Fabrication of Potentiometric Sensors for the Selective Determination of Ketoconazole

Abstract

The fabrication and analytical applications of two types of potentiometric sensors for the determination of ketoconazole (KET) are described. The sensors are based on the use of KET-molybdophosphoric acid (MPA) ion pair as electroactive material. The fabricated sensors include both polymer membrane and carbon paste electrodes. Both sensors showed a linear, stable and near Nernstian slope of 57.8 mV/decade and 55.2 mV/decade for PVC membrane and carbon paste sensors respectively over a relatively wide range of KET concentration (1 × 10^?2 ? 5 × 10^?5and 1 × 10^?2 ? 1 × 10^?6). The sensors showed a fast response time of < 30 sec and < 45 sec. A useful pH range of 3–6 was obtained for both types of sensors. A detection limit of 2.96 × 10^?5M was obtained for PVC membrane sensor and 6.91 × 10^?6 M was obtained for carbon paste sensor. The proposed sensors proved to have a good selectivity for KET with respect to a large number of ions. The proposed sensors were successfully applied for the determination of KET in pharmaceutical formulations. The results obtained are in good agreement with the values obtained by the standard method.     

Construction and Validation of New Electrochemical Carbon Nanotubes Sensors for Determination of Acebutolol Hydrochloride in Pharmaceuticals and Biological Fluids

A simple, rapid and a highly selective method for direct electrochemical determination of acebutolol hydrochloride (AC) was developed. The developed method was based on the construction of three types of sensors conventional polymer (I), carbon paste (II) and modified carbon nanotubes (MCNTs) carbon paste (III). The fabricated sensors depend mainly on the incorporation of acebutolol hydrochloride with phosphotungstic acid (PTA) forming ion exchange acebutolol‐phosphotungstate (AC‐PT). The performance characteristics of the proposed sensors were studied. The sensors exhibited Nernstian responses (55.6 ± 0.5, 57.14 ± 0.2 and 58.6 ± 0.4 mV mol L^?1) at 25 °C over drug concentration ranges (1.0 × 10^?6‐1.0 × 10^?2, 1.0 × 10^?7‐1.0 × 10^?2 and 5.0 × 10^?8‐1.0 × 10^?2 mol L^?1 with lower detection limits of (5.0 × 10^?7, 5.0 × 10^?8 and 2.5 × 10^?8 mol L^?1 for sensors (I), (II) and (III), respectively. The influence of common and possible interfering species, pharmaceutical additives and some related pharmacological action drugs was investigated using separate solution method and no interference was found. The stability indicating using forced degradation of acebutolol hydrochloride was studied. The standard addition method was used for determination of the investigated drug in its pharmaceutical dosage forms and biological fluids. The results were validated and statistically analysed and compared with those from previously reported methods.     

Lanthanum-selective sensors based on 3-amino-2-mercapto-3H-quinazolin-4-one in PVC matrix

A new solvent polymeric membrane (PME) and coated graphite (CGE) electrodes based on 3-amino-2-mercapto-3H-quinazolin-4-one as a suitable carrier for La(III) ion are described. The sensors exhibited a Nernstian response for La(III) ion over a wide concentration range (3.0 × 10^?7 to 1.0 × 10^?1 M for PME and 1.0 × 10^?7 to 1.0 × 10^?1 M for CGE) with a slope of 20.1 ± 0.3 (PME) and 23.4 ± 0.4 (CGE) mV decade^?1. The lower detection limits by PME and CGE were 2.0 × 10^?7 and 7.1 × 10^?8 M, respectively. The potentiometric response of the proposed electrodes was independent of the pH of the test solution in the pH range 3.0–9.0 with a fast response time (<10 s). The applications of prepared sensors were demonstrated in the determination of lanthanum ions in spiked water sample and also utilized for indirect determination of fluoride content of two mouth wash preparation samples.     

