Plastic membrane electrodes for the potentiometric determination of codeine in pharmaceutical preparations

Four PVC membrane electrode systems responsive to codeinium cation are described. These electrodes are based on the use of the ion-association complexes of the codeinium cation with tetraphenylborate and reineckate counter-anions as ion-exchange sites in a PVC matrix plasticized with dioctylphthalate and dibutylsebacate. The performance characteristics of these electrodes reveal fast, stable and near-Nernstian responses for codeine down to concentrations of 3.5–7.0 × 10^–5 M. Over the pH range 2.5–7, the electrodes are satisfactory for manual and flow injection determination of codeine in various pharmaceutical preparations. There is negligible interference from a number of inorganic and organic cations and some common drug excipients. In the direct determination of 30 g/ml -1.0 mg/ml codeine, the average recovery is 100.6% and the mean standard deviation is ± 0.8%. The results compare favorably with those obtained by the British Pharmacopoeia method.     

Membrane sensors for batch and flow injection potentiometric determination of ethamsylate (cyclonamine) in pharmaceutical preparations

The lipophilic nickel(II) and iron(II) bathophenanthroline derivatives of ethamsylate are used as ion-exchangers with high selectivity characteristics for ethamsylate. Poly(vinyl chloride) membrane sensors incorporating these electroactive materials display fast linear response for 1 × 10^–1–1 × 10^–4 M ethamsylate under static and hydrodynamic modes of operation. In an acetate buffer of pH 4, the calibration slope is 51–53 mV/concentration decade and the lower limit of detection is 5.3 g/ml. Except for salicylate and nitrate, most common anions, organic sulfonates, carboxylates, phenolates and various pharmaceutical excipients and diluents do not interfere. Determination of ethamsylate in various dosage forms shows an average recovery of 98.9% of the nominal and a mean standard deviation of 0.7%.     

Determination of cinnarizine in pharmaceutical preparations by spectrophotometry, atomic absorption spectrometry and potentiometry

New methods are developed for the determination of cinnarizine in various dosage forms. They are based on the reaction of cinnarizinium cation with cobalt tetrathiocyanate anion, whereby a sparingly soluble blue 21 drug: reagent ion-pair complex is quantitatively formed. The complex is (a) extracted with nitrobenzene and spectrophotometrically measured at 622 nm; (b) extracted with nitrobenzene and nebulized in an air-acetylene flame for atomic absorption spectrometric monitoring of cobalt at 242.5 nm; and (c) dispersed in a PVC membrane plasticized with 2-nitrophenyloctyl ether and used as a sensor for direct potentiometric determination of the drug. Optimum reaction conditions and performances of the three analytical techniques are evaluated and compared. At the 25 mg level of cinnarizine, the three methods give results with equal accuracy and precision. The average recovery is 98–99% of the nominal and the mean standard deviation is 0.7%. No significant interferences are caused by drug excipients and diluents.     

Determination of ethambutol in pharmaceutical preparations by atomic absorption spectrometry,spectrophotometry and potentiometry

Simple methods are described for the determination of ethambutol in pharmaceutical preparations. They are based on the reaction of the drug with copper phosphate suspension in a borate buffer of pH 9.2, whereby a blue 11 water-soluble copper-ethambutol complex is quantitatively formed. Four portions of the reaction solution are used for (i) measurement of copper by atomic-absorption spectrometry at 324.7 nm; (ii) potentiometric titration with EDTA with use of a solid-state copper ion-selective electrode; (iii) visual titration with EDTA (copper-PAN indicator); and (iv) spectrophotometric measurement of the copper-ethambutol complex at 640 nm. The results obtained are in good agreement and are better than those of the British Pharmacopoeia (BP) method.     

PVC matrix membrane sensor for potentiometric determination of dodecylsulfate

The construction and performance characteristics of a new potentiometric PVC membrane sensor for the determination of sodium dodecyl sulfate (SDS) are described. The sensor was based on the use of an N-cetyl-N,N,N trimethyl ammonium (CTA) dodecyl sulfate (DS) ion pair as ion exchange sites in PVC matrix in the presence of o-nitrophenyl octylether as plasticiser. The sensor exhibited a fast, stable, and near-Nernstian response for SDS over the concentration range of 1 × 10^?3 to 10^?6 M at 25°C and the pH range 4–8.5 with anionic slope of 52.5 ± 0.5 mV decade^?1. The lower detection limit was 3 × 10^?6 M, and the response time was 25 s. Selectivity coefficients of SDS with respect to a number of different species were investigated. There were negligible interferences caused by most of the investigated anions. The determination of 1.0–280.0 µg mL^?1 of SDS in aqueous solutions showed an average recovery of 99.1%, and the mean relative standard deviation was 1.4 at 100 µg mL^?1. The results obtained in the determination of SDS in liquid soap, water and in some pharmaceutical preparations compared favourably with those obtained by the Methylene Blue active substance method (MBAS). In the present investigation, the DS sensor has been used as an end-point indicator electrode for some precipitation titration reactions, e.g. titration of SDS with CTMABr and cetylpyridinium chloride with SDS.     

