Some regularities of interface formation in solid-contact potentiometric surfactant-selective sensors

The regularities of interface formation in solid-contact potentiometric sensors for surfactants of different types were found. It was shown that the nature of electronic conductors and ionophores, the state of ionophores in aqueous and organic media, and the composition and ratios of membrane components had the decisive effect on the electroanalytical properties of these sensors.Translated from Zhurnal Analiticheskoi Khimii, Vol. 60, No. 3, 2005, pp. 316–322.Original Russian Text Copyright © 2005 by Kulapin, Chernova, Kulapina.     

A disposable biosensor for the determination of alpha-amylase in human saliva

A disposable tri-enzymatic biosensor is presented for the determination of α-amylase in human saliva. It is based on the quantity of maltose generated by hydrolysis of maltopentose in the presence of salivary α-amylase. The biosensor is fabricated by co-immobilization of the enzymes α-glucosidase, glucose oxidase, and mutarotase on screen-printed electrodes modified with Prussian Blue. The assay can be performed with a “drop” of sample, this allowing for ease and simplicity. A linear relationship is found for the range from 5 to 250 units per mL, with an LOD of 5 units per mL. The biosensor is stable for at least one month and over this time retains 80% of its original activity. The system was then evaluated for matrix effects of human saliva and compared to a spectrometric method using a commercially available kit.     

Polypyrrole-calcion film as a membrane and solid-contact in an indicator electrode for potentiometric titrations

This paper shows the application of conducting polymers (CPs) for constructing potentiometric indicator electrodes. Two types of polypyrrole (PPy)-based calcium sensors are presented, one sensor with PPy-calcion film as the active part and the other sensor with PPy-calcion as a solid-state contact coated with a conventional membrane selective towards calcium ions. It is shown that the PPy-calcion film, due to the complexing properties of calcion ensuring high loading of the film with calcium, is sufficiently selective to be used as the active part or as a mediating layer of the indicator electrode. The electrode, with PPy-calcion film as the active part, was used as the indicator electrode in potentiometric titrations of calcium in mixed solvents, where conventional PVC-based electrode can not be used. For the first time, the practical applicability of PPy-based electrodes in titrations is demonstrated.     

A potentiometric multisensor system for determining lysine in aqueous solutions containing potassium and sodium chloride

A potentiometric multisensor system has been developed for the determination of lysine in aqueous solutions containing sodium and potassium chlorides. The sensor array includes a cross-sensitive sensor, the response of which is the Donnan potential at the ion-exchange polymer/test solution interface, a set of ion-selective electrodes, and a silver-silver chloride reference electrode. Multidimensional regression analysis has been employed for the calculation of component concentrations. The relative error of determining lysine, potassium, and sodium did exceed 10% in the tested solutions.     

A miniaturized and integrated galvanic cell for the potentiometric measurement of ions in biological liquids

A procedure for an all-plastic electrochemical cell comprising miniaturized planar indicator and reference electrodes is described. All electrodes are based on conducting polymers, are fully integrated, and contain no internal electrolyte. The reference microsensors were deposited via electrochemical polymerization from a water solution containing the monomer 3,4-ethylenedioxythiophene (EDOT) or 1-methylpyrrole (MPy) and a biochemical buffer 3-(N-morpholino) propanesulfonic acid [MOPS], 2-(N-morpholino) ethanesulfonic acid [MES], or 2-hydroxy-5-sulfobenzoic acid [SSA]). Ion-sensitive microelectrodes were prepared by the deposition of the ion-sensitive membrane solution (Ca²⁺, K⁺, and Cl⁻) directly onto the mediating poly-EDOT (PEDOT), PEDOT–SSA, PEDOT–MES, PEDOT–MOPS, or poly-MPy–MOPS layers.     

A potentiometric sensor for the determination of diclofenac

A diclofenacselective electrode with a plasticized poly(vinyl chloride) membrane containing an ion associate of diclofenac with Astrafloxin FF as an electrode-active substance was developed. The linearity range of the electrode function varied from 5 × 10^?5 to 5 × 10^?2 M; the slope of the electrode function was 59.0 ± 1.2 mV/pc, and the working pH range was 9–12. The effectiveness of the use of this electrode for monitoring diclofenac in pharmaceutical preparations was demonstrated.     

Unique potentiometric detection systems for HPLC determination of some steroids in human urine

Isocratic HPLC with potentiometric detection is used for the determination of some 17‐ketosteroids (17‐KS), e.g., androsterone, dehydroepiandrosterone and estrone, and their respective sulfated conjugates (17‐KSS). Glassy carbon or composite electrodes containing a mixture of graphite and poly(vinyl chloride), PVC, were used as substrate electrodes. These substrates were covered either by montmorillonite or potassium tetrakis(p‐chlorophenyl) borate containing PVC‐based rubber phase membranes. The neutral 17‐KS compounds were derivatized with Girard's reagent P (GP) to obtain cationic pyridinium acetohydrazones prior to the HPLC/potentiometric detection assay. No side reactions were observed, and the GP itself was not interfering. The method yielded accurate and reproducible results and was applicable to samples containing down to micromolar concentrations. Next, the 17‐KSS compounds, acting as anionic charged molecules, were determined directly in human urine samples with the HPLC/potentiometry combination without preliminary derivatization. For this purpose, a new anion‐sensitive potentiometric electrode was developed using a macrocyclic polyamine containing, PVC‐based, rubber phase membrane. The three 17‐KSS compounds were also determined accurately down to micromolar concentrations. Especially, the main androgen metabolites as dehydroepiandrosterone sulfate and androsterone sulfate could be selectively determined with a developed potentiometric sensor in human urine samples without time‐consuming cleanup and preconcentration step.     

High-performance liquid chromatographic determination of arecoline in human saliva

Arecoline (methyl-1,2,5,6-tetrahydro-1-methyl nicotinate) is an alkaloid found in the areca catechu nut which is a major component of the 'betel quid' chewed by a large proporation of the population in India, South Asia and the South Pacific islands. It is commonly associated with the development of oral leukoplakia, oral submucous fibrosis and oral cancer. We have developed a new ion-pairing reversed-phase high-performance liquid chromatographic (HPLC) method for the determination of arecoline in saliva, using arecaidine (1,2,5,6-tetrahydro-1-methylnicotinic acid) as an internal standard. The optimal wavelength was established using UV absorbance scans. It was showed that 215 nm is the optimal wavelength to maximise the signal in detecting arecoline in the mobile phase. Arecoline was extracted from saliva with hexane-isoamyl alcohol (1%) and reconstituted with mobile phase for HPLC analysis. The developed method is an easy and reliable method of determining arecoline concentrations in saliva. Sensitivity, specificity, precision, accuracy and reproducibility of the method were demonstrated to be satisfactory for measuring the arecoline level.     

A potentiometric determination of potassium ethyl xanthate

A potentiometric determination of potassium ethyl xantbate with Cu(II)-acetate is described From the results it follows that CS₂ reacts quantitatively with etimnolic KOH to give potassium ethyl xanthate The method may therefore be used for the determination of CS₂.     

Development of miniaturized potentiometric nitrate- and ammonium selective electrodes for applications in water monitoring

Mobile analysis with potentiometric sensors is well suited for field measurements. Ion-selective electrodes (ISE) based on polymeric membranes for in-situ determination of nitrate and ammonium contents in ground water, drinking water and surface water have been developed. The ISE are integrated in a multisensor module (MSM) for monitoring these ions over longer time intervals. The receptor is a PVC-membrane with tridodecylammonium nitrate (TDDA) for nitrate- and nonactine for ammonium-electrodes as ionophores. As plasticizer dibutylphthalate (DBT) was used. The main parameters for assessing the efficiency of these ISE are presented.     

Development of miniaturized potentiometric nitrate- and ammonium selective electrodes for applications in water monitoring

Mobile analysis with potentiometric sensors is well suited for field measurements. Ion-selective electrodes (ISE) based on polymeric membranes for in-situ determination of nitrate and ammonium contents in ground water, drinking water and surface water have been developed. The ISE are integrated in a multisensor module (MSM) for monitoring these ions over longer time intervals. The receptor is a PVC-membrane with tridodecylammonium nitrate (TDDA) for nitrate- and nonactine for ammonium-electrodes as ionophores. As plasticizer dibutylphthalate (DBT) was used. The main parameters for assessing the efficiency of these ISE are presented.     

A novel planar miniaturized potentiometric sensor for flow injection analysis of nitrates in wastewaters, fertilizers and pharmaceuticals

A novel all-solid-state miniaturized nitrate sensor is developed, characterized and used for flow injection analysis (FIA) of nitrates in various samples. The sensor incorporates silver bis(bathophenanthroline) nitrate [Ag(bath)₂NO₃] as an electroactive material in a plasticized PVC membrane. The sensing membrane (3 mm × 5 mm) is immobilized on a wafer polyimide microchip (size 13.5 mm × 3.5 mm) to offer a planar miniaturized design easily used in a single channel wall-jet flow injection system. Under hydrodynamic mode of operation (FIA) the sensor displays fast response, high sensitivity, long term stability and good selectivity for NO₃⁻ in the presence of many common associated anions. The calibration slope is 55.1 ± 0.1 mV decade⁻¹ over the concentration range 1.0 × 10⁻¹ to 1.0 × 10⁻⁶ mol L⁻¹, the lower detection limit is 0.05 μg mL⁻¹, the working pH is 2-9,and the output is 70-90 samples h⁻¹. Validation of the assay method reveals good performance characteristics and suggests application for routine determination of NO₃⁻ in industrial wastewaters, fertilizers and pharmaceuticals. The results agree fairly well with data obtained by the standard spectrophotometric methods.     

A novel ferroin membrane sensor for potentiometric determination of iron

A novel potentiometric approach for both batch and flow injection determination of iron(II) and/or iron(III) is described. It is based on the formation and monitoring of ferroin with a PVC membrane sensor containing ferroin-TPB as an electroactive component plasticized with 2-nitrophenyl phenyl ether. The sensor exhibits fast Nernstian response for ferroin with a cationic calibration slope of 30 +/- 0.2 mV/concentration decade down to 4 x 10(-7)M ferroin (0.03 ppm Fe) at pH 3-9. Interferences from common inorganic cations are negligible or can be eliminated by a pretreatment with DDC. The ferroin sensor was successfully applied to the determination of iron contents in water, alloys, rocks and pharmaceuticals. The results show good correlation with data obtained by the standard spectrophotometric ferroin method, the coefficient of correlation is better than 0.7%.     

A model of direct potentiometric determination of nitrate

Summary The paper represents a model for evaluation of the combined influence of four interferences in the direct potentiometric determination of nitrate in soil samples. The correction of the complex analytical signal is performed by the use of the system-oriented technique PAMS and modern statistical methods for modelling and optimization of multi-factorial systems. It is shown that within certain concentration intervals the effect of the interferences is not simply additive as predicted by the Nikolsky equation.On leave from Faculty of Chemistry, University of Sofia, 1126 Sofia, A. Ivanov Ave. 1, Bulgaria     

Textile-based sampling for potentiometric determination of ions

Potentiometric sensing utilizing textile-based micro-volume sampling was applied and evaluated for the determination of clinically (Na⁺, K⁺, Cl^–) and environmentally (Cd²⁺, Pb²⁺ and pH) relevant analytes. In this technological design, calibration solutions and samples were absorbed into textiles while the potentiometric cells (ion-selective electrodes and reference electrode) were pressed against the textile. Once the liquid, by wicking action, reached the place where the potentiometric cell was pressed onto the textile, hence closing the electric circuit, the potentiometric response was obtained. Cotton, polyamide, polyester and their blends with elastane were applied for micro-volume sampling. The textiles were found to influence the determination of pH in environmental samples with pH close to neutral and Pb²⁺ at low analyte concentrations. On the other hand, textile-based micro-volume sampling was successfully applied in measurements of Na⁺ using solid-contact sodium-selective electrodes utilizing all the investigated textiles for sampling. It was found that in order to extend the application of textile-based sampling toward environmental analysis of ions it will be necessary to tailor the physio-chemical properties of the textile materials. In general, textile-based sampling opens new possibilities for direct chemical analysis of small-volume samples and provide a simple and low-cost method to screen various textiles for their effects on samples to identify which textiles are the most suitable for on-body sensing.     

Comprehensive determination of trace elements in human saliva by ETA-AAS

A method is described for the comprehensive determination of a series of trace and ultratrace elements (Fe, Mn, Zn, Cu, Sr, Cr, Al and Si) in human saliva by atomic absorption spectrometry with electrothermal atomization and Zeeman-effect background correction. Procedures for sampling of total mixed saliva and its treatment including centrifugation and mineralization by HNO₃ are described in detail. To avoid the use of matrix modifiers, element standards with an artificial saliva matrix were used to construct calibration curves. Instrumental precision, tested by repeated analyses of natural salivas, is good (error less than 5%) for most elements. Lower precision was obtained for elements like Al and Si present in concentrations close to the detection limit. The analysis of some natural salivas clearly shows the influence of the sampling and treatment procedures on the reliability of the data. An accurate standardization of these procedures is thus recommended.     

A compact miniaturized continuous flow system for the determination of urea content in milk

A multicommutation-based flow system with photometric detection was developed, employing an analytical microsystem constructed with low temperature co-fired ceramics (LTCC) technology, a solid-phase reactor containing particles of Canavalia ensiformis DC (urease source) immobilized with glutaraldehyde, and a mini-photometer coupled directly to the microsystem which monolithically integrates a continuous flow cell. The determination of urea in milk was based on the hydrolysis of urea in the solid-phase reactor and the ammonium ions produced were monitored using the Berthelot reaction. The analytical curve was linear in the urea concentration range from 1.0 × 10⁻⁴ to 5.0 × 10⁻³ mol L⁻¹ with a limit of detection of 8.0 × 10⁻⁶ mol L⁻¹. The relative standard deviation (RSD) for a 2.0 × 10⁻³ mol L⁻¹ urea solution was lower than 0.4% (n = 10) and the sample throughput was 13 h⁻¹. To check the reproducibility of the flow system, calibration curves were obtained with freshly prepared solutions on different days and the RSD obtained was 4.7% (n = 6). Accuracy was assessed by comparing the results of the proposed method with those from the official procedure and the data are in close agreement, at a 95% confidence level.     

PVC membrane electrodes for potentiometric determination of tripelennamine

The construction of PVC matrix type tripelennamine ion selective electrodes and their use for direct potentiometry, potentiometric titration and flow injection analysis of tripelennamine cation are described. The membranes of these electrodes consist of tripelennamine-tetraphenylborate, reineckate and picrylsulfonate ion-association complexes dispersed in PVC matrix with tributyl phosphate (TBP) plasticizer. The electrodes exhibit near-Nernstian response over the concentration range of 10^–1-10^–4 M tripelennamine over the pH range 4.5–8.0. Selectivity coefficients data obtained for 17 different organic and inorganic ions are presented. The results obtained for the determination of 29 g/ml-29 mg/ml of tripelennamine with the proposed electrodes show average recoveries of 99.5–99.9% and mean standard deviations of 0.6–1.2%. The data agree well with those obtained by the standard methods.