A fluorescent chemical sensor for Hg(II) based on a corrole derivative in a PVC matrix

A fluorescent chemical sensor for Hg(II) using 5,10,15-tris(pentafluorophenyl)corrole (H₃(tpfc)) as fluorophore is described in this paper. The response of the sensor is based on the fluorescence quenching of H₃(tpfc) by coordination with Hg(II). H₃(tpfc) based sensor shows a linear response towards Hg(II) in the concentration range from 1.2 × 10⁻⁷ to 1.0 × 10⁻⁴ M, with a working pH range from 5.0 to 8.0. The response time for Hg(II) concentration ≤1.0 × 10⁻⁵ M is less than 5 min. The sensor shows good selectivity for Hg(II) over alkali, and alkaline earth, and most of transition metal cations. The effect of the composition of the sensor membrane has been studied and the experimental conditions optimized. The corrole based sensor membrane can be easily regenerated just by washing with blank buffer solution after each measurement. The sensor has been used for determination of Hg(II) in water samples with satisfactory results.     

A PVC plasticized membrane sensor for nickel ions

A new PVC membrane sensor, which is highly selective towards Ni (II) ions, has been developed using a thiophene-derivative Schiff base as the ionophore. The best performance was exhibited by the membrane having the composition percentage ratio of 5:3:61:31 (ionophore:NaTPB:DBP:PVC) (w/w), where NaTPB is the anion excluder, sodium tetraphenylborate and DBP is the plasticizing agent (dibutyl phthalate). The membrane exhibited a good Nernstian response for nickel ions over the concentration range of 1.0 × 10⁻¹–5.0 × 10⁻⁶ M (limit of detection is 1.8 × 10⁻⁶ M) with a slope of 29.5 ± 1.0 mV per decade of activity. It has a fast response time of <20 s and can be used for a period of 4 months with good reproducibility. The sensor is suitable for use in aqueous solutions of a wide pH range of 3.2–7.9. The sensor shows high selectivity to nickel ions over a large number of mono-, bi- and trivalent cations. It has been successfully used as an indicator electrode in the potentiometric titration of nickel ions against EDTA and also for direct determination of nickel content in real samples – wastewater samples from electroplating industries and Indian chocolates.     

A lead (II) selective PVC membrane potentiometric sensor based on a tetraazamacrocyclic ligand

A polymeric membrane based Pb(II) selective potentiometric sensor was developed by using 1,3,7,9-tetraaza-2,8-dithia-4,10-dimethyl-6,12-diphenylcyclododeca-4,6,10,12-tetraene (TDDDCT) as an electroactive material along with anion excluder sodium tetraphenylborate (NaTPB) and plasticizer dioctylphthalate (DOP). The best performance in terms of slope, concentration range and response time was exhibited by the membrane having TDDDCT:PVC:DOP:NaTPB in the ratio 3:32:62:3 (w/w%). Potentiometric results show that the developed sensor works well in the concentration range 5.0 × 10^?7–1.0 × 10^?1 M with a near Nernstian slope of 29.5 (±0.5) mV decade^?1. The detection limit is down to 2.5 × 10^?7 M. The working pH range of this sensor is 2.8–7.0 and it works well in partially nonaqueous medium up to 25 % (v/v) methanol and ethanol. It exhibits a fast response time of 10 s. Selectivity coefficient values of various interfering ions were determined by the fixed interference method (FIM). The sensor reveals good selectivity for Pb(II) ions over other metal ions investigated. The developed sensor is used in the determination of lead in ‘Eveready battery waste’ and as an indicator electrode in the potentiometric titration of Pb(II) against EDTA.     

