Potentiometric Multisensor System Research Articles

Feasibility study of multisensor systems for the assessment of water pollution index induced by heavy metal contamination

The development of the analytical instruments for rapid in-field evaluation of integral surface water quality parameters is an urgent analytical task. Using three different sensor devices (optical sensor for cadmium, voltammetric sensor for lead and potentiometric multisensor system), we have explored the possibility of direct quantification of water pollution index (WPI) for contaminations induced by heavy metals. We have applied linear (partial least squares, PLS) and non-linear (kernel regularized least squares, KRLS) multivariate regression tools to construct predictive models evaluating the content of individual metals and WPI in complex aqueous media simulating surface water composition. We have also explored the potential of data fusion at different levels combining the signals from all three sensor devices. The results indicate that all the instruments retain the sensitivity towards target analytes in complex aqueous samples containing humic substances and that the direct quantification of WPI in the range from 1 to 4 is possible using the employed instruments with RMSE values around 0.14.

Nonlinear dimensionality reduction methods for potentiometric multisensor systems data analysis

AbstractElectrochemical multisensor systems were proven to be a very perspective research direction in modern analytical chemistry. The multisensor approach assumes an employment of cross‐sensitive chemical sensors in combination with multivariate data processing methods. Dimensionality reduction of the data obtained from multisensor systems is a very important step and it is mostly based on the traditional tools of chemometrics, such as Principal Component Analysis (PCA). In case of chemically complex samples, the response of multisensor systems may have a complex nonlinear nature and the use of linear modelling methods does not seem optimal. However, the potential of nonlinear dimensionality reduction methods in the processing of multisensor data has not yet been systematically studied. In this report we aim to fill this gap and assess the performance of various nonlinear dimensionality reduction tools: Isomap, Self‐Organizing Kohonen Maps, and Autoencoder. These methods were explored using three datasets from potentiometric multisensor systems obtained in various real applications. It was shown that nonlinear dimensionality reduction methods give the possibility to obtain additional and more detailed information about the analyzed objects/processes compared to PCA. However, calculation time for nonlinear dimensionality reduction methods essentially exceeds that for PCA, and it can be a limiting factor for application of such algorithms.

Getting rid of reference electrode in potentiometric multisensor measurements

Reference electrodes are indispensable part of electroanalytical methods; however, their use may often limit the options for miniaturization of the measurement set-up which is an important requirement for handling small sample volumes in biomedical studies. This is also true for potentiometric multisensor systems (“electronic tongues”) that are currently being rapidly developed for numerous analytical applications. We describe an approach to potentiometric multisensor measurements allowing the elimination of reference electrode from the measurement scheme. The idea is based on the employment of “cross-voltages” – the potentials of the sensors measured against each particular sensor of multisensor array with subsequent chemometric processing of these data. In this scenario each sensor in turn becomes a pseudo-reference electrode, thus the overall measuring protocol is as simple as direct potentiometry with only difference at the data treatment stage, where chemometric processing is required to extract the analytical information. The feasibility of this scheme is demonstrated for analysis of several model mixtures and for real urine samples. The accuracy attained by this procedure is at least the same as in classical multisensor measurements scheme and in several cases the cross-voltage approach yielded two times better accuracy, thus proving the perspective of the proposed measuring protocol.

Simultaneous quantification of Zr, Mo, U, Np and Pu in technological solutions of spent nuclear fuel reprocessing with a potentiometric multisensor system

The chemical analysis of spent nuclear fuel (SNF) reprocessing is a very challenging research field due to the high radioactivity of process streams and their complex composition. The process managing requires thorough chemical analysis to ensure safe and efficient performance. Traditional ways of chemical control of SNF reprocessing are based on sampling methods and involve long and tedious procedures, failing to provide immediate information on the process status. Recent literature suggests that potentiometric multisensor systems can be employed for on-line control. However, up to now these systems were only studied in very simple model media. This work reports on the potentiometric multisensor array applied for the first time for the simultaneous quantification of the content of actinides (uranium, plutonium, neptunium) and several other analytes (zirconium, molybdenum and nitric acid) in the complex samples obtained from the pilot extraction unit for SNF reprocessing. The same samples were also analyzed by UV-Vis spectrometry (another prospective method for on-line control) and the analytical performance of these two methods was compared using established analytical figures of merit (sensitivity and analytical sensitivity metrics) for multivariate calibration. In spite of the extremely challenging analytical task, both simple methods provide the characteristics suitable for real industrial applications.