Modified Screen-Printed Electrode for Potentiometric Determination of Copper(II) in Water Samples

Modified screen printed (SPE) and carbon paste electrodes (CPE) with phenanthroline–tetraphenyl borate ionophore [Phen:TPB] were fabricated for the determination of copper(II). The modified electrodes have linear responses over a wide concentration range (1 × 10^?6–1 × 10^?2 mol·L^?1) of copper(II) ion at 25 °C with divalent cationic slopes of 29.85 ± 0.58 and 29.45 ± 0.81 mV·decade^?1 and exhibit a detection limit of 1 × 10^?6 mol·L^?1 for SPE and CPE. The selectivity coefficient was measured using the match potential method in acetate buffer of pH = 4.2. The modified SPE and CPE sensors show high selectivity and sensitivity for determination of copper(II) and also show stable and reproducible response over a period of five and three months for SPE and CPE sensors, respectively. This method can be used for determination of copper(II) in water, soil, plant and fish tissue samples and the results obtained agreed with those obtained with atomic absorption spectrometer (AAS).     

Determination of L‐Vesamicol in Serum Samples Using Enantioselective,Potentiometric Membrane Electrodes Based on Antibiotics

Abstract

Enantioselective, potentiometric membrane electrodes (EPMEs) based on antibiotics are proposed for the enantioanalysis of L‐vesamicol. A carbon paste was modified with antibiotics (vancomycin, teicoplanin, and teicoplanin modified with acetonitrile), as chiral selectors. The EPMEs based on antibiotics were reliably used for enantiopurity tests of L‐vesamicol using the direct potentiometric technique. The following linear concentration ranges: 1.0×10^?6–1.0×10^?4, 1.0×10^?6–1×10^?3 and 1×10^?7?1×10^?2 mol/L; and detection limits: 1.1×10^?7, 9.6×10^?8, and 3.6×10^?8 mol/L were determine for vancomycin, teicoplanin, and teicoplanin modified with acetonitrile–based EPMEs, respectively. The proposed EPMEs were applied for the enantioanalysis of L‐vesamicol in urine samples.     

Preparation and characterization of in situ carbon paste and screen-printed potentiometric sensors for determination of econazole nitrate: surface analysis using SEM and EDX

The construction and performance characteristics of new sensitive and selective in situ carbon paste (ICPE) and screen-printed (ISPE) potentiometric sensors modified with ion-pairing agents such as phosphotungstic acid, sodium tetraphenylborate, phosphomolybdic acid and ammonium reineckate for determination of econazole nitrate (ECN) have been developed. The reaction mechanism between ECN and ion-pairing agents at the electrode surface was studied through scanning electron microscope and energy-dispersive X-ray analysis. The electrodes under investigation showed potentiometric response for ECN in the concentration range from 1.0 × 10^?6 to 5.0 × 10^?3 mol L^?1 and from 1.0 × 10^?6 to 1.0 × 10^?2 mol L^?1 for ISPE (electrode I) and ICPE (electrode II) potentiometric sensors, respectively, at 25 °C. The electrode response was pH independent in the range 2.5–7.5 and 2.5–6.5 for electrodes I and II, respectively. These sensors have Nernstian slope values of 59.4 ± 0.2 and 59.10 ± 0.2 mV decade^?1 with detection limit of 1.0 × 10^?6 mol L^?1 for electrodes I and II, respectively. The electrodes showed fast response time of 4 and 9 s for electrodes I and II, respectively. The ISPE (electrode I) showed lifetime of 28 days, and this was considered as advantage over ICPE (electrode II). Selectivity for ECN with respect to a number of interfering materials was also investigated. The proposed electrodes were applied for determination of ECN in pure and pharmaceutical formulation using calibration, potentiometric titration and standard addition methods. The results showed good agreement with those obtained using official method. The t and F values indicated no significant difference between the suggested and reported methods. Method validation parameters were optimized according to ICH recommendations.     

