Polymeric Membrane Sensor Research Articles

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

AbstractMiniaturized 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.

FIA potentiometric system based on periodate polymeric membrane sensors for the assessment of ascorbic acid in commercial drinks

Abstract Ascorbic acid is found in many food samples. Its clinical and technological importance demands an easy-to-use, rapid, robust and inexpensive method of analysis. For this purpose, this work proposes a new flow procedure based on the oxidation of ascorbic acid by periodate. A new potentiometric periodate sensor was constructed to monitor this reaction. The selective membranes were of PVC with porphyrin-based sensing systems and a lipophilic cation as additive. The sensor displayed a near-Nernstian response for periodate over 1.0 × 10 −2 –6.0 × 10 −6 M, with an anionic slope of 73.9 ± 0.9 mV decade −1 . It was pH independent in acidic media and presented good selectivity features towards several inorganic anions. The flow set-up operated in double-channel, carrying a 5.0 × 10 −4 M IO 4 - solution and a suitable buffer; these were mixed in a 50-cm reaction coil. The overall flow rate was 7 ml min −1 and the injection volume 70 μl. Under these conditions, a linear behaviour against concentration was observed for 17.7–194.0 μg ml −1 , presenting slopes of 0.169 mV (mg/l) −1 , a reproducibility of ±1.1 mV ( n = 5), and a sampling rate of ∼96 samples h −1 . The proposed method was applied to the analysis of beverages and pharmaceuticals.

Limitations of Current Polarization for Lowering the Detection Limit of Potentiometric Polymeric Membrane Sensors

Ion fluxes across polymeric ion-selective membranes are a decisive parameter dictating the lower detection limit of potentiometric ion sensors. An applied current was earlier proposed to counteract such fluxes and reduce the detection limit to ultratrace levels. So far, however, the method has not been used in practical situations since the correct current amplitude requires prior knowledge of the sample composition. This paper explores the use of the stir effect to evaluate the optimal current by theory and experiments. It is shown that the traditionally used steady-state model assuming a uniform distribution of ion exchanger in the membrane, fixed with time, violates the electroneutrality condition. A modified steady-state model is introduced that allows for a concentration tilt of the ion exchanger and predicts that a stir effect can indeed be utilized to find the optimal current. Ideally, by choosing the optimal current and very long measurement times, the thermodynamic detection limit might be obtained. However, in practice the stir effect declines at low concentrations and the conditions are far from steady state. Therefore, the improvement of the lower detection limit achievable by galvanostatic control is only about 1 order of magnitude. A numerical finite-difference approximation is shown to trace the experimental potential responses of silver-selective electrodes well and to reproduce the stir effect adequately, even for different conditioning protocols. The stir effect is successfully used to improve the detection limit of electrodes with ill-optimized inner solutions; however, significant improvements beyond what is commonly feasible by chemical optimization does not seem to be easily achievable. The results indicate that with conventional membranes the possibility of improving the detection limit by current polarization is much more limited than assumed so far.

Thiopental and Phenytoin as Novel Ionophores for Potentiometric Determination of Lead (II) Ions

Two novel polymeric membrane sensors for the analysis of Pb(II) have been developed based on two therapeutic drugs, thiopental (TP) and phenytoin (PT) as two new ionophores and potassium tetrakis(p-chlorophenyl) borate (KTpClPB) as a lipophilic additive, in plasticized PVC membranes. The sensors show a Nernstian response for Pb(II) ions over the wide concentration ranges of 1×10−2 – 7×10−6 M and 1×10−2 – 8×10−6 M for the sensors based on thiopental and phenytoin, respectively. The proposed sensors have a fast response time and can be used for more than nine weeks without any considerable divergence in potentials. The sensors exhibit comparatively good selectivity with respect to alkaline, alkaline earth and some transition and heavy metal ions. They were employed for direct determination of lead in solder alloys and in galena rocks with a good agreement with the obtained results by atomic absorption spectroscopy.

