Optical chemical sensors (Micro- and Nanosystems) for analysis of liquids

A number of peculiar analytical systems applied in production of detecting elements for chemical sensors were considered, in which organic reagents are immobilized on opaque and optically transparent polymeric matrices. Fibrous non-fabricated materials filled with powdered ion exchangers (Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences) and polymeric films coated with a high-purity gelatin layer (Mendeleev Russian University of Chemical Technology) were suggested as solidstate matrices. The conditions for determination of elements at MPC (maximal permissible concentration) levels were identified. Rapid, highly sensitive and selective techniques were developed for reflectance-spectroscopic determination of coexisting mercury(II), cadmium(II) and lead(II); chromium(VI), copper, and nickel; lanthanum, uranium(VI), and thorium, as well as for spectrophotometric determination of calcium, thorium, nitrite, and sulfate ions. Sensitive optical sensors suitable both for single control step and long-term monitoring of the content of the elements in water objects were proposed.     

Thermodynamics of interactions between lead(II) and cadmium(II) ions and azulene-based complexing polymer films

In order to understand the essential processes/interactions between the metal ions and modified electrodes which are based on complexing polymeric films, access to thermodynamic characteristics is compulsory. The paper enlarges the information concerning the sorption of metal ions within complexing polymer films, particularly based on azulene, which can be involved in metal detection sensors. Interactions between lead(II) or cadmium(II) ions and complexing polymer films have been studied using chemical preconcentration–anodic stripping method. The films have been obtained by controlled potential electrolysis in millimolar solutions of 4-azulen-1-yl-2,6-bis(2-thienyl)pyridine (L) in acetonitrile. PolyL films affinities towards these metal ions have been quantified at different temperatures by means of sorption isotherms. Parameters for sorption of lead(II) and cadmium(II) ions within polyL films have been calculated for Freundlich, Langmuir and Redlich–Peterson isotherms. The best fit was obtained when using Langmuir isotherm. The results evidence that lead ions are better sorbed than cadmium within polyL film. Thermodynamic parameters for the chemical sorption of lead(II) and cadmium(II) ions within polyL films have been calculated.     

New lead (II) selective membrane potentiometric sensors based on chiral 2,6-bis-pyridinecarboximide derivatives

New membrane sensors with cylindrical configuration for lead (II) ions are described based on the use of three newly synthesized pyridine carboximide derivatives as neutral ionophores in plasticized PVC membranes. The sensors exhibit significantly enhanced response towards lead (II) ions over the concentration range 4×10⁻⁶-1×10⁻² mol l⁻¹ at pH 4.5-7 with a lower detection limit of 0.4-3.7 μg ml⁻¹. The sensors display near-Nernstian slope of 26.0-33.1 mV per decade for Pb(II) ions. Effects of plasticizers, lipophilic salts and various foreign common ions are tested. The sensors show long life span, good selectivity for Pb(II) over a wide variety of other metal ions, long term stability, high reproducibility, and fast response. Validation of the method by measuring the lower detection limit, range, accuracy, precision, repeatability and between-day-variability reveals good performance characteristics of the proposed sensors. The sensors are used for direct determination of lead in stack emissions of lead smelters, assay of lead in rocks and monitoring of potentiometric titration of Pb(II) with EDTA. The results obtained agree fairly well with data obtained by atomic absorption spectrometry.     

Coated,Wire-Based,New Schiff Base Potentiometric Sensor for Lead(II) Ion

An ion-selective electrode for lead(II) based on a dispersion of N,N"-bis(3-methyl salicylidine)-p-phenyl methane diamine particles into a polymeric membrane using coated-wire configuration is described. Membranes based on polyvinyl chloride containing different amounts of plasticizer and ionophore are studied. The best performance in terms of slope (30.3 ± 0.6 mV per decade) and response time (<15 s) is displayed. The sensor shows a Nernstian response for Pb(II) ions over a wide concentration range of 2.0 × 10^–5 to 0.10 M. The sensors can be used for more than three months without any considerable divergence in potentials. The selectivity is also good towards the most common univalent and divalent cations and the signal is constant in the pH range 1.6–6.0. An application to lead determination in mineral rocks and wastewater proved to be a success, and it was employed as an indicator electrode in potentiometric titration of CrO^2– ₄ with lead ions.     