Electrochemical Study of Interaction Between Clozapine and DNA and Its Analytical Application

Abstract

The interaction between clozapine (CLZ) as an orally administrated antipsychotic drug with double stranded calf thymus DNA (dsDNA) was investigated at electrode surface using differential pulse voltammetry (DPV). Activated carbon paste electrode (CPE) was modified with dsDNA and used for monitoring the changes of the characteristics peak of CLZ in 0.05 M acetate buffer (pH 4.3). The adsorptive stripping voltammetry on dsDNA‐modified carbon paste electrode (dsDNA‐CPE) was used for determination of very low concentration of CLZ. Under optimal conditions, the oxidation peak current is proportional to CLZ concentration in the range of 7×10^?9?1.2×10^?6 mol l^?1 with a detection limit of 1.5×10^?9 mol l^?1 for 180 s accumulation time by DPV. The proposed dsDNA‐CPE was successfully used for determination of CLZ in human serum samples with recovery of 97.0±2.5%.     

Evaluation of Surface Active Properties and Voltammetric Characterizations of Some New Anionic Copolymer Surfactants

The onset of micelles formations critical micelle concentration, diffusion coefficients as well as particle sizes for some new synthesized anionic copolymer surfactants PSA_4a, PSA_4b, and PSA_4c, were determined and discussed. Three different electrochemical techniques such as cyclic voltammetry (CV), rotating disk voltammetry (RDV), and chronocoulometry (CC) were used in this investigation. The voltammetry of electroactive hydrophobic probe ferrocene solubilized surfactants was investigated in aqueous buffer carbonate solutions of pH 10. The CMC for each PSA_4a, PSA_4b, and PSA_4c, was found to be 3.20 × 10^?4, 4.60 × 10^?4 and 6.30 × 10^?4 M, respectively, using both CV and RDV techniques. The amount of adsorption contribution of ferrocene solubilized surfactants at the glassy carbon electrode was determined from chronocoulometric measurements and it was found in the range from (1.4 to 2.7) × 10^?15 M. The apparent diffusion coefficients were estimated from RDV measurements and the real micelles diffusion coefficients were obtained. Re-quilibrium considerations of ferrocene probe kinetics at the electrode surface were treated according to two different modes of slow- and fast-kinetics. The corrected diffusion coefficient values showed constancy at (5.3 ± 0.1) × 10^?7, (4.8 ± 0.1) × 10^?7, and (3.6 ± 0.4) × 10^?7 cm²/sec for PSA_4a, PSA_4b, and PSA_4c, respectively in the concentration range from 20 to 200 mM. The morphological features of anionic copolymeric surfactants PSA_4a, PSA_4b, and PSA_4c, micelles showed globular self-assembled structure.     

Electrocatalytic Oxidation and Voltammetric Determination of Hydrazine in Industrial Boiler Feed Water Using a Cobalt Phthalocyanine-modified Electrode

Abstract

A carbon paste electrode modified with cobalt phthalocyanine (CPECoPc) was developed and applied to the determination of hydrazine [N₂H₄] in industrial boiler feed water. The CPECoPc exhibited good electrocatalytical activity for hydrazine oxidation at pH 13. A linear correlation was obtained between anodic peak current (I_ap) and hydrazine concentration in the range of 1.25 × 10^?4 to 9.80 × 10^?4 mol L^?1, fit by the equation I_ap = 1.47 + 4.90 × 10⁵ [N₂H₄] with a correlation coefficient of 0.9967. A detection limit of 7.35 × 10^?5 mol L^?1 was obtained. Recovery of hydrazine from three samples ranged between 99.0% and 102.9%. The modified electrode showed no interference by cations commonly present in boiler water, such as K⁺, Na⁺, Ca²⁺, Mg²⁺, Al³⁺, Pb²⁺, and Zn²⁺. The results obtained for hydrazine in boiler water using the proposed modified electrode are in agreement with the data obtained by a standard spectrophotometric method, at the 95% confidence level.     

