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Aptamer Library and Selection Aptamers vs. Find more information on the Altmetric Attention Score and how the score is calculated. In this paper, we raise questions that researchers have to ask if they intend to replace a conventional reference electrode with an ionic liquid-based reference electrode and try to answer these questions based on our experiences and literature data.

Among these questions, the most important is which ionic liquid should be used. However, beyond the chemical composition of the ionic liquid, to realize all the potential benefits of ionic-liquid based reference electrodes, there are additional, equally important considerations.

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Finally, we recommend methods to test the performance criteria of the ionic liquid-based reference electrodes. Generous gift from Professors M. Yamamoto and T. Kakiuchi; nd: not determined. The interference is expressed as response slopes measured in solutions containing interfering anions or cations in different concentrations.

The approximate concentration range is between 0. Figure 1. The numbers in the figure indicate test solutions: 1 mM NaCl, 1. The standard deviation of the potential values around the mean Figure 2. The membrane was clamped in a Philips electrode, which was secured in the wall-jet manifold as shown in the inset.

The dotted lines green indicate time intervals when the flow has been stopped. The numbers between the dashed vertical lines indicate time intervals when the test solutions, 1 mM NaCl, 1. Figure 3. Influence of the reference electrode membrane composition on its flow rate dependence. The membranes were clamped in Philips electrodes, which were secured in the wall-jet manifold as shown in the inset of Figure 2. The dotted green line between 0 and 30 min and between 90 and min indicate time periods when the electrodes were in quiescence solution or when the flow was stopped, respectively.

For better comparison the individual transients were shifted along the potential axes.

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Figure 4. In this experiment, all three electrodes were in the same beaker filled with 0. The tested membranes were fixed in Philips liquid membrane electrode bodies. Figure 5. Information on ionic liquids structures, logP values, performance characteristics, dynamic response, and synthesis PDF. The financial support from Instrumentation Laboratory IL Bedford, MA and the valuable discussions with the acute care diagnostic group at IL is gratefully acknowledged.

Yuki Onishi, in Prof. In electrochemistry the salt bridge connects two half cells. Lipophilicity and hydrophobicity are often used interchangeably but they are not synonymous. This article references 80 other publications. More by Marcin Guzinski. More by Taskia A. More by Bradford D. Cite this: ACS Sens. ACS Editors' Choice. Article Views Altmetric -. Citations 2. PDF 2 MB. Abstract High Resolution Image. In the preamble of their famous book on reference electrodes, Ives and Janz 1 expressed their intention to provide useful information for the experimentalist, some of which is difficult to track down even if the researcher traces back successively earlier references.

Our goal with this contribution is similar but much narrower in its focus; we hope to provide useful information on the critical aspects of ionic liquid-based reference electrodes without liquid junction. In these reference electrodes, room-temperature molten salts, also referred to as ionic liquids ILs or lipophilic electrolytes, comprising lipophilic cations and anions, are used as salt bridges in both free-flowing or immobilized forms, i.

These new reference electrodes, after more than years, offer a viable alternative to conventional reference electrodes with concentrated KCl solutions as salt bridge electrolyte. The trend in potentiometric analysis targets the development of simple calibration free analytical systems, e.

A LJFRE, which can be simply miniaturized, could be useful in many areas of electroanalytical chemistry, but it is expected to have a significant impact in multi analyte flow analytical systems e. Conventional reference electrodes most commonly are filled with a large volume of electrolyte solution inner filling solution, IFS , which is in contact with the sample through a flow-restricting sleeve junction, diaphragm, or frit. For a good reference electrode, the potential drop across this liquid junction liquid junction or diffusion potential is expected to be independent from the sample composition and stable in time.

With concentrated filling solutions in the reference electrodes e. With reference electrodes manufactured with nanoporous frits, however, especially in low ionic strength solutions, significant systematic errors were reported. Minute outflow of electrolyte is considered beneficial for reproducible liquid junction potentials LJP , 37 but large outflow can contaminate the sample and lead to potential drifts.

To eliminate the liquid filling solution of conventional reference electrodes, 38 reference electrodes with a variety of solidified reference electrolytes melted, gelled, embedded in a polymer matrix, etc. Although reference electrodes with solidified reference electrolyte can be implemented in microfluidic devices, 38 due to the geometrical constraints, the lifetime of these miniature reference electrodes is often limited.

