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1.
Anal Chim Acta ; 851: 78-86, 2014 Dec 03.
Artigo em Inglês | MEDLINE | ID: mdl-25440668

RESUMO

Three new calixarene Tl(+) ionophores have been utilized in Tl(+) ion-selective electrodes (ISEs) yielding Nernstian response in the concentration range of 10(-2)-10(-6)M TlNO3 with a non-optimized filling solution in a conventional liquid contact ISE configuration. The complex formation constants (logßIL) for two of the calixarene derivatives with thallium(I) (i.e. 6.44 and 5.85) were measured using the sandwich membrane technique, with the other ionophore immeasurable due to eventual precipitation of the ionophore during these long-term experiments. Furthermore, the unbiased selectivity coefficients for these ionophores displayed excellent selectivity against Zn(2+), Ca(2+), Ba(2+), Cu(2+), Cd(2+) and Al(3+) with moderate selectivity against Pb(2+), Li(+), Na(+), H(+), K(+), NH4(+) and Cs(+), noting that silver was the only significant interferent with these calixarene-based ionophores. When optimizing the filling solution in a liquid contact ISE, it was possible to achieve a lower limit of detection of approximately 8nM according to the IUPAC definition. Last, the new ionophores were also evaluated in four solid-contact (SC) designs leading to Nernstian response, with the best response noted with a SC electrode utilizing a gold substrate, a poly(3-octylthiophene) (POT) ion-to-electron transducer and a poly(methyl methacrylate)-poly(decyl methacrylate) (PMMA-PDMA) co-polymer membrane. This electrode exhibited a slope of 58.4mVdecade(-1) and a lower detection limit of 30.2nM. Due to the presence of an undesirable water layer and/or leaching of redox mediator from the graphite redox buffered SC, a coated wire electrode on gold and graphite redox buffered SC yielded grossly inferior detection limits against the polypyrrole/PVC SC and POT/PMMA-PDMA SC ISEs that did not display signs of a water layer or leaching of SC ingredients into the membrane.


Assuntos
Calixarenos/química , Eletrodos Íon-Seletivos , Tálio/análise , Acrilamidas/química , Interações Hidrofóbicas e Hidrofílicas , Ionóforos/química , Limite de Detecção , Membranas Artificiais , Polimetil Metacrilato/química , Tálio/química
2.
Anal Chem ; 85(21): 10495-502, 2013 Nov 05.
Artigo em Inglês | MEDLINE | ID: mdl-24080025

RESUMO

The ion-to-electron transduction reaction mechanism at the buried interface of the electrosynthesized poly(3-octylthiophene) (POT) solid-contact (SC) ion-selective electrode (ISE) polymeric membrane has been studied using synchrotron radiation-X-ray photoelectron spectroscopy (SR-XPS), near edge X-ray absorption fine structure (NEXAFS), and electrochemical impedance spectroscopy (EIS)/neutron reflectometry (NR). The tetrakis[3,5-bis(triflouromethyl)phenyl]borate (TFPB(-)) membrane dopant in the polymer ISE was transferred from the polymeric membrane to the outer surface layer of the SC on oxidation of POT but did not migrate further into the oxidized POT SC. The TFPB(-) and oxidized POT species could only be detected at the outer surface layer (≤14 Ǻ) of the SC material, even after oxidation of the electropolymerized POT SC for an hour at high anodic potential demonstrating that the ion-to-electron transduction reaction is a surface confined process. Accordingly, this study provides the first direct structural evidence of ion-to-electron transduction in the electropolymerized POT SC ISE by proving TFPB(-) transport from the polymeric ISE membrane to the oxidized POT SC at the buried interface of the SC ISE. It is inferred that the performance of the POT SC ISE is independent of the thickness of the POT SC but is instead contingent on the POT SC surface reactivity and/or electrical capacitance of the POT SC. In particular, the results suggest that the electropolymerized POT conducting polymer may spontaneously form a mixed surface/bulk oxidation state, which may explain the unusually high potential stability of the resulting ISE. It is anticipated that this new understanding of ion-to-electron transduction with electropolymerized POT SC ISEs will enable the development of new and improved devices with enhanced analytical performance attributes.


