Gallamine-tetraphenylborate-modified carbon paste electrode for the potentiometric determination of gallamine triethiodide (flaxedil)

The construction and general performance of a novel modified carbon paste electrode for the determination of gallamine triethiodide have been developed. The electrode shows a stable, potentiometric response for gallamine in the concentration range 1 x 10(-3)-2 x 10(-6) M at 25 degrees C independent of pH in the range 5-8. The electrode passes a near-Nernstian cationic slope of 17.0+/-0.7 mV and lower detection limit of 1 x 10(-6) M with a fast response time of 20-45 s. Selectivity coefficients for gallamine relative to a number of interfering substances were investigated. There is a negligible interference from the studied cations, anions, and pharmaceutical excipients. The determination of gallamine in aqueous solution shows an average recovery of 99.5% and a mean relative standard deviation (RSD) of 1.4% at 100 microg/ml. The direct determination of gallamine in injection solution gave results that compare favorably with those obtained by the British pharmacopoeia method. Potentiometric titration of gallamine with sodium tetraphenylborate and phosphotungstic acid as a titrant has been monitored with the modified carbon paste electrode as an end-point indicator electrode.     

Potentiometric sensors for the selective determination of sulbutiamine

Five novel polyvinyl chloride (PVC) matrix membrane sensors for the selective determination of sulbutiamine (SBA) cation are described. These sensors are based on molybdate, tetraphenylborate, reineckate, phosphotun gestate and phosphomolybdate, as possible ion-pairing agents. These sensors display rapid near-Nernstian stable response over a relatively wide concentration range 1x10(-2)-1x10(-6) M of sulbutiamine, with calibration slopes 28 32.6 mV decade(-1) over a reasonable pH range 2-6. The proposed sensors proved to have a good selectivity for SBA over some inorganic and organic cations. The five potentiometric sensors were applied successfully in the determination of SBA in a pharmaceutical preparation (arcalion-200) using both direct potentiometry and potentiometric titration. Direct potentiometric determination of microgram quantities of SBA gave average recoveries of 99.4 and 99.3 with mean standard deviation of 0.7 and 0.3 for pure SBA and arcalion-200 formulation respectively. Potentiometric titration of milligram quantities of SBA gave average recoveries of 99.3 and 98.7% with mean standard deviation of 0.7 and 1.2 for pure SBA and arcalion-200 formulation, respectively.     

PVC membrane ion-selective electrodes for the determination of Hyoscyamine in pure solution and in pharmaceutical preparations under batch and flow modes

New PVC membrane electrodes selective for the determination of hyoscyamine ion (Hy(+)) based on hyoscyamine tetraphenylborate (Hy-TPB) or hyoscyamine phosphotungstate (Hy-PT) ion-exchangers as electroactive materials are described. The electrodes show a linear response for Hy(+) over the concentration range of 1.00 x 10(-5) to 1.26 x 10(-2) mol L(-1) and 1.00 x 10(-4) to 1.00 x 10(-2) mol L(-1) in case of Hy-TPB electrode applying batch and flow injection analysis (FIA), respectively, and 1.00 x 10(-5) to 4.52 x 10(-3) mol L(-1) and 6.31 x 10(-5) to 1.00 x 10(-2) mol L(-1) in case of Hy-PT electrode for batch and FIA, respectively. The lower detection limits are 3.90 x 10(-6) and 4.51 x 10(-6) at 25 degrees C for Hy-TPB and Hy-PT electrodes, respectively. The electrodes posses near Nernstian slopes of 56.5 and 57.8 mV/decade for Hy-TPB and Hy-PT electrodes, respectively, and a fast potential response of < or =20 s which is almost constant over a pH range of 3-10. Selectivity coefficient data for some common inorganic cations, sugars, amino acids and the components, other than hyoscyamine, of the mixed drugs investigated show negligible interference. The electrodes have been applied to the potentiometric determination of hyoscyamine in pure solution and in pharmaceutical preparations under batch and FIA conditions and as end point indicator electrode for the determination of hyoscyanine using potentiometric titration. For the concentrations (1.08 x 10(-5) mol L(-1) to 3.16 x 10(-3) mol L(-1)) an average recovery of 99.95% with relative standard deviation of 0.63% has been achieved. The effect of temperature on the electrodes was also studied.     