If the reference electrolyte is implemented in highly cross-linked polymers for prolonged lifetime, the reference electrodes had high resistance and long equilibration times. Conventional reference electrodes have several inherent drawbacks: i leaching related sample contamination, and need for frequent renewal of the filling solution, ii clogging of the liquid junction in certain samples, and iii differences in the LJPs with different types of liquid junctions.

To overcome these problems, Horvai 39 envisioned a possible reference electrode design without liquid junction using a lipophilic salt loaded plasticized PVC membrane electrode.

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In this system, the reference electrode membrane is sandwiched between two aqueous electrolyte solutions, the sample and the IFS of the reference electrode. Such a membrane is expected to have a sample solution independent potential if the anion and cation of the lipophilic salt have moderate and comparable lipophilicities. Under these conditions, both the anion and the cation will partition into the sample and become potential determining ions eq 1. The validity of eq 1 assumes that the hydrophilic ions of the aqueous phase do not partition into the membrane.

Since eq 1 is valid for both cations and anions with z I having a positive or negative charge sign, respectively the membrane may act as a reference electrode membrane because its potential is determined by both the cations and the anions of the membrane partitioned into the aqueous sample. Instead of a lipophilic salt-loaded PVC membrane, Kakiuchi used room-temperature molten salts lately referred to as ionic liquids, ILs as separation membrane between two aqueous phases. Despite these encouraging data and all the claimed advantages of LJFREs, their spread in commercially available reference electrodes is minimal.

The advantage of conventional reference electrodes is that the potential errors related to the LJP can be estimated and a salt bridge electrolyte with minimal LJP can be selected for specific samples. For those who are considering the replacement of a conventional reference electrode with a LJFRE it would be essential to know which ionic liquid to choose, in which formulation and sensor construction, and to understand quantitatively the advantages of these novel reference electrodes in solving their own analytical problems in potentiometric, voltammetric, or coulometric analysis, impedance spectroscopy, and so forth.

In addition, we raise questions that researchers have to ask if they intend to replace a conventional reference electrode with an IL-based reference electrode. We also try to answer these questions based on our experiences and literature data. However, simultaneous with the ILs listed in Table 1 , we evaluated the performance of a variety of additional ILs.

The ILs tested were commercial products e. Kakiuchi and Yamamoto. The IL-based reference electrode responses were tested both in steady state and under variable flow conditions in a broad range of electrolyte solutions, e. Table 1. We will show that depending on the applications, a variety of ILs might be appropriate. Experimental Section. Yamamoto and Kakiuchi. The membrane cocktails were cast into a The aqueous solutions were prepared with For testing the responses of the pure ILs in liquid form, they were filled into a CHI reference electrode body with a porous glass frit on its lower end to hold the IL and separate it from the sample solution.

The responses of the IL-based LJFREs were tested in combination with commercial reference electrodes in steady and stirred or flowing solutions. For the potentiometric data acquisition, a Lawson Lab Malvern, PA channel high input impedance data acquisition system was used. The data acquisition system has been connected to a computer equipped with the EMF Suite version 2. The potentiometric measurements with the macro electrodes were performed at room temperature. Following the complete equilibration of the reference electrodes they were exposed to a variety of test solutions, which were replaced manually.

Between exposures to the different solutions, the electrodes were wiped dry with Kimwipes. The individual electrode potentials were recorded for 5 to 10 min after the electrodes were exposed to a new solution. For testing the influence of intense stirring on the potential of the LJFRE membranes, the electrode potentials were recorded upon periodically switching on and off a magnetic stirrer. For certain electrodes, the flow rate dependence was also tested in a wall jet type cell.

The sample solution was pumped perpendicularly to the center of the tested electrode surface with a Gilson Minipulse 3 peristaltic pump with adjustable flow rate. An advantage of the wall jet arrangement is that only the tested electrode is exposed the solution flow. Changes in the sample solution composition were induced with the help of a manual multiposition valve. The electrode potentials of the planar LJFREs in the flow channel were measured against conventional reference electrodes placed into this large volume KCl solution, i.

In the experiments the electrode potentials were recorded at 0. The electrode potentials during these experiments were continuously recorded. Results and Discussion.

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The theoretical and experimental challenges of assessing the performance characteristics of the IL-based reference electrodes are similar to the difficulties of pH measurement: i immeasurable nature of single ion activity coefficients, ii the differences in the determination of the pH of primary ion standards in cells without transference, Harned cell , and real samples with glass electrodes in electrochemical cells with liquid junction.

