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An outer layer of pure silicone rubber (SR), i.e. SR without any plasticizer, ionophore, or lipophilic anion, was applied on top of a conventional poly(vinyl chloride) (PVC) based K+-selective membrane in a solid-contact ion-selective electrode (SC-ISE). The influence of the outer SR coating on the analytical performance of the K+-ISEs was studied. The presence of the SR coating did not affect the selectivity of the SC-ISE, indicating that the plasticizer, ionophore, and lipophilic anion are spontaneously distributed from the PVC-based membrane into the SR layer. This was confirmed by electrochemical impedance spectroscopy (EIS). Interestingly, the reproducibility of the standard potential of the conditioned SC-ISE was significantly improved from E0 ± 35.3 mV to E0 ± 3.5 mV simply by adding the SR coating on top of the plasticized PVC based K+-selective membrane. Moreover, the adsorption of bovine serum albumin (BSA) was significantly reduced at the SR coated ion-selective membrane. Thus, the addition of a SR coating on a plasticized PVC ion-selective membrane seems to be a feasible method to improve the analytical performance and to reduce the biofouling of potentiometric ion sensors. Accepted version

Ion-selective electrodes (ISEs) are widely used analytical devices to selectively measure ionic species. Despite significant advances in recent years, ion-selective membranes are still mostly prepared in the same manner, by preloading the selective components into a solvent that is subsequently cast into a membrane or film. This paper describes an alternative method to prepare ISE membranes by mass transfer of the sensing components from an emulsion phase. Specifically, blank (undoped) plasticized poly(vinyl chloride) (PVC) membranes mounted into an electrode body are immersed into an aqueous solution containing analyte ions and an appropriate emulsion of the desired sensing components to allow their transfer into the membrane. The concept is demonstrated with conventional membrane electrodes containing an inner solution as well as all-solid-state electrodes. It is shown to be universally useful for the realization of ISEs for K+, Na+, Ca2+, and NO3-.

A fully inkjet-printed disposable and low cost paper-based device for potentiometric Na+- or K+-ion sensing has been developed. A printed ionophore-based all-solid-state ion selective electrode on a graphene/poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (G/PEDOT:PSS) nanocomposite solid contact and a printed all-solid state reference electrode consisting of a pseudosilver/silver chloride electrode coated by a lipophilic salt-incorporating poly(vinyl chloride) membrane overprinted with potassium chloride have been combined on a microfluidically patterned paper substrate. Devices are built on standard filter paper using off-the-shelf materials. Ion sensing has been achieved within 180 s by simple addition of 20 μL of sample solution without electrode preconditioning. The limits of detection were 32 and 101 μM for Na+ and K+, respectively. The individual single-use sensing devices showed near Nernstian response of 62.5 ± 2.1 mV/decade (Na+) and 62.9 ± 1.1 mV/decade (K+) with excellent standard potent...

Poly(vinyl chloride) (PVC) is today one of the most important commodity polymers. Its broad range of applications is due to the presence of plasticizers whose concentration largely impacts the microscopic and the macroscopic properties. Quantifying the concentration of plasticizer in PVC products is therefore of fundamental importance. Thus, in this paper, the applicability of terahertz (THz) time-domain spectroscopy for the characterization of plasticized PVC is for the first time evaluated in a systematic way. It could be demonstrated that the method is able to distinguish between PVC samples with different types and concentrations of plasticizers. Furthermore, a simple, fast, and efficient method is introduced to quantify the concentration of plasticizer in PVC samples of known plasticizer type but different thermal histories. The presented results are of key importance due to the need of reliable noninvasive and nondestructive analytical methods which can deliver onsite information about the remaining plasticizer concentration inside PVC products. Furthermore, it is expected that the proposed approach can be easily extended to other plasticized polymers.

Detection of mercapto-containing pesticides plays a crucial role in food and water safety. A new Re(I)-NCS-Pt(II) complex, [Re(4,4'-di-tert-butyl-2,2'-bipyridine)(CO)3(NCS)]-[Pt(DMSO)(Cl)2] (1), was synthesized and characterized. The synthetic procedure, characterization results, and photophysical data for 1 are reported in this paper. Solvated complex 1 demonstrated luminescent chemodosimetric selectivity for phorate, demeton, and aldicarb (three common mercapto-containing pesticides) with method detection limits (MDLs) of 1.00, 2.87, and 2.08 ppm, respectively. The binding constants (log K) of 1 toward them were in the 3.24-3.44 range. The analyte selectivity of the complex was found to be dependent on the bridging linkage (C≡N and N═C═S) between the Re(I) and Pt(II) centers. The solid-supported dosimetric device 1 was fabricated by blending complex 1 with Al2O3 and poly(vinyl chloride) (PVC) powder. The MDLs of the device toward the mercapto-containing pesticides were 0.48-0.60 ppm. The device was applicable to pesticides in real water bodies such as taps, rivers, lakes, and underground water bodies with excellent recoveries and relative standard deviations of 76.2-108.0% and 2.9-6.7%, respectively. Its spectrofluorimetric changes could be analyzed by naked eye within 20 min with a linear luminometric response toward increases in the phorate concentration (0-8.0 ppm) with R = 0.999.