Cross-sensitive chemical sensors based on tetraphenylporphyrin and phthalocyanine

The properties of solvent polymeric membrane sensors based on 5,10,15,20-tetraphenylporphyrin (TPP) and phthalocyanine (PHC) have been investigated. The sensitivity and selectivity of sensors towards wide range of mono- and di-valent cations have been measured. The selectivity towards the transition metal ions for TPP-based sensor does not correspond to the cation lipophilicity sequence. The dependence of response on pH was studied. The cross-sensitivity parameters, including average response slope, signal-to-noise ratio and “non-selectivity” factor for all sensors were calculated and compared. The influence of plasticizer and ionic additive on the response of sensors was characterized using principal component analysis (PCA).     

Photocured thiol-ene based optical fluorescence sensor for determination of gold(III)

This study describes the preparation and the characterization of a new thiol-ene based polymeric fluorescence sensor by photo initiated polymerization of trimethylolpropane tris(3-mercaptopropionate), 2-hydroxyethylacrylate, and 2,4,6-triallyloxy-1,3,5-triazine which are used as monomers and also a photo initiator (2,2-dimethoxy-2-phenylacetophenone) for its usage as optical sensor for gold ions. The thiol-ene based polymeric membrane sensor was characterized by using attenuated total reflectance-fourier transform infrared spectroscopy (ATR-FTIR) and scanning electron microscopy (SEM). The response characteristics of the sensors including dynamic range, pH effect, response time, and the effect of foreign ions were investigated. Fluorescence spectra showed that the excitation/emission maxima of the membrane were at 379/425 nm, respectively     

Determination of cyanide using flow-injection multisensor system

A flow-injection multisensor system (FIMS) comprising potentiometric sensors of different types for determination of free cyanide activity in basic solutions for extraction of noble metals was developed. The solvent polymeric membrane sensors based on metalloporphyrin and crystalline sensors were combined in the sensor system. The system allowed determination of cyanide activity in the range 10⁻⁴–1 mol l⁻¹ with an error less than 5% in individual cyanide solutions and acceptable precision (about 20%) in process liquids. The system was able to analyse up to 20 samples per h. The FIMS was also applied to detecting of silver ions in the presence of cyanide. Chalcogenide glass sensor was used as the detector that ensured the precision of 20%.     

Preparation of highly sensitive sensors based on polystyrene microspheres for the detection and removal of Hg2+ ions

Detection and the simultaneous removal of mercury ions are of vital importance. In this study, fluorescent monomers, small molecular sensors, were first synthesized using 4‐bromo‐naphthalic anhydride as precursor. These double bond bearing sensors were then grafted to polystyrene (PS) microspheres through dispersion polymerization. The sensors still retained their detecting ability when they were anchored on the surfaces of PS microspheres. Upon the addition of Hg²⁺ ions to the PS microspheres, both the color and the fluorescence intensity changed, which could be employed to detect Hg²⁺ ions. The absorption capacity of the two kinds of PS microspheres reached 0.557 mg g^?1 and 0.628 mg g^?1 respectively. The PS microspheres still remain their fluorescence and absorption even used for five times. These polymeric highly sensitive chemosensors may see their applications in purification of polluted environments. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 4592–4600     

Sorption isotherms of Nickel(II), Cobalt(II), Mercury(II), and Lead(II) ions on a phosphorus-containing polymeric sorbent

The influence of the concentration of a complexing ion on the sorption recovery of nickel, cobalt, mercury, and lead ions from aqueous solutions by a phosphorus-containing polymeric polybutadiene-based sorbent was studied. Sorption isotherms of the studied metal ions were processed by the Langmuir and Freindlich models. The affinity of metal ions to the functional groups of a sorbent and the stability of complexes were established to decrease in the order Hg(II) > Pb(II) > Co(II) > Ni(II).     

Potentiometric carbon paste sensors for lead(II) based on dithiodibenzoic and mercaptobenzoic acids.