Assuntos
Elétrons , Eletrodos Íon-Seletivos , Polímeros/química , Tiofenos/química , Propriedades de Superfície
3.
Analyst ; 136(16): 3252-8, 2011 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-21735000

RESUMO

Solid-contact (SC) ion-selective electrodes (ISEs) utilizing thin films of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and plasticized poly(vinylchloride) (PVC) have been produced using a spin casting procedure. This study was carried out with a view of characterizing this popular and well known SC ISE using a series of complementary surface analysis techniques. This work revealed that PEDOT:PSS prevents the separation of an undesirable water layer at the buried interface of this SC ISE due to the high miscibility of water in the hydrophilic PEDOT:PSS layer. The lack of a clearly defined and molecularly sharp buried interface prohibits the formation of a distinct water layer presumably by eliminating sites that promote the accumulation of water. This outcome is important to the chemical sensor community since it provides further insights into the compatibility of sensor components in SC ISEs.

4.
Anal Chem ; 82(14): 6203-7, 2010 Jul 15.
Artigo em Inglês | MEDLINE | ID: mdl-20557118

RESUMO

This paper reports on three-dimensional synchrotron radiation/Fourier transform-infrared microspectroscopy (SR/FT-IRM) imaging studies of water inclusions at the buried interface of solid-contact-ion-selective electrodes (SC-ISEs). It is our intention to describe a nondestructive method that may be used in surface studies of the buried interfaces of materials, especially multilayers of polymers. Herein, we demonstrate the power of SR/FT-IRM for studying water inclusions at the buried interfaces of SC-ISEs. A poly(methyl methacrylate)-poly(decyl methacyrlate) [PMMA-PDMA] copolymer revealed the presence of micrometer sized inclusions of water at the gold/membrane interface, while a coupling of a hydrophobic solid contact of poly(3-octylthiophene 2,5-diyl) (POT) prevented the accumulation of water at the buried interface. A similar study with a poly (3,4-ethylenedioxythiophene)/poly (styrenesulfonate) [PEDOT/PSS] solid contact also revealed an absence of distinct micrometer-sized pools of water; however, there were signs of absorption of water accompanied by swelling of the PEDOT/PSS underlayer, and these membrane zones are enriched with respect to water.


Assuntos
Polímeros/química , Espectroscopia de Infravermelho com Transformada de Fourier/métodos , Síncrotrons , Água/química , Ouro/química , Eletrodos Íon-Seletivos , Tiofenos/química
5.
Talanta ; 79(5): 1379-86, 2009 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-19635374

RESUMO

A recently introduced similarity measure is extended here for comparing two-dimensional spectra. Its applicability is demonstrated with heteronuclear single-quantum correlation (HSQC) NMR spectra. For testing the compatibility of a spectrum with the proposed chemical structure, first, the spectrum is predicted on the basis of that structure and then, the proposed comparison algorithm is applied. In this context, the topics of optimization are peak picking, signal intensity measures, and optimizing the parameters of the two-dimensional comparison method. The performance is analyzed with a test set of 289 structures of organic compounds and their HSQC and (1)H NMR spectra. The results obtained with HSQC spectra are better than those achieved using the previously described one-dimensional similarity test with (1)H NMR spectra alone.


Assuntos
Espectroscopia de Ressonância Magnética/métodos , Algoritmos , Estrutura Molecular
6.
Anal Chem ; 81(9): 3592-9, 2009 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-19338286

RESUMO

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.