This method has been used to show the utility of IL-based reference electrodes for pH measurements in low ionic strength solutions. In pure electrolyte solutions, Kakiuchi et al. A Nernstian response of the silver halide electrodes in these experiments was considered as proof for stable, concentration independent potential of the IL-based reference electrode. Although these experiments clearly prove the validity of the assumptions related the working mechanism of the IL-based reference electrodes, they might not provide the necessary information about the utility of these electrodes for solving specific tasks.

In complex solutions, however, testing the response of a LJFRE against a silver halide electrode 53,65,66 may not be feasible. Although, instead of a silver halide electrode, one might record the response of an ion-selective electrode against the IL-based reference electrode for the assessment of the IL-based reference electrode performance, the uncertainties related to i the determination of ionic activities, and ii deviations from the assumed Nernstian response of the ISE, especially in very dilute and very concentrated solutions, cannot be eliminated.

Alternatively, similar to this work, the IL-based reference electrode responses can be compared to commercial reference electrodes with liquid junction. The gelled IL separates the sample solution and the 0. However, those who do not have access to IL13 might test the commercially available ionic liquid IL2, in which the cation is the same as in IL13 and the bis trifluoromethanesulfonyl imide — anion in IL2 differs from the bis pentafluoroethanesulfonyl imide — anion of IL13 only by two difluoromethylene CF 2 groups. Indeed, Kakiuichi et al.

Among the ILs and lipophilic electrolytes, IL1 and its derivatives are probably the most commonly used as water immiscible salt bridge electrolytes or as the key ingredient in plasticized PVC membranes 44,45,54 or other gelling polymers 2,48 for liquid junction free reference electrodes with both solid and liquid contact. For example, Cicmil et al.

The authors used the IL1 derivatives in a range of electrochemical experiments direct potentiometry, potentiometric titrations, cyclic voltammetry, impedance spectroscopy and found the 1-ethylmethylimidazolium salt the most promising. In contrast to most of other studies on IL-based reference electrodes, in this work, we tested the potential responses of a variety of IL-based reference electrodes i.

As we discussed in the introduction, from the information published in the literature, e. Some of the ionic liquids were slightly hydrophilic e. As shown in Tables S2 and S3 , the potential of these IL-based reference electrode membranes is independent of the solution concentration.

The minor differences in the response slopes of membranes cast with or without plasticizers or using the different ILs in the membranes are statistically not significant.

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Apparently, the structure and the lipophilicity of the ILs or the composition of the IL-based membrane hardly influences the response behavior of these reference electrodes in pure NaCl or KCl solutions. As we will show later, beyond evaluating the IL-based reference electrodes in pure electrolyte solutions at steady state, as is done in most papers reporting on the LJFREs, it is important to evaluate their behavior in complex solutions and test the flow rate dependence of the reference electrode potential.

Among the drawbacks of the IL-based LJFREs, the interference of highly lipophilic anions and cations and the presence of ionic surfactants are considered the most serious. As seen in Table 2 in the presence of hydrophobic ions, there are significant differences between the IL-based reference electrode membrane responses. The 1. On the other hand, the membranes loaded with the highly hydrophobic IL3 showed a concentration dependent salicylate response.

Table 2. The differences in the level of interference induced by benzalkonium chloride on the IL-loaded membranes were even more significant. The membranes cast with IL3 showed close to Nernstian cationic response to benzalkonium chloride Table 2. Compared to the reference electrode membranes cast with the hydrophobic ionic liquids, the level of interference induced by the benzalkonium cations was small or negligible with membranes in which the ionic liquids were moderately hydrophobic and had finite solubility IL1, IL2, and IL Among the reference electrode membranes, the interference was more significant for those which were cast with plasticizer.

Such large differences in the response slopes were not experienced with other IL-based membranes. It was assumed that the batch-to-batch inconsistency in the level of salicylate interference was a consequence of small differences in the purity of IL3, e. In agreement of this assumption, the significant salicylate interference experienced with certain batches of IL3 gradually diminished after soaking the IL3-loaded membranes in 0.

To test this hypothesis, reference electrode membranes were cast from the batch of IL3, which showed significant salicylate interference, with additional 0. Related to interferences induced by sample anions and cations, it would be important to understand the sources of the differences in the levels of interference experienced with membranes of different compositions, e.