Comparative study of carbon paste electrodes modified by new pentaaza macrocyclic ligands and gold nanoparticles embedded in three-dimensional sol–gel network for determination of trace amounts of Ag(I)

Two new Ag(I) chemically modified carbon paste electrodes were prepared with comparative potentiometric study of 1,3,6,10,13-pentaaza-2,14-(2,6-pyridyl)-cyclotetradecane-4,12-dione (PPCT) and 1,3,6,9,11,12-pentaaza-2,13-(2,6-pyridyle)-bicycle[2,2,9]pentadecane-4,11-dione (PPBP) as ionophore. These sensors have been modified with sol–gel–Au nanoparticles to obtain a wide concentration range for potentiometric determination of Ag(I) in aqueous solutions. The sensors exhibit significantly enhanced selectivity toward Ag(I) ions over a wide concentration range of 4.0 × 10^?9–2.2 × 10^?2 and 2.2 × 10^?7–2.0 × 10^?2 mol L^?1 with a lower detection limit of 2.5 × 10^?9 and 2.0 × 10^?7 mol L^?1 for PPCT and PPBP modified electrodes respectively. The electrodes are highly selective to Ag(I) ions over a large number of mono, bi, and tri-valent cations. These electrodes were successfully used as indicator electrode for potentiometric determination of silver in sulphadiazine (burning cream) and radiological film.     

Carbon paste electrodes electrochemically modified with cyclodextrins

Cyclic voltammetry was used in order to obtain carbon paste electrodes (CPEs) modified with α- and β-cyclodextrins (CPE_α-CD, CPE_β-CD) in HClO₄ media as electrolyte. The modified CPEs were obtained by applying 30 potential cycles, thus forming on the substrate a film with electroactive characteristics; a rise in current for the anodic and cathodic peaks became apparent as the number of cycles increased. Such behaviour confirmed the CPE modification by the species mentioned. The CPE_α-CD and CPE_β-CD exhibited significant stability before various electrolytes. In order to evaluate the sort of modification attained on the CPEs, a study was conducted, varying the potential scan rate, that confirmed the CD's presence. The modified electrodes were used to determine Pb(II) ions in solution within the range from 1×10^–5 M up to 1×10^–3 M. The CPE_α-CD and CPE_β-CD electrochemical response was studied by means of anodic stripping voltammetry of the Pb(II) ions, thereby giving a linear relation between the current for the anodic peak as a function of Pb(II) concentration with r ²=0.996 for the CPE_β-CD and 0.992 for the CPE_α-CD. Electronic Publication     

Detection of rutin at DNA modified carbon paste electrode based on a mixture of ionic liquid and paraffin oil as a binder

A DNA-modified carbon paste electrode (DNA-CPIE) was designed by using a mixture of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate and paraffin oil as the binder. The electrochemistry of rutin at the DNA-CPIE was investigated by cyclic voltammetry and differential pulse voltammetry. Rutin exhibits a pair of reversible redox peaks in buffer solutions of pH 3.0, and respective electrochemical parameters are established. Under the optimal conditions, the oxidative peak current is linear with the concentration of rutin in the range from 8?×?10^?9 to 1?×?10^?5 mol L^?1, and the detection limit is 1.3?×?10^?9 mol L^?1 (at S/N?=?3). The electrode exhibits higher sensitivity compared to DNA modified carbon paste electrode without ionic liquid and better selectivity comparing with electrodes without DNA. It also showed good performance, stability, and therefore represents a viable method for the determination of rutin.     

Direct electrochemistry and electrochemical biosensing of glucose oxidase based on CdSe@CdS quantum dots and MWNT-modified electrode