Phosphorus-doped and undoped glassy carbon indicator electrodes in controlled-current potentiometric titrations of bromide- or chloride-containing active ingredients in some pharmaceutical preparations

Phosphorus-doped glassy carbon (as a novel material) and glassy carbon (Sigri commercial sample) were applied as potentiometric indicator electrodes in the titrimetric determination of active components with bromide or chloride in their molecules in different pharmaceutical preparations (Buscopan, Prostigmine, Isoptin, Bedoxin, Akineton and Trodon). After the necessary pre-treatment of the electrode surfaces and sample dissolution, the halide was titrated with a standard solution of silver nitrate (indirect determination). Amounts of 10-20 micromol of the investigated active ingredients per titration were determined with a relative standard deviation that, depending on the nature of indicator electrode, determined molecules and filler components, was in the range of 0.3-2.7%. The results obtained were compared with those of the official methods and with those obtained by potentiometric titrations using silver electrode. The titrimetric procedures developed are relatively fast, easy, economical and can be used to analyse of a large number of pharmaceutical products.     

Rutin determination in pharmaceutical formulations using a carbon paste electrode modified with poly(vinylpyrrolidone)

A carbon paste electrode modified with poly(vinylpyrrolidone) (PVP) was developed for the determination of rutin. PVP enhances the adsorption of rutin on the electrode surface due to the presence of hydrogen bonding between the imide group in PVP and the hydroxyl group in rutin. The current responses in cyclic and linear sweep voltammetric experiments were investigated and an oxidation peak was observed at +0.87 V vs. Ag/AgCl. Several parameters were investigated to evaluate the performance of the modified electrode. The best analytical response was obtained employing (75:15:10%, w/w/w) graphite powder:Nujol:PVP, with an accumulation time of 10 min, scan rate of 100 mV s(-1) and 0.1M phosphate buffer solution (pH 6.0) as supporting electrolyte. The analytical curve was linear for rutin concentrations of 3.9 x 10(-7) to 1.3 x 10(-5)M (r=0.9991) and the detection limit was 1.5 x 10(-7)M. The recovery of rutin from pharmaceutical samples ranged from 98.3 to 101.7% and the relative standard deviation was 3.3% for a solution containing 7.7 x 10(-6)M rutin (n=5). This electrode was successfully applied to the determination of rutin in pharmaceutical formulations. The results obtained using the proposed modified carbon paste electrode and those obtained by the standard method are in agreement at the 95% confidence level.     

Characteristics of new composite- and classical potentiometric sensors for the determination of pioglitazone in some pharmaceutical formulations

The construction and electrochemical response characteristics of poly(vinyl chloride) membrane sensors for pioglitazone HCl (PG) are described. The sensing membranes incorporate ion association complexes of pioglitazone cation and sodium tetraphenylborate (NaTPB) (sensor 1) or phosphomolybdic acid (PMA) (sensor 2) or phosphotungstic acid (PTA) (sensor 3) as electroactive materials. The sensors display a fast, stable and near-Nernstian response over a relative wide pioglitazone concentration range (1x10(-2) to 10(-6)M), with cationic slopes of 55.0+/-0.5, 58.0+/-0.5 and 53.0+/-0.5mV per concentration decade over a pH range of 1.0-5.0. The sensors show good discrimination of pioglitazone from several inorganic and organic compounds. The direct determination of 2.5-3900.0mug/ml of pioglitazone show an average recovery of 98.5, 99.0 and 98.4% and a mean relative standard deviation of 1.6, 1.5 and 1.7% at 100.0mug/ml for sensors 1, 2 and 3, respectively. The proposed sensors have been applied for direct determination of pioglitazone in some pharmaceutical preparations. The results obtained by determination of pioglitazone in tablets using the proposed sensors are comparable favorably with those obtained using the HPLC method. The sensors have been used as indicator electrodes for potentiometric titration of pioglitazone.     