Assuntos
Membranas Artificiais , Polímeros/química , Potenciometria/métodos , Calibragem , Eletrodos , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Prata/química , Fatores de Tempo
7.
J Electroanal Chem (Lausanne) ; 633(1): 137-145, 2009 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-20376292

RESUMO

A straightforward theoretical description of the time-dependent response of ion-selective membrane electrodes to multiple sample changes is presented. The derivation makes use of an approximation for the ion fluxes in the membrane, and of the superposition of partial fluxes induced by the step-changes. The general theory allows for any number of samples and ions. It is applied for the analysis of memory effects that reflect the influence of preceding samples on subsequent measurements. Various phenomena are discussed, including super-, near-, or sub-nernstian responses, shifts of apparent reference potentials, and potential dips with domains of reversed slopes. The theoretical results agree well with virtual experiments based on computer simulation.

8.
J Solid State Electrochem ; 13(1): 137-148, 2009 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-20802817

RESUMO

High integrity solid-contact (SC) polymeric ion sensors have been produced by using spin casting and electropolymerization techniques in the preparation of the SC employing the conductive polymer, poly(3-octylthiophene) [POT]. The physical and chemical integrity of the POT SCs have been evaluated using scanning electron microscopy (SEM), atomic force microscopy (AFM), secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS). Furthermore, the electrochemical stability of SC polymeric ion sensors has been investigated using electrochemical impedance spectroscopy (EIS). The results of this study demonstrate that electropolymerization and spin casting methods also comprising annealing of the synthesized SC film are capable of producing SCs that are relatively free of imperfections such as pores and pinholes. This leads to electrochemically stable and robust polymeric ion sensors where the SC/sensor interface is resistant to the formation of a detrimental water layer that normally gives rise to spurious ion fluxes and a degradation in the sensitivity and selectivity of the SC polymeric ion sensor.

9.
Analyst ; 134(8): 1601-7, 2009 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-20448926

RESUMO

An enzyme-linked immunosorbent assay (ELISA) for prostate specific antigen (PSA) detection in human serum was developed based on the potentiometric detection of 6,8-difluoro-4-methylumbelliferone (DiFMU). The assays were carried out in anti-human PSA capture antibody modified microtiter plates (150 microL volume). After incubation in the PSA-containing serum samples, beta-galactosidase-labeled PSA tracer antibody was added. The beta-galactosidase label catalyzed the hydrolysis of 6,8-difluoro-4-methylumbelliferyl-beta-D-galactopyranoside (DiFMUG) and the resulting DiFMU(-) anion was detected by potentiometric microelectrodes with anion-exchanger membrane. The selectivity of the anion-exchanger electrode is governed by the lipophilicity of the anions in the sample. Since DiFMU(-) is much more lipophilic (log P = 1.83) than any of the inorganic anions normally present in the working buffers and occurs in its anionic form at the physiological pH (pK(a) = 4.19), it was chosen as the species to be detected. The potentiometric ELISA-based method detects PSA in serum with a linear concentration range of 0.1-50 ng/mL. These results confirm the applicability of potentiometric detection in diagnostic PSA assays. Owing to simple methodology and low cost, potentiometric immunoassays seem to offer a feasible alternative to the development of in vitro diagnostic platforms.


Assuntos
Ensaio de Imunoadsorção Enzimática/métodos , Potenciometria/métodos , Antígeno Prostático Específico/análise , Ânions , Galactosídeos/química , Galactosídeos/metabolismo , Humanos , Himecromona/análogos & derivados , Himecromona/química , Himecromona/metabolismo , Imunoensaio/métodos , Masculino , beta-Galactosidase/metabolismo
10.
Anal Chem ; 80(19): 7516-23, 2008 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-18778039

RESUMO

A recent new direction in ion-selective electrode (ISE) research utilizes a stir effect to indicate the disappearance of an ion concentration gradient across a thin ion-selective membrane. This zeroing experiment allows one to evaluate the equilibrium relationship between front and backside solutions contacting the membrane by varying the backside solution composition. This method is attractive since the absolute potential during the measurement is not required, thus avoiding standard recalibrations from the sample solution and a careful control of the reference electrode potential. We report here on a new concept to alleviate the need to continuously vary the composition of the backside solution. Instead, transmembrane ion fluxes are counterbalanced at an imposed critical current. A theoretical model illustrates the relationship between the magnitude of this critical current and the concentration of analyte and countertransporting ions and is found to correspond well with experimental results. The approach is demonstrated with lead(II)-selective membranes and protons as dominating interference ions, and the concentration of Pb(2+) was successfully measured in tap water samples. The principle was further evaluated with calcium-selective membranes and magnesium as counterdiffusing species, with good results. Advantages and limitations arising from the kinetic nature of the perturbation technique are discussed.