Determination of diclofenac in pharmaceuticals and urine samples using a membrane sensor based on the ion associate of diclofenac with Rhodamine B

The potentiometric response characteristics of a diclofenac selective electrode, based on ion association in different plasticizers, were compared. The sensitivity, working range, detection limit and selectivity of membrane sensors demonstrated significant dependence on the type of plasticizers. The potentiometric unit presented a linear response toward diclofenac concentrations between 1 × 10⁻⁵ − 5 × 10⁻² mol L⁻¹, with slopes of approximately 60 mV dec⁻¹, and exhibited a response time of 3 s. The potentiometric analysis of sodium diclofenac in pharmaceutical formulations was perfomed by the membrane electrode proposed and compared with the results of potentiometric titration given by the Pharmacopoeia of Ukraine.      

Potentiometric determination of moxifloxacin in some pharmaceutical formulation using PVC membrane sensors

Background

The construction and electrochemical response characteristics of Poly (vinyl chloride) membrane sensors for moxifloxacin HCl (MOX) are described. The sensing membranes incorporate ion association complexes of moxifloxacin cation and sodium tetraphenyl borate (NaTPB) (sensor 1), phosphomolybdic acid (PMA) (sensor 2) or phosphotungstic acid (PTA) (sensor 3) as electroactive materials.

Results

The sensors display a fast, stable and near-Nernstian response over a relative wide moxifloxacin concentration range (1 × 10^-2 - 4.0 × 10^-6, 1 × 10^-2 - 5.0 × 10^-6, 1 × 10^-2 - 5.0 × 10^-6 M), with detection limits of 3 × 10^-6, 4 × 10^-6 and 4.0 × 10^-6 M for sensor 1, 2 and 3, respectively over a pH range of 6.0 - 9.0. The sensors show good discrimination of moxifloxacin from several inorganic and organic compounds. The direct determination of 400 μg/ml of moxifloxacin show an average recovery of 98.5, 99.1 and 98.6% and a mean relative standard deviation of 1.8, 1.6 and 1.8% for sensors 1, 2 and 3 respectively.

Conclusions

The proposed sensors have been applied for direct determination of moxifloxacin in some pharmaceutical preparations. The results obtained by determination of moxifloxacin in tablets using the proposed sensors are comparable favorably with those obtained using the US Pharmacopeia method. The sensors have been used as indicator electrodes for potentiometric titration of moxifloxacin.

     

Determination of phosphate in hydroponic nutrient solutions using flow injection potentiometry and a cobalt-wire phosphate ion-selective electrode

The direct flow injection potentiometric (FIP) analysis of phosphate in hydroponic nutrient solution has been carried out using a cobalt-wire ion-selective electrode (ISE). Synthetic hydroponic nutrient solution, commercial hydroponic nutrient solution and working hydroponic farm nutrient solution were analysed for phosphate using the FIP technique. It is shown that FIP results compare favourably to standard methods of analysis such as spectrophotometry and indirect photometric ion-pair chromatography. Reproducible FIP response curves with a slope of −(47.57±0.03) mV per decade and intercept of −(169.7±0.1) mV were obtained for four separate calibrations in the concentration range 5.0×10⁻⁴–1.0×10⁻² M H₂PO₄⁻. Anion corrections for interferences by Cl⁻, NO₃⁻ and SO₄²⁻ were applied to all samples using the selectivity coefficients determined independently using a fixed interference method. Nevertheless, it was found that anion corrections were not necessary, as the deviations fell within the bounds of experimental error for the cobalt-wire ISE technique (i.e.±2–5% R.S.D.). The proposed FIP method enables the direct determination of phosphate in hydroponic nutrient solutions.     

A New Poly (Vinyl Chloride) Matrix Membrane Electrode for Manual and Flow Injection Determination of Pilocarpine in Some Pharmaceutical Preparations

Abstract

A novel pilocarpinium ion selective membrane electrode is prepared, characterized and used in pharmaceutical analysis. The electrode system incorporates a PVC membrane with pilocarpine-reineckatc ion pair complex as an electroactive material. The electrode exhibits a fast near-Nernstian response for 10^?1-4x10^?5M pilocarpine over the pH range 4-6.5. The electrode displays a good selectivity for pilocarpine with respect to a number of foreign cations. Pilocarpine in various pharmaccutical preparations is determined either by direct potentiometry or potentiometric titration with NaTPB using the proposed sensor. Pilocarpinereineckate membrane is also used in a flow through sandwich cell as a detector for flow injection determination of pilocarpine. Results with an average recovery of 99% and a relative standard deviation of ± 0.3% are obtained. The data compare favorably with those obtained by the standard US Pharmacopeia method.     

Determination of Fluoride Ions in Mouthwash Samples by a PVC Membrane Samarium(III) Sensor

Abstract

In this study, a new ion-selective electrode for Sm³⁺ is described, illustrating 2-[(E)-1-(1H-pyrrol-2-yl)methylidene]-1-hydrazinecarbothioamide (PMH) in a poly(vinylchloride) (PVC) membrane with nitrobenzene (NB) as a plasticizer and sodium tetraphenyl borate (NaTPB) as an anionic additive. The proposed sensor exhibited a Nernstian response for Sm³⁺ ions over a wide concentration range between 1.0 × 10^?2 and 1 × 10^?6 M, with a detection limit of 5.2 × 10^?7 M in the pH range of 4.2–8.5. Moreover, the sensor displayed the Nernstian slope of 19.8 ± 0.3 mV per decade, having a fast response time within 10 s over the entire concentration range. This electrode presented very good selectivity and sensitivity toward the Sm³⁺ ions over a wide variety of cations, including alkali, alkaline earth, transition-metal, and heavy-metal ions. It was used as an indicator electrode in the potentiometric titration of Sm³⁺ ions with EDTA. The membrane sensor was also applied to the determination of fluoride ions in mouthwash samples.     

Indirect spectrophotometric determination of benzylpenicillin and cloxacillin in pharmaceutical preparations

An indirect spectrophotometric method for the determination of benzylpenicillin and cloxacillin is based on extraction of iodine produced by reduction of potassium iodate in acidic medium, where hydrolytic cleavage of a -lactam is achieved with sodium hydroxide. Beer's law is obeyed within the concentration ranges 0.04–0.8 mg ml^–1 benzylpenicillin and 0.02–0.5 mg ml^–1 cloxacillin. The precision, accuracy of the method and the effect of foreign substances were studied. The results have been statistically compared with those using the ammonium vanadate method. An oxidation mechanism is proposed.     

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.     

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.     

Microdetermination of L-ascorbic acid in pharmaceutical preparations by iodide ion-selective electrode and spectrophotometry

Two methods for determining low levels of L-ascorbic acid in pharmaceutical preparations are described. The potentiometric method is based on oxidation of an aqueous ascorbic acid solution with iodine in chloroform. The iodide ions produced in the aqueous phase are determined with the iodide ion-selective electrode using a standard calibration graph technique. The spectrophotometric method is based on oxidation of ascorbic acid with iron(III). The equivalent amount of iron(II) produced is determined as iron(II)-2,4,6-tri(2-pyridyl)-triazine chelate at 595 nm. The results show a mean recovery of 100.067±0.1435 for the potentiometric method, 100.267±0.32 for the spectrophotometric method.     

Simultaneous determination of ofloxacin and ornidazole in pharmaceutical preparations by capillary zone electrophoresis

A simple, rapid and validated capillary electrophoretic method has been developed for the separation and determination of ofloxacin and ornidazole in pharmaceutical formulations with detection at 230 nm. Optimal conditions for the quantitative separations were investigated. Analysis times shorter than 4 min were obtained using a background electrolyte solution consisting of 25 mmol/L phosphoric acid adjusted with 1 m Tris buffer to pH 8.5, with hydrodynamic injection of 5 s and 20 kV separation voltage. The validation criteria for accuracy, precision, linearity and limits of detection and quantitation were examined and discussed. An excellent linearity was obtained in concentration range 25–250 µg/mL. The detection limits for ofloxacin and ornidazole were 1.03 ± 0.11 and 1.80 ± 0.06 µg/mL, respectively. The proposed method has been applied for the analysis of ofloxacin and ornidazole both individually and in a combined dosage tablet formulation. The proposed validated method showed recoveries between 96.16 and 105.23% of the nominal contents. Copyright © 2009 John Wiley & Sons, Ltd.     

Direct analysis of palladium in active pharmaceutical ingredients by anodic stripping voltammetry

Anodic stripping voltammetry, a classical electroanalytical method has been optimized to analyze trace Pd(II) in active pharmaceutical ingredient matrices. The electroanalytical approach with an unmodified glassy carbon electrode was performed in both aqueous and 95% DMSO/5% water (95/5 DMSO/H₂O) solutions, without pretreatment such as acid digestion or dry ashing to remove the organics. Limits of detection (LODs) in the presence of caffeine and ketoprofen were determined to be 11 and 9.6 μg g⁻¹, with a relative standard deviation (RSD) of 5.7% and 2.3%, respectively. This method is simple, highly reproducible, sensitive, and robust. The instrumentation has the potential to be portable and the obviation of sample pretreatment makes it an ideal approach for determining lost catalytic metals in pharmaceutical-related industries. Furthermore, the simultaneous detection of Pd(II) with Cd(II) and Pb(II) in the low μg L⁻¹ range indicates that this system is capable of simultaneous multi-analyte analysis in a variety of matrices.     

A cobalt(II)-selective PVC membrane based on a Schiff base complex of N,N′-bis(salicylidene)-3,4-diaminotoluene

A new PVC membrane electrode for Co²⁺ based on N,N′-bis(salicylidene)-3,4-diaminotoluene, an excellent neutral carrier, has been fabricated using sodium tetraphenylborate (NaTPB) as an anionic excluder and dioctylphthalte (DOP) as a solvent mediator. The electrode exhibits a linear potential response in the concentration range of 7.9 × 10⁻⁸ to 1.0 × 10⁻¹ M with a slope of 30 ± 0.2 mV per decade. The detection limit of the proposed sensor is 5.0 × 10⁻⁸ M and it can be used over a period of 5 months. The proposed sensor revealed good selectivity over a wide variety of other cations including alkali, alkaline earth, heavy and transition metals and could be used in the pH range of 2.0-9.0. This electrode was successfully applied for the determination of Co²⁺in real samples and as an indicator electrode in potentiometric titration of cobalt ions.     

盐酸依匹斯汀PVC膜电极的研制及应用

以四苯硼酸钠与盐酸依匹斯汀生成的离子缔合物为电活性物质,研制了盐酸依匹斯汀PVC膜选择性电极。在pH 5的HCl-NaOH溶液中,电极的线性范围为6.3×10-7~1.0×10-1mol/L,斜率为49 mV/pC(10℃),检出限为1.89×10-7mol/L。应用此电极测定药物中盐酸依匹斯汀含量,RSD3%,回收率为97.5%~100.2%。     

Flow injection determination of ketotifen fumarate using PVC membrane selective electrodes

In this study a PVC membrane electrode for determination of ketotifen fumarate is reported, where ketotifen tetraphenylborate (Keto-TPB) was used as ion exchanger. The electrode has linear range of 5.6 × 10^− 6–1.0 × 10^− 2 and 1.0 × 10^− 5–1.0 × 10^− 2 mol/L, with detection limits 2.37 × 10^− 6and 4.60 × 10^− 6 mol/L in batch and flow injection analysis (FIA), respectively. The electrodes show a Nernstian slope value (58.40 and 61.50 mV/decade in batch and FIA, respectively), and the response time is very short (≤ 10 s). The potential is nearly stable over the pH range 2.0–8.0. Selectivity coefficient values towards different inorganic cations, sugars and amino acids reflect high selectivity of the prepared electrodes. These are used for determination of Ketotifen using potentiometric titration and standard addition methods in pure samples and its pharmaceutical preparations (Zaditen tablets and syrup). The average recovery values are 99.5 and 99.2% with RSD 1.4 and 1.2% for potentiometric titrations and standard addition methods, respectively. The electrode response at different temperatures was also studied.     

Determination of diclofenac in pharmaceutical preparations using a potentiometric sensor immobilized in a graphite matrix

The characteristics, performance, and application of an electrode, namely Pt|Hg|Hg₂(DCF)₂|graphite, where DCF stands for diclofenac ion, are described. This electrode responds to diclofenac with sensitivity of (58.1 ± 0.8) mV/decade over the range 5.0 × 10⁻⁵ to 1.0 × 10⁻² mol l⁻¹ at pH 6.5-9.0 and a detection limit of 3.2 × 10⁻⁵ mol l⁻¹. The electrode is easily constructed at a relatively low cost with fast response time (within 10-30 s) and can be used for a period of 5 months without any considerable divergence in potentials. The proposed sensor displayed good selectivity for diclofenac in the presence of several substances, especially concerning carboxylate and inorganic anions. It was used to determine diclofenac in pharmaceutical preparations by means of the standard additions method. The analytical results obtained by using this electrode are in good agreement with those given by the United States Pharmacopeia procedures.