Plasticized PVC Membrane Research Articles

Novel Potentiometric Sensors for Determination of Melatonin and Oxomemazine in Biological Samples and in Pharmaceutical Formulations

AbstractSimple, selective and accurate sensors were developed for the determination of melatonin and oxomemazine in biological samples (urine) and in pharmaceutical preparations. Potentiometric measurements were based on bismus tetraiodate‐drug ion‐pair as novel electroactive materials incorporating a plasticized PVC membrane with o‐nitrophenyl octyl ether or dioctyl phthalate. Each sensor was conditioned for at least two days in 0.1 M drug solution before use. It exhibited fast and stable Nernstian response for melatonin and oxomemazine over the concentration range of 1.0×10−6–1.0×10−2 M and 1.0×10−5–1.0×10−2 M, pH range of 3.0–6.5 and 3.5–6.0 for melatonin and oxomemazine sensors, respectively. Results with an average recovery not more than 101 % and a mean standard deviation less than 1.0 % of the nominal were obtained for the four sensors. The sensors showed reasonable selectivity towards investigated drugs in presence of many cations.

Development of a Fluoride-Selective Electrode based on Scandium(III) Octaethylporphyrin in a Plasticized Polymeric Membrane

- between 10 -4.6 to 10 -1 M was observed at a glycine-phosphate buffer (pH 3.0). The selectivity pattern was observed as F - , salicylate >> SCN - > Cl - , Br - , NO3 - , ClO4 - , which is consistent with the binding constant data measur- ed in the plasticized PVC membrane based on a sandwich membrane method. This highly selective and reversible fluo- ride-sensitive electrode was employed for the analysis of hydrofluoric acid (HF). A disposable differential-type HF sen- sor was fabricated on the screen-printed electrode and demonstrated its ability to detect the neutral HF in the acidic solu- tion.

Optical sensor based on 1,3-di(2-methoxyphenyl)triazene for monitoring trace amounts of mercury(II) in water samples

A new optical sensor for highly sensitive and selective determination of mercury(II) ion in aqueous solutions is developed. The mercury sensing membrane was prepared by incorporating 1,3-di(2-methoxyphenyl)triazene (MPT) as chromoionophore in the plasticized PVC membrane containing tris(2-ethylhexyl)phosphate (TEHP) as plasticizer. The proposed sensor displays a wide linear range of 9.0 × 10 − 10–2.5 × 10 − 7 M with a low detection limit of 2.0 × 10 − 10 M in aqueous solutions at pH 4.0. This sensor has a relatively fast response time of less than 5 min. In addition to high stability and reproducibility, it shows a unique selectivity towards Hg 2+ ion with respect to common coexisting cations. The sensor can readily be regenerated by exposure to a solution of sodium iodide (0.01 M). The proposed optode was applied to the determination of Hg 2+ in water samples.

Determination of terbium in phosphate rock by Tb 3+-selective fluorimetric optode based on dansyl derivative as a neutral fluorogenic ionophore

For the first time a highly sensitive and selective fluorimetric optode membrane was prepared for determination of trace amounts of Tb(III) ions in phosphate rock samples. The Tb(III) sensing system was constructed by incorporating 5-(dimethylamino)-N′-(2-hydroxy-1-naphthoyl) naphthalene-1-sulfonohydrazine (L) as a neutral Tb(III)-selective fluoroionophore, in the plasticized PVC membrane containing sodium tetraphenyl borate as a liphophilic anionic additive. The response of the optode is based on the strong fluorescence quenching of L by Tb 3+ ions. At a pH value of 5.0, the optode displays a wide concentration range of 1.0 × 10 −7 to 1.0 × 10 −2 M, with a relatively fast response time of less than 45 s. In addition, to high stability and reproducibility, the sensor shows a unique selectivity towards Tb 3+ ion with respect to common cations. The optode was applied successfully to the trace determination of terbium ion in binary mixture and water samples and the determination of Tb 3+ in phosphate rock samples.