Novel Pillar[5]arenes Show High Cross-Sensitivity in PVC-Plasticized Membrane Potentiometric Sensors

In this study a variety of novel symmetrically and asymmetrically functionalized pillar[5]arenes were synthesized, structurally characterized and applied as ionophores in PVC-plasticized membrane potentiometric sensors. During the sensitivity studies it was found that these novel sensors demonstrate pronounced cationic response towards different metal ions in aqueous solutions. A selectivity evaluation revealed that the developed sensors do not possess sharp preferences to particular ions, but offer a broad cross-sensitivity and can be employed in potentiometric multisensor systems.

Nonlinear Multivariate Regression Algorithms for Improving Precision of Multisensor Potentiometry in Analysis of Spent Nuclear Fuel Reprocessing Solutions

Potentiometric multisensor systems were shown to be very promising tools for the quantification of numerous analytes in complex radioactive samples deriving from spent nuclear fuel reprocessing. Traditional multivariate calibration for these multisensor systems is performed with partial least squares regression—an intrinsically linear regression method that can provide suboptimal results when handling potentiometric signals from very complex multi-component samples. In this work, a thorough investigation was performed on the performance of a multisensor system in combination with non-linear multivariate regression models for the quantification of analytes in the PUREX (Plutonium–URanium EXtraction) process. The multisensor system was composed of 17 cross-sensitive potentiometric sensors with plasticized polymeric membranes containing different lipophilic ligands capable of heavy metals, lanthanides, and actinides binding. Regression algorithms such as support vector machines (SVM), random forest (RF), and kernel-regularized least squares (KRLS) were tested and compared to the traditional partial least squares (PLS) method in the simultaneous quantification of the following elements in aqueous phase samples of the PUREX process: U, La, Ce, Sm, Zr, Mo, Zn, Ru, Fe, Ca, Am, and Cm. It was shown that non-linear methods outperformed PLS for most of the analytes.

Quantification of phosphatides in sunflower oils using a potentiometric e-tongue.

Consisting of two fatty acyl groups, phospholipids are a vital part of vegetable oils and the source of essential fatty acids. Moreover, phospholipids influence oxidative and flavor stability and color evolution of vegetable oils, and their quantification has a significant role in the quality assessment of oils. In this study, we proposed a new highly efficient, affordable, environmentally friendly, and simple approach for the evaluation of phospholipid concentrations based on potentiometric multisensor systems coupled with chemometric data processing. Support vector machines, partial least squares, and multiple linear regressions were used to predict phosphatide concentrations based on potentiometric multisensor system responses. Application of multivariate regression tools yielded the following root mean square errors of prediction: 0.005 mg/100 g of oil in the range 0.0-59.4 mg/100 g for refined oils; 0.008 mg/100 g in the range 0.0-100 mg/100 g for low phosphatide oils and 0.24 mg/100 g in the range 100-2270 mg/100 g for high phosphatide oils. This approach can be considered as a rapid and straightforward method to quantify the phosphatides in sunflower oils.

One shot evaluation of NPK in soils by “electronic tongue”

Smart introduction of fertilizers in the soil should help to decrease the negative impact of chemicals on the environment without dramatic reduction of crop yield. The amounts of fertilizers have to be carefully tuned according to actual nutrients content in the soil and vegetation period of the plants. Since most of the chemical soil analyses are performed in the laboratory nowadays, fast and simple analytical tools have to be developed for this task. In this study, a potentiometric multisensor system was used for simultaneous determination of the N, P and K in the water extracts of the soils. It was shown that potentimetric sensors with multivariate data processing can be used for assessment of all three macronutrients, along with estimation of pH and conductivity of soil samples. Correlation coefficients between targeted parameters and sensor responses varied from 0.69 to 0.96. The quantification of N was possible with RMSE of 50 mg/kg in the range 60–426 mg/kg. The main benefits of the proposed approach are the short measurement duration – just 8 min for all the parameters, and reagentless procedure.

Distinguishing paracetamol formulations: Comparison of potentiometric “Electronic Tongue” with established analytical techniques

Fast and inexpensive analytical tools for identification of the origin of pharmaceutical formulations are important to ensure consumers safety. This study explores the potential of potentiometric multisensor systems (“electronic tongues”) in this type of application. 72 paracetamol samples purchased in different countries and produced by various companies were studied via infrared spectroscopy (IR), near infrared spectroscopy (NIR), nuclear magnetic resonance spectroscopy (NMR) and multisensor system (ET). A variety of chemometric tools was applied to explore and compare the information yielded by these methods. It was found that ET is capable of distinguishing paracetamol formulations from different producers. The chemical information derived from potentiometric sensor responses has something in common with that derived from NIR and IR; however, it is orthogonal to that from NMR. ET can be a valuable tool in express quality assessment of drugs.

Quantification of thorium and uranium in real process streams of Mayak radiochemical plant using potentiometric multisensor array

The task of real time chemical composition control of radiochemical process streams is a great challenge to analytical chemistry due to very complex composition of the media and high radioactivity. Most of the analytical methods employed at the moment assume tedious and time-consuming steps of sampling, sample pretreatment and sophisticated analysis. In this study we have developed potentiometric multisensor system which is capable of fast and simple direct quantification of U and Th in real process streams of radiochemical plant with relative errors around 10%. This appears to be a reasonable precision sufficient for technological monitoring purposes and gives a good promise for the development of novel approach to radiochemical analytics.

Rapid Evaluation of Integral Quality and Safety of Surface and Waste Waters by a Multisensor System (Electronic Tongue).

The paper describes a wide-range practical application of the potentiometric multisensor system (MS) (1) for integral safety evaluation of a variety of natural waters at multiple locations, under various climatic conditions and anthropogenic stress and (2) for close to real consistency evaluation of waste water purification processes at urban water treatment plants. In total, 25 natural surface water samples were collected around St. Petersburg (Russia), analyzed as is, and after ultrasonic treatment. Toxicity of the samples was evaluated using bioassay and MS. Relative errors of toxicity assessment with MS in these samples were below 20%. The system was also applied for fast determination of integral water quality using chemical oxygen demand (COD) values in 20 samples of water from river and ponds in Kolkata (India) and performed with an acceptable precision of 20% to 22% in this task. Furthermore, the MS was applied for fast simultaneous evaluation of COD, biochemical oxygen demand, inorganic phosphorous, ammonia, and nitrate nitrogen at two waste water treatment plants (over 320 samples). Reasonable precision (within 25%) of such analysis is acceptable for rapid water safety evaluation and enables fast control of the purification process. MS proved to be a practicable analytical instrument for various real-world tasks related to water safety monitoring.

Potentiometric multisensor system as a possible simple tool for non-invasive prostate cancer diagnostics through urine analysis

We report a simple potentiometric multisensor system for distinguishing the urine samples from the patients with diagnosed prostate cancer and from healthy control group. The sensors of the system are sensitive towards variety of cationic and anionic species in urine, as well as to the presence of RedOx pairs. The response of the system represents a complex chemical fingerprint of urine sample that can be related with patient status through multivariate modelling. 89 urine samples were studied (43 from cancer patients confirmed by prostatic puncture biopsy and 46 from healthy control group) and variety of multivariate classification techniques was applied to the potentiometric data. The best results were obtained with logistic regression model yielding 100% sensitivity and 93% specificity in the independent test set of samples.