In this study, we, for the first time, developed a plasticized poly(vinyl chloride) (PVC)-based two-dimensional photonic crystal (2D-PhC) optical sensor using nanoimprint lithography (NIL), which can perform highly sensitive, fast, and selective ion sensing based on ion extraction. Concerning the principle of response, present plasticized PVC-based PhC works as a waveguide and a grating. Incident light was guided in the bulk of plasticized PVC and, then, guided light of a specific wavelength was diffracted by a periodic nanostructure. The guided and diffracted light intensity changes of PVC-based PhCs possessing various thicknesses were monitored at 580 nm; then, we found that the 0.35 μm-thick PhC film exhibited the highest diffraction intensity. For the ion-sensing application, potassium-selective sensing elements involving potassium ionophore and lipophilic dye were dissolved in a plasticized PVC-based PhC, and the K(+)-selective response was successfully observed by monitoring the diffracted peak intensity change. The present 2D-PhC optical sensor exhibited a fast response within 5 s (95% response time) due to the use of thin film, and sensitivity was 20 times higher than that of a PVC plane-film optical sensor, due to efficient collection of diffracted light by employing a periodic nanostructure of the photonic crystal.

Optode-based fluorescent nanosensors are being developed for monitoring important diseased states such as hyponatremia and diabetes. However, traditional optode-based sensors are composed of nonbiodegradable polymers such as polyvinyl chloride (PVC) raising toxicity concerns for long-term in vivo use. Here, we report the development of the first biodegradable optode-based nanosensors that maintain sensing characteristics identical to traditional optode sensors. The polymer matrix of these sensors is composed of polycaprolactone (PCL) and a citric acid ester plasticizer. The PCL-based nanosensors yielded a dynamic and reversible response to sodium, were tuned to respond to extracellular sodium concentrations, and had a lifetime of at least 14 days at physiological temperature. When in the presence of lipase, the nanosensors degraded within 4 hours at lipase concentrations found in the liver but were present after 3 days at lipase concentrations found in serum. This development of biodegradable nanosensors is not only necessary for future in vivo applications, but it has also created a new sensor platform that can be extended to other sensing mechanisms such as for small molecules or enzymes.

Several porphyrin and salophen complexes with Rh(III) are examined as ionophores to prepare nitrite selective polymeric membrane electrodes. All ionophores tested exhibit preferred selectivity toward nitrite anion. Enhanced potentiometric nitrite selectivity is observed in the presence of either lipophilic anionic as well as cationic sites within the membranes, suggesting that the ionophores can function via either a charged or a neutral carrier response mechanism. Among a range of complexes and membrane formulations examined, optimal nitrite selectivity and reversible response down to 5 x 10(-6) M is achieved using Rh(III)-tetra(t-butylphenylporphyrin) as the ionophore in the presence of lipophilic cationic sites in plasticized poly(vinyl chloride) membrane. Response times are substantially longer than typical membrane electrodes apparently because of a slow nitrite ligation reaction with Rh(III); however, a significant improvement in dynamic EMF response can be realized by optimizing the membrane formulation and increasing the temperature. The selectivity observed with these membranes is greater than the best nitrite selective electrodes reported to date in the literature based on lipophilic Co(III)-corrin complexes, allowing the new nitrite electrodes to be utilized to determine the level of nitrite in meats with good correlation to the colorimetric Griess assay method.

We present a simple, rapid, and inexpensive electrochemical sensor based on a reversible pulsed chronopotentiometric polyanion-selective membrane electrode for the detection and quantification of oversulfated chondroitin sulfate (OSCS) and other high charge-density polyanions that could potentially be used to adulterate heparin. The membrane is free of ion exchanger and is formulated with plasticized poly(vinyl chloride) (PVC) and an inert lipophilic salt, tridodecylmethylammonium-dinonylnaphthaline sulfonate (TDMA-DNNS). The neutral salt is used to reduce membrane resistance and to ensure reversibility of the sensor. More importantly, TDMA(+) is used as the recognition element for the polyanions. Here an anodic galvanostatic current pulse is applied across the membrane to cause the extraction of the polyanions from the sample into the membrane and potential is measured at the sample-membrane interface. The measured electromotive force (emf) is proportional to the concentration and the charge density of the polyanions. High charge-density polyanion contaminants and impurities in heparin can be detected using this method since the overall equilibrium potential response of polyions increases with increasing charge density of the polyions. Here, first the potential response of pure heparin is measured at a saturation concentration, the concentration beyond which further addition of heparin does not produce a change in potential response. Then the potential response of heparin tainted with different quantities of the high charge-density contaminant is measured at a fixed total polyion concentration (heparin concentration + contaminant concentration). The latter gives a greater negative potential response due to the presence of the high charge-density contaminant. The increase in the negative potential response can be used for detection and quantification of high charge-density contaminants in heparin. We demonstrate here that 0.3% (w/w) OSCS as well as 0.1% (w/w) dextran sulfate can be detected in heparin at 20-mg/mL total polyion concentration. It has also been shown that 1% (w/w) of dextran sulfate can readily be detected in heparin at only 2-mg/mL total polyanion concentration with a linear response (R(2) = 0.994).