Kakiuchi recommended repeating the washing step 30 times 66 and testing the washing water for traces of chloride by adding a few drops of AgNO 3 to the solution until no precipitation is observed. In summary, deviations from the stoichiometric composition or presence of impurities in the ionic liquids, or in the components of the polymers utilized to immobilize the ILs, may have detrimental influence on the performance of IL-based reference electrode membranes.

The requirements for a generally applicable reference electrode beyond stable, reproducible, sample composition, and concentration independent potential are short equilibration time and insensitivity to solution movement changes in the rate and direction of flow. The importance of short equilibration time and flow rate independent potential are probably most important in integrated, multianalyte, flow analytical systems, e. In flow analytical methods with potentiometric detectors, it is assumed that the potential transients recorded during changes in the compositions of the samples are dominated by the dynamic response of the indicator electrode.

However, these assumptions are not always true because time dependent changes in the LJP may distort the potential transients 76 and bias the equilibrium potentials. When the concentration, composition, or flow conditions of the solution in contact with an IL-based reference electrode membrane are changed, a new phase boundary potential is established across its interface with the sample. In many practical applications, however, only a quasi-distribution equilibrium is established within a diffusion layer. High Resolution Image. As seen in the figure, the equilibration processes following changes in the composition of the sample solution are sluggish, but the potential values measured after about 5 min equilibration time appear to be independent from the solution composition.

The standard deviation of the data, measured after 5 min, was less than 0. Mattinen 50 reported similarly slow transients and concentration independent potential values after approximately 5 min equilibration with By repeating the experiment in a wall jet type flow cell Figure 2 the recorded potential had significant flow rate dependence with extremely slow equilibration about 60 min following changes in the flow rate. However, once the reference membrane potential, corresponding to a given flow rate, stabilized, changes in the solution composition hardly influenced the measured potential.

The standard deviation of the potential values measured in solutions 1, 2, and 3 was 0. While the sample composition and concentration dependence of the phase boundary potential at the interface of IL-based reference electrode membranes are discussed in detail in several publications, to the best of our knowledge, the flow rate dependence of these potentials and their significance in the utility of the IL-based reference electrodes was not studied systematically. In contrast, it is difficult to find any information on the dynamic response of IL-based reference electrodes or on the performance characteristics of these electrodes in flow analytical systems.

Tracing the source of the potential transients recorded with the LJFREs is also not straightforward because the reported data were measured with different i methods differences in the application of activity steps 77 ; ii experimental conditions e. We also recorded the flow rate dependence of the reference electrode membrane in which IL13 was incorporated in P VdFHFP as membrane matrix and assessed the flow sensitivity of a reference electrode in which IL2 was used in liquid form, i.

The flow rate dependence of the IL13 loaded PVC membranes cast both with and without plasticizer was also negligible. However, these membranes showed a slight negative drift between 0. The flow rate dependence of the reference electrode in which IL2 was utilized in its liquid form in combination with a glass frit to separate from the solution was also negligible not shown. In this contest, it is important to note that the reproducibility of the transients recorded in repeated experiments with significant time delay between the experiments days or weeks was poor.

Without specific experimental evidence, we assumed that the poor reproducibility is a consequence of the reference electrode membrane composition changing during the excessive soaking, i. When a LJFRE membrane is brought into contact with an aqueous solution, a distribution equilibrium is established with a diffuse layer of charges. The potential of an IL-based membrane is a function of this distribution and termed as distribution potential.

The flow rate dependence of the LJFRE potential is related to the time dependent establishment of a new equilibrium or steady state distribution concentration profile at the reference electrode membrane surface. Related to the significant flow rate dependence of certain IL-based reference electrode membranes, we assessed the flow rate dependence of a reference electrode system recommended by Nagy et al.

As can be seen from Figure S1 the mean of the potential values of the cation and anion exchanger membranes in all four solutions are the same as the potential values measured with the IL3 TDDA-TPFPhB loaded membrane in the same solutions and both are independent from the NaCl concentration. The shortcomings of this arrangement are related to deviations from the Nernstian response of the anion and cation exchanger membrane in the presence of different ions, as discussed in detail by Bakker. The electrodes with ion-exchanger membranes Figure 4 a,b , similar to other ion-selective electrodes, do not have flow rate dependence because the phase boundary potentials, in contrast to the LJFRE membranes, are determined by the high exchange current densities of solution anions or cations.