Cobalt phthalocyanine as a novel molecular recognition reagent for batch and flow injection potentiometric and spectrophotometric determination of anionic surfactants

Cobalt(II) phthalocyanine [Co(II)Pc] is used as both an ionophore and chromogen for batch and flow injection potentiometric and spectrophotometric determination of anionic surfactants (SDS), respectively. The potentiometric technique involves preparation of a polymeric membrane sensor by dispersing [Co(II)Pc] in a plasticized PVC membrane. Under batch mode of operation, the sensor displays a near-Nernstian slope of −56.5 mV decade −1, wide response linear range of 7.8 × 10 −4 to 8.0 × 10 −7 mol L −1, lower detection limit of 2.5 × 10 −7 mol L −1 and exhibits high selectivity for anionic surfactants in the presence of many common ions. Under hydrodynamic mode of operation (FIA), the slope of the calibration plot, limit of detection, and working linear range are −51.1 mV decade −1, 5.6 × 10 −7 and 1.0 × 10 −3 to 1.0 × 10 −6 mol L −1, respectively. The spectrophotometric method is based on the use of [Co(II)Pc] solution in dimethylsulfoxide (DMSO) as a chromogenic reagent. The maximum absorption of the reagent at 658 nm linearly decreases with the increase of anionic surfactant over the concentration range 2–30 μg mL −1. The lower limit of detection is 1 μg mL −1 and high concentrations of many interfering ions are tolerated. Flow injection spectrophotometric measurements are carried out by injection of the surfactant test solution in a stream of the reagent in DMSO. The sample throughput, working range and lower detection limit are 25–30 samples h −1, 4–60 and 2 μg mL −1, respectively. The potentiometric and spectrophotometric techniques are applied to the batch and flow injection measurements of anionic surfactants in some commercial detergent products. The results agree fairly well with data obtained using the standard methylene blue spectrophotometric method.

Polymeric Membrane Sensors for the Selective Determination of Dextromethorphan in Pharmaceutical Preparations

The construction and electrochemical response characteristics of poly(vinyl chloride) matrix ion-selective electrodes (ISEs) for dextromethorphan (DXM) hydrobromide are described. The membranes incorporate ion-association complexes of DXM with reineckate salt {[Cr(NH3)2(SCN)4]NH4} or phosphomolybdic acid [H3(PMo12O40)], as electroactive materials and dioctylphthalate or dibutylsebacate as a plasticizing solvent mediator. The sensors display a fast, stable and linear response with slopes of 54.4 to 59.5 mV/decade at pH 2.5-6.5 and a detection limit of 1.0 x 10(-6) M. Moreover, the sensors exhibit very good selectivity for DXM over opiate alkaloids, as well as organic and inorganic cations. The sensors proved to be useful for the determination of 5.0 x 10(-5)-1.0 x 10(-3) M DXM hydrobromide in pure as well as in dosage forms by direct potentiometry and standard addition methods. Determination of 5.0 x 10(-4) M DXM using the standard addition method and a sensor based on phosphomolybdate and dioctylphthalate shows an average recovery of 99.8% and a relative standard deviation (RSD) of 0.4%.

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

AbstractTwo 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−, SO42−, 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

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

AbstractPoly(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 (SeO32−) ions. Fast Nernstian response for SeO32− 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.

Development of Polymeric Membrane Sensor for the Determination of Histamine: Experimental and Theoretical Study

Some original histamine membrane sensors were prepared by incorporating thiopyrilium (TP) derivative as an excellent charged carrier. Among these sensors, TP2 shows the best response to histamine in a wide concentration range from 2.5×10−6 to 1.0×10−1 mol L−1 with a slope of 55.6±0.7 mV decade−1 and with a detection limit of 1.0 µmol L−1 (∼0.1 ppm). The interference between histamine and several amino acids and common inorganic anions was negligible as shown by the potentiometric selectivity coefficient data. The prepared electrode was used for the determination of histamine in a human serum synthetic sample. Theoretical calculations were carried out to find the best interactions between histamine and different ligands.

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

AbstractTwo 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.