Assuntos
Chumbo/química , Modelos Químicos , Potenciometria/métodos , Calibragem , Cátions Bivalentes/análise , Cátions Bivalentes/química , Íons/análise , Íons/química , Cinética , Chumbo/análise , Membranas Artificiais
11.
Anal Chem ; 80(17): 6731-40, 2008 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-18671410

RESUMO

This study aimed to develop a novel approach for the production of analytically robust and miniaturized polymeric ion sensors that are vitally important in modern analytical chemistry (e.g., clinical chemistry using single blood droplets, modern biosensors measuring clouds of ions released from nanoparticle-tagged biomolecules, laboratory-on-a-chip applications, etc.). This research has shown that the use of a water-repellent poly(methyl methacrylate)/poly(decyl methacrylate) (PMMA/PDMA) copolymer as the ion-sensing membrane, along with a hydrophobic poly(3-octylthiophene 2,5-diyl) (POT) solid contact as the ion-to-electron transducer, is an excellent strategy for avoiding the detrimental water layer formed at the buried interface of solid-contact ion-selective electrodes (ISEs). Accordingly, it has been necessary to implement a rigorous surface analysis scheme employing electrochemical impedance spectroscopy (EIS), in situ neutron reflectometry/EIS (NR/EIS), secondary ion mass spectrometry (SIMS), and small-angle neutron scattering (SANS) to probe structurally the solid-contact/membrane interface, so as to identify the conditions that eliminate the undesirable water layer in all solid-state polymeric ion sensors. In this work, we provide the first experimental evidence that the PMMA/PDMA copolymer system is susceptible to water "pooling" at the interface in areas surrounding physical imperfections in the solid contact, with the exposure time for such an event in a PMMA/PDMA copolymer ISE taking nearly 20 times longer than that for a plasticized poly(vinyl chloride) (PVC) ISE, and the simultaneous use of a hydrophobic POT solid contact with a PMMA/PDMA membrane can eliminate totally this water layer problem.


Assuntos
Polímeros/química , Água/química , Impedância Elétrica , Eletroquímica , Eletrodos , Interações Hidrofóbicas e Hidrofílicas , Difração de Nêutrons , Nêutrons , Cloreto de Polivinila/química , Espalhamento a Baixo Ângulo , Sensibilidade e Especificidade , Prata/química , Espectrometria de Massa de Íon Secundário , Análise Espectral , Propriedades de Superfície
12.
Anal Chem ; 80(3): 707-12, 2008 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-18184015

RESUMO

We here report on the first example of an aptamer-based potentiometric sandwich assay of proteins. The measurements are based on CdS quantum dot labels of the secondary aptamer, which were determined with a novel solid-contact Cd2+-selective polymer membrane electrode after dissolution with hydrogen peroxide. The electrode exhibited cadmium ion detection limits of 100 pM in 100 mL samples and of 1 nM in 200 microL microwells, using a calcium-selective electrode as a pseudoreference electrode. As a prototype example, thrombin was measured in 200 microL samples with a lower detection limit of 0.14 nM corresponding to 28 fmol of analyte. The results show great promise for the potentiometric determination of proteins at very low concentrations in microliter samples.


Assuntos
Aptâmeros de Peptídeos/química , Técnicas Biossensoriais/métodos , Eletrodos Íon-Seletivos , Potenciometria/métodos , Proteínas/análise , Técnicas Biossensoriais/instrumentação , Compostos de Cádmio/química , Imunoensaio , Potenciometria/instrumentação , Proteínas/química , Pontos Quânticos , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Coloração e Rotulagem , Sulfetos/química , Trombina/análise , Trombina/química
13.
Phys Chem Chem Phys ; 10(1): 73-6, 2008 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-18075683

RESUMO

This paper presents the very first direct structural evidence for the formation of a 100 +/- 10 A water layer in coated-wire polymeric-membrane ion-selective electrodes (ISEs).