Laser ablation inductively coupled plasma mass spectrometry was used to evaluate ion depth profiles across ion-selective membranes. Advantageously, this approach does not require incorporation of additional components (e.g., chromoionophore) in the membrane composition, as compared to that used in typical potentiometric applications. Moreover, comparison of the distribution of ions in differently pretreated membranes is possible. Concentration profiles of primary and interfering agent (Na+) ions were recorded, for example, of Pb2+-selective poly(vinyl chloride)-based membranes. It was found that the contents and the distribution of Pb(2+) and Na+ ions across the membrane is strongly dependent on the composition of the solutions to which both sides of the membrane are exposed during preconditioning and on the plasticizer included in the membrane formulation. Typical plasticizers, bis(2-ethylhexyl sebacate) (DOS) and the more polar 2-nitrophenyl octyl ether (o-NPOE), were used. It was found that faster ion transport occurs for o-NPOE, and the membrane saturation with Pb2+ ions was achieved within less than 20 h for a 400-microm-thick membrane. In the case of the less polar plasticizer DOS, due to slower rate of ion transport, even after 20 h, the Pb2+ concentration gradients were still visible within the membrane. On the basis of concentration profiles, primary ion diffusion coefficients in both membranes were calculated, and the value obtained for o-NPOE containing membrane was found to be approximately 2 times higher than for its DOS-plasticized counterpart.

A potentiometric sol-gel derived (xerogel) pH sensor based on covalently attached amine groups is described. The sensor consists of a Ag/AgCl electrode coated with a hybrid aminosilane/alkylsilane xerogel film. Various combinations of aminosilanes and alkylsilanes are evaluated for their potentiometric response to pH. The optimal sensor design is composed of (aminoethylaminomethyl)phenethyltrimethoxysilane and methyltrimethoxysilane. This sensor exhibits near-Nerstian response (-55 mV.decade(-)(1)), responds rapidly (< or =3 s) to changes in pH, and has H(+) selectivity coefficients (log K(pot)(H)()+ (, )(j)()) of -13 and -11 for interfering j cations Na(+) and K(+), respectively. In vitro platelet adhesion tests indicate that the xerogel coatings are more blood compatible than conventional poly(vinyl chloride) and poly(urethane) ion-selective electrode coatings.

A simple and powerful method based on UV-visible spectroscopy is presented for studying the stability of the inner electrically conducting polyaniline (PANI) solid contact (SC) layer in all-solid-state ion-selective electrodes (ISE). The influence of the plasticized poly(vinyl chloride) (PVC) membrane (ISM) composition and the pH of the sample solution on the stability of the solid contact is reported. PANI is used as a model compound in this study, but the method presented is universal and can be applied to different types and combinations of SCs and ISMs. It provides a tool for finding the best combination of conducting polymer and ISM for solid contact ISEs. PANI is deposited electrochemically either on glassy carbon or quartz glass covered with a thin layer of tin oxide, and a K+-selective ISM is deposited on top of the PANI layer. The short-term stability of the inner PANI layer is good for all membrane types in buffer solutions with pH 2, 6, and 9, indicating that the outer plasticized PVC membrane hinders the emeraldine salt-emeraldine base transition of the highly pH sensitive PANI layer. The solid contact K+-selective electrodes studied showed a Nernstian response of 58.2 +/- 0.1 mV/log aK. Significant differences are observed in the long-term stability of the inner PANI layer between the different membrane types. This indicates that water uptake of the PVC membrane and its permeability to OH- ions are critical parameters affecting the stability of the PANI layer. The solid contact electrodes based on PANI may require a composition of the PVC membrane different from those typically used in conventional ISEs with an inner solution.

The detection limit of conducting polymer (CP) poly(pyrrole)-based potentiometric chloride-sensitive electrodes was lowered over 3 orders of magnitude, applying anodic current of density in the range microamperes per centimeter squared. This effect was attributed to compensation of doping chloride ion leakage from the membrane into adjacent solution layer, caused by self-discharge of CP. This method was successfully applied to lower the detection limit of all-solid-state chloride-selective potentiometric sensors containing plastic, poly(vinyl chloride) chloride ion-selective membrane, and conducting poly(pyrrole) film applied as ion-to-electron transducer. The control of the leakage of chloride ions from the CP transducer phase to the plastic membrane resulted in linear response of ion-selective electrode shifted down to lower activities. A 2 orders of magnitude lowered detection limit, equal to 4 × 10-7 M, was achieved for current densities corresponding to extended linear range of CP film electrode, i.e...