N, N′ -Bis(3-methyl-1-phenyl-4-benzylidine-5-pyrazolone)propylenediamine Schiff base as a neutral carrier for silver (I) ion-selective electrodes

New highly selective silver (I) electrodes were prepared by incorporating N, N′-bis(3-methyl-1-phenyl-4-benzylidine-5-pyrazolone)propylenediamine ( I2) as a neutral ionophore into plasticized PVC membranes. The best response characteristics were obtained using the composition— I2:KTpClPB:PVC:DBP in the percentage ratio of 4:1.5:60:120 (w:w). The electrodes exhibit a linear response with a near Nernstian slope of 59.3 mV/decade within the silver ion concentration range of 10 −6–0.1 mol L −1, with a working pH range (4–10). The electrodes possessed a fast response time of 30 s for low concentration (10 −6 mol L −1) and 5 s for higher concentration (10 −5–0.1 mol L −1). The electrodes showed excellent selectivity towards Ag + ion over a wide range of alkali, alkaline earth, and transition metals ions. The electrodes displayed a very good selectivity for silver ion against the serious interferents Hg 2+ and Cu 2+ ions, which is a valuable property of these electrodes. The high selectivity arises from the strong complexation of I2 with Ag + compared with other ions as determined by the sandwich membrane method. Density Functional Theory calculations performed using the Gaussian 03 program indicate a tetradentate coordination of the metal ion by I2. Calculated binding energies for different metal ions also support high selectivity for silver (I) ion. These electrodes were successfully used in the potentiometric titration of halides with silver ion and in the determination of silver in radiology films.

Novel selective optode membrane for terbium ion based on fluorescence quenching of the 2-(5-(dimethylamino) naphthalen-1-ylsulfonyl)-N-henylhydrazinecarbothioamid

For the first time, a highly sensitive and selective fluorimetric optode membrane sensor for determination of trace amounts of Tb(III) ions was prepared. The Tb(III) sensing system was prepared by incorporating 2-(5-(dimethylamino) naphthalen-1-ylsulfonyl)-N-phenylhydrazinecarbothioamide (L) as a neutral Tb(III)-selective fluoroionophore, in the plasticized PVC membrane containing sodium tetraphenyl borate as a liphophilic anionic additive. The response of the sensor is based on the strong fluorescence quenching of L by Tb(III) ions. At pH 4.7, the proposed sensor displays a calibration curve over a wide concentration range of 1.0 × 10 −2 to 1.0 × 10 −8 M, with a relatively fast response time of less than 1 min, high stability, high reproducibility and a relatively long working lifetime. The sensor shows a good selectivity towards Tb(III) ion respect to all lanthanide and common coexisting cations. The proposed fluorescence optode was applied successfully to determination of Tb(III) ion in water and phosphate rock samples.

Enantiomeric discrimination of chiral crown ether ionophores containing phenazine subcyclic unit by ion-selective potentiometry

In this paper the enatiomeric selectivity of two chiral phenazino-18-crown-6 ether hosts ((R,R)-\textbf1 and (R,R)-\textbf2) is quantified. These hosts were incorporated into plasticized PVC membranes and used as recognition elements of ion-selective electrodes. The potentiometric response towards the two enantiomers of 1-phenylethylammonium ions (PEA+) was measured. Potentiometric selectivity coefficients were calculated which reflect the ratio of the stability constants of the diastereomeric complexes. Ligand (R,R)-\textbf1 does not show enantiomeric recognition, while ligand (R,R)-\textbf2 has a slight preference for the (S)-(-) enantiomer over the (R)-(+) enantiomer manifested by a selectivity coefficient of 0.77. The results were compared to enantioselectivity patterns of the ligands towards α -(1-naphthyl)ethyl ammonium perchlorate (NEA+ClO4-) enantiomers measured by circular dichroism and by 1H NMR titrations.

New biomimetic sensors for the determination of tetracycline in biological samples: Batch and flow mode operations

New potentiometric membrane sensors with cylindrical configuration for tetracycline (TC) are described based on the use of a newly designed molecularly imprinted polymer (MIP) material consisting of 2-vinylpyridine as a functional monomer in a plasticized PVC membrane. The sensor exhibited significantly enhanced response towards TC over the concentration range 1.59 × 10−5–1.0 × 10−3 mol L−1 at pH 3–5 with a lower detection limit of 1.29 × 10−5 mol L−1. The response was near-Nernstian, with average slopes of 63.9 mV decade−1. The effect of lipophilic salts and various foreign common ions were tested and were found to be negligible. The possibility of applying the proposed sensor to TC determination in spiked biological fluid samples was demonstrated.

New potentiometric sensors based on two competitive recognition sites for determining tetracycline residues using flow-through system

New potentiometric membrane sensors for tetracycline (TC) are described based on the use of a newly designed molecularly imprinted polymer (MIP) material based on 2-vinylpyridine as a functional monomer, AmION (I) [Calix-4-arene tetraacetic acid ester] as neutral ionophore in plasticized PVC membranes. Effects of lipophilic salts and various foreign common ions are tested. The sensors exhibit significantly high sensitivity, stability and selectivity for TC+ ions over many common ions and are successfully used for determining TC+ ions in spiked biological fluid samples under static and hydrodynamic mode of operations.