The direct electron transfer of glucose oxidase (GOx) was achieved based on the immobilization of CdSe@CdS quantum dots on glassy carbon electrode by multi-wall carbon nanotubes (MWNTs)-chitosan (Chit) film. The immobilized GOx displayed a pair of well-defined and reversible redox peaks with a formal potential (E ^θ’) of ?0.459 V (versus Ag/AgCl) in 0.1 M pH 7.0 phosphate buffer solution. The apparent heterogeneous electron transfer rate constants (k _s) of GOx confined in MWNTs-Chit/CdSe@CdS membrane were evaluated as 1.56 s^?1 according to Laviron's equation. The surface concentration (Γ*) of the electroactive GOx in the MWNTs-Chit film was estimated to be (6.52?±?0.01)?×?10^?11?mol?cm^?2. Meanwhile, the catalytic ability of GOx toward the oxidation of glucose was studied. Its apparent Michaelis–Menten constant for glucose was 0.46?±?0.01 mM, showing a good affinity. The linear range for glucose determination was from 1.6?×?10^?4 to 5.6?×?10^?3?M with a relatively high sensitivity of 31.13?±?0.02 μA?mM^?1?cm^?2 and a detection limit of 2.5?×?10^?5?M (S/N=3).     

Novel Thorium Membrane Sensors with Anionic Response Based on Trioctylphosphine Oxide and Toluate Ionophores

Two novel potentiometric polymeric membrane sensors for rapid and accurate determination of thorium are described. These are based on the use of trioctylphosphine oxide (TOPO) and thorium toluate (Th‐TA) as ionophores dispersed in poly(vinyl chloride) matrix membranes plasticized with nitrophenyloctyl ether. In strong nitric acid medium, Th(IV) nitrate is converted into [Th(NO₃)₆]^2? complex and sensed as anionic divalent ion which exclude most cationic effect. Validation of the assay methods using the quality assurance standards (linearity range, accuracy, precision, within‐day variability, between‐day‐repeatability, lower detection limit and sensitivity) reveals excellent performance characteristics of both sensors. The sensors exhibit near‐Nernstian response for 1.0×10^?6–1.0×10^?1 M Th over the pH range 2.5–4.5. Calibration slopes of ?32.3±0.3 and ?27.2±0.2 mV/decade, precision of ±0.5 and ±0.8% and accuracy of 98.8±0.9 and 97.9±0.7% are obtained with TOPO and Th‐TA based sensors, respectively. Negligible interferences are caused by most interfering mono‐, di‐, tri‐, tetra‐, penta‐, and hexa‐valent elements commonly associated with thorium in naturally occurring minerals and ores. High concentrations of Cl^?, F^?, SO₄^2?, and NO₃^? ions have no diverse effect. Complete removal of the effect of the interferents in complex matrices is achieved by retention of [Th(NO₃)₆]^2? complex from 5 M nitric acid/methanol mixture (1 : 9 v/v) on a strong anion exchanger, washing out the cationic interferents followed by stripping off thorium anion complex and measurements. Both sensors are used for determining thorium in certified thorium ore samples (20–120 mg Th/kg) and some naturally occurring ores (200–600 mg Th/kg). The results obtained agree fairly well with the certified labeled values or the data obtained using X‐ray fluorescence spectrometry     

A new nano-composite electrode as a copper (II) selective potentiometric sensor

A macrocyclic ligand “7,10,13-triaza-1-thia-4,16-dioxa-20,24-dimethyl-2,3;17,18-dibenzo-cyclooctadecane-6,14-dione” as an efficient ionophore was used into a new Cu²⁺ nano-composite potentiometric carbon paste sensor containing multi-walled carbon nanotubes (MWCNTs), nanosilica particles, and room temperature ionic liquid (1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, [BMP]Tf₂N). This potentiometric sensor responds to copper ions in a wide linear dynamic range of 4.50 × 10^?8 to 1.00 × 10^?2 mol L^?1 with Nernstian slope of 29.64 ± 0.10 mV per decade. The detection limit of 2.34 × 10^?8 mol L^?1 was obtained at the pH range 3.5–6.0. It has a fast response with response time of about 10 s, and can be used for at least 16 weeks without any considerable divergence in the potentials. The suggested sensor thus allows sensitive, selective, simple, low cost, and stable electrochemical sensing of Cu²⁺ ions in the presence of a large number of alkali, alkaline earth, transition and heavy metal ions. This sensor was successfully applied in the determination of copper ions in water and waste water samples.     

