However, tissue measurement indicated that both cultivars had similar nitrate content in leaves and roots and similar remobilization rate in roots. Microelectrode measurement showed that vacuolar nitrate activity （concentration） in roots of QM was lower than that in roots of YN, especially in epidermal cells. Nitrate remobilization rates from root vacuoles of two cultivars were also identical. Moreover, vacuolar nitrate remobilization rate was proportional to vacuolar nitrate activity. During N starvation, nitrate reductase activity （NRA） was decreased but there were no significant differences between the two cultivars. Nitrate efflux from roots reduced after external N removal and QM seemed to have higher nitrate efflux rate.

Ion Selective Electrode Array Analysis Using Variable Step-Size Generalized Simulated Annealing

A global optimum location algorithm called Variable Step-Size Generalized Simulated Annealing(VSGSA) was applied to treating the data obtained by using an array of ion-electrodes in solutions containing mixtures of Na+, K+, Ca2+. Unlike traditional optimization algorithms such as simplex procedure, VSGSA can be used to determine the model parameters without any priori information about the analytical system under investigation and overcome the disadvantage of simplex method which might converge to local extrema depending on the starting positions. The algorithm was applied to po-tentiometric determination of ions in mixture solutions.

Solid-Contact Perchlorate Sensor with Nanomolar Detection Limit Based on Cobalt Phthalocyanine Ionophores Covalently Attached to Polyacrylamide

Novel solid-contact perchlorate sensors based on cobalt phthalocyanine-C-monocarboxylic acid (I), and cobalt phthalocyanine-C,C,C,C-tetracarboxylic acid (II) as free ionophores and covalently attached to polyacryla- mide (PAA)—ionophores III and IV, respectively were prepared. The all solid-state sensors were constructed by the application of a thin film of a polymer cocktail containing a phthalocyanine ionophore and cetyltrimethylammonium bromide (CTMAB) as a lipophilic cationic additive onto a gold electrode precoated with the conducting polymer poly (3,4-ethylenedioxythiophene) (PEDOT) as an ion and electron transducer. The sensor with 10.3% of ionophore (III) covalently attached to plasticizer-free poly (butyl methacrylate-co-do- decyl methacrylate) (PBDA) exhibited a good selectivity for perchlorate and discriminated many ions, in- cluding F–, Cl–, Br–, I–, SCN–, , S2– and . The covalent attachment of the ionophore to the polymer resulted in a near-Nernstian anionic slope of –62.3 mV/decade whereas a super-Nernstian slope of –79.9 mV/ decade was obtained for the free ionophore. The sensor covered a linear concentration range of 5 × 10–9 - 1 × 10–2 mol?L–1 with a lower detection limit (LDL) of 1 × 10–9 mol?L–1 and gave a stable response over a pH range of 4 - 10.5. The all-solid state sensors were utilized for the selective flow injection potentiometric determination of perchlorate in natural water and human urine samples in the nanomolar concentration range.

A New Potentiometric Sensor for Determination of Pethidine hydrochloride in Ampoules and Urine

A simple, precise, rapid and low-cost potentiometric method for pethidine determination in pharmaceuticals and urine is proposed. A chemically modified carbon paste electrode (CMCPE) for pethidine hydrochloride (PDCl) based on pethidine-phosphotungstate (PD-PT) as ion-pair complex was prepared and fully character-ized in terms of composition, usable pH range, response time and temperature. The pethidine electrode showed Nernstain responses in the concentration range 2.1 × 10–6-1.0 × 10–2 M with a detection limit of 7.3 × 10-7 and usable within the pH range 3.5-6.6. This sensor exhibited a fast response time (about 5-8 s), good stability. The value (dE/dt) of the electrode was found to be 0.00071 V/?C, which indicates fairly high ther-mal stability. Selectivity coefficients determined by matched potential method (MPM) and separate solution method (SSM) showed high selectivity for PDCl with respect to a large number of inorganic cations, organic cations, sugars and some common drug excipients. The sensor could be used successfully in the estimation of PDCl in ampoules and in spiked urine samples.

Binding mechanism of halide ions to bovine serum albumin and hemoglobin: investigated by ion selective-electrode

The binding mechanism of the interactions of halide ions (F–, Br– and I–) with bovine serum albumin (BSA) and hemoglobin (Hb) were studied at different temperatures, by using ion-selective electrodes. The experimental data were treated according to Klotz equation, and the number of binding sites and the binding constants were determined. The results show that the binding sites of F– on protein molecules are more than those of Br– and I–. Additionally, the number of the binding sites for halide ions on protein molecules increases with increasing temperature. This study also indicates that the binding constants for the interactions of halide ions with proteins gradually decrease as the size of halide ions and temperature increases. These behaviors were reasonably interpreted with the structural and thermodynamic factors. The thermodynamic functions at different temperatures were calculated with thermodynamic equations, and the enthalpy change for the interactions were also determined by isothermal titration calorimetry (ITC) at 298.15 K, which indicate that the interactions of halide ions with proteins are mainly electrostatic interaction.