A Long Wavelength Excitable Fluorophore; Chloro Phenyl Imino Propenyl Aniline (CPIPA) for Selective Sensing of Hg (II)

In this study, a very sensitive and highly selective irreversible optical chemical sensor (optode) for mercury ions was described. The sensing scheme was based on the interaction of Hg (II) with a newly synthesized fluoroionophore; chloro phenyl imino propenyl aniline (CPIPA) in plasticized PVC membrane. The sensor membranes were tested for the determination of mercury ion in aqueous solutions by batch and flow-through methods. The optodes allow determination of Hg (II) in the working range of 1.0 x 10(-9)-1.0 x 10(-5) M with a detection limit of 4.3 ppb. The sensor exhibited excellent selectivity for Hg (II) with respect to several common alkali, alkaline earth and transition metal ions. The association constant of the 1:1 complex formation for Hg (II) was found to be K(a) = 1.86 x 10(5) M(-1). The CPIPA exhibited high fluorescence quantum yield, long excitation and emission wavelength and high Stokes' shift values in the solid matrix which makes it compatible with solid state optics.

Synthesis of new optically active acridino-18-crown-6 ligands and studies of their potentiometric selectivity toward the enantiomers of protonated 1-phenylethylamine and metal ions

Starting from commercially available and relatively inexpensive chemicals, new enantiopure diisobutyl- and dioctyl-substituted acridino-18-crown-6 ether-type ligands [( R,R)- 3] and [( R,R)- 4], respectively were prepared. The two lipophilic isobutyl [( R,R)- 3] and octyl [( R,R)- 4] groups on the stereogenic centers of these macrocycles made it possible to use them as potentiometric sensor molecules when incorporated into plasticized PVC membrane electrodes. Ligand ( R,R)- 3 showed appreciable enantioselectivity toward the enantiomers of 1-phenylethylammonium chloride while macrocycle ( R,R)- 4 exhibited a high selectivity toward the silver ion.

Novel fluorimetric bulk optode membrane based on 5,8-bis((5′-chloro-8′-hydroxy-7′-quinolinyl)methyl)-2,11-dithia-5,8-diaza-2,6-pyridinophane for selective detection of lead(II) ions

A novel fluorescence chemical sensor for the highly sensitive and selective determination of Pb(2+) ions in aqueous solutions is described. The preliminary potentiometric and spectrofluorimetric complexation studies in solution revealed that the lipophilic ligand 5,8-bis((5'-chloro-8'-hydroxy-7'-quinolinyl)methyl)-2,11-dithia-5,8-diaza-2,6-pyridinophane (L2) forms a highly stable and selective [PbL2](2+) and [Pb(L2)(2)](2+) complexes which results in a strong fluorescence quenching of the ligand. Thus, a novel fluorescence Pb(2+) sensing system was prepared by incorporating L2 as a neutral lead-selective fluoroionophore in the plasticized PVC membrane containing tetrakis(p-chlorophenyl) borate as a liphophilic anionic additive. The response of the sensor is based on the strong selective fluorescence quenching of L2 by Pb(2+) ions. At pH 5.5, the proposed sensor displays a calibration curve over a wide concentration range of 3.0 x 10(-7) to 2.5x 10(-2)M with a relatively fast response time of less than 5 min. In addition to high stability, reversibility and reproducibility, the sensor shows a unique selectivity towards Pb(2+) ion with respect to common coexisting cations. The proposed fluorescence optode was successfully applied to the determination of lead in plastic toys and tap water samples.

On the origin of the Hofmeister effect in anion-selective potentiometric electrodes with tetraalkylammonium salts

