Fluorescent ion-selective optode membranes incorporated onto a centrifugal microfluidics platform

The development of an integrated analysis system for small ions based on ion-selective optodes and centrifugal microfluidics is reported. The performance of this system was evaluated through five-point calibration plots for two types of optode membranes, one being cation-selective and the other anion-selective, which were incorporated into a microfluidics platform on which fluid motion is induced via angular rotation. Additionally, the application of the microfluidic platform to ion analysis is studied via a two-point calibration protocol used to quantify an unknown sample. Calibrant solutions are delivered from reservoirs fabricated onto the platform to a measuring area that contains the optode membrane, with a change in membrane fluorescence being monitored. This work demonstrates the first instance of a microfluidic-based analysis system with detection based on ion-selective optode membranes monitored with fluorescence transduction. Furthermore, in addition to employing a standard excitation source where a fiber-optic probe is coupled to a tungsten-halogen lamp, laser diodes such as those employed in portable CD/DVD players were studied as excitation sources to enhance the observed fluorescence signals.     

Multiplexed flow cytometric sensing of blood electrolytes in physiological samples using fluorescent bulk optode microspheres

Polymeric bulk optode microsphere ion sensors in combination with suspension array technologies such as analytical flow cytometry may become a power tool for measuring electrolytes in physiological samples. In this work, the methodology for the direct measurement of common blood electrolytes in physiological samples using bulk optode microsphere sensors was explored. The simultaneous determination of Na(+), K(+), and Ca(2+) in diluted sheep blood plasma was demonstrated for the first time, using a random suspension array containing three types of mixed microsphere bulk optodes of similar size, fabricated from the same chromoionophore without additional labeling. Sodium ionophore X, potassium ionophore III, and grafted AU-1 in poly(butyl acrylate) were the ionophores used in the bulk optode microsphere ion sensors for Na(+), K(+), and Ca(2+), respectively, in combination with the cation-exchanger NaTFPB (sodium tetrakis-[3,5-bis(trifluoromethyl)phenyl]borate) and the same concentration of the chromoionophore ETH 5294 (9-(di-ethylamino)-5-octadecanoylimino-5H-benzo[a]phen-oxazine) in plasticized poly(vinyl chloride). Excellent reproducibility was achieved for the sensing of potassium ions. The effect of sample pH was relatively small at near-physiological pH and followed theoretical predictions, yet the sample temperature was found to influence the sensor response to a larger extent. Multiplexed ion sensing was achieved by taking advantage of the chemical tunability of the sensor response, adjusting the sensor compositions so that the three types of ion sensors responded with distinct levels of protonation of the chromoionophore. Consequently, three well-resolved peaks were simultaneously observed in the single-channel histogram during the multiplexed calibration as well as in the subsequent measurement of the three cations in 10-fold-diluted sheep plasma. The assigned peak positions corresponded very well to the physiological range of the measured ions.     

Centrifugal microfluidics with integrated sensing microdome optodes for multiion detection

An array of four sensing microdome optodes (potassium, sodium, calcium, and chloride) was incorporated into a centrifugal microfluidics platform to obtain a multiion analysis system. The behavior of each sensing microdome was in good agreement with a theoretical model describing the response. The selectivity of each optode over common interfering ions was established and was used to identify calibrant solutions that can be employed for the simultaneous calibration of all four optodes without significant cross-interference. The microfluidic platform was designed to facilitate both three-point calibration of the optodes and triplicate analysis of a sample within a single run, which increases the accuracy of the determination. The optimized microfluidic system was used to determine simultaneously the concentration of potassium, sodium, calcium, and chloride in aquarium water (with the composition of Lake Tanganyika water) with less than 6% error. The simple process of fabrication of these microdomes and their incorporation into a centrifugal microfluidic platform should facilitate the development of portable ion-sensing analysis systems.     