Consequently, when the two ion exchanger-based electrodes were connected parallel, the resulting potential was also independent from flow rate Figure 4 d. Apparently, the exudation of plasticizer and ionic liquid from the reference electrode membranes, loaded with both ionic liquid and oNPOE, is significantly larger than previously reported for conventional plasticized PVC membranes cast without additional ionic liquid. Only membranes with significant loss of mass showed substantial flow rate dependence.

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Apparently, the level of flow rate dependence is correlated with the mass loss of membrane ingredients, which has been observed only with the plasticized, IL-loaded PVC membranes. Consequently, preventing this disruption should eliminate the flow rate dependence.

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As we show in Figure 5 , this mass transport controlling filter paper almost completely eliminated the flow rate dependence of the reference electrode potential. So, the membrane potential becomes independent from the flow rate. Reference electrodes with liquid junction are often the major source of the uncertainties in potentiometric measurements. Based on the published data and our results summarized in this paper, IL-based reference electrodes offer significant potential advantages in a variety of applications over conventional reference electrodes with liquid junction.

However, before their use, it is important to establish the required performance criteria and assess whether these criteria can be met with the IL-based reference electrodes in specific applications. Due to the significant differences in the required performance criteria and the applications, one cannot offer an IL-based reference electrode that would be ideal for all the tasks where reference electrodes are implemented. However, there are guidelines that should help in selecting an IL-based reference electrode and there are relatively simple experiments that would allow at least preliminary assessment of each specified criterion.

In our view, one of the most significant advantages of the IL-based reference electrodes is that they can be miniaturized without compromising their performance, although the small-sized electrodes have shorter lifetime. An additional benefit of the IL-based reference electrodes is that they can easily be integrated into multianalyte sensor arrays or microfluidic systems with miniaturized ionophore-based liquid membrane ion-selective electrodes using the same fabrication technology.

On the other hand, we consider the flow rate dependence of certain reference membrane formulations a significant disadvantage. However, as we have shown in this paper, through the optimization of the reference electrode membrane or the reference electrode construction the flow rate dependence can be minimized or eliminated. Finally, when ionic liquid-based reference electrodes are aimed for specific practical application, some information about the presence of highly lipophilic anions, cations, and surfactant molecules in the sample is essential for reliable assessment of the expected interference induced by these interfering compounds on the reference electrode potential.

Indeed, this is similar to measurements with conventional reference electrodes where information on the sample composition and the mobility of the individual ions in the potential samples is essential for estimating the magnitude of the diffusion potentials. In our experience, the reference electrodes made with almost any ionic liquid in which the anion and cation lipophilicities are similar had stable, reproducible sample composition independent potential values in pure salt solutions, e.

However, as we show in our paper, one should not claim the utility of a novel IL-based reference electrode based on measurements only in quiescent pure electrolyte solutions. Considering all the assessments in this work, the reference electrode membranes loaded with IL13 performed the best. Although IL2 and IL13 have very similar chemical structures, the potential of the ILbased reference electrode membranes was less influenced if at all by highly lipophilic sample ions or by changes in the movement of the solution.

Although the superior performance of the IL13 based reference electrodes may be related to the slightly more lipophilic property of IL13 compared to IL2, we assume that it is rather related to the greater purity of IL13 as confirmed by liquid chromatography compared to its commercially available counterpart IL2. Although the performance characteristics of the reference electrodes with free-flowing ILs were satisfactory, they might be impractical in certain applications where the LJFREs might have unique advantages.

The possibility of incorporating ionic liquids into a PVC matrix is very attractive due to the similarities between the ion-selective and reference electrode membrane fabrication process. On the other hand, the reference electrode membranes in which the ionic liquid serves both as the plasticizer of the PVC-based membranes and as its key ingredient providing sample solution independent potential have very promising performance characteristics. The only disadvantage of these plasticizer free PVC membranes is that they are quite rigid and have relatively large resistance.

Supporting Information. The authors declare no competing financial interest. Reference Electrodes, Theory and Practice. Academic Press : New York, London , A new salt bridge based on the hydrophobic room-temperature molten salt. Chemical Society of Japan. A conceptually new salt bridge based on a hydrophobic room-temp. KCl phase. The phase-boundary potential between the interface is detd. The gelation of the molten salt phase does not affect the phase-boundary potential. The new salt bridge is free from most of the problems inherent to KCl-based salt bridges. Phase-boundary potential across the nonpolarized interface between the room-temperature molten salt and water.

