Potentiometric Dipyridamole Sensors Based on Lipophilic Ion Pair Complexes and Native Ionic Polymer Membranes

Abstract

A new spectrofluorimetric method was developed for the determination of trace amounts of lecithin. Using enoxacine (ENX)‐terbium ion (Tb³⁺) as a fluorescent probe, in a buffer solution at pH=5.80, lecithin can remarkably reduce the fluorescence intensity of the ENX‐Tb³⁺ complex at λ=545 nm; the reduced fluorescence intensity of the Tb³⁺ ion is proportional to the concentration of lecithin. Optimum conditions for the determination of lecithin were also investigated. The linear range and detection limit for the determination of lecithin were 1.96×10^?7–9.8×10^?6 mol l^?1 and 9.74×10^?8 mol l^?1. This method is simple, practical and relatively free of interference from coexisting substances, and can be successfully applied to assess lecithin in serum samples.     

Potentiometric Membrane Sensor for Determination of Saccharin

A potentiometric poly(vinyl chloride) membrane sensor for determination of saccharin is described. It is based on the use of Aliquat 336S-saccharinateion-pair as an electroactive material in plasticized PVC membranes with o-nitrophenyloctylether or dioctylphthalate. The sensor is conditioned for at least two days in 0.1 mol L⁻¹ sodium saccharinate before use. It exhibits fast, stable and Nernstian response for saccharinate ions over the concentration range of 1.0 × 10⁻¹–5.0 × 10⁻⁵ mol L⁻¹ and pH range of 4.5–11. The sensor is used for determination of saccharin in some dosage forms. Results with an average recovery of 101% and a mean standard deviation of 0.2% are obtained which is compared favourably with data obtained using the British pharmacopoeia method. The sensor shows reasonable selectivity towards saccharin in presence of many anions and natural sweeteners.     

Novel Biomedical Sensors for Flow Injection Potentiometric Determination of Creatinine in Human Serum

Coated‐wire (CW) and tubular (Tu) type membrane sensors for creatinine are developed. These consist of creatinine tungstophosphate(CTP), creatinine molybdophosphate (CMP) and creatinine picrolonate (CPC) ion‐pair complexes as electroactive materials dispersed in plasticized poly(vinyl chloride) matrix membranes. Electrochemical evaluation of these sensors under static (batch) mode of operation reveals near‐Nernstian response with slopes of 62.9, 58.1, and 55.2 mV decade^?1 over the concentration range 1×10^?2–5.0×10^?6, 1×10^?2–7.5×10^?5, and 1×10^?2?3.1×10^?5 mol L^?1. The lower detection limits are 0.39, 3.49, and 2.20 μg mL^?1 creatinine with CTP, CMP and CPC membrane based sensors plasticized with o‐NPOE, respectively. Tubular and coated wire CTP membrane sensors are incorporated in flow‐through cells and used as detectors for flow injection analysis (FIA) of creatinine. The intrinsic characteristics of the detectors under hydrodynamic mode of operation in a low dispersion manifold are determined and compared with data obtained under static mode of operation. With 10^?2 mol L^?1 phosphate buffer of pH 4.5 as a carrier solution, the tubular and coated wire CTP detectors exhibit rapid response of 58.9 and 50.7 mV decade^?1 over the concentration range 1×10^?2–1×10^?5 mol L^?1 and detection limits of 0.39 μg mL^?1 and 0.85 μg mL^?1, respectively. Validation of the assay methods with the proposed sensors by measuring the lower detection limit, range, accuracy, precision, repeatability and between‐day‐variability reveals good performance characteristics confirming applicability for continuous determination of creatinine. The sensors are used for determining creatinine in human blood serum at an input rate of 40 samples per hour. No interferences are caused by creatine, most common anions, cations and organic species normally present in biological fluids. The results favorably compare with data obtained using the standard spectrophotometric method.     