Theory and Practice of Rapid Flow-Through Analysis Based on Optode Detection and Its Application to pH Measurement as a Model Case

Rapid flow-through analysis (RFA) based on optode (optical chemical sensor) detection is proposed, and its performance is discussed using the RFA system equipped with a pH-sensitive optode as a model case. To demonstrate and understand the usefulness of the RFA system, long-lifetime pH-sensitive optodes were prepared using a hydrophilic poly(hydroxyethyl methacrylate) (poly-HEMA) membrane covalently immobilized with a dye containing an amino group such as Congo Red or Nile Blue. The response equation for the optode with the RFA system was proposed, and satisfactory estimation for rapid pH analysis was obtained. The proposed RFA can stand as an advanced method for conventional flow injection analysis.     

Mass-produced lonophore-based fluorescent microspheres for trace level determination of lead ions

The development and characterization of small, uniform, and mass-produced plasticized PVC-based sensing microspheres in view of rapid trace level analysis of lead ions is reported. Micrometer-sized particles obtained via an automated casting process were rendered selective for lead ions by doping them with highly selective components in a manner analogous to traditional optode sensing films. Single particles that contained the lipophilic ionophore N,N,N',N'-tetradodecyl-3-6-dioxaoctane-1-thio-8-oxodiamide (ETH 5493), the chromoionophore ETH 5418 together with a lipophilized indocarbocyanine derivative as internal reference dye (DiIC18), and lipophilic ion-exchanger sites sodium tetrakis[3,5-bistrifluoromethylphenyl]borate, yielded measurable lead responses at the low nanomolar level in pH buffered solutions. The detection limit for single particles was 3 x 10(-9) M at pH 5.7. The microspheres were fabricated via a reproducible formation of polymer droplets within a flowing aqueous phase followed by collection of spherical particles of approximately 13 microm in size. The particles were immobilized and assayed individually in a microflow cell via fluorescence microscopy. Selectivity patterns found were in agreement with those reported earlier for the lead-selective ligand ETH 5493, and all response functions were fully described by theory. In contrast to optode films that necessitated very long equilibration times and large sample volumes in diluted samples of analyte, particles exhibited extremely enhanced equilibrium response times. Thus, for lead sample concentrations at and above 5 x 10(-8) M, response times were approximately 3 min, whereas at the detection limit, complete equilibrium was recorded after just 15 min, with required sample volumes on the order of 1 mL This new class of microspheres appears to be suitable for rapid and sensitive ion detection at trace levels in environmental and biological applications.     

Procion Green H-4G immobilized poly(hydroxyethylmethacrylate/chitosan) composite membranes for heavy metal removal

The effective removal of toxic heavy metals from environmental samples still remains a major topic of present research. Metal-chelating membranes are very promising materials as adsorbents when compared with conventional beads because they are not compressible, and they eliminate internal diffusion limitations. The purpose of this study was to evaluate the performance of a novel adsorbent, Procion Green H-4G immobilized poly(hydroxyethylmethacrylate (HEMA)/chitosan) composite membranes, for the removal of three toxic heavy metal ions, namely, Cd(II), Pb(II) and Hg(II) from aquatic systems. The Procion Green H-4G immobilized poly(hydroxyethylmethacrylate/chitosan) composite membranes were characterized by elemental analysis, scanning electron microscopy and Fourier transform infrared (FTIR) spectroscopy. The immobilized amount of the Procion Green H-4G was calculated as 0.018+/-0.003 micromol/cm(2) from the nitrogen and sulphur stoichiometry. The adsorption capacity of Procion Green H-4G immobilized poly(hydroxyethylmethacrylate/chitosan) composite membranes for selected heavy metal ions from aqueous media containing different amounts of these ions (30-400mg/l) and at different pH values (2.0-6.0) was investigated. The amount of Cd(II), Pb(II) and Hg(II) adsorbed onto the membranes measured at equilibrium, increased with time during the first 45 min and then remained unchanged toward the equilibrium adsorption. The maximum amounts of heavy metal ions adsorbed were 43.60+/-1.74, 68.81+/-2.75 and 48.22+/-1.92 mg/g for Cd(II), Pb(II) and Hg(II), respectively. The heavy metal ion adsorption on the pHEMA/chitosan membranes (carrying no dye) were relatively low, 6.31+/-0.13 mg/g for Cd(II), 18.73+/-0.37 mg/g for Pb(II) and 18.82+/-0.38 mg/g for Hg(II). Competitive adsorption of the metal ions was also studied. When the metal ions competed with each other, the adsorbed amounts were 12.74+/-0.38 mg Cd(II)/g, 28.80+/-0.86 mg Pb(II)/g and 18.41+/-0.54 mg Hg(II)/g. Procion Green H-4G immobilized poly(hydroxyethylmethacrylate/chitosan) membranes can be regenerated by washing with a solution of nitric acid (0.01 M). The percent desorption achieved was as high as 95%. These novel membranes are suitable for repeated use for more than five adsorption/desorption cycles without any considerable loss in adsorption capacity. Adsorption equilibria were well described by Langmuir equation. It can be concluded that Procion Green H-4G immobilized poly(hydroxyethylmethacrylate/chitosan) membranes may effectively be used for the removal of Cd(II), Pb(II) and Hg(II) ions from aqueous solutions.     