Elsevier Science B. The phase-boundary potential across the interface between an aq. The phase-boundary potential across the interface is detd. The interfaces exptl. By changing the concn. That a normal saturated KCl solution the diffusion potential between two diluted solutions degrades 3. Author compares the water reaction of a saturated and a halfsaturated KCl solution with one another. The errors of the extrapolated values are at the most from the order of magnitude of the difference between measurements with the two strong KCl solutions. Usually extrapolation is to strong.

But extrapolation seems to be more favorably or at least just as favorable as the simple use of the value received with the saturated KCl solution or the computation after PLANCK. Finally author sets up a formula for the diffusion potential between a strong KCl and diluted solution of monovalent strong electrolytes. The mathematical derivation must be seen in the original. An exact computation of the potential differences arising between KCl solutions is hardly possible, since the transport number of the KCl in more highly concentrated solutions is not exactly known.

In the emergency one knows the KCl solution by a concentrated mixture of strong electrolytes replace, if only the sum of the migration speed that multiplies anions by their concentrations equal the size concerned of the cations is for the example 86 mole KNO3 14 mole NaNO3. Likewise one could eliminate the error, which depends on the transport number of the KCl, by an addition. It closes: Since after the theoretical computation a saturated solution destroys the influence of the diluted solution hardly twice as strongly, like a half-saturated, and this theory with it in all other respects tunes, seems experiments there legitimate to expect from the electrode potential found with saturated KCl solution by addition of the difference between this potential and with half-saturated a found still better number.

This paper is intended to show that Planck's formula is applicable to a cell of the type MnO2 Acid KCl Acid MnO2 and that the electromotive force of these cells differs from that of the combination MnO2 Acid Acid MnO2 chiefly by the potential difference between the acid solutions in the latter case. His experiments confirm both conclusions fairly well, the error being about one millivolt in a total of thirty. Sodium chloride satisfies the second conclusion better than potassium chloride, rather to the author's surprise.

The author has not shown that Planck's formula requires the second conclusion to be fulfilled when the migration velocities of the cation and anion are equal in the salt solution; but assumes it as self-evident. One interesting fact appears in the paper, that Zn Zn NO3 2 does not give a constant potential difference. The author does not refer this to the action of metallic zinc on zinc nitrate as he should.

It would be interesting to know what hypothesis could be devised in respect to which the experiment recorded in table 10, page , could prove anything either way. American Chemical Society. Novel ref. After a short period of soaking in a KBr soln. The described ref. These electrodes can also be fabricated in miniaturized form, and thus used to produce miniaturized multielectrode probes.

An analytical quality solid-state composite reference electrode. Analyst , 18 , — , DOI: Royal Society of Chemistry. A all-solid-state ref. A rigorous testing procedure was used to reveal the possible influence of pH, soln. The tests demonstrated the insensitivity of the electrodes to the matrix effects, excellent stability of the potential readings, and significantly reduced leakage of inorg.

In the performed tests the composite ref. The ref. Ready-to-use single-strip paper based sensor for multiplex ion detection. Actuators, B , , — , DOI: Armas, Stephanie M. Elsevier B. Ion-selective electrodes ISEs are an efficient and versatile tool for ion detection. However, portability and applicability for field applications are often limited by the need of a conditioning step, and high cost of the needed bulky ref.

ILs to create and maintain a stable potential that is un-affected by a change in ionic activity. Low-cost and reagent-free paper-based device to detect chloride ions in serum and sweat. Talanta , , — , DOI: The recent goal of sustainability in anal. Due to the recent focus in sustainability, the authors report the use of low-cost filter paper as a sustainable material to print silver electrodes and to load reagents for a reagent-free electrochem.

The electrochem. During the oxidn. Chloride ions were detected with the addn. Moreover, the results achieved with the paper-based device were pos. Paper-based microfluidic sampling and separation of analytes for potentiometric ion sensing. This work demonstrates a paper-based microfluidic sampling and sepn. The device was composed of two pieces of paper with different shapes and pore sizes. A filter paper with a pore size of 2. The two pieces of the paper were joined together just like a jigsaw. A solid-contact Cl- -selective electrode and a ref.

This system offers a convenient platform for both sampling and sepn. Current paper-based potentiometric ion-sensing platforms are planar devices used for clin. These devices, however, have not been designed for the potentiometric biosensing of proteins or small mol. A three-dimensional origami paper-based device, in which a solid-contact ion-selective electrode is integrated with an all-solid-state ref.