Potentiometric Flow Injection Analysis of Anionic Surfactants in Industrial Products and Wastes

A new sensor for anionic surfactants with a membrane consisting of 33wt% poly(vinyl chloride) (PVC), 66wt% dioctylphthalate (DOP) plasticizer, and 1wt% tridodecylmethylammonium chloride (TDMAC) is developed and used for flow injection analysis. The sensor displays a working response range of 5×10^–7–5×10^–3M dodecylbenzene sulfonate (DBS^–) with a Nernstian slope of 58.5±0.2mV decade^–1, a response time of 30s and a detection limit of 1.5×10^–7M DBS^–. Selectivity measurements with different anionic species indicate good membrane selectivity towards DBS^–. The sensor is used to measure anionic surfactants (DBS^–) in different wastewater samples, commercial detergent products, and for monitoring the rate of surfactant biodegradation in sewage treatment plants. The results obtained agree fairly well with data obtained by the standard extraction-spectrophotometric method. The proposed potentiometric method offers the advantages of simplicity, accuracy, automation feasibility, and applicability to turbid and colored sample solutions.     

Potentiometric Determination of Menadione (Vitamin K3)

 The construction and electrochemical response characteristics of poly(vinyl) chloride matrix membrane sensors for menadione (vitamin K₃) are described. Membranes incorporating the ion association complexes of menadione anion with bathophenanthroline nickel(II) and iron(II) as electroactive materials show linear response for menadione over the range 10⁻¹–10⁻⁵ M with anionic slopes of 58.2–51.4 mV per concentration decade. Both sensors exhibit fast response time (20–30 s), low detection limit (2 × 10⁻⁵ M), good stability (4–6 weeks) and selectivity coefficient (10⁻¹–10⁻³). Direct potentiometric determination of menadione under static and hydrodynamic mode of operations shows average accuracies of 98.8 and 98.5% with relative standard deviations of 0.6% and 1.3%, respectively. Application of the method for the determination of menadione in human plasma gives favourable results compared with those obtained by the standard spectrophotometric method. Received February 26, 2001. Revision October 1, 2001.     

Original Potentiometric Ytterbium(III) PVC-Membrane Sensor Based on N1,N2-Bis-[1-(2-hydroxy-1,2-diphenyl)ethylidene]ethanedihydrazide

Abstract

In this work, we describe the construction, performance, and applications of an original ytterbium(III) sensor based on N¹,N²-bis-[1-(2-hydroxy-1,2-diphenyl)ethylidene]ethanedihydrazide (BHDEH), which acts as a suitable carrier. Because it has a low detection limit of 4.2 × 10^?7 M, the sensor response for the Yb(III) ion is Nernstian over a wide concentration range: four decades of concentration (1.0 × 10^?6 to 1.0 × 10^?2 M). The response time of the electrode is less than 10 s, it can be used in the pH range of 3.2–8.3, and its duration is at least 2 months without any considerable potential divergence. The sensor revealed very good selectivity for Yb(III) in the presence of several metal ions. To investigate the sensor analytical applicability, it was tested as an indicator electrode in the potentiometric titration of Yb(III) solution with standard EDTA solution. The proposed electrode was also used to determine fluoride ions in mouthwash.     

Potentiometric determination of diclofenac in pharmaceutical formulation by membrane electrode based on ion associate with base dye

The characteristics,performance and application of membrane electrode based on ion associate of diclofenac with base dye Safranine T are described.The electrode response to diclofenac has the sensitivity of 47±1.0 mV decade~(-1)over the range of 5×10~(-5)to 5×10~(-2)mol/L at pH 6-12,and the detection limit of 3.2×10~(-5)mol/L.The electrode is easy assembled at a relatively low cost has fast response time(2-4 s)and can be used for a period up to 3.5 months without any considerable divergence in potential.The proposed sensor displayed good selectivity for diclofenac in the presence of different substances.It was used to determine diclofenac in pharmaceuticals by means of the standard addition method.     

Flow‐Through Assay of Quinine Using Solid Contact Potentiometric Sensors Based on Molecularly Imprinted Polymers