Dithiodibenzoic (DTB) acid and mercaptobenzoic (MB) acid were studied to characterize their abilities as modifier agents for lead(II) sensors. For both sensors, the best results were obtained with modified carbon paste electrodes with 24.1% of ligand. The pH influence on the potentiometric response was studied. The selectivity coefficients for both modified electrodes were tabulated. A potentiometric sensor based on DTB acid exhibited a more sensitive and selective response to lead ions than an MB electrode. The limits of detection for the DTB and MB electrodes were very similar, 5.01 x 10(-8) M and 3.98 x 10(-8) M, respectively, for lead(II) activity. The DTB sensor was applied to lead(II) ion determination in real samples and as an indicator electrode in potentiometric titrations. Natural and commercial humic acids were titrated using the DTB electrode to estimate the stability constant between these organic compounds and the lead(II) ions with successful results.     

Aluminum as a superior endpoint sensor in some potentiometric titrations

Summary Aluminum rod and wire sensors surpassed conventional sensors in the magnitude of potentiometric breaks obtained in the titration of halides vs. silver ions, aluminum vs. fluoride ions, fluoride vs. lanthanum ions, and phosphate vs. lead, cerous, and lanthanum ions. In the titration of fluoride vs. aluminum or thorium, sulfate vs. lead, and phosphate vs. silver ions, however, conventional sensors were superior to aluminum. In the titration of phosphate vs. lead, cerous, or lanthanum ions endpoint breaks occurred in the negative direction, unlike the usual breaks in the titration of anions vs. cations. The theoretical basis for these phenomena remains unexplained.

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Aluminium als vorteilhafter Endpunkt-Sensor bei potentiometrischen Titrationen

Zusammenfassung Stab- und Draht-Sensoren aus Aluminium übertreffen konventionelle Sensoren durch die Grö\e der potentiometrischen Stufe bei folgenden Titrationen: Halogenide gegen Silber, Aluminium gegen Fluorid, Fluorid gegen Lanthan, Phosphat gegen Blei, Cer(III) oder Lanthan. Dagegen sind bei Titrationen von Fluorid gegen Aluminium oder Thorium sowie von Sulfat gegen Blei und Phosphat gegen Silber konventionelle Sensoren vorteilhafter. Bei der Titration von Phosphat gegen Blei, Cer(III) oder Lanthan verlaufen die Endpunktstufen in negativer Richtung, im Gegensatz zu den üblichen Stufen bei der Titration von Kationen vs. Anionen. Die theoretischen Grundlagen für diese Erscheinungen sind noch ungeklÄrt.

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Work performed under the auspices of the U.S. Department of Energy by the Lawrence Livermore National Laboratory under contract number W-7405-ENG-48.     

Monomer and polymer quinoxaline derivatives for cationic recognition

Monomeric and polymeric 5-nitroquinoxaline derivatives disubstituted in the 2 and 3 positions with 2-pyrrolyl (A), 2-furyl (B) and 2-thienyl (C) groups were prepared and characterized. The substituted 5-nitroquinoxalines were used as active components in poly(vinyl chloride)-membrane and electropolymerized electrodes that were then tested as possible sensors for various cationic species. In contrast to the difurylnitroquinoxaline-based systems, the monomeric and polymeric dipyrrolyl- and dithienylquinoxaline electrodes displayed a good selectivity for Ag(+) ions, providing a near-Nernstian response in the 10(-5) to 10(-2) mol L(-1) concentration range. The similar potentiometric behavior displayed by the monomeric and polymeric forms of systems A and C supports the contention that the main binding modes displayed by the monomeric forms are retained in the corresponding polymeric structures.     

Potentiometric and theoretical studies of the carbonate sensors based on 3-bromo-4-hexyl-5-nitrotrifluoroacetophenone

Novel carbonate ionophore, trifluoroacetophenone derivative (TFA) substituted by two acceptor substituents in the phenyl ring (3-bromo-4-hexyl-5-nitrotrifluoroacetophenone), was synthesized. Solvent polymeric membrane sensors based on this ionophore exhibited heightened selectivity to carbonate ions in the presence of the most important interfering anions. A wide range of potentiometric properties were studied and compared with those of sensors based on mono-substituted ionophores. Special attention was paid to pH dependence of sensor responses and to elaboration of appropriate conditions for carbonate analysis. A segmented-sandwich membrane method was applied for determination of the stoichiometry of ionophore-carbonate complexes, which was determined to be 1:3, and apparent complex formation constants which were 14.4 and 13.6 for DOS- and NPOE-plasticized membranes, respectively. Theoretical studies on TFA derivatives by semi-empirical (AM1 and PM3) and ab initio(6-31+G*) methods were performed, considering different types of possible ionophore-ion interactions. The formation of hydrogen bonds between carbonate and hydrated TFA was proved to be much more favourable in terms of energy compared to tetrahedral nucleophilic adducts that earlier were postulated to being formed in the membrane phase. The final conclusion on the mechanism of carbonate sensing by TFA-based solvent polymeric membrane sensors was made on the basis of computational data and detailed analysis of the literature.     