Assuntos
Eletrodos Íon-Seletivos , Polímeros/química , Água/química , Membranas Artificiais
15.
Trends Analyt Chem ; 27(7): 612-618, 2008.
Artigo em Inglês | MEDLINE | ID: mdl-19122854

RESUMO

Potentiometric sensors share unique characteristics that set them apart from other electrochemical sensors. Potentiometric nanoelectrodes have been reported and successfully used for many decades, and we review these developments. Current research chiefly focuses on nanoscale films at the outer or the inner side of the membrane, with outer layers for increasing biocompatibility, expanding the sensor response, or improving the limit of detection (LOD). Inner layers are mainly used for stabilizing the response and eliminating inner aqueous contacts or undesired nanoscale layers of water. We also discuss the ultimate detectability of ions with such sensors and the power of coupling the ultra-low LODs of ion-selective electrodes with nanoparticle labels to give attractive bioassays that can compete with state-of-the-art electrochemical detection.

16.
Anal Chem ; 79(22): 8705-11, 2007 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-17929899

RESUMO

A new direction in potentiometric sensing, termed backside calibration potentiometry, was recently introduced. It makes use of the fact that the stir effect disappears in the absence of an ion-ionophore complex concentration gradient across supported liquid ion-selective membranes. This method is especially suitable for measurements in which recalibration in the sample is not feasible, such as in remote monitoring applications. Here, a theoretical model is established to predict the working concentration range of the method. Lead(II)-selective Celgard membranes were used here with H+ as the dominant interfering ions. The emf difference for stirred and unstirred solutions was measured, and the magnitude of this emf change as a function of the sample Pb2+ concentration was found to exhibit a bell shape that spans approximately 3 orders of magnitude. The concentration of interfering ions and the selectivity of the membrane were demonstrated to be important factors that affect the working range. Smaller ratios of primary ion concentrations at both aqueous sides of the membrane gave smaller emf difference values, and emf changes could still be observed with a logarithmic concentration ratio of 0.05. All experimental results correlated satisfactorily with the theoretical model.


Assuntos
Potenciometria/métodos , Calibragem , Sensibilidade e Especificidade , Soluções
17.
Anal Chem ; 79(13): 5107-10, 2007 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-17530777

RESUMO

Potentiometric sensors based on polymer membrane electrodes, if properly optimized, are useful for measurements at trace levels. The expected independence of the electrochemical signal of the sample size makes them extremely attractive for measurements in small volumes. Here, we report on electrodes for the potentiometric detection of cadmium ions that reach a detection limit of 6 nM and utilize a Na(+)-selective electrode as pseudoreference in order to facilitate measurements in 150-microL samples. A potentiometric immunoassay of mouse IgG is performed via CdSe quantum dot labels on a secondary antibody according to a sandwich immunoassay protocol in a microtiter plate format. The CdSe quantum dots are found to be easily dissolved/oxidized in a matter of minutes with hydrogen peroxide, allowing us to maintain the pH at a near-neutral value. The potentiometric protein immunoassay exhibits a log-linear response ranging from 0.15 to 4.0 pmol of IgG, with a detection limit of <10 fmol in 150-microL sample wells.