Mixtures of poly(vinyl chloride) (PVC) with plasticizers have been used in ion-selective electrodes for many years. The same material has proven useful in solid-phase microextraction (SPME), both with and without artificial receptors. We hypothesized that by changing the polymer concentration in plasticized PVC membranes containing artificial receptor from the standard 33 wt %, the selectivity of the extraction of barbiturates over similar molecules could be improved. Partition coefficients and receptor-substrate formation constants of a target species, phenobarbital, in membranes with various polymer concentrations were determined. Diffusion coefficients of the solute phenobarbital in receptor-free membranes were also determined. Kamlet-Taft solvatochromic properties beta and pi* were measured for the PVC/dioctyl sebacate materials. Cohesive energy densities were calculated for the same materials. Partition coefficients for phenobarbital (from aqueous solution to membrane) decrease as [PVC] increases, while the formation constants for the complex of the solute with its receptor increase. Diffusion coefficients decrease as the polymer concentration increases as well. The increase in polymer concentration brings about a decrease in hydrogen-bonding basicity and an increase in dipolarity and cohesive energy density. The values of the solvatochromic parameters determined at various compositions are highly correlated; thus, it is impossible to calculate how much each factor contributes to the changes associated with partition and complex formation. The solvatochromic "polarizability correction factor" has been determined to be 0 for PVC. In SPME experiments at 30%, 40%, and 50% (w/w) PVC, as polymer concentration increases, selectivity for barbiturate extraction over other cyclic imides becomes better in the presence of barbiturate receptor and worse without receptor.

Here we report on ion-transfer voltammetry of perfluoroalkanesulfonates and perfluoroalkanecarboxylates at the interface between a plasticized polymer membrane and water to enable the ultrasensitive detection of these persistent environmental contaminants with adverse health effects. The ion-transfer cyclic voltammograms of the perfluoroalkyl oxoanions are obtained by using a ∼1 μm thick poly(vinyl chloride) membrane plasticized with 2-nitrophenyl octyl ether. The cyclic voltammograms are numerically analyzed to determine formal ion-transfer potentials as a measure of ion lipophilicity. The fragmental analysis of the formal potentials reveals that the 10(4) times higher lipophilicity of a perfluoroalkanesulfonate in comparison to the alkanesulfonate with the same chain length is due to the inductive effect of perfluorination on lowering the electron density of the adjacent sulfonate group, thereby weakening its hydration. The fragmental analysis also demonstrates that the lipophilicities of perfluoroalkyl and alkyl groups with the same length are nearly identical and vary with the length. Advantageously, the high lipophilicity of perfluorooctanesulfonate allows for its stripping voltammetric detection at 50 pM in the presence of 1 mM aqueous supporting electrolytes, a ∼10(7) times higher concentration. Significantly, this detection limit for perfluorooctanesulfonate is unprecedentedly low for electrochemical sensors and is lower than its minimum reporting level in drinking water set by the U.S. Environmental Protection Agency. In comparison, the voltammetric detection of perfluoroalkanecarboxylates is compromised not only by the lower lipophilicity of the carboxylate group but also by its oxidative decarboxylation at the underlying poly(3-octylthiophene)-modified gold electrode during voltammetric ion-to-electron transduction.

Available array-type, chemical-sensing image sensors generally only provide on/off responses to the sensed chemical and produce qualitative information. Therefore, there is a need for an array sensor design that can detect chemical concentration changes to produce quantitative, event-sensitive information. In this study, a 128 × 128 array-type image sensor was modified and applied to imaging of biogenic amines released from stimulated rat mast cells, providing recordable responses of the time course of their release and diffusion. The imaging tool was manufactured by an integrated circuit process, including complementary metal oxide semiconductor and charge-coupled device technology. It was fitted with an amine-sensitive membrane prepared from plasticized poly(vinyl chloride) including a hydrophobic anion, which allowed the sensor to detect amines, such as histamine and serotonin, in Tyrode's solution. As mast cells were larger in diameter than the pixel hollows, some pixels monitored amines released from single cells. The image from the array responses yielded sequential snapshots at a practical frame speed that followed amine concentration changes over time, after mast cell amine release was synchronized by chemical stimulation. This sensor was shown to be sensitive to amine release at very low stimulus concentrations and was able to detect localized spots of high amine release. The entire time course of the amine release was recorded, including maximum concentration at 4-6 s and signal disappearance at 30 s after stimulation. With further development, this sensor will increase opportunities to study a variety of biological systems, including neuronal chemical processes.