Fabrication of an optical sensor based on the immobilization of Qsal on the plasticized PVC membrane for the determination of copper(II)

A novel optical sensor has been proposed for sensitive determination of Cu(II) ion in aqueous solutions. The copper sensing membrane was prepared by incorporating Qsal (2-(2-hydroxyphenyl)-3H-anthra[2,1-d]imidazole-6,11-dione) as ionophore in the plasticized PVC membrane containing tributyl phosphate (TBP) as plasticizer. The membrane responds to Cu(II) ion by changing color reversibly from yellow to dark red in acetate buffer solution at pH 4.0. The proposed sensor displays a linear range of 6.3 × 10^?7?1.00 × 10^?4 M with a limit of detection of 3.3 × 10^?7 M. The response time of the optical sensor was about 3?C5 min, depending on the concentration of Cu(II) ions. The selectivity of the optical sensor to Cu(II) ions in acetate buffer is good. The sensor can readily be regenerated by hydrochloric acid (0.1 M). The optical sensor is fully reversible. The proposed optical sensor was applied to the determination of Cu(II) in environmental water samples.     

A multi-channel sensor based on 8-hydroxyquinoline ferrocenoate for probing Hg(II) ion

A new sensing molecule 8-hydroxyquinoline ferrocenoate (Fc-Q) which combines ferrocene and 8-hydroxyquinoline moieties was synthesized and applied as a multi-channel sensor for the detection of Hg²⁺ ion. Fc-Q can coordinate with Hg²⁺ to give colorimetric, fluorescent and electrochemical responses. Upon complexation with Hg²⁺ ion, the characteristic absorption peak is red-shifted (Δλ = 45 nm), the fluorescent intensity is quenched at 303 nm, and the oxidation peak is cathodic shifted (ΔE_1/2 = −149 mV). Quantitatively analyzed Hg²⁺ ions at the range of ppb level could be achieved by electrochemical response. For the practical application of sensing Hg²⁺ in real world water, Fc-Q modified screen-printed carbon electrodes were obtained for facile, sensitive, and on-site analysis of Hg²⁺.     

Manganese (II) selective PVC based membrane sensor using a Schiff base

N,N′,N″,N′′′-1,5,8,12-tetraazadodecane-bis(salicylaldiminato)(H₂L) has been used as ionophore for preparing Mn²⁺ selective sensor. Membranes of different composition with regard to ratio of H₂L:PVC:NPOE:NaTPB have been prepared and investigated. The best performance was obtained with the membrane of composition 10:150:150:10 (H₂L:PVC:NPOE:NaTPB) (w/w; mg). This membrane generated linear potential response in the concentration range of 5.0 × 10⁻⁶ to 1.0 × 10⁻¹ M with a Nernstian slope of 30.0 mV/decade of activity and fast response time (10 s). Hydrogen ion does not effect to the performance of sensor in the pH range 3.0-6.5. The sensor was found to be sufficient selective for Mn²⁺ over a number of alkali, alkaline and heavy metal ions and could therefore be used for the determination of manganese in various samples by direct potentiometry.     

Kinetics of annealing of nitrite in gamma-irradiated cis-nitrato bis-(ethylenediamine) Ni(II) perchlorate and trans-dinitrato bis-(ethylenediamine) Ni(II)

The kinetics of annealing of nitrite in γ-irradiated (1.0 MGy) cis-nitrato bis-(ethylenediamine) Ni(II) perchlorate and trans-dinitrato bis-(ethylenediamine) Ni(II) is explored. The data reveal that annealing of nitrite, NO^-₂ between 130.0 and 170.0°C in both the complexes follows a combination of one first order and one second order process. The extent of recombination in trans-dinitrato complex (ϕ = 0.89) is higher than that in the cis-nitrato compound (ϕ = 0.69), though the radiolytic decomposition is in the reverse order. The data are analysed in the light of theories of diffusion controlled mechanics like Fletcher-Brown, Waite and Vand-Primak treatment.     