Abstract A new, adsorption-based mechanism of potentiometric response of the plasticized PVC membranes is proposed. In contrast to previous mechanistic studies of the membrane-based Ion-Selective Electrodes (ISE), the membranes in this study did not contain any purposely-added additives: lipophilic salt or ionophore. Cationic or anionic response of such “blank” ISEs was observed upon contact with ionic surfactants: cationic cetyltrimethylammonium bromide (CTAB) and anionic sodium dodecyl sulfate (SDS), respectively. Such behavior cannot be explained using a classical Interface between Two Immiscible Electrolyte Solutions (ITIES) formalism, based on the Nernst equation for ion partitioning between the aqueous and the membrane phases. Moreover, the “blank” membranes responded anionically (with a negative slope) to the presence of sodium salts of bromide, nitrate and fluoride at constant concentration of CTAB. Also in this case, the theoretical Galvani potential difference vs. added salt concentration, calculated with the ITIES formalism did not fit well the measured potential differences. Better agreement was obtained when assuming that the potentiometric response stems from partitioning between the aqueous phase and the interface (adsorption), and not between the aqueous phase and the membrane phase (bulk partition), as in the classical approach. The Stern layer potentials were calculated from interfacial tension isotherms for CTAB, both alone and in the presence of sodium bromide, nitrate and fluoride using the Surface quasi-Two Dimensional Electrolyte model (STDE). The calculated Stern potentials compare well with those obtained experimentally using ISE.

Novel erbium (III)-selective fluorimetric bulk optode

For the first time a highly sensitive and selective fluorimetric optode membrane was prepared for the determination of trace amounts of Er(III) ions. The Er(III) sensing system was constructed by incorporating 5-(dimethylamino) naphthalene-1-sulfonyl-4-phenylsemicarbazide (L) as a neutral Er(III)-selective fluoroionophore, in the plasticized PVC-membrane containing sodium tetraphenyl borate as a lipophilic anionic additive. The response of the optode is based on the strong fluorescence quenching of L by Er 3+ ions. At a pH value of 5.0, the proposed optode displays a wide concentration range of 1.0 × 10 −10 to 1.0 × 10 −2 M, with a relatively fast response time of less than 50 s. In addition, to high stability and reproducibility, the sensor shows a unique selectivity towards Er 3+ ion with respect to common cations. The proposed optode was applied successfully to the trace determination of erbium ion in binary mixture and water samples.

FTIR-ATR Study of Water Uptake and Diffusion through Ion-Selective Membranes Based on Poly(acrylates) and Silicone Rubber

For the first time, FTIR-ATR spectroscopy was used to study the water uptake and its diffusion in ion-selective membranes (ISMs) based on poly(acrylates) (PAs) and silicone rubber (SR), which are emerging materials for the fabrication of ISMs for ultratrace analysis. Three different types of PA membranes were studied, consisting of copolymers of methyl methacrylate with n-butyl acrylate, decyl methacrylate, or isodecyl acrylate. Numerical simulations with the finite difference method showed that in most cases the water uptake of the PA and SR membranes could be described with a model consisting of two diffusion coefficients. The diffusion coefficients of the PA membranes were approximately 1 order of magnitude lower than those of plasticized poly(vinyl chloride) (PVC)-based ISMs and only slightly influenced by the membrane matrix composition. However, the simulations indicated that during longer contact times, the water uptake of PA membranes was considerably higher than that for plasticized PVC membranes. Although the diffusion coefficients of the SR and plasticized PVC membranes were similar, the SR membranes had the lowest water uptake of all membranes. This can be beneficial in preventing the formation of detrimental water layers in all-solid-state ion-selective electrodes. With FTIR-ATR, one can monitor the accumulation of different forms of water, i.e., monomeric, dimeric, clustered, and bulk water.

Poly(3,4-ethylenedioxythiophene) (PEDOT) doped with carbon nanotubes as ion-to-electron transducer in polymer membrane-based potassium ion-selective electrodes

Negatively charged multi-walled carbon nanotubes (MWCNTs) were used as dopants in the electrochemical synthesis of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT). The resulting electroactive film, PEDOT(CNT), was used as ion-to-electron transducer (solid contact) in potassium ion-selective electrodes (K +-ISEs) based on plasticized PVC membrane containing valinomycin as neutral ionophore. Potentiometric measurements were carried out to study the analytical performance of solid-contact K +-ISEs, the influence of dissolved O 2 and CO 2 on the potential of the electrodes, and the formation of the interfacial aqueous film. The prepared electrodes were also characterized by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and chronopotentiometry. The experimental results showed that PEDOT(CNT) has the capability to function as solid contact in fabrication of K +-ISEs. These electrodes, based on PEDOT(CNT) as ion-to-electron transducer, showed high sensitivity and selectivity to K + ion which can be related to the plasticized PVC-based ion-selective membrane containing valinomycin. The stability of the electrode potential, however, was found to depend on the conducting substrate used for deposition of the PEDOT(CNT) film. Results from the CV and EIS revealed that the PEDOT(CNT) contact exhibits high redox capacitance that is favorable for a solid contact.