A convenient method for the preparation of monodisperse, plasticized poly(vinyl chloride) particles based on an automated particle casting technique is described. The particles are made highly selective for a number of ions by doping them with ionophores and other active components, in complete analogy to thin-film or fiber-optic chemical sensors. The approach used here produces spheres of high monodispersity at a rate of approximately 20000 particles/s. The casting process is based on a reproducible polymer drop formation and precipitation process, and the particles are formed under very mild, nonreactive conditions. This allows one to conveniently incorporate known amounts of different active components into the polymers. As an initial example, the particles are doped with three optical sensing components, the sodium ionophore tert-butylcalix[4]arene tetraethyl ester, the H+-chromoionophore ETH 5294, and the anionic additive sodium tetrakis[3,5-bis(trifluoromethyl)phenyl] borate. The particles are found to be of spherical shape with a diameter of approximately 10 microm. They respond individually and selectively to sodium according to classical optode theory, as determined by fluorescence microscopy. With a RSD of 1.6%, sensing reproducibility from particle to particle is excellent. This technique may allow the development of mass-produced chemically selective microspheres on the basis of bulk extraction processes.

Fluorescent spherical nanosensors, or PEBBLEs (probes encapsulated by biologically localized embedding), in the 500 nm-1 microm size range have been developed using decyl methacrylate as a matrix. A general scheme for the polymerization and introduction of sensing components creates a matrix that allows for the utilization of the highly selective ionophores used in poly(vinyl chloride) and decyl methacrylate ion-selective electrodes. We have applied these optically silent ionophores to fluorescence-based sensing by using ion-exchange and highly selective pH chromoionophores. This allows the tailoring of selective submicrometer sensors for use in intracellular measurements of important analytes for which selective enough fluorescent probes do not exist. The protocol for sensor development has been worked out for potassium sensing. It is based on the BME-44 ionophore (2-dodecyl-2-methyl-1,3-propanediylbis[N-[5'nitro(benzo-15-crown-5)-4'-yl]carbamate]). The general scheme should work for any available ionophore used in PVC or decyl methacrylate ion-selective electrodes, with minor adjustments to account for differences in ionophore charge and analyte binding constant. The reversible and highly selective sensors developed have a subsecond response time and an adjustable dynamic range. Applications to live C6 glioma cells demonstrate their utility; the intracellular potassium activity is followed in real time upon extracellular administration of kainic acid.

Microscale plasticized PVC particles doped with hydrophobic ionophores are prepared by solvent evaporation of aqueous suspensions of sensing cocktails (poly(vinyl chloride), plasticizer, active sensing components, and tetrahydrofuran) and tested as particulate microoptical sensors. The particles contain either only the chromoionophore ETH 2458 as active reagent or the potassium ionophore BME-44, chromoionophore ETH 5294, and lipophilic anionic sites NaTFPB. The former system functions according to an anion-hydrogen ion coextraction mechanism and shows a Hofmeister anion selectivity pattern, while the latter sensor containing additional ionophores represents the more complex, truly selective optical sensors based on ion-exchange equilibria. Single microspheres are simultaneously characterized spatially and spectrally by fluorescence microscopy, coupled to a spectrometer equipped with a CCD detector. The results indicate that these microspheres respond in complete analogy to traditional thin-film-based optodes previously reported in the literature. The introduction of small, spherical ionophore-based sensing particles that operate on the basis of bulk extraction principles holds the promise of significantly expanding the available chemical palette of microsphere-based analytical assays.

Microtiter plate wells modified with thin (approximately 20 microm) polymeric films capable of optically sensing macromolecular protamine and other polycationic species are described. The plates are prepared by coating the bottom of each well of a conventional 96-well polypropylene plate with an adherent polymer film (a mixture of poly(vinyl chloride) and polyurethane) containing a lipophilic 2',7'-dichlorofluorescein derivative. Surprisingly, optical response toward polycations is shown to result from the extraction of the fluorescein derivative from the polymer film into a lyophobic colloidal phase at the sample/film interface. This new phase is likely composed of a micellular-type ion pair complex between the analyte polycation from aqueous sample phase and the deprotonated form of the fluorescein derivative. Accumulation of the deprotonated fluorescein species in this interfacial region induces an absorbance change measured at 540 nm. Optimized plates can be used to sense protamine concentrations in the range of 0-100 microg/mL in 10 min with little or no response to physiological levels of common cationic species (Na+, K+, Ca2+, etc.). The modified plates are shown to be useful as simple optical detectors for measuring heparin levels in plasma via titrations with protamine and for monitoring protease activities (trypsin and plasmin) that cleave polycationic peptides/proteins such as protamine into smaller peptide fragments that are not detected by the sensing films. Assays for "clot busting" plasminogen activators (streptokinase, urokinase, and tissue plasminogen activator) are also demonstrated using this relatively simple microtiter plate-based polycation detection system.