Molecular Design, Characterization, and Application of Multiinformation Dyes for Multidimensional Optical Chemical Sensings. 2. Preparation of the Optical Sensing Membranes for the Simultaneous Measurements of pH and Water Content in Organic Media

Optical chemical sensing of pH and water content in organic solvents is proposed, using multiinformation dyes (MIDs) based on the support matrixes for the dyes. In this investigation, four kinds of merocyanine-type dyes having a polymerizable olefin unit as the MIDs were synthesized. These dyes were copolymerized with hydrophilic monomer molecules to obtain dye-immobilized optical chemical sensor (optode) membranes. In this case, selection of the monomer molecule gave optode membranes having different color change properties, because different monomer molecules provided different chemical environments around the immobilized dye. These optode membranes were used for the measurement of pH and water content in organic solvents. These membranes offered two-dimensional sensing information in one spectrum when they were employed for water content sensing in organic solvents, in which the maximum wavelength represents the water content and the absorbance at this wavelength represents the pH of the water present. These polymer membranes have a long lifetime, which can be adequate for practical use.     

Fiber-optic microsensor array based on fluorescent bulk optode microspheres for the trace analysis of silver ions

An optical microsensor array is described for the rapid analysis of silver ions at low parts per trillion levels. Because the ionophore o-xylylenebis(N,N-diisobutyldithiocarbamate) (Cu-I) was reevaluated and shown to exhibit excellent selectivity for silver ions, ion-selective electrode (ISE) membranes were optimized and found to exhibit the lowest reported detection limit so far (3 x 10(-10) M). A corresponding Ag+-selective fluorescent optical microsensor array for the rapid sensing of trace level Ag+ was then developed. It was fabricated using plasticized PVC-based micrometer-scale fluorescent microspheres that were produced via a sonic particle casting device. They contained 156 mmol/kg Cu-I, 10 mmol/kg 9-(diethylamino)-5-[4-(15-butyl-1,13-dioxo-2,14-dioxanodecyl) phenylimino]benzo[a]phenoxazine (chromoionophore VII, ETH 5418), 2.3 mmol/kg 1,1' '-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (internal reference dye), and 14 mmol/kg sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate and were deposited onto the etched distal end of a 3200-microm-diameter optical fiber bundle. The microarray was characterized by fluorescence spectroscopy in samples containing 10(-12)-10(-8) M AgNO3 at pH 7.4, with selectivity characteristics comparable to the corresponding ISEs. The response time of the microsensor array was found to be less than 15 min for 10(-9) M AgNO3, which is drastically shorter than earlier data on optode films (8 h) and corresponding ISEs (30 min). A detection limit of 4 x 10(-11) M for Ag+ was observed, lower than any previously reported optode or silver-selective ISE. The microsensor array was applied for measurement of free silver levels in buffered pond water samples.     