A new PVC matrix membrane sensor for determination of praseodymium(III) ion based on bis(salicylaldehyde)thiocarbohydrazone as an ion carrier

The sufficient amounts of bis(salicylaldehyde) thiocarbohydrazone (STCH) as a lipophilic selective element (3%, w/w), sodium nitrobenzene (NB) as a plasticizer (64%, w/w), tetraphenyl borate (NaTPB) as an anionic additive (3%, w/w), and poly vinyl chloride (PVC) as a polymeric matrix (30%, w/w) was employed to form a PVC membrane of a new Pr³⁺ ions selective sensor to apply as an indicator electrode in analytical applications. The best electrode response was observed in the slope (19.5 ± 0.7 mV per decade) over a wide concentrations from lower (1.0 × 10^?6 mol L^–1) to higher (1.0 × 10^?2 mol L^–1) of Pr³⁺ ion solution with a detection limit of 8.5 × 10^–7 mol L^–1. This electrode showed the fast response time about 10 second for praseodymium ion concentration range of 1.0 × 10^–6 to 1.0 × 10^–2 mol L^–1, in the pH range of 2.3–7.9. The matched potential method was applied to study the selectivity of electrode toward Pr³⁺ ions in comparison with many common cations. The results showed the negligible disturbance of all other cations on the proposed praseodymium(III) electrode. The making sensor has been employed successfully as an indicator electrode in the potentiometric titration of praseodymium(III) solution with EDTA at pH 6.0. Moreover the applicability of the sensor was studied in determination of Pr³⁺ ion in mixtures of different ions.     

Strontium(II) sensor based on a modified calix[6]arene in PVC matrix.

5,11,17,23,29,35-Hexakis(1,1,3,3-tetramethylbutyl)-37,38,39,40,41,42-hexakis(carboxy methoxy)calix[6]arene (I) has been evaluated as an ionophore for the analysis of Sr2+. The influences of the nature of the plasticizers (DBA, CN, DOP, NPOE) and of the anion excluder (NaTPB) on the characteristics of the electrode were discussed. The best electrode was fabricated with a membrane having composition 6:150:170:3 (I:PVC:DBA:NaTPB). The response to Sr2+ was Nernstian in the range 1.9 x 10(-5) to 1.0 x 10(-1) M of Sr2+. The influence of pH has also been studied. The electrode exhibited better potential stability and had an operational lifetime of 4 months. The K(A,B)(Pot) values showed that other alkaline earth metal ions are well discriminated. The sensor has also been used as an indicator electrode in the potentiometric titration of sodium carbonate with strontium(II) ions.     

Copper(II) ion sensor based on electropolymerized undoped conducting polymers

A solid state copper(II) ion sensor is reported based on the application of electropolymerized undoped (neutral) polycarbazole (PCz) and polyindole (PIn) modified electrodes. The new sensor shows high selectivity to Cu²⁺ ions with a detection limit of 10^–5 M. PCz and PIn are formed respectively by the anodic oxidation of 50 mM carbazole and 5 mM indole monomers in dichloromethane containing 0.1 M tetrabutylammonium perchlorate on a platinum electrode using a single compartment cell. Potentiostatic polymerization of both the monomers are carried out at 1.3 V and 1.0 V vs. Ag/AgCl, respectively. Perchlorate ions were electrochemically removed from the polymer films by applying – 0.2 V vs. Ag/AgCl. Polymer-coated electrodes are incubated in 1 M KCl solution for 8 h followed by incubation in distilled water for 2 h before using as a metal ion sensor. The undoped PCz and PIn electrodes were found to be highly selective and sensitive for Cu²⁺ ions with little selectivity for Pb²⁺ and negligible response towards Ag⁺, Hg²⁺, Cu⁺, Ni²⁺, Co²⁺, Fe²⁺, Fe³⁺ or Zn²⁺. Potentiometric responses for Cu²⁺ ions are recorded for both the sensor electrodes together with a double-junction Ag/AgCl reference electrode. Calibration curves for Cu²⁺ are reported for both ion sensors. The polymer-modified electrodes were found to be stable for several weeks. Electronic Publication     