The device is made by impregnation of paper with appropriate bioreceptors and reporting reagents on different zones. By folding and unfolding the paper structures, versatile potentiometric bioassays can be performed. A USB-controlled miniaturized electrochem. Using butyrylcholinesterase as a model enzyme, the device has been successfully applied to the detection of enzyme activities and organophosphate pesticides involved in the enzymic system as inhibitors.

The proposed 3D origami paper device allows the potentiometric biosensing of proteins and small mols. Ion-selective electrodes ISEs are widely used tools for fast and accurate ion sensing. Herein their design is simplified by embedding a potentiometric cell into paper, complete with an ISE, a ref. The disposable planar paper-based ion-sensing platform is suitable for low-cost point-of-care and in-field testing applications. The design is sym. For a demonstration of clin. The single-use devices can be fabricated by a scalable method, do not need any pretreatment prior to use, and only require a sample vol.

Paper-Based Potentiometric Ion Sensing. This paper describes the design and fabrication of ion-sensing electrochem. Ion-sensing EPADs use printed wax barriers to define electrochem. Single-layer EPADs for sensing of chloride ions include wax-defined sample and ref. After the addn. Ion-selective EPADs provide a portable, inexpensive, and disposable way of measuring concns. Paper-based microfluidic sampling for potentiometric determination of ions. In this work, paper-based microfluidic sampling was used together with potentiometric detn. Calibration solns.

The paper substrate was found to influence the detn. Paper-based microfluidic sampling was successfully applied in measurements of pH in various foodstuffs and environmental samples by employing a conventional pH glass electrode. However, some influence of the paper substrate on the measured pH was obsd. Despite some limitations, paper-based microfluidic sampling with potentiometric sensing opens new possibilities for direct chem. The method described in this work is particularly interesting for anal. Xavier; Andrade, Francisco J.

A new approach to develop ultra low-cost, robust, rugged, and disposable potentiometric sensors is presented. A suspension of carbon nanotubes in a water-surfactant mixt. The electrodes are made by drop casting a membrane on a small circular area of the conductive paper. In this way, the carbon nanotubes act as both elec. In all cases, the anal. This opens new avenues for very low-cost platforms for generation of chem.

Devices are built on std. Ion sensing has been achieved within s by simple addn. The individual single-use sensing devices showed near Nernstian response of The current work demonstrates the promising possibility of obtaining low-cost and disposable paper-based potentiometric sensing devices potentially manufacturable at large scales with industrial inkjet printing technol.

Few-layer graphene and polyaniline composite as ion-to-electron transducer in silicone rubber solid-contact ion-selective electrodes. We have used for the first time a composite consisting of few-layer exfoliated graphene and elec. The drop cast transducer deposited from the graphene-PANI dispersion in N-methylpyrrolidone makes use of the synergistic effect of these two materials.

It maintains the ion-to-electron transduction which is characteristic for the elec. Guzinski, Marcin; Jarvis, Jennifer M. The aim of this study was to find a conducting polymer-based solid contact SC for ion-selective electrodes ISEs that could become the ultimate, generally applicable SC, which in combination with all kinds of ion-selective membranes ISMs would match the performance characteristics of conventional ISEs.

The accumulation of an aq. Although there is a test for the presence of an undesirable water layer, if the conditions for this test are not selected properly, it does not provide an unambiguous answer. However, recording the potential drifts of SC electrodes with pH-sensitive membranes in samples with different CO2 levels can effectively prove the presence or absence of a water layer in a short time period.

Electropolymerized hydrophobic polyazulene as solid-contacts in potassium-selective electrodes. Analyst , 10 , — , DOI: The effectiveness of the redox buffer-free approach presented here in stabilizing E0 is strengthened by the absence of light, oxygen and carbon dioxide sensitivity of the PAz SC-ISEs. No evidence was found for the formation of an aq. In terms of the specific application, the PAz solid contact ISEs were found to show a remarkably good potential stability at their first contact with an aq. Overall, the PAz solid contact shows significant advantages as compared to the state-of-the-art of elec.

Hu, Jinbo; Ho, Kieu T. Here, all-solid-state ref. Such a ref.

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Due to the intrinsic properties of CIM carbon, ref. The potential drift of CIM carbon-based ref. To demonstrate the compatibility of CIM carbon-based ref. These sensing devices are inexpensive, easy to use, and offer highly reproducible Cl- measurements with sample vols. Electroanalysis , 30 , — , DOI: