A new procedure for the construction of flow-through optodes. Application to determination of copper (II)

A new procedure for constructing an optical fibre reflectance, bulk optode membrane type, sensor is presented. The optode membrane consists of a plasticized poly (vinyl chloride) membrane in which the ionophore is dissolved, entrapped in a cellulose support. The new optode with the dye indicator 1-(2-pyridylazo)-2-naphthol (PAN) was incorporated in a new flow-through cell and the injection system was optimized to determine Cu (II) at 567 nm in the range 5 x 10(-5)-10(-3) M. The response was reproducible and the optode can be regenerated using 10(-2) M EDTA followed by water. The method was applied to the determination of copper in real samples.     

Poly(vinyl chloride)-membrane ion-selective bulk optode based on 1,10-dibenzyl-1,10-diaza-18-crown-6 and 1-(2-pyridylazo)-2-naphthol for Cu and Pb ions

An ion-selective bulk optode (ISBO) for sensing Cu²⁺ and Pb²⁺ ions based on plasticized poly(vinyl chloride) containing 1,10-dibenzyl-1,10-diaza-18-crown-6 (DBzDA18C6) as ionophore and 1-(2-pyridylazo)-2-naphthol (PAN) as chromoionophore was prepared. The effects of DBzDA18C6/PAN and NaTPB/PAN mole ratios on the response behavior of the ISBO were investigated. The ISBO membrane shows enhanced selectivities for Cu²⁺ (at 530 nm) and Pb²⁺ (at 467 nm) over alkali, alkaline earth and other transition metal ions. The optical selectivity coefficients were measured using the separate solution method (SSM) in the two corresponding wavelengths at pH=5. The detection limit for Cu²⁺ and Pb²⁺ are 3.2×10⁻⁷ and 1.0×10⁻⁸ M, respectively.     

Chromogenic betaine lariates for highly selective calcium ion sensing in aqueous environment

This paper describes the design, synthesis, and the characterization of the two new chromogenic crown ethers 2,2′-[1,4,10,13-tetraoxa-7,16-diazacyclooctadecane-7,16-diylbis(methylene)]bis[4-[(1-methyl-4-(1H)-pyridinylidene)ethylidene]-2,5-cyclohexadien-1-one (KBC-001) and the lipophilic derivative 2,2′-[1,4,10,13-tetraoxa-7,16-diazacyclooctadecane-7,16-diylbis(methylene)]bis[4-[(1-dodecyl-4-(1H)-pyridinylidene)ethylidene]-2,5-cyclohexadien-1-one (KBC-002). A merocyanine dye that forms a betainic structure upon intramolecular charge transfer and shows solvent polarity dependent spectral sensitivity was selected as the chromophore system to develop the new chromoionophores. This approach allows the design of overall electrically neutral ligands bearing charged groups without the need of external counter ions. A proton ionizable group in the dye moiety acts as a charged ion-binding site and is an integral part of a lariat crown ether ionophore. A chromoionophore for calcium ion sensing has been developed, which combines the size-selective binding character of a crown ether with strong electrostatic attraction between the positively charged calcium ion and two negatively charged lariat side arms in the overall neutral compound. This water-soluble dye selectively responds to the presence of calcium ions in water at pH 8.5 with a dynamic response range between 10 μM and 10 mM. The binding event can be monitored both by absorption spectrometry and by fluorescence spectrometry. No cross-sensitivity was found for the physiologically important cations Mg²⁺, Li⁺, Na⁺, and K⁺ up to concentrations of 0.1 M under the same experimental conditions. In contrast to the water-soluble reagent KBC-001, the lipophilized derivative KBC-002 having two long alkyl chains was successfully applied to ion-exchange type optode membranes made from plasticized poly(vinyl chloride) (PVC). The dynamic response range of the optode at pH 9.0 was between 10 μM and 10 mM while retaining the high calcium selectivity.     