Solid-Contact Electrochemical Polyion Sensors for Monitoring Peptidase Activities

We report here on improved solid-contact electrochemical polyion sensors for the detection of polyion protamine. The polymeric membrane sensors were fabricated with a conducting polymer as an ion-electron transduction layer. We observed that decreasing the magnitude of the applied current pulse caused a significant improvement of the sensor sensitivity to low protamine levels. The protamine sensors exhibited a stable and reversible response to protamine concentrations ranging from 0.05 to 30 mg L-1. The sensors were used for monitoring peptidase activities utilizing galvanostatically controlled solid-contact membrane sensors. The polyion protamine was used as a substrate to detect the activity of the protease trypsin. The enzyme activity was continuously monitored by measuring the protamine concentration as it is cleaved by enzyme into smaller fragments to which the sensor is less sensitive. In the presence of a given level of protamine the initial rate of reaction can be linearly related to the trypsin activity within a 0-5 U mL-1 concentration range. The interference with the enzymatic reaction product arginine was specifically examined.

Polymeric membrane sensors based on Cd(II) Schiff base complexes for selective iodide determination in environmental and medicinal samples

The two cadmium chelates of schiff bases, N, N′ -bis(salicylidene)-1,4-diaminobutane, (Cd-S 1) and N, N′ -bis(salicylidene)-3,4-diaminotoluene (Cd-S 2), have been synthesized and explored as ionophores for preparing PVC-based membrane sensors selective to iodide(I) ion. Potentiometric investigations indicate high affinity of these receptors for iodide ion. Polyvinyl chloride (PVC)-based membranes of Cd-S 1 and Cd-S 2 using as hexadecyltrimethylammonium bromide (HTAB) cation discriminator and o-nitrophenyloctyl ether ( o-NPOE), dibutylphthalate (DBP), acetophenone (AP) and tributylphosphate (TBP) as plasticizing solvent mediators were prepared and investigated as iodide-selective sensors. The best performance was shown by the membrane of composition (w/w) of (Cd-S 1) (7%):PVC (31%):DBP (60%):HTAB (2%). The sensor works well over a wide concentration range 5.3 × 10 −7 to 1.0 × 10 −2 M with Nernstian compliance (59.2 mV decade −1 of activity) within pH range 2.5–9.0 with a response time of 11 s and showed good selectivity for iodide ion over a number of anions. The sensor exhibits adequate life (3 months) with good reproducibility (S.D. ± 0.24 mV) and could be used successfully for the determination of iodide content in environmental water samples and mouth wash samples.

Cu(II) complexes as receptor molecules for development of new chloride sensors

Highly sensitive and selective chloride polymeric membrane sensors are developed that employ Cu(II) complexes as anion carriers. Optimized membrane sensors showed a near-Nernstian response towards chloride anion over a wide concentration range of 2.5 × 10 −5 to 1.0 × 10 −1 M and have micromolar level detection limits. These sensors have fast response time and work well in the pH range of 4.2–9.6. They exhibited enhanced potentiometric selectivity for chloride over other anions, including more lipophilic anions such as perchlorate, thiocyanate, nitrate, etc. Response characteristics (e.g. detection limit, linear range, response slope and selectivity) of these sensors remain essentially the same over a period of ∼5 months, reflecting remarkable stability.

Application of N, N′-bis(2-quinolinecarboxamide)-1,2-benzene as an ionophore in the construction of a novel polymeric membrane sensor for the selective monitoring of the holmium(III) concentration