Flow‐Through Potentiometric Sensors for Alizarin Red S Dye and Their Application for Aluminum Determination

Novel selective and sensitive poly (vinyl chloride) membrane sensors are developed for measuring alizarin red S (AR) based on the use of aliquate 336, Mg^IIphthalocyanine (MgPc), Cu^IIphthalocyanine (CuPc) and Fe^II phthalocyanine (FePc) plasticized poly (vinyl chloride) membrane. The sensors display Nernestian response with slopes of ‐50.6 ± 0.6 , ‐37.4 ± 0.5 , ‐37.7 ± 0.8 and ‐35.0 ± 0.7 mV decade^?1 over the range of 5.2 × 10^?6 to 1 × 10^?2 mol L^?1 for all of them and detection limits of 5.9 × 10^?7, 1.9 × 10‐^?6 2.3 × 10^?6 and 1.9 × 10^?6 mol L^?1 for aliquate, MgPc, CuPc and FePc membrane based sensor, respectively. The sensors exhibit long life span, long term potential stability, high reproducibility, fast response and good discrimination ability towards alizarinate ion in comparison with many other anions. A tubular detector based on aliquate, MgPc, CuPc and FePc was further developed and coupled to a flow‐injection system for alizarin (AR) determination. Under optimized conditions, the linearity range is 1.0 × 10^?5‐ 1.0 × 10^?1 mol L^?1, with a slope of ‐52.1 ± 0.8, 20.9 ± 0.7, 23.6 ± 0.4 and 25 ± 1.1 mV decade^?1 and a reproducibility of ± 0.8 mV (n = 6) for aliquate, MgPc, CuPc and FePc membrane based sensors, respectively. The sensor based on aliquate is further utilized for a potentiodynamic quantification of aluminum in sludge samples and deodorants. The buffered solution of alizarin was allowed to react in a flow system with aluminum. The calibration curve of Al was found to be linear over a concentration range of 0.1 to 1.8 and 1.0 ‐ 40 μg mL^?1 with a slope = 16.9 (r² = 0.993) and 1.76 (r² = 0.994) mV (μg/mL)^?1 and a detection limit of 0.08 and 0.5 μg mL^?1 for 10^?4 and 10^?3 mol L^?1 AR^? as a carrier, respectively. The method was successfully used for determining aluminum in sludge samples and deodorants. The data agree fairly well the nominal values and with results obtain by continuous flow hydride generation inductively coupled plasma (ICP) method.     

Polymeric membrane and coated graphite electrode based on newly synthesized tetraazamacrocyclic ligand for trace level determination of nickel ion in fruit juices and wine samples

Novel polymeric membrane electrode (PME) and coated graphite electrode (CGE) for nickel ion were prepared based on 2,9-(2-methoxyaniline)₂-4,11-Me₂-[14]-1,4,8,11-tetraene-1,5,8,12-N₄ as a suitable neutral ionophore. The addition of lipophilic anion excluder (NaTPB) and various plasticizers viz o-nitrophenyloctylether (o-NPOE), dioctylphthalate (DOP), dibutylphthalate (DBP), 1-chloronaphthalene (CN) and tri-n-butylphosphate (TBP) have found to improve the performance of the sensors. The best performance was obtained for the membrane sensor having a composition of I:NaTPB:TBP:PVC in the ratio 6:4:100:90 (w/w; mg). The electrodes exhibit Nernstian slopes for Ni²⁺ ions over wide concentration ranges of 4.6 × 10^?7–1.0 × 10^?1 M for PME and 7.7 × 10^?8–1.0 × 10^?1 M for CGE with limits of detection of 2.7 × 10^?7 M for PME and 3.7 × 10^?8 M for CGE. The response time for PME and CGE was found to be 10 and 8 s respectively. The potentiometric responses are independent of the pH of the test solution in the pH range 3.0–8.0. The proposed electrodes revealed good selectivities over a wide variety of other cations including alkali, alkaline earth, transition and heavy metal ions. The coated graphite electrode was used as an indicator electrode in the potentiometric titration of nickel ion with EDTA and in direct determination in different fruit juices and wine samples.     