Development a Simple PVC Membrane Bulk Optode for Determination of Lead Ions in Water Samples

A sensitive reversible optical chemical sensor for detecting lead ions is described. The sensor is based on the interaction of Pb(II) with diphenylcarbazone in plasticized PVC membrane incorporating a plasticizer (tributylphosphate). The membranes were cast onto glass substrates and used for the determination of lead ions in aqueous solutions by batch and flow-through methods. When the sensing film came in contact with lead(II) ions at pH 6.0, its color changed from pale orange to pink. Parameters affecting the optode response such as pH, type of plasticizer, plasticizer/PVC ratio, and diphenylcarbazone percent were studied. The optode was found to have a long linear dynamic range, 6 9×10−6 to 1 1×10−2 mol L−1 Pb(II), and a short response time of 180 s with a detection limit of 6 5×10−6 mol L−1 Pb(II) by batch spectrophotometric method. In addition, the sensor has been incorporated into a home-made flow-through cell for determining lead ions in flowing streams with improved sensitivity, precision, and detection limit. In the flow system, the linear calibration range was 1 0×10−6 to 5 0×10−3 mol L−1 Pb(II). The optode could be recovered several times after treating with a 0.005 mol L−1 nitric acid solution. Under the experimental conditions, the response of the optode was fully reversible. The effect of the sample matrices on the determination of Pb(II) was studied. The sensor was used for the determination of Pb(II) ions in river water, tap water, and industrial waste samples with satisfactory results.

Development of a cobalt (ІІ) optical sensing film based on N 5-(2, 4-dinitro-phenyl)-N 1,N 1-diethyl-penta-1,3-diene-1,5-diamine

An optical sensing film has been proposed for sensitive determination of cobalt (Co) (ІІ) ion in aqueous solutions. The cobalt sensing membrane was prepared by incorporating N 5-(2, 4-dinitro-phenyl)-N 1,N 1-diethyl-penta-1,3-diene-1,5-diamine (HDDA) as ionophore in the plasticised PVC membrane containing o-nitro-phenyl octyl ether as plasticiser. The membrane responds to cobalt ion by changing colour irreversibly from yellow to green in acetate buffer solution at pH = 5.5. The proposed sensing film displays a linear range of 0.028–29.68 µg mL−1 with a limit of detection 0.012 µg mL−1. Moreover, upon the introduction of a negatively charged lipophilic additive (oleic acid) into the membrane, the optode displayed enhanced sensitivity. In addition, satisfactory analytical sensing characteristics for determining Co(II) ion were obtained in terms of the selectivity, stability and reproducibility. The response time of the optode was about 15–25 min, depending on the concentration of Co(ІІ) ions. The optode membrane has been applied to determine Co(II) in various water samples and copper-free alloys.

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.

Complexes of tetra- tert-butyl-tetraazaporphine with Al(III) and Zr(IV) cations as fluoride selective ionophores

In this work, complexes of Zr(IV) and Al(III) cations with 2,7,12,17-tetra- tert-butyl-5,10,15,20-tetraazaporphine (TAP) were tested as ionophores in plasticized PVC membranes of ion-selective electrodes. It was found that both tested ionophores show enhanced affinity towards fluoride anion. High fluoride selectivity was observed in the presence of anionic or cationic additives in the membrane, which indicates that proposed compounds work according to charged or neutral carrier mechanism, depending on membrane composition and pretreatment. tert-Butyl substituents, present in the structure of tested compounds, were supposed to prevent formation of ionophore dimers within the membrane phase. This process was found to be responsible for some unfavorable potentiometric properties of electrodes based on complexes of Zr(IV) and Al(III) cations with porphyrins (compounds closely related to tetra- tert-butyl-5,10,15,20-tetraazaporphine). As it was shown using spectrophotometrical measurements, Al(III)–TAP was not susceptible to dimerization, while dimer formation was observed for Zr(IV)–TAP. In full agreement with these observations, electrodes with membranes containing Al(III)–TAP responded in near-Nernstian and fast manner towards fluoride anion, while the employment of Zr(IV)–TAP as ionophore resulted in super-Nernstian and sluggish response. Plasticized PVC membranes doped with Al(III)–TAP and 20 mol% of lipophilic anionic additives shown remarkable F − selectivity, with selectivity coefficients, log K F − , Y − pot. , as follows: −4.4 (Y − Br −), −4.3 (Cl −), −4.2 (NO 3 −), −3.6 (SCN −), −2.9 (ClO 4 −).