Increasing the Sensitivity of pH Glass Electrodes with Constant Potential Coulometry at Zero Current.

It has recently become possible to increase the sensitivity of ion-selective electrodes (ISEs) by imposing a constant cell potential, allowing one to record current spikes with a capacitor placed in series in the circuit. The approach requires a transient current to pass through the measurement cell, which unfortunately may introduce measurement errors and additionally excludes the use of high-impedance indicator electrodes, such as pH glass electrodes. We present here an electronic circuit that overcomes these limitations, where the cell is measured at zero current in combination with a voltage follower, and the current spike and capacitor charging occur entirely within the instrument. The approach avoids the need for a counter electrode, and one may use any electrode useful in potentiometry regardless of its impedance. The characteristics of the circuit were found to approach ideality when evaluated with either an external potential source or an Ag/AgCl electrode. The current may be linearized and extrapolated to further reduce the measurement time. The circuit is further tested with the most common yet very challenging electrode, the pH glass electrode. A precision of 64 µpH was obtained for 0.01 pH change up to 0.05 from a reference solution. Similar pH changes were also measured reliably further away from the reference solution (0.5-0.55) and resulted in a precision of 377 µpH. The limitations of this experimental setup were explored by performing pH calibrations within the measuring range of the probe.

Ion transfer mediated by TEMPO in ionophore-doped thin films for multi-ion sensing by cyclic voltammetry.

We report here on the development of thin-layer ion-selective membranes containing lipophilic TEMPO as a phase-transfer redox mediator for the simultaneous detection of non-redoxactive ions. This redox probe was recently introduced by our group and provides ideal ion-transfer waves when the membrane is interrogated by cyclic voltammetry. To perform multianalyte detection in the same sensing film, plasticized PVC-based membranes were doped with lithium and potassium ionophores in addition to a lipophilic cation-exchanger. The ionophores allow for ion discrimination owing to the different ionophore-cation complexation constants and the oxidation of TEMPO to the oxoammonium form results in the selective transfer of lithium and potassium at different potentials. The resulting voltammograms have half-peak widths of 100 and 102 mV, and the peak separation between anodic and cathodic scans is 8 and 9 mV for lithium and potassium, respectively, close to theoretical expectations. High peak resolution was observed, and the ion-transfer waves are still distinguishable when the ion activities differ by three orders of magnitude. These parameters are remarkably better than those obtained with other redox probes, which is important for multianalyte detection in the same voltammetric scan. Optimized membranes showed independent Nernstian shifts (slopes of 59.23 mV and 54.8 mV for K+ and Li+, respectively) of the peak position for increasing ion concentrations. An idealized model for two ionophore-based membranes combining redox and phase-boundary potentials was applied to the proposed system with excellent correlation. Potassium and lithium ions were simultaneously detected in undiluted human serum samples with good accuracy and precision.

Heath-related quality of life and functional outcomes in patients with congenital or juvenile idiopathic scoliosis after an average follow-up of 25 years: a cohort study.

BACKGROUND CONTEXT: Congenital and juvenile scoliosis are both early-onset deformities that develop before the age of 10. Children are treated to prevent curve progression and problems in adulthood such as back pain and a decreased quality of life but literature on long-term outcomes remains scarce. PURPOSE: To evaluate the health-related quality of life (HRQoL) and potential disability of children with congenital scoliosis (CS) or juvenile idiopathic scoliosis (JIS) after a minimum of 20 years follow-up. STUDY DESIGN: Comparative cohort study. PATIENT SAMPLE: A consecutive cohort of CS and JIS patients were retrospectively identified from a single-center scoliosis database. Patients born between 1968 and 1981 and treated during skeletal growth were eligible for participation. OUTCOME MEASURES: HRQoL (SF-36, SRS-22r, ODI). METHODS: The primary aim was to evaluate the HRQoL of CS and JIS patients using the general SF-36 questionnaire. Both patient cohorts were compared with age-matched national norms. The secondary aim was to analyze the differences between conservatively and surgically treated patients using the scoliosis-specific Scoliosis Research Society-22r questionnaire (SRS-22r) and the Oswestry Disability Index (ODI). T-tests were used for statistical comparison. RESULTS: In total, 114 patients (67% of the eligible patients) completed the questionnaire, with a mean follow-up of 25.5±5.5 years after their final clinical follow-up. Twenty-nine patients with CS were included with a mean age of 44.4±3.8 years (79.3% female), and 85 patients with JIS with a mean age of 43.7±4.2 years (89.4% female). Of the SF-36 domains, only the vitality score (60.6±18.0 for CS and 58.1±17.6 for JIS cohort) and mental health score (70.0±18.4 for CS and 72.1±18.1 for JIS cohort) were significantly lower compared with the general population (68.6±19.3 for vitality, and 76.8±17.4 for mental health). These decreased scores were larger than the determined minimum clinically important difference threshold of 4.37. Surgically treated JIS patients had a significantly lower score on the SRS-22r pain domain than their nonsurgically treated peers (3.6±0.9 vs 4.1±0.7l p=.019). Surgically treated CS patients had a significantly higher score on the SRS-22r mental health domain than their nonsurgically treated peers (4.3±0.5 vs 3.5±1.0; p=.023). No significant differences were found in the other domains. CONCLUSIONS: Except for vitality and mental health domains, congenital and juvenile idiopathic scoliosis patients treated during skeletal growth had similar HRQoL on most SF-36 domains in adulthood compared with national norms. Surgical treated JIS patients experienced more pain compared with brace treated patients, while braced CS patients had a significantly lower mental scores compared with surgical treated patients. These long-term outcomes are essential to inform patients and can guide shared decision-making between clinicians and patients.

Avoiding Potential Pitfalls in Designing Wired Glucose Biosensors.

Glucose sensing has been studied for more than half a century, leading many to believe that further progress comes mainly from engineering efforts. Our society requires robust, reliable, compact, and easy-to-use sensing solutions for decentralized applications such as wearables, and engineering solutions are essential. However, true progress is only possible by understanding and improving the underlying working principles and fundamental limitations. This Perspective discusses the delicate relationship between the observed current and glucose concentration when using wired enzyme biosensors. Some of the potential pitfalls often encountered in the recent literature are discussed. These include the need to suppress the influence of enzyme turnover kinetics on the sensor signal and the undesired faradaic charging of the electron transfer mediator that gives a continuously decaying baseline signal. These fundamental issues must be carefully evaluated and resolved for the realization of continuously operating enzyme biosensor systems.

Distance-Based Self-Powered Signal Transduction of Ion-Selective Electrodes to an Electronic Paper Display Array.

In this article, we report on the first distance-based readout self-powered potentiometric sensor. The approach is considered more user-friendly for detection by the naked eye and is less prone to optical interferences compared with a direct observation of the pixel darkening. pH-selective electrodes were chosen as a model system to demonstrate the principle in which seven bar-shaped pixels connected in series on one e-paper share one common ground. By connecting each of the pixels serially to capacitors of different capacitances, the fraction of the measurement cell voltage loaded onto the pixels becomes controllable. Consequently, the pixels give different gray values when powered by the same ion-selective electrode (ISE). As a result, the pH information on the sample is visualized as a distance-based signal and the dependence between the capacitance and 1/K (the reciprocal slope in the relationship between absorbance and pH) was constructed. In the current system, a 1 µF capacitance difference changes the value of 1/K by 4.18. With the current setup, the pH accuracy is about 0.5 when comparing the e-paper output to a color card.

Self-Powered Potentiometric Sensor Based on a Passive Signal Amplifier with Electronic Paper Display.

Self-powered potentiometric sensors are attractive because of their simple operation, low cost, fast response, and ability to be integrated with electronic components. Self-powered potentiometric sensors that give a direct colorimetric output are especially interesting, because no power supply is needed, which dramatically reduces waste. Recently reported work from our group using an electronic paper display, however, exhibits limitations, because the visualization of small pH changes is difficult. A self-powered ion-selective potentiometric sensor is introduced here that may amplify the e-paper pixel sensitivity by improving the self-powered circuit. The voltage is amplified by changing the circuit from incorporating parallel to incorporating serial capacitors. With three such capacitors, a greatly improved sensitivity is observed, amplifying the absorbance 3-fold. A portable device is realized that changes the position of the capacitors from parallel to serial through a simple mechanical sliding action. As a result, the pH information on the sample is more easily visualized with a pH uncertainty of about 0.1 when comparing the e-paper output to a color card.

Reliability of 2D video analysis assessing running kinematic variables in patients with exercise-related leg pain in a primary care practice.

BACKGROUND: Suboptimal lower limb and trunk positionings is known to influence exercise-related leg pain (ERLP). It is unknown whether simple 2D video analysis is useful for recording and interpreting running variables in a primary care practice. RESEARCH QUESTION: Is 2D video analysis a reliable instrument to assess running variables in patients with ERLP in a primary care practice? METHODS: Participants undergoing an evaluation for ERLP in two primary care practices were studied. In this reliability study, analysis of running variables was performed by 4 blinded raters on one-stride videos captured with non-high speed cameras (30 fps). Intraclass correlation coefficients (two-way random; ICC 2,1) were calculated to determine the inter-rater reliability. The intra-rater reliability was presented by ICC type two-way mixed (3,1). Footstrike pattern was analyzed by calculating the Fleiss' kappa for inter-rater agreement and Cohen's kappa for intra-rater agreement. Sample size calculation indicated that 16 participants would be required for answering the research question. RESULTS: Data of all 16 participants (9 males, age 31 ± 10 yr) were of sufficient quality for analysis. The 2D video analysis demonstrated excellent inter-rater reliability with an overall ICC value of 0.999 (95 % CI = 0.998-0.999). The ICC value of the eversion was 0.384 (95 % CI = 0.148-0.66) and after correction of the systematic error, 0.817 (95 % CI = 0.664-0.922). The agreement on footstrike was substantial with a Fleiss kappa of 0.737. The overall intra-rater reliability was excellent with an ICC value of 0.997 (95 % CI = 0.996-0.997). The intra-rater agreement of the footstrike was excellent with a Cohen's kappa of 0.868. SIGNIFICANCE: 2D video analysis provides a highly reliable, relative inexpensive, feasible and suitable measuring instrument for determining running variables in patients ERLP in a primary care setting. This simple technique may identify possible running variables associated with different types of ERLP and may serve as an instrument for tailor-made gait retraining programs.

Measuring Adherence to Pulmonary Rehabilitation: A Prospective Validation Study of the Dutch Version of the Rehabilitation Adherence Measure for Athletic Training (RAdMAT-NL).

Purpose: Measuring exercise adherence is important in patients with chronic obstructive pulmonary disease (COPD). For this, the Rehabilitation Adherence Measure for Athletic Training (RAdMAT) seems to be a promising instrument, and a Dutch version (RAdMAT-NL) is available. The aim of this study was to explore the dimensionality and construct validity of the RAdMAT-NL in patients with COPD. Secondly, we examined whether the items of the RAdMAT-NL could be summed to a single score. Patients and Methods: This prospective study included 193 patients with COPD from 53 primary physiotherapy practices in The Netherlands and Belgium. Patients and their physiotherapist provided data including the RAdMAT-NL, at one, two, and three months after inclusion. Horn's parallel analysis and exploratory factor analysis (EFA) were used to assess the dimensionality of the RAdMAT-NL. Fit to the dichotomous Rasch model for measurement was used to confirm the unidimensionality of the extracted RAdMAT-NL subscales and total scale. To evaluate construct validity, Spearman correlations with other indicators of adherence were calculated, including SIRAS score, percentage attendance and change in exercise skills. Results: EFA identified two dimensions of the RAdMAT-NL, "Participation" (13 items) and "Communication" (3 items), explaining 50.8% of the total variance. Rasch analysis confirmed the unidimensionality of the two dimensions. The unidimensional Rasch model was rejected for a summed score of all 16 RAdMAT-NL items. Medium to large significant positive correlations between the RAdMAT-NL subscale participation and different measures of adherence supported its convergent validity. Conclusion: The RAdMAT-NL exhibited two subscales that fitted the unidimensional Rasch model for objective measurement. Construct validity was supported by convergence with other established measures of adherence.