Development of a Novel Automatic Potentiometric System for Determination of Selenium and Its Application in Pharmaceutical Formulations and Anodic Slime

Poly(vinyl chloride) polymeric membrane sensors containing Sn(IV) phthalocyanine dichloride (SnPC) and Co(II) phthalocyanine (CoPC) as novel electroactive materials dispersed in o‐nitrophenyl octylether (o‐NPOE) as a plasticizer are examined potentiometrically with respect to their response toward selenite (SeO₃^2?) ions. Fast Nernstian response for SeO₃^2? ions over the concentration ranges 7.0×10^?6–1.0×10^?3 and 8.0×10^?6–1.0×10^?3 mol L^?l at pH 3.5–8.5 with lower detection limit of 5.0×10^?6 and 8.0×10^?6 mol L^?1 and calibration slopes of ?25.4 and ?29.7 mV decade^?1 are obtained with SnPC and CoPC based membrane sensors, respectively. The proposed sensors reveals by the modified separate solution method (MSSM) a good selectivity over different anions which differ significantly from the classical Hofmeister series. A segmented sandwich membrane method is used to determine complex formation constants of the ionophores in situe in the solvent polymeric sensing membranes. Membrane incorporating CoPC in a tubular flow detector is used in a two channels flow injection set up for continuous monitoring of selenite at a frequency of ca. 50 samples h^?1. Direct determination of selenium in pharmaceutical formulations and anodic slime gives results in good agreement with data obtained using standard ICP method.     

New sensing material of molecularly imprinted polymer for the selective recognition of sulfamethoxazole in foods and plasma and employing the Taguchi optimization methodology to optimize the carbon paste electrode

A new man-tailored biomimetic sensor for sulfamethoxazole host–guest interactions and potentiometric transduction is presented. The host cavity was shaped on a polymeric surface assembled with methacrylic acid monomers by radical polymerization. Molecularly imprinted particles (MIP) were mixed with graphite powder, paraffin oil and ionic site. Using the Taguchi method, this study analyzed the optimum conditions for preparing the carbon paste electrode. The controllable factors used in this study consisted the weights of (1) MIP, (2) paraffin oil, (3) graphite, and (4) the ionic site. The percentage contribution of each controllable factor was also determined. MIP-modified electrode exhibited a Nernstian response (57.2 mVdecade^?1) in a wide concentration range of 6.0 × 10^?8 to 3.1 × 10^?3 mol L^?1 with a lower detection limit of 3.5 × 10^?9 mol L^?1. The sensor was successfully applied to the determination of sulfamethoxazole concentrations in foods and plasma.     

Magnesium-PVC Membrane Sensor Based on 4,5-Bis(Benzoylthio)-1,3-Dithiole-2-Thione

Abstract

This report describes an attempt to develop potentiometric Mg²⁺ sensors based on a liquid polymeric membrane. Membrane incorporating 4,5-Bis(benzoylthio)-1,3- dithiole-2-thione (Bz₂dmit) as ionophore, with composition Bz₂ dmit:NaTPB:NB:PVC in the ratio 2.5:2.5:65:30 (w/w), exhibits the best result for potentiometric sensing of Mg²⁺ ions. The proposed electrode, based on Bz₂ dmitwith nitrobenzene (NB) as a solvent mediator in a polyvinyl chloride (PVC) membrane matrix, exhibited a near-Nernstian response to Mg²⁺ in the concentration range of 1.0 × 10^?5 to 1.0 × 10^?1 M, with a slope of 29.2 mV per decade of activity of Mg²⁺. The lower limit of detection was 1.0 × 10^?5 M. This sensor showed high selectivity with respect to alkaline, alkaline earth, transition, and heavy metal ions, except for Sr²⁺, and could be used over a pH range of 3.5–9.0. It can be used for at least 2 mo without considerable divergence in potentials and has a relatively fast response of <10 s. It was applied successfully as an indicator electrode in potentiometric titration of Mg²⁺ ions with EDTA.