Cesium-selective optode membrane based on the lipophilic calix[4]biscrown in the 1,3-alternate conformation

One type of lipophilic calix[4]biscrowns in the 1,3-alternate conformation which are highly selective complexant for cesium has been used to construct cesium poly(vinyl chloride) (PVC) membrane optode. The reversible sensing system has been formed by incorporating the lipophilic neutral H⁺—selective chromoionophore ETH5294 in the plasticized PVC membrane with 1,3-calix[4]bisnaphtyl-crown-6. The measuring range of cesium ions can be conditioned by buffering different pH in the cesium solutions. At pH 7.0, the measuring range of the optode membrane for cesium ions is from 1×10⁻⁶ to 1×10⁻² M. The response behavior of optode membrane including response time, selectivity, reproducibility and lifetime, has been described in detail.     

Design and evaluation of a thorium (IV) selective optode

A novel optical sensor has been proposed for sensitive determination of thorium (IV) ion in aqueous solutions. The thorium sensing membrane was prepared by incorporating 4-(p-nitrophenyl azo)-pyrocatechol (NAP) as ionophore in the plasticized PVC membrane containing tributyl phosphate (TBP) as plasticizer. The membrane responds to thorium ion by changing color reversibly from yellow to red-brown in glycine buffer solution at pH 3.5. The proposed sensor displays a linear range of 8.66 × 10⁻⁶-2.00 × 10⁻⁴ M with a limit of detection of 6 × 10⁻⁶ M. The response time of the optode was about 8.8-12.5 min, depending on the concentration of Th (IV) ions. The selectivity of optode to Th (IV) ions in glycine buffer is good. The sensor can readily be regenerated by exposure to a solution mixture of sodium fluoride and 5-sulfosalicylic acid (dihydrate) (0.01 M each). The optode is fully reversible. The proposed optode was applied to the determination of thorium (IV) in environmental water samples.     

A new procedure for the construction of flow-through optodes. Application to determination of copper (II)

A new procedure for constructing an optical fibre reflectance, bulk optode membrane type, sensor is presented. The optode membrane consists of a plasticized poly (vinyl chloride) membrane in which the ionophore is dissolved, entrapped in a cellulose support. The new optode with the dye indicator 1-(2-pyridylazo)-2-naphthol (PAN) was incorporated in a new flow-through cell and the injection system was optimized to determine Cu (II) at 567 nm in the range 5 × 10^?5–10^?3 M. The response was reproducible and the optode can be regenerated using 10^?2 M EDTA followed by water. The method was applied to the determination of copper in real samples.     

Development of a selective optical sensor for Cr(VI) monitoring in polluted waters

An optical sensor is described for the sensitive and selective determination of the Cr(VI) ion in aqueous solutions. The optode membrane is prepared by incorporating Aliquat 336 as an ionophore and a chromoionophore (4',5'-dibromofluorescein octadecyl ester) in a poly(vinyl chloride) (PVC) membrane containing ortho-nitrophenyloctyl ether (o-NPOE) as a plasticizer. The response to Cr(VI) is indicated by co-extraction of the target species and of hydrogen ions into the bulk of the membrane yielding large absorbance changes which can easily be measured in the visible spectral range. The optode membrane shows a reversible response in the concentration range of 1.1x10(-5)-1.0x10(-3) M and has been shown to be more selective towards the HCrO4(-) ion than other anions with a selectivity pattern HCrO4(-) > SCN- approximately = ClO4(-) > NO3(-) approximately = I- approximately = NO2(-) > H2PO4(-) approximately = Cl- approximately = SO4(2-). The sensing method developed has successfully been applied to the determination of Cr(VI) in spiked river water as well as in electroplating rinse waters.     