Correction: A submersible probe with in-line calibration and a symmetrical reference element for continuous direct nitrate concentration measurements.

Correction for 'A submersible probe with in-line calibration and a symmetrical reference element for continuous direct nitrate concentration measurements' by Tara Forrest et al., Environ. Sci.: Processes Impacts, 2023, 25, 519-530, https://doi.org/10.1039/D2EM00341D.

Feasibility, effectiveness and safety of self-management in pulmonary rehabilitation: a study protocol using a hybrid type 1 effectiveness-implementation design.

Background: As population ageing accelerates worldwide, chronic diseases will place an increasing burden on society and healthcare systems. Self-management interventions may become a key strategy for addressing chronic disease burden and healthcare costs, also in pulmonary rehabilitation (PR). One of the challenges here is long-term adherence. Understanding the level of adherence to PR may help inform clinical decision-making to focus more on self-management and less on clinical supervision. For this reason, a prediction model (PATCH) was developed. The presented protocol concerns a study that aims 1. to evaluate the safety and effectiveness of self-management within pulmonary rehabilitation (PR) on health outcomes in patients with chronic obstructive pulmonary disease (COPD), 2. to evaluate the predictive validity of the PATCH tool, and 3. to evaluate feasibility and acceptability of self-management and the PATCH tool by patients and physiotherapists. Methods and analysis: This is a protocol of a hybrid type 1 effectiveness-implementation design, performed in primary physiotherapy practices in The Netherlands. The aim is to include 108 patients with COPD who have already followed PR for at least six weeks (maintenance stage of PR). According to the Dutch KNGF Guideline COPD, physiotherapists should reduce the number of supervised treatments after the maintenance phase and support self-management. In practice, this does not (always) happen. This protocol is based on implementing guideline advice: clinical supervision will be halved but patients are stimulated to engage in self-management by exercising unsupervised, leading to no change in the total planned exercise frequency. During the supervised sessions physiotherapists will assess and stimulate self-management. At baseline, and after 3, 6, 9 and 12 months, health outcomes (including adherence) will be evaluated as the primary outcome of this study. At each measurement, the physiotherapist will decide on the basis of individual scores whether the patient needs more clinical supervision or not. Secondary outcomes are the discriminatory power of the PATCH tool (can patients be correctly classified as adherent or non-adherent), and feasibility and acceptability of self-management and the PATCH tool by patients and physiotherapists. Questionnaires and semi-structured interviews will be used for assessment of the outcomes.Trial registration number: METc 2023/074.

Prognostic factors of adherence to home-based exercise therapy in patients with chronic diseases: A systematic review and meta-analysis.

Background: Patients with a chronic disease may have an increased risk of non-adherence to prescribed home-based exercise therapy. We performed a systematic review with the aim to identify variables associated with adherence to home-based exercise therapy in patients with chronic diseases and to grade the quality of evidence for the association between these prognostic factors and adherence. Methods: Cohort studies, cross-sectional studies and the experimental arm of randomized trials were identified using a search strategy applied to PubMed, Embase, PsychINFO and CINAHL from inception until August 1, 2022. We included studies with participants ≥18 years with a chronic disease as an indication for home-based exercise therapy and providing data on prognostic factors of adherence to home-based exercise. To structure the data, we categorized the identified prognostic factors into the five WHO-domains; (1) Patient-related, (2) Social/economic, (3) Therapy-related, (4) Condition-related, and (5) Health system factors. Risk of bias was assessed using the Quality in Prognostic Studies (QUIPS) tool. Prognostic factors of adherence were identified and the quality of the evidence between the prognostic factors and adherence were graded using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) framework for predictor studies. We performed a meta-analysis of the obtained information. Results: A total of 57 studies were included. Within patient-related factors moderate- and high-quality evidence suggested that more self-efficacy, exercise history, motivation and perceived behavioral control predicted higher adherence. Within social-economic factors moderate-quality evidence suggested more education and physical health to be predictive of higher adherence and within condition-related factors moderate- and low-quality evidence suggested that less comorbidities, depression and fatigue predicted higher adherence. For the domains therapy-related and health-system factors there was not enough information to determine the quality evidence of the prognostic factors. Conclusion: These findings might aid the development of future home-based exercise programs as well as the identification of individuals who may require extra support to benefit from prescribed home-based exercise therapy. Systematic Review Registration: https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=277003, identifier PROSPERO CRD42021277003.

Development and Validation of a Multivariable Exercise Adherence Prediction Model for Patients with COPD: A Prospective Cohort Study.

Purpose: Pulmonary rehabilitation (PR) is considered a cost-effective method of improving health-related quality of life in patients with chronic obstructive pulmonary disease (COPD). However, increasing demand and increasing costs of supply demands for sustainable and affordable care. One of the possible solutions to keep care affordable is self-management. A challenge here is non-adherence. Understanding who are adherent and who are non-adherent could be helpful to differentiate between patients who need more or less support. Therefore, the aim of this study was to develop and validate a model to predict adherence to PR in patients with COPD. Patients and methods: A multivariable logistic regression model for exercise adherence was developed. Eight candidate predictors, that were prespecified, were obtained in a prospective cohort study from 196 patients with COPD following PR in 53 primary physiotherapy practices in the Netherlands and Belgium, between January 2021 and August 2022. To create a parsimonious model, variable selection using backward selection was performed with a p-value of >0.05 for elimination. Model performance was assessed by discrimination, calibration and clinical utility. Internal validation was assessed by bootstrapping (n = 500). Results: The final model included four predictors: intention, depression, MRC-score and alliance. The optimism-corrected AUC after bootstrap internal validation was 0.79 (95% CI, 0.72-0.85). Calibration plots suggested good calibration and decision curve analysis showed great net benefit in a wide range of risk thresholds. Conclusion: The exercise adherence prediction model has potential for clinical utility to predict adherence in patients with COPD. Information from such a model can be used to manage the patient instead of managing the disease, and thereby to determine the treatment frequency for each individual patient. As a result, healthcare capacity might be better distributed, potentially reducing pressure on healthcare without compromising the effectiveness of PR for the individual patient.

On-field high-resolution quantification of the cobalt fraction available for bio-uptake in natural waters using antifouling gel-integrated microelectrode arrays.

We report the optimization, characterization, and validation of Adsorptive Square Wave Cathodic Stripping Voltammetry on antifouling gel-integrated microelectrode arrays for autonomous, direct monitoring of cobalt(II) metal species. Detection is accomplished by complexation with an added nioxime ligand. The limit of detection established for a 90 s accumulation time was 0.29 ± 0.01 nM in freshwater and 0.27 ± 0.06 nM in seawater. The microelectrode array was integrated in a submersible probe to automatically dose the complexing agent nioxime and realize an integrated sensing system. For the first time ever, the potentially bioavailable Co(II) fraction was determined in La Leyre River-Arcachon Bay continuum, enabling to evaluate the potential ecotoxicological impact of freshwater-carried Co(II) in the Arcachon Bay. The measured potentially bioavailable Co(II) concentrations were hazardous for aquatic biota along the continuum. The electrochemical Co(II) data were compared to ICP-MS data in various fractions to determine spatial Co(II) speciation.