Development of a specific and highly sensitive optical chemical sensor for determination of Hg(II) based on a new synthesized ionophore

A novel optode for determination of Hg(II) ions is developed based on immobilization of a recently synthesized ionophore, 7-(1H-imidazol-1-ylmethyl)-5,6,7,8,9,10-hexahydro-2H-1,13,4,7,10 benzodioxatriaza cyclopentadecine-3,11(4H,12H)-dione, in a PVC membrane. Dioctyl sebacate was used as a plasticizer, sodium tetraphenylborate as an anionic additive and ETH5294 as a chromoionophore. The response of the optode was based on the complexation of Hg(II) with the ionophore in the membrane phase, resulting an ion exchange process between Hg(II) in the sample solution and H⁺ in the membrane. The effects of pH and amounts of the ionophore, chromoionophore, ionic additive and type of plasticizer on the optode response were investigated. The selectivity of the optode was studied in the present of several cations. The optode has a linear response to Hg(II) in the range of 7.2 × 10^? 13–4.7 × 10^? 4 mol L^? 1 with detection limit of 0.18 pmol L^? 1. The optode was successfully applied to the determination of Hg(II) in real samples.     

Optode Membrane for Determination of Nicotine via Generation of Its Bromoethane Derivative

A plasticized poly(vinyl chloride) optode membrane incorporated with a valinomycin ionophore, a H(+)-selective chromoionophore (ETH 5294), and a lipophilic potassium tetrakis(4-chlorophenyl)borate was used as a reversible sensing device for the indirect optical determination of nicotine. Nicotine was extracted from a tobacco product (1-5 g) and converted to its bromoethane derivative (NBD(+)Br(-)) by reacting with a solution of bromoethane in ethanol. NBD(+)Br(-) in a solution of 0.05 M boric acid-Borax buffer and 0.2 mM Triton X-100 was extracted into the bulk of the membrane and subsequently caused changes in optical absorption of the sensing layer. The response slope, dynamic working range, detection limit, sensitivity, selectivity, effects of buffer solution and neutral surfactant Triton X-100, and lifetime were discussed in detail. The response was pH dependent. At pH 8.5, the detection range was extended from 0.4 μM to 1 mM. Typical response times (t(95)) of the samples were 2-4 min. The optode method was successfully used to detect nicotine in a tobacco sample from the market (average content 0.720%; RSD 0.044%; n = 11). The interference of K(+) on the optode method can be prevented by the pre-extraction procedure. Malic acid and citrate showed no interferences. The recovery of nicotine as NBD(+) was 84-119% in the range 0.035-5% nicotine. The result was satisfactory compared with an AOAC UV standard method.     

Multicolor quantum dot encoding for polymeric particle-based optical ion sensors

Multicolor quantum dot-encoded polymeric microspheres are prepared with controllable and uniform doping levels that function as chemical sensors on the basis of bulk optode theory. TOP/TOPO-capped CdSe quantum dots and CdTe quantum dots capped with CdS (lambdaem = 610 and 700 nm, lambdaex = 510 nm) are blended with a THF solution of poly(methyl methacrylate-co-decyl methacrylate), poly(n-butylacrylate), or poly(vinyl chloride) plasticized with bis(2-ethylhexyl) sebacate without a need for ligand exchange. Polymeric microspheres are generated under mild, nonreactive conditions with a particle caster that breaks down a polymer stream containing the quantum dots into fine droplets by the vibration of a piezocrystal. The resulting microspheres exhibit uniform size and fluorescence emission intensities. Fluorescent bar codes are obtained by subsequent doping of two quantum dots with different colors and mass ratios into the microspheres. A linear relationship is found between the readout fluorescence ratio of the two types of nanocrystals and the mixing ratio. Quantum dot-encoded ion sensing optode microspheres are prepared by simultaneous doping of sodium ionophore X, chromoionophore II, a lipophilic tetraphenylborate cation exchanger, and TOPO-capped CdSe/CdS quantum dot as the fluorescent label. A net positive charge of the quantum dots is found to induce an anion-exchange effect on the sensor function, and therefore, an increased concentration of the lipophilic cation exchanger is required to achieve proper ion sensing properties. The modified quantum dot-labeled sodium sensing microspheres show satisfactory sodium response between 10(-4) and 0.1 M at pH 4.8, with excellent selectivity toward common interferences. The amount of the carried positive charges of the CdSe quantum dots is estimated as 2.8 mumol/g of quantum dots used in this study.     