Assuntos
Compostos de Cádmio/química , Imunoensaio/métodos , Imunoglobulina G/análise , Eletrodos Íon-Seletivos , Pontos Quânticos , Compostos de Selênio/química , Animais , Eletroquímica , Peróxido de Hidrogênio/química , Concentração de Íons de Hidrogênio , Imunoensaio/instrumentação , Camundongos , Sensibilidade e Especificidade , Sódio/química
18.
Nano Lett ; 7(6): 1609-12, 2007 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-17488052

RESUMO

The inner walls of gold nanotubes, prepared by template synthesis in the nanopores of polycarbonate track etch membranes, have been chemically modified with peptide nucleic acid (PNA) and used for label-free quantification of complementary DNA sequences. Selective binding of DNA to the PNA-modified nanotubes is shown to decrease the flux of optically detected anionic markers through the nanotubes in a concentration-dependent manner. The strong dependence of the biorecognition-modulated ion transport through the nanopores on the ionic strength suggests a dominantly electrostatic exclusion mechanism of the ion flux decrease as a result of DNA binding to the PNA-modified nanopores.


Assuntos
DNA/química , DNA/genética , Ouro/química , Hibridização In Situ/métodos , Nanotubos/ultraestrutura , Ácidos Nucleicos Peptídicos/química , Análise de Sequência de DNA/métodos , Cristalização/métodos , DNA/ultraestrutura , Transporte de Íons , Substâncias Macromoleculares/química , Teste de Materiais , Conformação Molecular , Nanotecnologia/métodos , Nanotubos/química , Tamanho da Partícula , Ácidos Nucleicos Peptídicos/ultraestrutura , Coloração e Rotulagem , Propriedades de Superfície
19.
Angew Chem Int Ed Engl ; 46(30): 5660-8, 2007.
Artigo em Inglês | MEDLINE | ID: mdl-17457791

RESUMO

For most chemists, potentiometry with ion-selective electrodes (ISEs) primarily means pH measurements with a glass electrode. Those interested in clinical analysis might know that ISEs, routinely used for the determination of blood electrolytes, have a market size comparable to that of glass electrodes. It is even less well known that potentiometry went through a silent revolution during the past decade. The lower detection limit and the discrimination of interfering ions (the selectivity coefficients) have been improved in many cases by factors up to 10(6) and 10(10), respectively, thus allowing their application in fields such as environmental trace analysis and potentiometric biosensing. The determination of complex formation constants for lipophilic hosts and ionic guests is also covered in this Minireview.


Assuntos
Potenciometria/métodos , Calibragem , Concentração de Íons de Hidrogênio , Imunoensaio , Eletrodos Íon-Seletivos , Sensibilidade e Especificidade
20.
Anal Chem ; 79(2): 632-8, 2007 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-17222030

RESUMO

In direct potentiometry, the magnitude of the measured potentials is used to determine the composition of the sample. While this places rather formidable demands on the required reproducibility of the associated potential measurements, typically on the order of microvolts, in vitro clinical analyses of blood samples are today successfully performed with direct potentiometry using ion-selective electrodes (ISEs). Unfortunately, most other analytical situations do not permit the sensor to be recalibrated every few minutes, as in environmental monitoring or in vivo measurements, and direct potentiometry is often bound to fail as an accurate method in these circumstances. This paper introduces a novel direction for potentiometric sensing, termed backside calibration potentiometry. Chemical asymmetries across thin supported liquid ISE membranes are assessed by determining the direction of potential drift upon changing the stirring rate on either side of the membrane. Disappearance of this drift indicates the disappearance of concentration gradients across the membrane and is used to determine the sample composition if the solution composition at the backside of the membrane and the interfering ion concentration in the sample are known. For practical determinations, the concentration of either the primary or the interfering ion is varied in the reference solution until the stirring effect disappears. The procedure is demonstrated with a Ca2+-selective membrane using Ba2+ as the dominant interfering ion. Another example includes the determination of Pb2+ in environmental samples where the pH is adjusted to a known level. At pH 4.0, H+ turns out to be the dominant interfering ion. The practical applicability of the method is shown with different environmental water samples, for which the results obtained with the novel method are compared with those obtained by traditional calibration using standard additions. The limitations of the novel method in terms of accuracy and applicable concentration ranges are discussed.


Assuntos
Eletrodos Íon-Seletivos , Membranas Artificiais , Potenciometria/normas , Bário/química , Cálcio/química , Calibragem , Cátions Bivalentes/química
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