Mass Transfer from Ion-Sensing Component-Loaded Nanoemulsions into Ion-Selective Membranes: An Electrochemical Quartz Crystal Microbalance and Thin-Film Coulometry Study.

Recent work has shown that ion-selective components may be transferred from nanoemulsions (NEs) to endow polymeric membranes with ion-selective sensing properties. This approach has also been used for nanopipette electrodes to achieve single-entity electrochemistry, thereby sensing the ion-selective response of single adhered nanospheres. To this date, however, the mechanism and rate of component transfer remain unclear. We study here the transfer of lipophilic ionic compounds from nanoemulsions into thin plasticized poly(vinyl chloride) (PVC-DOS) films by chronoamperometry and quartz crystal microbalance. Thin-film cyclic coulovoltammetry measurements serve to quantify the uptake of lipophilic species into blank PVC-DOS membranes. Electrochemical quartz crystal microbalance data indicate that the transfer of the emulsion components is insignificant, ruling out simple coalescence with the membrane film. Ionophores and ion-exchangers are shown to transfer into the membrane at rates that correlate with their lipophilicity if mass transport is not rate-limiting, which is the case with more lipophilic compounds (calcium and sodium ionophores). On the other hand, with less lipophilic compounds (valinomycin and cation-exchanger salts), transfer rates are limited by mass transport. This is confirmed with rotating disk electrode experiments in which a linear relationship between the diffusion layer thickness and current is observed. The data suggests that once the nanoemulsion container approaches the membrane surface, transfer of components occur by a three-phase partition mechanism where the aqueous phase serves as a kinetic barrier. The results help better understand and quantify the interaction between nanoemulsions and ion-selective membranes and predict membrane doping rates for a range of components.

On-Chip Antifouling Gel-Integrated Microelectrode Arrays for In Situ High-Resolution Quantification of the Nickel Fraction Available for Bio-Uptake in Natural Waters.

We aimed to monitor in situ nickel (Ni(II)) concentrations in aquatic systems in the nanomolar range. To achieve this, we investigated whether an analytical protocol for the direct quantification of cobalt (Co(II)) using adsorptive cathodic sweep voltammetry (Ad-CSV) on antifouling gel-integrated microelectrode arrays (GIME) we recently developed is also suitable for direct Ni(II) quantification. The proposed protocol consists of the reduction of the complex formed between Ni(II) (or Ni(II) and Co(II)) and nioxime adsorbed on the surface of the GIME-sensing element. The GIME enables to (i) avoid fouling, (ii) control the metal complex mass transport and, when interrogated by Ad-CSV, (iii) selectively determine the dynamic (kinetically labile Ni-nioxime) fraction that is potentially bioavailable. The nioxime concentration and pH were optimized. A temperature correction factor was determined. The limit of detection established for 90 s of accumulation time was 0.43 ± 0.06 in freshwater and 0.34 ± 0.02 nM in seawater. The sensor was integrated in a submersible probe in which the nioxime-containing buffer and the sample were mixed automatically. In situ field measurements at high resolution were successfully achieved in Lake Geneva during a diurnal cycle. The determination of the kinetically labile Ni-nioxime fraction allows one to estimate the potential ecotoxicological impact of Ni(II) in Lake Geneva. Additional Ni fractions were measured by ICP-MS and coupled to the in situ Ad-CSV data to determine the temporal Ni(II) speciation.

Aerosol-into-liquid capture and detection of atmospheric soluble metals across the gas-liquid interface using Janus-membrane electrodes.