Aspartame optical biosensor with bienzyme-immobilized eggshell membrane and oxygen-sensitive optode membrane

An aspartame optical biosensor has been fabricated by employing a bienzyme system composed of alpha-chymotrypsin and alcohol oxidase immobilized onto an eggshell membrane and an oxygen-sensitive optode membrane as the transducer. The detection schemes involve the enzymatic reactions of aspartame leading to the depletion of the oxygen level of the medium with a concomitant enhancement of the fluorescence intensity of the oxygen-sensitive membrane. The scanning electron and transmission electron micrographs show the microstructure of the eggshell membrane which is successfully immobilized with bienzyme. Using this novel immobilization technique, the aspartame biosensor shows extremely good stability with a shelf life of at least 8 months. The rate change of the fluorescence intensity in 4 min is found to be linearly related to the concentration of aspartame. The useful analytical working range of the biosensor is from 0.056 to 3.07 mM aspartame. The effects of temperature, pH, and ionic strength on the response of the aspartame biosensor are investigated in detail. Citric acid, cyclamic acid, D-fructose, D-galactose, D-glucose, hydrogen peroxide, DL-malic acid, L-phenylalanine, saccharin, sodium benzoate, and sucrose show no interferences but ethanol interferes strongly. The aspartame biosensor has been applied to determine aspartame contents in some commercial products.     

Investigation into the applicability of the centrifugal microfluidics platform for the development of protein-ligand binding assays incorporating enhanced green fluorescent protein as a fluorescent reporter

The incorporation of a protein-ligand binding assay into a centrifugal microfluidics platform is described. The platform itself is a disc-shaped polymer substrate, upon which a series of microfluidic channels and reservoirs have been machined. Centrifugal microfluidics platforms require no internal moving parts, and fluid propulsion is achieved solely through rotation of the disc. Fluid flow is controlled by passive valves, the opening of which is dependent on the angular frequency of the rotating platform, the channel dimensions, and the physical properties of the fluid. To evaluate the effectiveness of incorporating a protein-based assay onto the centrifugal microfluidics analytical platform, a class-selective, homogeneous assay for the detection of phenothiazine antidepressants was employed. This class of drugs is known to bind to calmodulin, a calcium binding protein. Specifically, a fusion protein between calmodulin and enhanced green fluorescent protein was utilized. Calmodulin undergoes a conformational change upon binding to phenothiazines that alters the fluorescence properties of the attached fluorescent protein, which can be correlated to the concentration of the drug present. Another important aspect of this work was to study the efficacy of the platform to perform reconstitution assays. To do this, the biological reagent was dried on the platform and rehydrated to carry out the assay. The ability to prealiquot reagents on the platform should enhance its versatility and portability. The integration of protein-based assays in this platform should be useful in the design of analytical systems for high-throughput screening of pharmaceuticals and clinical diagnostics.     

聚丙烯－胰蛋白酶膜的制备与性能

讨论了用空气等离子体活化处理技术制备聚丙烯－胰蛋白酶膜的方法。研究了等离子体处理参数和接枝反应条件对聚丙烯接枝丙烯酸的接枝率和聚丙烯－胰蛋白酶固定化酶膜活力的影响。评价了聚丙烯－胰蛋白酶膜的稳定性。用ＩＲ和ＥＳＣＡ分析了接枝膜和聚丙烯－胰蛋白酶的结构与组成。     

Biodegradable optode-based nanosensors for in vivo monitoring

Optode-based fluorescent nanosensors are being developed for monitoring important disease states such as hyponatremia and diabetes. However, traditional optode-based sensors are composed of nonbiodegradable polymers such as poly(vinyl 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 similar to those of 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 h at lipase concentrations found in the liver but were present after 3 days at lipase concentrations found in serum. The development of biodegradable nanosensors is not only a positive step towards their future use in in vivo applications, but they also represent a new sensor platform that can be extended to other sensing mechanisms.     