Fluorescent and colorimetric sensors for detection of lead, cadmium, and mercury ions

Exposure to even very low levels of lead, cadmium, and mercury ions is known to cause neurological, reproductive, cardiovascular, and developmental disorders, which are more serious problems for children particularly. Accordingly, great efforts have been devoted to the development of fluorescent and colorimetric sensors, which can selectively detect lead, cadmium, and mercury ions. In this critical review, the fluorescent and colorimetric sensors are classified according to their receptors into several categories, including small molecule based sensors, calixarene based chemosensors, BODIPY based chemosensors, polymer based chemosensors, DNA functionalized sensing systems, protein based sensing systems and nanoparticle based sensing systems (197 references).     

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.     

Determination of Cadmium(ii), Copper(ii), Mercury(ii), and Lead(ii) in Water Using Stochastic Sensors Based on Graphite and Diamond Paste Modified with 1H-Pyrrole-1-Hexanoic Acid

Graphite/diamond pastes modified with 1H-pyrrole-1-hexanoic acid were used for the design of stochastic sensors. The proposed stochastic sensors were used to determine four heavy metals, copper(II), cadmium(II), mercury(II), and lead(II), in water samples. The sensitivities of the stochastic sensors were high for all four metal ions, and their limits of determination were sufficiently low to enable detection at very minute concentrations; in some cases, unreachable using standard methods of analysis. The recoveries of copper(II), cadmium(II), mercury(II), and lead(II) in water samples were higher than 93.00%, with relative standard deviation values lower than 1.00%. The sensors were used to simultaneously determine copper(II), cadmium(II), mercury(II), and lead(II) in water samples. The obtained results were in agreement with those obtained using standard analytical methods.     

Highly Selective All‐Plastic,Disposable, Cu2+‐Selective Electrodes

Conducting polymers (CP) remain a promising material to construct stable potential all‐solid‐state ion‐selective potentiometric electrodes. The unique properties of poly(3,4‐ethylenedioxythiophene) doped with poly(4‐styrenesulfonate) ions, PEDOT‐PSS: high CP stability and affinity of doping anions towards Cu²⁺ ions, make it highly attractive for construction of all‐solid‐state copper(II)‐selective electrodes with outstanding selectivity. The additional benefits can arise from solution processability of commercially available PEDOT‐PSS system. This material was highly promising for a new sensor arrangement, i.e. to obtain disposable, planar and flexible all‐plastic Cu²⁺‐selective electrodes. These sensors can be obtained by casting a commercially available dispersion of PEDOT‐PSS (Baytron P) on a plastic, non‐conducting support material. The CP being both electrical lead and ion‐to‐electron transducer, was covered with plastic, solvent polymeric Cu²⁺ selective membrane. This extremely simple arrangement, after conditioning in dilute Cu²⁺ solution, was characterized with linear Nernstian responses within the activities range from: 0.1 to 10^?4 M, followed by super‐Nernstian responses for lower activities. The latter result points to effective elimination of primary ions leakage from the plastic membrane / transducer phase and has resulted in significantly improved selectivities. Obtained log K values were equal to ?7.6 for Co²⁺, ?7.4 for Zn²⁺, ?7.2 for Ca²⁺ and ?6.8 for Na⁺, respectively.     

Metal ion-imprinted polymers--novel materials for selective recognition of inorganics

Ion-imprinted polymers (IIPs) are recently identified nano-porous polymeric materials which on leaching the imprint ion can rebind, sense or transport (when cast as membranes) selectively the target analyte in presence of closely related inorganic ions. The IIPs find interesting applications in solid phase extraction, sensors and membrane separations of inorganics. Unlike the molecularly imprinted polymers, the IIP field is in its infancy and has been briefly reviewed here along with some rough guidelines and concepts for further development of IIPs.