PVC based 5,10,15,20-tetrakis (4-methoxyphenyl) porphyrinatocobalt(II) membrane potentiometric sensor for arsenite

PVC based membranes of 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrinatocobalt(II) (TMOPP-Co) (I) as electroactive material with dibutyl butyl phosphonate (DBBP), dioctyl phthalate (DOP), 1-chloronaphthalene (CN), tri-n-butyl phosphate (TBP) and tris(2-ethylhexyl) phosphate (TEP) as plasticising solvent mediators have been prepared and tried for arsenite determination. The membrane having a composition 150:5:150 (PVC:I:DBBP) exhibited the best results with linear potential response in the concentration range of 7.9 × 10⁻⁵ to 1.0 × 10⁻¹ M of AsO₂⁻ with a slope of 28.8 mV/decade. The useful pH range of the sensor is 6.0-10.5. The membrane worked satisfactorily in non-aqueous medium up to 5% (v/v) non-aqueous content. The selectivity coefficient values for mono- and divalent anions indicate good selectivity for arsenite over a large number of anions.     

Thermal analysis of ethylenediamine complexes of Ni(II) chloride

Thermal analysis of mono-, bis- and trisethylenediamine (en) complexes of Ni(II) chloride was carried out using TG, DTG and DTA techniques. The kinetic parameters were estimated from dynamic TG studies using the Coats and Redfern equation. The thermal stability of the metal-ligand (Ni-N) bond in, the complex was found to decrease with increasing Nien ratio. The DTA studies showed that the loss of en was initially endothermic but became increasingly exothermic with the progress of the decomposition. The final step in the case of all the three complexes was always composite in nature causing the loss of both Cl atoms with simultaneous oxidation of Ni to NiO. The dissociation of the Ni-en bonds appears to be regulated by the nucleation and growth mechanism. Kinetic parameters corresponding to various steps of decomposition of all the three complexes were evaluated.

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Zusammenfassung Mittels TG-, DTG- und DTA-Verfahren wurde eine Thermountersuchung des mono-, bis- und tris-Äthylendiammin (en) komplexes von Ni(II)-chlorid durchgeführt. Unter Zuhilfenahme der Gleichung von Coats und Redfern wurden die kinetischen Parameter anhand der Daten aus dynamischen TG-Untersuchungen abgeschätzt. Es wurde gefunden, daß die thermische Stabilität der Metall-Ligand Bindung (Ni-N) der Komplexe mit anwachsendem Ni:en Verhältnis absinkt. Aufgrund der DTA Untersuchungen erwies sich die Abgabe von en anfänglich als endotherm, mit fortschreitender Zersetzung jedoch als zunehmend exotherm. Bei allen drei Komplexen war der letzte Schritt immer komplexer Natur und beinhaltete die Abgabe beider Chloratome verbunden mit einer gleichzeitigen Oxidation von Ni zu NiO. Die Dissoziation der Ni-en Bindung scheint durch einen Keimbildungs- und Wachstums-mechanismus bestimmt zu werden. Die kinetischen Parameter für die einzelnen Zersetzungsschritte aller drei Komplexe wurden ermittelt.

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A research grant to LSP from the C.S.I.R. (India) and a JRF to SRN are thankfully acknowledged.     

Nickel(II)-selective sensor based on dibenzo-18-crown-6 in PVC matrix

Nickel(II)-selective sensors have been fabricated from poly(vinyl chloride) (PVC) matrix membranes containing neutral carrier dibenzo-18-crown-6 as electroactive material, sodium tetraphenylborate (NaTPB) as an anion excluder and tris-(2-ethylhexyl) phosphate (TEHP) as plasticizing solvent mediator. The membrane having the composition of crown ether:NaTPB:TEHP:PVC in the ratio 10:1:200:200 (w/w) exhibits best results with linear potential response in the concentration range of 1.0 × 10⁻⁵ to 1.0 × 10⁻¹ M and a Nernstian slope of 29.5 mV/decade of activity between 2.6 and 6.8. The sensor exhibits a fast response time of <25 s, is inert towards non-aqueous medium up to 15% (v/v) and was used over a period of 4 months with good reproducibility. It is selective over a number of mono-, bi- and trivalent cations. The practical utility of the sensor has been demonstrated by using it as an indicator electrode in the potentiometric titration of Ni²⁺ against EDTA and also for the estimation of Ni²⁺ in some Indian brand chocolates.     

A tetranuclear Cr(III)Ni(II)3 cyano-bridged complex based on M(tacn) derivative building blocks

The reaction of Cr(Bztacn)(CN)3 (Bztacn is 1,4,7-trisbenzyl-1,4,7-triazacyclononane) with Ni(iPrtacn)Cl2 (iPrtacn is 1,4,7-trisisopropyl-1,4,7-triazacyclononane) affords a CrNi3 tetranuclear complex. Variable temperature and magnetization versus field measurements show a S = 9/2 ground state and an appreciable magnetic anisotropy with a negative D(9/2) value equal to -0.54 cm(-1). Magnetization studies on one single crystal using a micro-SQUID show a fast tunneling process at zero field at very low temperature.     

A selective membrane electrode for lanthanum(III) ion based on a hexaaza macrocycle derivative as ionophore.

We have developed a highly La(III)-selective PVC membrane electrode based on a hexaaza macrocycle, 8,16-dimethyl-6,14-diphenyl-2,3,4:10,11,12-dipyridine-1,3,5,9,11,13-hexaazacyclohexadeca-3,5,8,11,13,16-hexaene [Bzo2Me2Pyo2(16)-hexaeneN6] (I) as membrane carrier, dibutylbutyl phosphonate (DBBP) as solvent mediator and sodium tetraphenylborate (NaTPB) as lipophilic additive. The best performance was given by the membrane of macrocycle I having a composition 10:260:5:120 (I:DBBP:NaTPB:PVC). The electrode exhibits a Nernstian response to La(III) ion in the concentration range 1.0x10(-1)-7.94x10(-7) M with a slope of 19.8+/-0.2 mV/decade of concentration and a detection limit of 5.62x10(-7) M. The response time of the sensor is 12 s and it can be used over a period of 4 months with good reproducibility. The electrode works well over a pH range of 2.5-10.0 and in partially non-aqueous medium with up to 30% organic content. The sensor was also used as an indicator electrode in potentiometric titration of La(III) ions with EDTA and for determining La(III) concentration in real samples.     

A highly selective turn-on colorimetric and luminescence sensor based on a triphenylamine-appended ruthenium(Ⅱ) dye for detecting mercury ion

A dual colorimetric and luminescent sensor based on a heteroleptic ruthenium dye[Ru(Hipdpa)(Hdcbpy)(NCS)_2]~-·0.5H~+ 0.5[N(C_4H_9)_4]~+ Ru(Hipdpa) {where Hdcbpy = monodeprotonted-4,4'-dicarboxy-2.2'-bipyridineand Hipdpa = 4-(1H-imidazo[4,5-f][l,10]phenanthroIin-2-yl)-N,N-diphenylaniIine} for selective detection of Hg~(2+) is presented.The results of spectrophotometric titrations revealed an evident luminescence intensity enhancement(I/I_0 =11) and a considerable blue shift in visible absorption and luminescence maxima with the addition of Hg~(2+).The sensitive response of the optical sensor on Hg~(2+) was attributed to the binding of the electron-deficient Hg~(2+) to the electron-rich sulfur atom of the thiocyanate(NCS) ligand in the Ru(Hipdpa).which led to an increase in the energy gap between the highest occupied molecular orbital(HOMO) and the lowest unoccupied molecular orbital(LUMO).Accordingly,the blue shift in the absorption spectrum of Ru(Hipdpa) due to the binding of Hg~(2+) was obtained.Ru(Hipdpa) was found to have decreased Hg~(2+) detection limit and improved linear region as compared to di(tetrabutylammonium) ris-bis(isothiocyanato)bis(2,2'-bipyridine-4-carboxylic acid-4'-carboxylate)ruthenium(Ⅱ) N719.Moreover,a dramatic color change from pink to yellow was observed,which allowed simple monitoring of Hg~(2+) by either naked eyes or a simple colorimetric reader.Therefore,the proposed sensor can provide potential applications for Hg~(2+) detection.     

Calcium(II)-selective potentiometric sensor based on p -isopropylcalix6arene in PVC matrix

In Japan, large amounts of fertilizer nitrogen are applied to tea plantations. We collected samples of tea plantation soil each season for a year. Samples were analyzed for their contents of various inorganic chemicals and total N. Nitrogen was present mainly in the top 0 to 30?cm of soil. However, at times the concentration of nitrate N in the soil water was more than 35?mg?L^?1, even in the deepest layers. The contents of various metal elements in the soil were examined. Ba, Fe, Sr and Zn contents were high in the top 0 to 30?cm of soil. But Al and Mn contents were not always high in the top 0 to 30?cm of soil. From the correlation analysis among contents of various inorganic chemicals, it was suggested that increased leaching of Al, Mn, and Zn from tea plantation soil occurred with increased nitrate N concentration.     

A fluorescence turn-on sensor for iodide based on a thymine-Hg(II)-thymine complex

Iodide plays a vital role in many biological processes, including neurological activity and thyroid function. Due to its physiological relevance, a method for the rapid, sensitive, and selective detection of iodide in food, pharmaceutical products, and biological samples such as urine is of great importance. Herein, we demonstrate a novel and facile strategy for constructing a fluorescence turn-on sensor for iodide based on a T-Hg(II)-T complex (T=thymine). A fluorescent anthracene-thymine dyad (An-T) was synthesized, the binding of which to a mercury(II) ion lead to the formation of a An-T-Hg(II)-T-An complex, thereby quenching the fluorescent emission of this dyad. In this respect, the dyad An-T constituted a fluorescence turn-off sensor for mercury(II) ions in aqueous media. More importantly, it was found that upon addition of iodide, the mercury(II) ion was extracted from the complex due to the even stronger binding between mercury(II) ions and iodide, leading to the release of the free dyad and restoration of the fluorescence. By virtue of this fluorescence quenching and recovery process, the An-T-Hg(II)-T-An complex constitutes a fluorescence turn-on sensor for iodide with a detection limit of 126 nM. Moreover, this sensor is highly selective for iodide over other common anions, and can be used in the determination of iodide in drinking water and biological samples such as urine. This strategy may provide a new approach for sensing some other anions.     

Preparation of ethambutol-copper(II) complex and fabrication of PVC based membrane potentiometric sensor for copper

Copper(II) complex of ethambutol (I) was prepared and used in the fabrication of Cu(2+) selective ISE membrane. The membrane having Cu(II)-ethambutol complex (I) as electroactive material, along with sodium tetraphenylborate (NaTPB) as anion discriminator, dioctylphthalate (DOP) as plasticizer in poly(vinyl chloride) (PVC) matrix in the percentage ratio 6:2:190:200 (I:NaTPB:DOP:PVC) (w/w) gave a linear response in the concentration range 7.94x10(-6) to 1.0x10(-1) M of Cu(2+) with a slope of 29.9+/-0.2 mV per decade of activity and a fast response time of 11+/-2 s. The sensor works well in the pH range 2.1-6.3 and could be satisfactorily used in presence of 40% (v/v) methanol, ethanol and acetone and is selective for copper over a large number of cations with slight interference from Na(+) and Co(2+) if present at a level 1.5x10(-5) and 6.5x10(-5) M, respectively. It works well over a period of 6 months and can also be used as indicator electrode for the end point determination in the potentiometric titration of Cu(2+) against EDTA as well as in the determination of Cu(2+) in real samples.