It was found that N, N′-bis(2-quinolinecarboxamide)-1,2-benzene (H 2BQB) containing PVC membranes show a good Ho(III) selectivity in comparison to most common first and second main group elements (representative), transition, and lanthanide ions. Hence we studied its application as a neutral ionophore, for preparing an Ho(III) PVC-membrane sensor. The primarily studied PVC-based membranes contained sodium tetraphenyl borate (NaTPB) as an anionic additive, and were tested by using different solvent mediators such as benzyl acetate (BA), nitrobenzene (NB), and o-nitrophenyloctyl ether (NPOE). The optimum ratio of H 2BQB:PVC:NaTPB:BA was found to be 6.0:30.0:4.0:60.0. The sensor has a Nernstian response of 19.5 ± 0.3 mV/decade of Ho(III) activity, and a linear range from 2.0 × 10 −5 to 1.0 × 10 −2 M. The mentioned sensor can be used in a pH range of 2.5–10.5 and has a detection limit (DL) of 5.0 × 10 −6 M. Another advantage of the sensor is its excellent Ho(III)-selectivity with regard to most common metal ions, and especially, all lanthanide ions. To investigate the analytical applicability of the sensor, it was successfully used as an indicator electrode for titration of 25 ml of a 1.0 × 10 −4 M Ho(III) solution with a 1.0 × 10 −2 M EDTA solution, and vice versa.

A novel barium polymeric membrane sensor for selective determination of barium and sulphate ions based on the complex ion associate barium(II)–Rose Bengal as neutral ionophore

A simple, long life, rapid response and sensitive barium(II)–PVC membrane sensor that typically follows Nernstian behavior has been developed for the assay of barium(II) ions. The developed sensor has been made by incorporating the complex ion associate of barium(II)–Rose Bengal (Ba–RB) as an ionophore into a plasticized PVC matrix. The sensor is stable and exhibited fast potential response of 20 s and gave a good linear response with a Nernstian slope of 28.5 ± 0.4 mV/decade of activity within the concentration range 5 × 10 −5 to 10 −1 M over a wide range of pH 4.5–10.0 for barium(II) ions. The developed sensor showed comparatively good selectivity for barium(II) ions with respect to other alkali, alkaline earth, transition and heavy metal ions. The plasticizer o-nitrophenyloctyl ether controlled significantly the calibration slope and the lifetime of the fabricated sensor. The proposed sensor was used successfully for the analysis of barium(II) ions in wastewater samples and in lithophone pigment with excellent recovery percentages in the range 98.9–99.8 ± 1.6%. The determination of sulphate in fresh and potable water samples with the developed sensor has been also achieved successfully. The described sensor provides a reliable means with good correlation with the data obtained by atomic absorption spectrometry (AAS) and other spectrophotometric methods for the analysis of trace amounts of barium(II) and/or sulphate ions in different matrices.

Nano-level monitoring of ytterbium(III) by a novel ytterbium(III) membrane sensor based on 3-hydroxy- N′-[(2-hydroxyphenyl) methylene]-2-naphthohydrazide

In this work, a highly sensitive ytterbium(III)-selective solvent polymeric membrane sensor based on 3-hydroxy- N′-[(2-hydroxyphenyl)methylene]-2-naphthohydrazide (HPMN), poly(vinyl chloride) (PVC), the plasticizer dibutyl phthalate (DBP), and sodium tetraphenyl borate (NaTPB) anionic site is described. This sensor responds to Yb(III) activity in a linear range from 1.0 × 10 −7 to 1.0 × 10 −2 M, with a slope of 19.2 ± 0.2 mV per decade and a detection limit of 4.0 × 10 −8 M at a pH range of 3.0–8.5. It has a very fast response time of <6 s in the whole concentration range, and can be used for at least 6 weeks without any considerable divergences in its potentials. The proposed sensor revealed comparatively good selectivity with respect to common alkali, alkaline earth, transition and heavy metal ions, and especially lanthanide ions. It was used as an indicator electrode in the potentiometric titration of Yb(III) ions with EDTA and in determination of concentration of Yb 3+ ions in binary mixtures.

Determination of Salbutamol, Amikacin and Paromomycin Sulfate by a Novel Sulfate Polymeric Membrane Sensor Based on 2,6-diphenyl 4-(4-methoxyphenyl) pyrylium perchlorate

A novel sulfate polymeric membrane sensor based on 2,6-diphenyl 4-(4-methoxyphenyl) pyrylium perchlorate (DMPP) as a sensing material is presented. The electrode displays a very low detection limit (4.0×10−7 M) and wide working concentration range (8.0×10−7–1.0×10−1 M). The sensor shows remarkable selectivity toward sulfate over most common organic and inorganic anions, including chloride, acetate, nitrate, nitrite, bromide, iodide, thiocyanate, phosphate, fluoride, sulfite, hydrogen sulfite, hydrogen carbonate, citrate, tartarate and oxalate. The sensor reveals a Nernstian behavior (slope of −29.7±0.5 mV per decade) in a wide pH range (3.0–9.5). The proposed sensor shows a short response time over the entire working range (∼15 s) and was successfully applied to the direct determination of salbutamol, amikacin and paromomycin sulfate.

Novel Dy(III) Sensor Based on a New Bis‐Pyrrolidene Schiff's Base

AbstractIn this work a dysprosium [Dy(III)]‐selective solvent polymeric membrane sensor based on N,N‐bis(pyrrolidene) benzne‐1,2‐diamine, poly(vinyl chloride)(PVC), the plasticizer benzylacetate (BA), and anionic site is described. This sensor responds to Dy(III) activity in a linear range from 1.0×10−5 to 1.0×10−1 M, with a slope of 20.6±0.2 mV per decade and a detection limit of 6.0×10−6 M at the pH range of 3.5–8.0. It has a fast response time of&lt;20 s in the entire concentration range, and can be used for at least 2 months without any considerable divergence in the electrode potentials. The proposed sensor revealed comparatively good selectivity with respect to common alkali, alkaline earth, transition and heavy metal ions. It was used as an indicator electrode in the potentiometric titration of fluoride ions and in determination of concentration of F – ions in some mouth washing solutions.

Novel terbium(III) sensor based on a new bis-pyrrolidene Schiff’s base

Here a terbium-selective solvent polymeric membrane sensor based on N, N,-bis(pyrrolidene) benzene-1,2-diamine, poly(vinyl chloride) (PVC), benzylacetate (BA) plasticizer, and an anionic additive is described. At a pH range of 3.5–7.7, this sensor responds to dysprosium in a linear range from 1.0 × 10 −5 to 1.0 × 10 −1 M, with a slope of 19.8 mV per decade and a detection limit of 7.0 × 10 −6 M. It has a fast response time of <20 s in the whole concentration range, and can be used for at least 2 months without any considerable divergences in the potentials. The proposed sensor revealed comparatively good selectivity with respect to common alkali, alkaline earth, transition and heavy metal ions. It was used as an indicator electrode in potentiometric titration of fluoride ions, and in determination of F − ion in some mouth washing solutions preparations.

A novel membrane sensor for histamine H1-receptor antagonist "fexofenadine".

The construction and general performance of thirteen new polymeric membrane sensors for the determination of fexofenadine hydrochloride based on its ion exchange with reineckate, tetraphenylborate and tetraiodomercurate have been studied. The effects of membrane composition, type of plasticizer, pH value of sample solution and concentration of the analyte in the sensor internal solution have been thoroughly investigated. The novel sensor based on reineckate exchanger shows a stable, potentiometric response for fexofenadine in the concentration range of 1 x 10(-2) - 2.5 x 10(-6) M at 25 degrees C that is independent of pH in the range of 2.0 - 4.5. The sensor possesses a Nernstian cationic slope of 62.3+/-0.7 mV/concentration decade and a lower detection limit of 1.3 x 10(-6) M with a fast response time of 20 - 40 s. Selectivity coefficients for a number of interfering ions and excipients relative to fexofenadine were investigated. There is negligible interference from almost all studied cations, anions, and pharmaceutical excipients, however, citrizine that has a structure homologous to that of fexofenadine was found to interfere. The determination of fexofenadine in aqueous solution shows an average recovery of 99.83% with a mean relative standard deviation (RSD) of 0.5%. Direct potentiometric determination of fexofenadine in tablets gave results that compare favorably with those obtained by standard spectrophotometric methods. Potentiometric titration of fexofenadine with phosphomolybdic acid as a titrant has been monitored with the proposed sensor as an end point indicator electrode.