New salicylate-selective electrodes based on aluminum-(III) and tin(IV) salophens are described. The electrodes were prepared by incorporating the ionophores into plasticized poly(vinyl chloride) (PVC) membranes, which were directly coated on the surface of graphite electrodes. These novel electrodes display high selectivity for salicylate with respect to many common inorganic and organic anions. The influence of membrane composition and pH and the effect of lipophilic cationic and anionic additives on the response properties of the electrodes were investigated. The electrode based on aluminum salophen, with 32% PVC, 65.8% plasticizer, and 2.2% ionophore, shows the best potentiometric response characteristics and displays a linear log [Sal-] vs EMF response over the concentration range 1 x 10(-6) - 1 x 10(-1) M in phosphate buffer solutions of pH 7.0, with a Nernstian slope of -59.2 mV/decade of salicylate concentration. Highest selectivity was observed for the membrane incorporating 38.8% PVC, 57.3% plasticizer, 2.6% Sn(salophen), and 1.3% sodium tetraphenylborate. The electrodes exhibit fast response times and micromolar detection limits (approximately 1 x 10(-6) M salicylate) and could be used over a wide pH range of 3-8. Applications of the electrodes for determination of salicylate in pharmaceutical preparations and biological samples are reported.

The preparation and response features of a micrometer-sized sodium ion-selective fiber optode based on a liquid membrane were described. The sensing membrane is a plasticized poly(vinyl chloride)-based copolymer with a neutral sodium ionophore and an anionic dye. To fabricate a micrometer-sized fiber optode, a “micropipet fabrication method” was proposed to fix a liquid membrane-based optode on the small tip of an optical fiber probe, in which the optode size can be varied from ∼1 μm to more than 10 μm. Our first optode incorporated a 16-crown-5 derivative as the neutral sodium ionophore and a dibromofluorescein derivative as the single-emission anionic dye. The sensor response was monitored by measuring the fluorescence intensity under a time-resolved photon-counting method. At the first stage of the investigation, it was found that the ionophore including a sodium ion in its cavity leached from the membrane phase. However, we have discovered that the problem can be resolved by using a “tailed” ionophore...

Microtiter plate-format optodes could be assembled by casting bulk-response membranes into the standard 96-well polypropylene-based plate or by screen printing them on an optically transparent substrate with 96-well pattern. The compositions of thick optode membranes, especially the ratios of poly(vinyl chloride) (PVC) to plasticizer [bis(2-ethylhexyl) sebacate (DOS)], were carefully optimized to provide reproducible and rapid response. Adjusting the ratio of PVC to DOS by 1:6, bulk-response membranes containing neutral carrier (4-tert-butyl calix[4]arene tetraacetic acid tetraethyl ester for sodium-selective membrane or valinomycin for potassium-selective membrane) and lipophilic pH indicator (ETH 5294) could exhibit equilibrium response in 5 min. The practical utility of microtiter plate-format optodes has been examined by determining clinically relevant electrolytes in serum samples. It was demonstrated that microtiter plate-format optodes can provide high sample throughput (∼100 samples in less than 5...

Reduced dicyanovinyl dyes, a new type of pH-sensitive chromophores with absorption bands reaching into the near-infrared (near-IR) spectral range, are presented. Side-chain residues with different properties were attached to the chromophore backbone to influence the pKa values of the indicator dyes. The resulting dyes were suitable to be incorporated into lipophilic optical sensing bulk membranes (optodes) made from plasticized poly(vinyl chloride). The characteristics of the indicators were studied in pH-sensitive membranes. Full signal reversibility for protonation and deprotonation and high chromophore stability were observed. As an example of application for ion-sensing, a calcium-selective optode is demonstrated. The dynamic measuring range for calcium was 10-6−10-1 M in aqueous solutions, buffered at pH 2.7. The response behavior, short-time reproducibility, and stability of the optodes are discussed.

To quantitatively investigate the relationship between the surface charge densities and the phase boundary potentials at poly(vinyl chloride)-based liquid membranes of ion-selective electrodes, lip...

The solid phase microextraction device is based on plasticized poly(vinyl chloride) (PVC) as an extraction solvent, which is coated on a primed steel rod. The plasticizer is a phosphate triester. A simple device for back-extraction of analytes into a few microliters of back-extraction solution is described. A Teflon tube, with an inside diameter just larger than the PVC-coated extraction rod, is terminated at one end by a syringe. A few microliters of back-extraction solution is placed into the open end of the tube. Because the Teflon does not wet, the drop remains together. After exposure to sample, the PVC-coated extraction rod containing the analytes is inserted into the back-extraction solution-containing tube. The aqueous back-extraction solvent spreads out in the narrow annular space thus formed. After a suitable period, the rod is removed, and the droplet re-forms. It can be ejected into a sample vial with the syringe. The device has been used in a CE-based determination of barbiturates. Extraction...