Miniaturized potentiometric membrane sensors for quinine incorporated with molecular imprinted polymer (MIP) were synthesized and implemented. Planar PVC based polymeric membrane sensors containing quinine‐methacrylic and/or acrylic acid‐ethylene glycol methacrylate were dispensed into anisotropically etched wells on polyimide wafers. The determination of quinine was carried out in acidic solution at pH 6, where positively charged species predominated prevalently. The suggested miniaturized planner sensors exhibited marked selectivity, sensitivity, long‐term stability and reproducibility. At their optimum conditions, the sensors displayed wide concentration ranges of 4.0×10^?6–1.0×10^?2mol L^?1 and 1.0×10^?5–1.0×10^?2 mol L^?1 with slopes of about 61.3–55.7 mV decade^?1; respectively. Sensors exhibit detection limits of 1.2×10^?6 and 8.2×10^?6 mol L^?1 upon the use of methacrylic and acrylic acid monomers in the imprinted polymer, respectively. Validation of the assay method according to the quality assurance standards (range, within‐day repeatability, between‐day variability, standard deviation, accuracy, and good performance characteristics) which could assure good reliable novel sensors for quinine estimation was justified. Application of the proposed flow‐through assay method for routine determination of quinine in soft drinks was assayed and the results compared favorably with data obtained by the standard fluorimetric method.     

Potentiometric Studies on SomeCephalosporin Complexes

Summary.  The interaction of Ca(II), Cu(II), Zn(II), Pb(II), and La(III) ions with the antibiotics cephalexin, cefadroxil, cephaloridine, and cefoperazone as secondary ligands was investigated potentiometrically. The formation constants were determined for a ligand-to-metal ratio of 1:1 at 25°C and KNO₃. The protonation constants of the complexes were evaluated for the system . The order of stability of the binary and ternary complexes were examined. It was found that glycine adds preferably [M(II)-cephalosporin] rather than to the aqueous complexes of M(II). In all cases 1:1:1 complexes were formed. Received February 4, 2000. Accepted (revised) May 10, 2000     

Potentiometric determination of mefenamic acid in pharmaceutical formulation by membrane sensor based on ion-pair with basic dye

The characteristics,performance and application of membrane sensors based on ion-pair Brilliant Green mefenamate are described.The sensor’s response to the mefenamate ion has the sensitivity of （86.0±2.0） mV/pC over the range of 9×10^-5-1×10^-2moI/Land the detection limit of 4.5×10^-5mol/L at pH 8.5-12.The sensor is easily assembled at a relatively low cost and has fast response time（5-10 s）.The proposed sensor displayed good selectivity for mefenamate ion in the presence of different substances.It was used to determine mefenamic acid in pharmaceuticals.     

Colorimetric Estimation of Melatonin in Pharmaceutical Formulations

 Three simple and sensitive colorimetric methods (A–C) for the determination of melatonin in bulk samples and in pharmaceutical formulations are described. They are based on the formation of coloured species by reaction of ninhydrin with the drug (method A, λ_max 397 nm) by oxidation of the indol moiety in melatonin with potassium persulphate (method B, λ_max 450 nm) or by reduction of osmium (VIII) (method C, λ_max 516 nm). Regression analysis of Beer-Lambert plots showed good correlations in concentration ranges between 0.8–14.2, 70.0–140.0 and 2.0–40.0 μg/mL for methods A, B and C, respectively. The molar absorptivity, Sandell sensitivity and detection limit were calculated. For more accurate analysis, Ringbom optimum concentration ranges were calculated. The validity of the proposed methods was tested by analysing pharmaceutical formulations containing melatonin. The relative standard deviations were ≤ 0.95% with recoveries 99.0–101.33%. Received October 20, 1999. Revision February 10, 1999.     

A Novel Potentiometric Membrane Sensor Based on Aryl Palladium Complex for Selective Determination of Thiocyanate in the Saliva and Urine of Cigarette Smokers

A highly selective potentiometric sensor for thiocyanate ion based on the use of a newly synthesized organo‐palladium ion exchanger complex dispersed in a plasticized poly(vinyl chloride) membrane is described. The sensor displays a Nernstian response (?57.8±0.2 mV decade^?1) over a wide linear concentration range of thiocyanate (1.0×10^?6–1.0×10^?1 mol L^?1 ), low detection limit (6.3×10^?7 mol L^?1), fast response (20 s), stable potential readings (±0.4 mV), good reproducibility (±0.9%), long term stability (8 weeks), high precision (±0.7%) and applicability over a wide pH range (4–10). Negligible interferences are caused by F^?, Cl^?, I^?, Br^?, NO₃^?, NO₂^?, CN^?, SO₄^2?, S₂O₃^2?, PO₄^3?, citrate, acetate and oxalate ions. Under hydrodynamic mode of operation (FIA), the calibration slope is ?51.1±0.1 mV decade^?1, the linear response range is 1.0×10^?5–1.0×10^?1 mol L^?1 SCN^? and the sample throughput is 40–45 per hour. The sensor is satisfactory used for manual and flow injection potentiometric determination of SCN^? in the saliva and urine of cigarette smokers and non smokers. The data agree fairly well with results obtained by the standard spectrophotometric technique. Direct potentiometry and potentiometric titration of SCN^? with Ag⁺ are also monitored with the sensor.     