The soluble fraction of atmospheric transition metals is particularly associated with health effects such as reactive oxygen species compared to total metals. However, direct measurements of the soluble fraction are restricted to sampling and detection units in sequence burdened with a compromise between time resolution and system bulkiness. Here, we propose the concept of aerosol-into-liquid capture and detection, which allowed one-step particle capture and detection via the Janus-membrane electrode at the gas-liquid interface, enabling active enrichment and enhanced mass transport of metal ions. The integrated aerodynamic/electrochemical system was capable of capturing airborne particles with a cutoff size down to 50 nm and detecting Pb(II) with a limit of detection of 95.7 ng. The proposed concept can pave the way for cost-effective and miniaturized systems, for the capture and detection of airborne soluble metals in air quality monitoring, especially for abrupt air pollution events with high airborne metal concentrations (e.g., wildfires and fireworks).

A submersible probe with in-line calibration and a symmetrical reference element for continuous direct nitrate concentration measurements.

Current methods to monitor nitrate levels in freshwater systems are outdated because they require expensive equipment and manpower. Punctual sampling on the field or at a fixed measuring station is still the accepted monitoring procedure and fails to provide real-time estimation of nitrate levels. Continuous information is of crucial importance to evaluate the health of natural aquatic systems, which can strongly suffer from a nitrogen imbalance. We present here a nitrate-selective potentiometric probe to measure the analyte continuously without requiring maintenance or high-power consumption. Owing to a simple design where the sensors are located directly in contact with the sample, the need for constant pump usage is eliminated, requiring just 0.7 mW power per day instead of 184 mW per day and per pump. It is estimated that with this power consumption, the setup can easily run for more than 97 h on four simple Li-ion batteries. A simple in-line one-point calibration step was implemented to allow for drift correction. At the same time, a symmetrical design was used involving a second nitrate probe as a reference electrode placed in the calibrant compartment. This, combined with an in situ calibration step, allows one to quantify nitrate ion concentrations directly, instead of yielding activities. The dependence on ion activity was removed by using the analysed sample spiked with nitrate as the calibrant. This results in essentially the same activity coefficients and additionally reduces junction potentials to a fraction of a millivolt. In addition, a symmetrical reference element served to compensate for fluctuations caused by environmental factors (temperature, convection, etc.) to achieve improved stability and signal reproducibility compared to a traditional Ag/AgCl based reference electrode. The final prototype was deployed in the Arve River in Geneva for 75 h without requiring any intervention. The nitrate levels measured using the symmetrical reference element over this period were estimated at 44.0 ± 3.5 M and agreed well with the values obtained with ion chromatography (38.2 ± 2.1 µM) used as the reference method. Thanks to a modular sensing head the potentiometric sensors can be easily exchanged, making it possible to quantify other types of analytes and leading the way to a new monitoring strategy.

Symmetric cell for improving solid-contact pH electrodes.

Traditional pH glass electrodes are designed in a symmetrical manner to guarantee the most reliable and reproducible potentiometric measurements possible. Solid-contact and other pH probes not based on glass membranes are desirable because they allow for new types of applications, may be mass fabricated and less prone to breakage. Unfortunately, however, they introduce electrochemical asymmetry because the reference element used in the reference electrode compartment is now different. This work shows how symmetry may be restored with solid-contact pH probes, using a H+-selective ionophore-based polymeric membrane deposited on top of a conductive polymer (PEDOT-C14) as a transducer layer. The new cell implements a reference element that is composed of a similarly formulated pH probe immersed into a buffer solution and an Ag/AgCl element directly connected to a single-junction Ag/AgCl/3.0 M KCl reference electrode that is placed in contact with the sample solution. By implementing this design, the zero point of the solid-contact pH sensing system may be shifted to the conventional value of pH 7.0. The value of the zero point was experimentally confirmed as 6.96 ± 0.02 pH units at three different temperatures in the range from 5 to 25 °C. This symmetric solid-contact potentiometric cell gave a long-term potential drift of 48 ± 16 µV h-1, comparable to that of a combination pH glass electrode.