Chemically modified carbon paste electrode for the potentiometric flow injection analysis of piribedil in pharmaceutical preparation and urine

A new carbon paste electrode selective for piribedil (PD) was prepared and fully characterized in terms of composition, usable pH range, response time and thermal stability. The electrode active recognition is by liquid ion-exchange mechanism via the use of piribedil phosphomolybdate as ion-exchanger dissolved in tricresyl phosphate as a more suitable solvent mediator for the paste. The modified electrode showed a Nernstian slope of 58.4+/-0.6 mV over the concentration range of 7.5 x 10(-7) to 1 x 10(-3)M with an average recovery of 98.3-101.0% and R.S.D. of 0.45-1.31%. The electrode exhibits good selectivity for PD with respect to a large number of inorganic cations, organic cations, sugars and amino acids. The developed electrode was successfully used for the potentiometric determination of PD in its aqueous solutions, pharmaceutical preparation, and urine in batch and flow injection analysis (FIA).     

s-Benzylthiuronium PVC matrix membrane sensor for potentiometric determination of cationic surfactants in some pharmaceutical formulation

The construction and characteristic performance of s-benzylthiuronium (s-BT)-PVC membrane sensor responsive for cetylpyridinium chloride (CPC) are described. The sensor is based on the use of s-BT-tetraphenylborate (TPB) ion pair as electroactive material in PVC matrix in presence of dioctylphthalate as solvent mediator. The membrane sensor shows a fast, stable and near Nernstian response for CPC over the concentration range of 6 x 10(-6)-1 x 10(-3)M at 25 degrees C and pH range 6-12 with cationic slope of 57.0+/-0.4. The lower detection limit is 4 x 0(-6)M and the response time is 10-30 s. Selectivity coefficients for CPC relative to a number of different species were investigated, which there is negligible intereferences are caused by most of investigated cations, anions, and some organic compounds. The determination of 2.0-350.0 microg/ml of CPC in aqueous solutions shows an average recovery of 98.8%and a mean relative standard deviation of 1.87% at 64.0 microg/ml. The determination of CPC in mouthwash pharmaceutical solution gave results that compare favorably with those obtained by the British pharmacopoeia method. The s-benzylthiuronium electrode has been utilized as an end point indicator electrode for some precipitation titration reactions involving CPC as titrant.     

Improving the detection limits of antispasmodic drugs electrodes by using modified membrane sensors with inner solid contact

Three coated wire electrodes (CWEs) for the antispasmodic drugs; dicyclomine (Dc), mebeverine (Mv) and drotaverine (Dv) hydrochlorides were developed. Each electrode based on ion-associate of a heteropoly anion with the drug cation incorporated in membrane sensor modified with graphite and deposited on silver internal solid contact. The influence of addition of graphite to the membranes and the type of the internal solid contact on the potentiometric responses of the electrodes was investigated. The characteristics of the new electrodes were compared to the characteristics of previously reported traditional liquid inner contact electrodes of the same drugs. The lower detection limits of the proposed electrodes were somewhat better than those observed with the corresponding liquid contact ISEs and reached (1.2-2.0)x10(-7)M. The potentiometric selectivity of the CWEs revealed a significant improvement and much faster response times compared to the liquid contact ISEs. The practical utility of each electrode has been demonstrated by using it successfully in potentiometric determination of its respective drug in pharmaceutical preparations both in batch and flow injection conditions. Each electrode was also used as an indicator electrode in the potentiometric titration of the drug against standard silicotungstic acid and in potentiometric determination of the drug concentration in urine samples.     

Ion-selective electrode for the determination of prazosin in tablets

A poly (vinylchloride) (PVC) membrane electrode selective for prazosinium cation based on prazosinium-phosphotungstate (PZ)(3)PT ion-associate is prepared. The electrode exhibits a linear response with an approximate Nernstian slope over the range of 2.7 x 10(-6)-10(-2) M. Calibration graph slope of the electrode is 58 mV PZ(-1) concentration decade when preconditioned by soaking in distilled water for 1 h-20 days. The working pH of the electrode ranged from 1.5 to 6.4 and exhibits very good selectivity for the PZ with respect to a large number of inorganic cations and organic substances of biological importance. The standard additions method and potentiometric titration are used to determine the PZ in pure solution and in pharmaceutical preparations with satisfactory results.     

Fast BIA-amperometric determination of isoniazid in tablets

This paper proposes a new, fast and precise method to analyze isoniazid based on the electrochemical oxidation of the analyte at a glassy carbon electrode in 0.1M NaOH. The quantification was performed utilizing amperometry associated with batch injection analysis (BIA) technique. Fast sequential analysis (60 determinations h(-1)) in an unusually wide linear dynamic range (from 2.5 x 10(-8) to 1.0 x 10(-3)M), with high sensitivity and low limits of detection (4.1 x 10(-9)M) and quantification (1.4 x 10(-8)M), was achieved. Such characteristics allied to a good repeatability of the current responses (relative standard deviation of 0.79% for 30 measurements), were explored for the specific determination of isoniazid in isoniazid-rifampin tablet.     

PVC membrane electrode without inner reference solution for the direct determination of ephedrine in pharmaceutical preparations

A PVC membrane electrode, without inner reference solution, based on an ion association extraction system responding to ephedrine is described. It incorporates an ephedrine-tetrakis (4-chlorophenyl)borate ion-pair complex in 2-nitrophenyloctyl ether. The prepared electrode exhibits a near Nernstian response (57.5 mV per decade) over the concentration range of 2 x 10(-5)-10(-1) M ephedrine in solutions of pH 2.5-9. The reproducibility of the electrode potentials were +/- 1 mV by day during at least 6 months. Response time was about 6 s for ephedrine concentrations between 10(-5) and 10(-1) M. Determinations of ephedrine in pharmaceutical preparations (tablets, nasal drops and syrups) by direct potentiometry gave an average recovery of 99.1% (w/w) and a mean standard deviation of 1.9% (w/w).     

Determination of diclofenac in pharmaceutical preparations using a novel PVC membrane sensor

A novel potentiometric PVC membrane sensor for determination of diclofenac in pharmaceutical preparations has been developed. The sensor is based on the use of the 2,4,6-tri(2-pyridyl)-s-triazine iron(II) diclofenac complex [diclofenac-TPTZ-Fe(II)] as an electroactive material in a plasticized PVC membrane matrix. The sensor exhibits fast, stable and near Nernstian response for diclofenac over the concentration range 10(-2)-10(-6) M and pH 5.5-9.5. Application to quality control analysis of diclofenac in various dosage forms shows an average recovery of 99% with a mean standard deviation of 0.2%. No significant interferences are caused by inorganic and organic anions and various drug excipients and diluents.     

Determination of 5-aminosalicylic acid in pharmaceutical formulation by differential pulse voltammetry

The oxidative behaviour of 5-aminosalicylic acid (5-ASA) has been investigated by differential pulse voltammetry using a glassy carbon electrode in different buffer systems. Linear sweep voltammetry was used to study the influence of pH on the peak current and peak potential. The solution conditions and instrumental parameters were optimized to obtain a good sensitivity. The Britton-Robinson buffer of pH 1.81 was selected as a suitable analytical medium in which 5-ASA exhibited a sensitive diffusion controlled oxidative peak at 0.564 V (vs. Ag/AgCl). The peak current varied linearly with drug concentration in the range between 1 x 10(-4) and 2 x 10(-6) M. The proposed voltammetric method has been applied to the determination of the drug in commercial delayed-release tablet forms. A mean recovery of 101.23% with a relative standard deviation of 1.35% was obtained.     

PVC matrix membrane sensor for potentiometric determination of metoclopramide hydrochloride in some pharmaceutical formulations

The construction and characteristic performance of metoclopramide (MCP)-polyvinyl chloride (PVC) membrane sensor are described. The sensor is based on the use of MCP-tetraiodomercurate ion pair as electroactive material in PVC matrix in presence of dioctylphthalate (DOP) as solvent mediator. MCP membrane sensor shows a stable, near Nernstian response over the concentration range 1 x 10(-2)-6 x 10(-5) M of MCP at 25 degrees C in the pH range 3-7 with cationic slope of 53.0+/-0.5. The detection limit of 4 x 10(-5) M and the response time of 30-60 s have been attained. Selectivity coefficient data for some common ions show negligible intereferences. Direct potentiometric determination of 15-3540 microg/ml MCP show an average recovery of 98.5% and a mean relative standard deviation (R.S.D.) of 1.6% at 100.0 microg/ml. The determination of MCP in Primperan tablets, injection, and syrup gave results that compare favorably with those obtained by the British pharmacopoeia method. Precipitation titrations involving MCP as titrant are monitored with the MCP sensor for some potentiometric precipitation reaction, e.g. sodium tetraphenylborate (STPB) and phosphomolybdic acid (PMA).     

Flow-injection analysis of dopamine in injections with a periodate-selective electrode

Dopamine determination in pharmaceutical preparations based on its oxidation with periodate (IO(4)(-)) using a new IO(4)(-)-selective electrode under flow conditions is presented. An electrode with a tubular configuration, no internal reference solution, and a PVC (31. 2%) membrane, with metaperiodate bis(triphenylphosphoranylidene)ammonium (1.3%) as ion exchanger and 2-nitrophenyloctylether (67.5%) as mediator solvent, was used. Optimization procedures were directed at potentials versus dopamine readings instead of potential versus the remaining IO(4)(-). This approach was achieved by selecting a 50-cm reactor and an overall flow of 7 mL/min, and injecting 70 microL of dopamine standards in a 3.0 x 10(-4) M IO(4)(-) solution. Under these conditions, a linearity range of 8.0 x 10(-3) to 2.7 x 10(-1) g/L, with a slope of 310.1 +/- 7.4 mV L g(-1) and a reproducibility of +/-0.4 mV, were recorded (n = 8). Interference from common excipients was negligible. Under these conditions, analysis of dopamine injections (n = 12) presenting 200 mg/injection gave average and standard deviation values of 201.0 and 3.3 mg/injection, respectively. A simple and inexpensive flow-injection analysis (FIA) manifold, with a good potentiometric detector, enabled the analysis of 200 samples/h without requiring pretreatment procedures. Comparison with the dopamine injection analysis in the United States Pharmacopoeia monograph showed good accuracy, with a relative deviation of -0.2%.     

Automatic potentiometric flow titration procedure for ascorbic acid determination in pharmaceutical formulations

A flow procedure for the determination of ascorbic acid in pharmaceutical formulations exploiting potentiometric titration is described. The method is based on the reduction of IO₃⁻ by ascorbic acid and the detection was carried out employing a flow-through ion selective electrode for iodide. The flow network controlled by a microcomputer was designed to implement multicommutation for ease of operation and robustness. The titration system allowed the determination of ascorbic acid in pharmaceutical formulations with concentrations ranging from 7.5 to 15.0 mmol l⁻¹. No significant differences at the 95% confidence level were observed in comparison with results obtained by a manual procedure. Merit figures of results such as a relative standard deviation of 1.0% (n=6) and a reagent consumption of 21.4 mg IO₃⁻ per determination were obtained.     

Potentiometric flow-injection determination of vitamin C and glutathione with a chemically prepared tubular silver electrode

This paper describes the preparation and use of a tubular electrode by means of chemical pretreatment of a silver tube with mercuric (II) chloride solution and iodide solution in flow injection analysis (FIA). The electrode was used as a potentiometric sensor for the indirect determination of vitamin C and glutathione in a carrier stream containing iodine. A simple FIA system that consists of a peristaltic pump, an injection T valve, a tubular silver electrode and a saturated calomel reference electrode (SCE) was used. Some typical FIA parameters such as flow rate, tube length, sample volume and composition of the carrier stream were varied. After optimisation of these parameters, the electrode was further characterised by a constant linear response within the concentration range for the vitamin C between 5 x 10(-5) and 5 x 10(-3) M at the slope of 60.5 +/- 1.0 mV/p (vitamin C). Glutathione has a linear concentration range between 5 x 10(-5) and 10(-2) M at a slope of 55.2 +/- 1.0 mV/p (glutathione). The experimental slope was in good agreement with the theoretical values. Some pharmaceutical products containing vitamin C were also tested. These results can be compared to the results obtained by the standard volumetric method for the determination of vitamin C and are also in good agreement with values declared by pharmaceutical manufacturers.     

Determination of the antihyperlipidemic simvastatin by various voltammetric techniques in tablets and serum samples

The electrochemical behavior and determination of simvastatin (SMV), a lipid-lowering drug, were studied in aqueous alcohol medium at a stationary glassy carbon electrode. Cyclic voltammetry studies showed one main, well-defined, sharp oxidation peak between pH 2 and 8. The oxidation was irreversible and exhibited a diffusion controlled mechanism. Differential pulse and square wave voltammetric methods for the quantitative determination of SMV in pharmaceutical dosage forms and spiked serum samples were developed based on the linear relationship between the peak current and the concentration. Differential pulse and square wave voltammetric techniques for the determination of SMV in 0.1 M H2SO4 and a constant amount of methanol (20%), which allow quantitation over the 2 x 10(-6)-1 x 10(-4) M range in supporting electrolyte with a detection limit of 2.71 x 10(-7) M and 5.50 x 10(-7) M for differential pulse and square wave voltammetric methods, respectively, are proposed. The repeatability and reproducibility of the methods were determined. Precision and accuracy were also checked. These methods were used for the determination of SMV in tablets. The standard addition method was used in biological media. No electroactive interferences from endogenous substances and excipients were found in biological fluids and pharmaceutical dosage forms, respectively.     

Quantitative analysis of trazodone hydrochloride in tablets by an ion-selective electrode

A simple assay procedure for the quantitation of trazodone hydrochloride in tablets, without prior separation, has been developed using a trazodone-selective electrode. The electrode was based on a trazodone:tetrakis(p-chlorophenyl)borate ion-pair complex, dioctyl phthalate, and polyvinyl chloride matrix that were mounted on a PTFE membrane. The electrode showed a near-Nernstian response in the range of 10(-2) to 5 x 10(-6) M trazodone over the pH range of 2.5 to 5.0, with a cationic slope of 58 mV/concentration decade. The durability of the electrode and the reproducibility of the performance among the electrodes were sufficient. The electrode was used for the determination of the pKa value of trazodone. The selectivity of the electrode to a number of interferences was investigated. Many inorganic cations (alkali and alkaline earth metals) and pharmaceutical excipients did not interfere, but some organic ammonium compounds interfered according to their extractability. Determination of 10 to 3000 micrograms/mL of trazodone hydrochloride in aqueous solution showed an average recovery of 100.6% (mean standard deviation 0.4%) by direct potentiometry. This assay was applied to determine trazodone hydrochloride in tablets and the results compared favorably with those obtained by high-performance liquid chromatography.