Lead-Selective Membrane Potentiometric Sensor Based on a Recently Synthesized Bis(Anthraquinone) Sulfide Derivative

Abstract

A new PVC membrane electrode for lead ions, based on bis[(1-hydroxy-9,10-anthraquinone)-2-methyl]sulfide as membrane carrier, was prepared. The sensor exhibits a Nernstian response for Pb²⁺ over a wide concentration range (5.6 × 10^?3-4.0 × 10^?6 M). It has a response time of about 30 s and can be used for at least 3 months without any divergence in potentials. The proposed membrane sensor revealed good selectivities for Pb²⁺ over a wide variety of other metal ions. It was used as an indicator electrode in potentiometric titration of lead ion.     

Novel Polymeric Membrane Sensors Based on Mn(III) Porphyrin and Co(II) Phthalocyanine Ionophores for Batch and Flow Injection Determination of Azide

Two novel potentiometric azide membrane sensors based on the use of manganese(III)porphyrin [Mn(III)P] and cobalt(II)phthalocyanine [Co(II)Pc] ionophores dispersed in plasticized poly(vinyl chloride) PVC matrix membranes are described. Under batch mode of operation, [Mn(III)P] and [Co(II)Pc] based membrane sensors display near‐ and sub‐Nernstian responses of ?56.3 and ?48.5 mV decade^?1 over the concentration ranges 1.0×10^?2?2.2×10^?5 and 1.0×10^?2?5.1×10^?5 mol L^?1 azide and detection limits of 1.5×10^?5 and 2.5×10^?5 mol L^?1, respectively. Incorporation of both membrane sensors in flow‐through tubular cell offers sensitive detectors for flow injection (FIA) determination of azide. The intrinsic characteristics of the [Mn(III)P] and [Co(II)Pc] based detectors in a low dispersion manifold show calibration slopes of ?51.2 and ?33.5 mV decade^?1 for the concentration ranges of 1.0×10^?5?1.0×10^?2 and 1.0×10^?4?1.0×10^?2 mol L^?1 azide and the detection limits are1.0×10^?5 and 3.1×10^?5 mol L^?1, respectively. The detectors are used for determining azide at an input rate of 40–60 samples per hour. The responses of the sensors are stable within ±0.9 mV for at least 8 weeks and are pH independent in the range of 3.9?6.5. No interferences are caused by most common anions normally associated with azide ion.     

Spectrophotometric Quantitation of Fluoxetine Hydrochloride Using Benzoyl Peroxide and Potassium Iodide

 Fluoxetine hydrochloride reacts with benzoyl peroxide and potassium iodide, after heating for 1 min at 30 °C, to give a blue colour having maximum absorbance at 570 nm. The reaction is selective for fluoxetine with 0.01 mg/mL as visual limit of quantitation and provides a basis for a new spectrophotometric determination. The colour reaction obeys Beer’s law from 0.1 mg/10 mL to 2.0 mg/10 mL of fluoxetine and the relative standard deviation is 0.68%. The qualitative assessment of tolerable amounts of other drugs is also studied. Received September 21, 1998. Revision September 10, 1999.     

Construction of a Triphenyltetrazolium Liquid Membrane Ion Selective Electrode and its Analytical Application to the Assay of Vitamin C

 The construction of a liquid triphenyltetrazolium cation (TT⁺) ion-selective electrode (ISE) based on [TT⁺]₃[P(W₃O₁₀)₄] salt dissolved in 2-nitrotoluene is described. The liquid membrane electrode exhibits a rapid and almost Nernstian response to triphenyltetrazolium cations in the concentration range from 2×10⁻⁴ to 1×10⁻² mol l⁻¹. The Nernstian slope is 56–58 mV decade⁻¹ which remains constant for at least two months. The response is virtually unaffected by pH changes in the range 3–12. Major interferents are periodate and malate. Deviation from linearity is also observed in the presence of bromide, iodide and thiocyanate, due to their precipitation with triphenyltetrazolium cations. Analytical applications such as direct potentiometry for the determination of TT⁺ in aqueous solutions and indirect potentiometry for the assay of ascorbic acid (vitamin C) in pharmaceutical preparations are described. Ascorbic acid in the range of 150–500 mg l⁻¹, under specified experimental conditions, can be determined with mean relative error of 1.9%. Received February 25, 2000. Revision April 4, 2000.     