A Simple Procedure to Assess Limit of Detection for Multisensor Systems.

Currently, there are no established procedures for limit of detection (LOD) evaluation in multisensor system studies, which complicates their correct comparison with other analytical techniques and hinders further development of the method. In this study we propose a simple and visually comprehensible approach for LOD estimation in multisensor analysis. The suggested approach is based on the assessment of evolution of mean relative error values in calibration series with growing analyte concentration. The LOD value is estimated as the concentration starting from which MRE values become stable from sample to sample. This intuitive procedure was successfully tested with a variety of real data from potentiometric multisensor systems.

Potentiometric multisensor system for tetra- and hexavalent actinide quantification in complex rare earth metal mixtures related to spent nuclear fuel reprocessing

A potentiometric multisensor system, composed of 12 cross-sensitive sensors, is proposed for uranium and thorium quantification in multi-component mixtures simulating PUREX process tailing solutions. Various ligands with high extraction capacity to lanthanides and actinides were used as active compounds in plasticized polymeric sensor membranes. The sensitivity of the individual sensors to tetra- and hexavalent actinides (UO22+ and Th4+) in aqueous nitric acid solutions with pH = 2 has been studied for the first time. The sensors with pronounced sensitivity to actinides were comprised into the multisensor system that was applied for UO2+2 and Th4+ quantitative determination in presence of each other and lanthanides cations (La3+, Pr3+, Sm3+, Gd3+, Yb3+). The nitric acid quantification in the set of mixtures with UO2+2 and La3+ was also performed using the same system. Projection on latent structures (PLS) algorithm was used for multivariate regression models calculation. The results of PLS models validation with independent test set show the possibility of UO2+2 and Th4+ quantification with mean relative error (MRE) equal to 17% and 14% correspondingly, and HNO3 quantification with MRE = 7%. This accuracy is appropriate for real-time technological control of PUREX process.

Determination of three quality parameters in vegetable oils using potentiometric e-tongue

In this study the possibility of using potentiometric multisensor system (e-tongue) based on solid-state membrane electrodes for express evaluation of various quality parameters in vegetable oils was investigated. Optimization of oil sample preparation procedures for potentiometric analysis was performed. It was shown that developed multisensor system is capable to distinguish vegetable oil varieties prepared from different raw materials and pure oils from their mixture. Important edible oil quality indicators, such as peroxide value (PV), p-anisidine value (p-AV), and concentration of total tocopherols (TT) can be predicted from potentiometric multisensor system response using multivariate data processing. The parameters under study have the following ranges: PV (0.0–4.0); p-AV (0.4–3.8); TT (37.0–100.7). Application of multivariate regression tools yielded root mean square errors of prediction: 0.5 meq/kg for PV; 0.8 arbitrary units for p-AV; 10 mg/100 g for TT, thus showing a good promise for development of fast and simple method for express quality evaluation.

Quantification of immobilized protein in pharmaceutical production by bio-assisted potentiometric multisensor system

Quantification of proteins is a key biochemical assay in molecular biology, biotechnology, medicine and pharmacology. Protein quantification protocols can be based on spectrophotometry, enzyme-linked immunosorbent assay, mass spectrometry or quantitative immunoblotting depending on analyte. In case of immobilized protein these methods require suitable sample preparation. Thus, sophisticated analysis becomes even more complex, expensive and time-consuming. Such drawbacks are highly undesirable in industry. In this study we propose a new approach for evaluation of immobilized protein concentration based on application of bio-assisted potentiometric multisensor system. Surface-immobilized recombinant protein A from Staphylococcus aureus (SpA, expressed in Escherichia coli), which is commonly used as affinity ligand immobilized to stationary phase (сhromatography media) for monoclonal antibody purification was employed as the model object. Chromatography media samples containing different amounts of immobilized SpA were analyzed. Proteinase K from Tritirachium album was employed as a bio-transducer. We demonstrated that the suggested approach provides information about immobilized SpA concentration with 0.8mg/ml accuracy in the range 1–6.7mg/ml and within just 16min. Moreover, the proposed procedure requires no expensive materials and equipment and no bio-transducer immobilization. This method has potential of application for fast monitoring of other immobilized proteins in different tasks.