Flow cytometric ion detection with plasticized poly(vinyl chloride) microspheres containing selective lonophores

The use of flow cytometry as a rapid, high-throughput diagnostic tool for the analysis of ions is described. Monodisperse, uniform microspheres, which obey bulk optode theory and are governed by bulk extraction processes rather than surface phenomena, were prepared under mild, nonreactive conditions using a sonic stream particle casting apparatus. As an initial example demonstrating the utility of this approach, microspheres that contained a H+-selective fluorescent chromoionophore (ETH 5294), a cation-exchanger (NaTFPB), and either a highly sodium-selective (sodium ionophore X) or a potassium-selective ionophore (BME-44) were prepared. Separate solution analysis of sodium- and potassium-selective microspheres resulted in the generation of functional response curves using peak channel fluorescence intensities. The selectivity observed for both types of particles is sufficient for the clinical determination of Na+ and K+. Furthermore, sodium- and potassium-selective microspheres were analyzed in parallel using sodium sample solutions, resulting in the successful determination of sodium ion concentrations and providing important information about the selectivity of the potassium-selective sensors over sodium. This work demonstrates the potential applicability of flow cytometry as a means for developing multiplexed, rapid, high-throughput analyses for clinically relevant ions.     

Integrated plastic microfluidic devices with ESI-MS for drug screening and residue analysis

For this work, two different plastic microfluidic devices are designed and fabricated for applications in high-throughput residue analysis of food contaminants and drug screening of small-molecule libraries. Microfluidic networks on copolyester and poly(dimethylsiloxane) substrates are fabricated by silicon template imprinting and capillary molding techniques. The first device is developed to perform affinity capture, concentration, and direct identification of targeted compounds using electrospray ionization mass spectrometry. Poly(vinylidene fluoride) membranes sandwiched between the imprinted copolyester microchannels in an integrated platform provide continuous affinity dialysis and concentration of a reaction mixture containing aflatoxin B1 antibody and aflatoxins. The second microfluidic device is composed of microchannels on the poly(dimethylsiloxane) substrates. The device is designed to perform miniaturized ultrafiltration of affinity complexes of phenobarbital antibody and barbiturates, including the sequential loading, washing, and dissociation steps. These microfabricated devices not only significantly reduce dead volume and sample consumption but also increase the detection sensitivity by at least 1-2 orders of magnitude over those reported previously. Improvements in detection sensitivity are attributed to analyte preconcentration during the affinity purification step, limited analyte dilution in the microdialysis junction, minimal sample loss, and the amenability of ESI-MS to nanoscale sample flow rates.     

The covalent grafting of fibronectin at the surface of poly(ethylene terephthalate) track-etched membranes improves adhesion of rat hepatocytes

[³H]methylated fibronectin (FN) has been immobilized on the surface of poly(ethylene terephthalate) track-etched membranes (PET), carboxylated and then activated or not with water-soluble carbodiimide (WSC). Upon washing in 10% SDS or in the nutritive medium used for hepatocytes cultivation (supplemented with 15% newborn calf serum), respectively, 76% and 43% of [³H]FN are released from the unactivated PET membranes and those WSC activated. This difference is almost totally abolished when the-NH₂ functions of FN have been fully acetylated, to impair their reaction with activated-COOH groups. These results strongly suggest that part of FN is covalently grafted to the activated-COOH of PET but that, in addition, FN is also adsorbed on this surface. Rat hepatocytes were inoculated on PET membranes on which FN had been adsorbed and/or grafted. Image analysis clearly indicates that, during the first hours of culture, the FN immobilization on WSC activated, carboxylated PET membranes, significantly favours the adhesion of hepatocytes. After 24 h, the difference between these substrates decreases, probably due to the reconditioning of the PET surface by extracellular matrix constituents secreted by the hepatocytes. Our results confirm that the nature of the protein-polymer interaction strongly affects cell behaviour.This paper was accepted for publication after the 1995 conference of the European Society of Biomaterials, Oporto, Portugal, 10–13 September.     

Laser ablation inductively coupled plasma mass spectrometry assisted insight into ion-selective membranes

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.