A pyrolysis gas chromatography method was developed to determine the composition and microstructure of chlorinated polyethylene (CPE). This method utilized specific aromatic compounds which were formed through dehydrochlorination of trimers after pyrolysis of CPE polymers at elevated temperatures. The composition and microstructure calculation was based on the difference between the levels of ethylene and vinyl chloride trimers formed. This method is valid for CPE polymers containing between 25 and 48 wt % chlorine. The composition of CPE polymers used in this study was corroborated with 13C-NMR results and the manufacturer's product specification.

An organic−inorganic hybrid sol−gel matrix was used as host for tridodecylmethylammonium chloride (TDMAC), which is an ionophore for chloride. The sol−gel precursor was prepared by the reaction of (3-isocyanopropyl)triethoxysilane with 1,4-butanediol. On mixing with TDMAC, the sol-state precursor slowly gelled, to give a TDMAC-containing membrane. The performances of the sol−gel membrane-based electrodes were compared to those of TDMAC-based poly(vinyl chloride) (PVC) membrane electrodes. Membranes with an optimum ratio of TDMAC:sol−gel precursor (0.1:3 by weight) showed very stable baseline potential. The response slope toward chloride was approximately 55 mV/decade between 10-4 and 5 × 10-1 M Cl- at room temperature. Moreover, selectivity toward chloride over salicylate and other lipophilic anions was improved, deviating from the Hofmeister selectivity pattern which is observed in most dissociated charged carrier-based potentiometric membrane sensors. The selectivity coefficients measured by the separat...

The design of luminescent oxygen sensors is guided by optimizing sensitivity and/or the form of the calibration function. Both qualities are governed by the molecular processes of luminescence quenching. To evaluate the influence of matrix effects, we prepared membranes based on oxygen-sensitive phosphorescent complexes of porphyrin ketones dissolved in plasticizer-free poly(vinyl chloride) (PVC) and polystyrene (PS). In a PVC matrix, both platinum(II) and palladium(II) octaethylporphyrin ketones exhibited perfectly linear Stern-Volmer intensity plots and almost single-exponential excited state decays. In a PS matrix, the sensitivity of palladium(II) octaethylporphyrin ketone was among the highest reported to date. Yet, slightly nonlinear Stern-Volmer plots and nonexponential decays illustrate the significance of matrix effects of PS. Addition of plasticizers to PVC-based sensors allowed tuning of the oxygen sensitivity in a wide range, while the Stern-Volmer plots became pronouncedly nonlinear. For the plasticizer bis(2-ethylhexyl) adipate, the decay profile was single-exponential in the absence but nonexponential in the presence of oxygen, which is attributed to a distribution of quenching rate constants.

The influence of poly(ethylene oxide)-based nonionic surfactants (i.e., Triton X-100 and Brij 35) in the sample phase on the response properties of hydrogen ion-selective polymeric membrane electrodes containing mobile (lipophilic amines) or covalently bound (aminated-poly-(vinyl chloride)) hydrogen ion carriers is reported. In the presence of these nonionic surfactants, membrane electrode response toward interfering cation activity (e.g., Na+) in the sample phase is increased substantially and the pH measuring range shortened. The degree of cation interference for pH measurements is shown to correlate with the basicity of the hydrogen ion carrier doped within the membrane phase. The observed deterioration in selectivity arises from the partitioning of the surfactant into the membrane and concomitant extraction of metal cations by the surfactants in the organic phase. The effect of nonionic surfactants on pH electrodes prepared with aminated-PVC membranes is shown to be more complex, with additional large shifts in EMF values apparently arising from multidentate interactions between the surfactant molecules and the polymeric amine in the membrane, leading to a change in the apparent pKa values for the amine sites. The effects induced by nonionic surfactants on the EMF response function of hydrogen ion-selective polymeric membrane electrodes are modeled, and experimental results are shown to correlate well with theoretical predictions.

A dual-sorption-site model in which both miscible and phase-separated water droplets are present in ion-selective, poly(vinyl chloride) (PVC)-based membranes is applied to data obtained for the H2O concentration profiles during the later stages of water uptake. A finite difference algorithm for calculating the concentration profiles is presented, and the calculated curves are shown to match the experimental data over the entire equilibration period. A relaxation process is identified which is associated with an increasing content of immobilized H2O, Cim, as described by Cim = C°im(1 − y e-βt), where y = 0.7, β = 0.27 h-1 for membranes with about 45 mM salt added, and y = 0.6, β = 0.40 h-1 with 5 mM added salt. Calculations are presented showing water equilibration times required for 40−100 μm thick membranes contacted by water on both sides, a solid on one side, or a 10−40 μm thick hydrogel serving as an inner electrolyte reservoir on one side. For membranes thinner than 200 μm that are contacted on both ...