A Potentiometric Multisensor System of Anion-Selective Electrodes Based on Ionic Liquids

The possibility of using solid-state and liquid PVC-membrane electrodes based on ionic liquids to design a potentiometric multisensor system is assessed. Ionic liquids with 1,3-dihexadecylimidazolium cation and chloride, bromide, iodide, and nitrate anions are used. The sensitivity parameters of the sensors are determined. A multisensor array is applied to detect chloride and iodide anions in the multicomponent mixture. The designed system is used to discriminate between mineral waters of different compositions by applying the method of principal component analysis (PCA).

Multivariate Calibration Transfer between two Potentiometric Multisensor Systems

AbstractA multivariate calibration of multisensor systems is a very important stage in their application. Construction of reliable calibration model requires significant investment of time and money. Once established, calibration model can be applied normally only together with that particular multisensor system, which was employed for its’ construction – this can be a serious limitation for a wide adoption of multisensor systems in common laboratory practice. In order to address this issue we have studied the applicability of several calibration transfer techniques, such as direct standardization, single wavelength standardization and standardization with regularization coefficient for the data obtained from two potentiometric multisensor systems in analysis of complex lanthanide mixtures. It was found that mathematical correction of sensor array response using standardization with regularization coefficient allows for using the regression model derived for one sensor array together with the data obtained from another sensor array. The value of root mean squared error of prediction for total lanthanide concentration increased insignificantly (0.10 instead of 0.07 in log scale) compared with that provided by the first multisensor system.

Multivariate calibration transfer between two different types of multisensor systems

The most popular sensors in multisensor systems (electronic tongues) are voltammetric and potentiometric ones. Practical application of multisensor systems for evaluation of particular target parameters requires calibration step. Even if both types of sensors (voltammetric and potentiometric) can be sensitive towards the same parameter of an analyte and can be used for its quantification, corresponding multisensor systems cannot operate in the framework of a single unified calibration model interpreting the responses of both systems. This research is dedicated to experimental verification of calibration transfer feasibility between voltammetric and potentiometric multisensor systems. The algorithm of direct standardization suggested earlier in spectroscopy was applied for transformation of potentiometric data into voltammetric format, and vice versa. Such transformations allowed for interpretation of a system response by multivariate regression model built employing the data from another type of multisensor system. For example, concentration of the tartaric acid in the grape musts can be determined with the regression model developed for voltammetric system using the data obtained from potentiometric system. Only 20% decrease in precision was observed for the converted potentiometric data compared to initial voltammetric model.

Critical view on drug dissolution in artificial saliva: A possible use of in-line e-tongue measurements

Proper monitoring of drug's dissolution is a prerequisite for assessing of taste masking efficacy of pharmaceuticals. Corresponding dissolution procedure is likely to be performed with water. Since the objective of these tests is to examine fate of a pharmaceutical formulation in oral cavity, this choice of solvent seems unsuitable because physical and chemical properties of human saliva are quite far from those of water. Obviously, dissolution profiles registered in water may differ significantly from what really happens with a drug in a mouth cavity. In order to address this discrepancy we examined three different compositions of artificial saliva in dissolution test context in present study. It was found that certain compositions preclude the employment of traditional UV–vis spectroscopy as a detection tool due to strong light scattering in the media caused by viscosity and protein composition modifiers. This issue was circumvented by the use of in-line applied potentiometric multisensor system (e-tongue) and the potential of this new approach for more biorelevant dissolution tests was demonstrated with two model formulations of quinine and ibuprofen.