Spectrophotometric Estimation of Nimesulide and its Formulations

 Four simple and sensitive visible spectrophotometric methods (A–D) have been described for the assay of nimesulide (NMD) either in pure form or in pharmaceutical formulations. Methods A and B are based on the oxidative coupling between the reduced product of NMD (RNMD) and p-N,N-dimethyl phenylenediamine dihydrochloride (DMPD) in presence of chloramine – T (CAT) or 3-methyl-2-benzothiazolinone hydrazone hydrochloride (MBTH) in presence of ferric chloride (Fe III) to form coloured products with λ_max at 540 nm and 600 nm respectively. Method C is based on the diazotization of RNMD with excess nitrous acid (HNO₂) and estimating the consumed HNO₂ with cresyl fast violet acetate (CFVA). Method D is based on the formation of the coloured charge-transfer complex, when RNMD is treated with metol (p-methyl aminophenol sulphate, PMAP) in presence of potassium dichromate. All variables have been optimized and the reaction sequence is presented. The concentration measurements are reproducible within a relative standard deviation of 1.0%. Recoveries are 98.6–100.2%. Received February 5, 1998. Revision February 20, 1999.     

Spectrophotometric Determination of Prochlorperazine Maleate in Pure and Pharmaceutical Preparations

 Prochlorperazine maleate reacts with 1-naphthylamine and sodium nitrite, after heating for 110 s at 80 °C to give an orange red colour having maximum absorbance at 460 nm. The reaction is selective for prochlorperazine maleate with 0.01 mg/mL as visual limit of quantitation and provides a basis for a new spectrophotometric determination. The colour reaction obeys Beer’s law from 0.01 mg/10 mL to 0.33 mg/10 mL of prochlorperazine maleate and the relative standard deviation is 0.68%. The quantitative assessment of tolerable amounts of other drugs is also studied. Received September 22, 2000. Revision June 19, 2001     

A Generic Design of a Flow-Through Potentiometric Sensor Array

 In this paper, a flow-through potentiometric microsensor is described which is based on semi-permeable tubing. The ion selective electrodes proposed are of the liquid membrane type in which a dialysis tube captures the ion selective cocktail. Ion selective sensors and a reference electrode based on the same design were constructed by guiding a 0.3 mm diameter dialysis tube through a cavity precision machined in Perspex?. Commercia lly available ionophore or ion-exchanger cocktails were applied to provide ion selectivity whilst a saturated KCl solution was used in the reference electrode. A number of flow-through microsensors selective to different ions (Na, K, Li, pH) were constructed and tested. Each showed good performance in a broad range of concentrations. Advantages of the proposed approach are the generic technology to make sensors with incorporate d reference electrodes, capable of measuring a wide variety of analytes for which cocktails are readily available and the fact that sub-microliter amounts of sample can be measured. Secondly, in comparison to other sensors applied in microchannels, the impedance of the flow-through sensor is much smaller because of the relatively large sensing surface formed by the tube wall. Moreover, the use of dialysis tubing enables easy integration with a so-called microdialysis probe for in-vivo sampling of the blood stream or subcutaneous tissue. Received December 6, 1999. Revision March 24, 2000.     

The Potentiometric Biosensor Acetylcholine Esterase as a Model System

 In a methodical investigation of pH-detection systems (glass and polymer membrane electrodes and ion selective field effect transistor (ISFET)), the possible use of the acetylcholine esterase biosensor as a model for all pH-based biosensors is shown. It revealed that the biomembrane properties are more important for the result than the technology itself. All techniques resulted in a ΔH⁺ detection limit of 6*10⁻⁷ mol/L. Received January 20, 2001; accepted December 18, 2001; published online July 15, 2002