An osmotic pressure-driven model for uptake of water in rubber is combined with dual-sorption-site theory to describe the transport of water in highly plasticized, poly(vinyl chloride) (PVC)-based ion-selective electrode membranes, both at equilibrium and during the initial stages of water uptake. During the first hour, mobile, miscible water is predicted to have a diffusion coefficient given by Dmo = D/(1 + Cis/so), where Dmo and D are the observed and true diffusion coefficients, respectively, Cis is the molar concentration of salt impurity and so is the maximum miscible water concentration. Addition of CoCl2 to PVC plasticized with dioctyl adipate (DOA) or nitrophenyl octyl ether (NPOE) showed that Dmo followed this expression during initial stages of water uptake. Values of D = (1.5 ± 0.1) × 10-6 cm2/s and so = 51 ± 5 mM, versus D = (4.3 ± 0.2) × 10-7 cm2/s and so = 82 ± 7 mM, were obtained for membranes with 66% DOA or NPOE as plasticizer, respectively. Added CoCl2 or KB(C6H5)4 reduced Dmo. The depen...

Silicone rubber-based Na + -sensing membranes, which do not require any special plasticizer and are therefore quite resistant to membrane deterioration, can be practically applied to Na + -selective electrodes, as far as the neutral carrier is highly dispersible in silicone rubber. The silicone rubber membrane Na + -selective electrodes based on an oligosiloxane-modified calix[4]arene neutral carrier are reliable for sodium assays in human body fluids such as blood sera and urine. Two other Na + neutral carriers that are excellent ones for plasticized poly(vinyl chloride) membranes did not give good results for silicone rubber membranes of the ion-selective electrodes, due to their poor dispersibility in silicone rubber.

Thin plasticized polymer films, poly(vinyl chloride) doped with a specific ion pairing quaternary ammonium compound, tridodecylmethylammonium chloride, and a lipophilic pH indicator, 3-hydroxy-4-(4-nitrophenylazo)phenyl octadeconate, are shown to exhibit significant and analytically useful optical response toward macromolecular heparin. The response mechanism is based on favorable extraction of heparin into the bulk organic film, owing to the specific ion-pairing complexation reaction between the quaternary ammonium species and the polyanion. A simultaneous coextraction of hydrogen ions results in protonation of the pH chromophore and hence a change in the optical absorbance of the polymeric film. When used in a limited volume/fixed exposure (10 min) detection mode, film absorbances change as a function of the initial heparin concentration in the range of 0.2-3.0 units/mL (1.2-18 micrograms/mL). The practical measurement response time is controlled by heparin diffusion through the stagnant diffusion layer adjacent to the surface of the film as well as within the bulk of the polymer film and is shown to increase with the molecular weight of the heparin species tested. No optical response to heparin is observed when a strong heparin complexing agent (e.g., protamine) is present in the test solution, suggesting that the polymer film can be used to conveniently monitor heparin-protamine (or other antagonist) titrations. The theory relating to the operation of the sensing film in either the equilibrium or the kinetic mode and the selectivity of the optimized film to heparin relative to small anions are presented.

The water uptake of plasticized poly(vinyl chloride) (PVC) and silicone rubber (SR) based calcium-selective membranes which are commonly used in solid-contact and coated-wire ion-selective electrodes (SC-ISEs and CWEs) was quantified with the oven based coulometric Karl Fischer (KF) technique. Two different membrane types were studied: (1) the plasticized PVC or SR (RTV 3140) membrane matrix without other added membrane components and (2) the full Ca(2+)-selective membrane formulation consisting of the membrane matrixes, potassium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate and calcium ionophore IV (ETH 5234) or calcium ionophore I (ETH 1001). The membranes were contacted for 24 h either asymmetrically from one side or symmetrically from both sides with deionized water (DIW) or 0.1 M solutions of CaCl(2), KCl, or NaCl. It was found that the water uptake was higher for symmetrically contacted membranes. The highest water uptake (0.15-0.17 wt %) was obtained for the plasticized PVC based Ca(2+)-selective membranes in DIW, whereas the water uptake was lower in 0.1 M electrolyte solutions. Symmetrically contacted Ca(2+)-selective SR membranes had much lower water uptake in 0.1 M CaCl(2) (0.03 wt %) than their plasticized PVC counterparts (0.1 wt %). However, the (noncontacted) SR membranes contained initially much more water (0.09-0.15 wt %) than the PVC membranes (0.04-0.07 wt %). Furthermore, in good accordance with the KF measurements, it was verified with FT-IR-attenuated total reflection (ATR) spectroscopy that the water content at the substrate/membrane interface and consequently in the whole membrane was influenced by the electrolyte solution.