PVC-membrane ion-selective bulk optode for Ag<Superscript>+</Superscript> ion based on hexathia-18-crown-6 and 1,2-benzo-3-octadecanoylimino-7-diethylaminophenoxazine

A silver-selective optode membrane incorporating hexathia-18-crown-6 for cation recognition and a lipophilic chromoionophore 1,2-benzo-3-octadecanoylimino-7-diethylaminophenoxazine for transduction has been prepared. The PVC membrane composition was optimized to result in the largest working concentration range. The response range of the proposed optode is 5.0 x 10(-9)-5.0 x 10(-5) mol L(-1) Ag(+) with a limit of detection of 1.0 x 10(-9) mol L(-1). The probe works well at pH 5.0 and revealed small ion interference and good selectivity, reproducibility and stability.     

Copper(II)-selective fluorimetric bulk optode membrane based on a 1-hydroxy-9,10-anthraquinone derivative having two propenyl arms as a neutral fluorogenic ionophore

A new optical chemical sensor has been developed for the selective determination of copper(II) ions in aqueous solutions. The reversible sensing system was prepared by incorporating 1-hydrpxy-2-(prop-2'-enyl)-4-(prop-2'-enyloxy)-9,10-anthraquinone (AQ) as a neutral Cu2+-selective fluoroionophore in the plasticized PVC membrane with potassium tetrakis(p-chlorophenyl borate) as an anionic additive. The response of the sensor is based on the fluorescence quenching of AQ by Cu2+ ions. At a pH 5.5, the proposed sensor displays a calibration response for Cu2+ over a wide concentration rang of 1.0 x 10(-2) to 1.0 x 10(-6) M, with a relatively fast response of less than 40 s. In addition to high stability and reproducibility, the sensor shows a unique selectivity towards Cu2+ ion with respect to common co-existing cations. The proposed fluorescence optode was applied successfully to the determination of copper(II) in black tea samples.     

Development of a new fluorimetric bulk optode membrane based on 2,5-thiophenylbis(5-tert-butyl-1,3-benzexazole) for nickel(II) ions

A highly sensitive and selective fluorimetric optode membrane for the determination of ultra trace amounts of Ni²⁺ ions was prepared. The plasticized PVC-membrane incorporating potassium tetrakis(p-chlorophenyl)borate (KTpClPB) and 2,5-thiophenylbis(5-tert-butyl-1,3-benzexazole) (TTBB), as a highly fluorescent chromoionophore, displays a calibration response for Ni²⁺ ions over a wide concentration range of 1.0×10⁻³ to 1.0×10⁻⁸ M. It has a relatively fast response of <40 s. In addition to high stability and reproducibility, and relatively long working lifetime, the sensor possesses good selectivity for nickel ions over several common diverse ions. The fluorescence signal of the optode membrane can be easily recovered by immersion in EDTA solution. The optode was applied successfully to the determination of traces of Ni²⁺ ion in edible oil and a wastewater sample from nickel electroplating industries.     

Hydrophilic sensor membrane based on cation-selective protic chromoionophore

The first potassium optode based on a protic chromoionophore immobilized in a hydrogel matrix is presented. The highly selective protic chromoionophore consists of a cryptohemispherand moiety and a trinitroanilino chromophore part. The acidifying power of potassium ions over sodium ions is 0.6 pH units. This correlates with the findings in solution. In contrast to several crown and aza-crown based chromophores the highly pre-organized moiety allows ion detection even in aqueous environment. The detection limit for potassium ions at ¶pH 7.7 is 5 μM.     

Phosphate-selective fluorescent sensing microspheres based on uranyl salophene ionophores

Optical dihydrogen phosphate-selective sensors that function on the basis of bulk optode principles and are based on two different uranyl salophene ionophores are reported here for the first time. The influence of the optode composition and measuring conditions such as sample pH on the optode response are characterized, along with sensor selectivity and long-term stability. Three plasticizers of different polarity are considered for optode fabrication: bis(2-ethylhexyl)sebacate (DOS), dodecyl 2-nitrophenyl ether (o-NPDDE), o-nitrophenyloctylether (o-NPOE). The compounds 9-(diethylamino)-5-(octadecanoylimino)-5H-benzo[a]phenoxazine (ETH 5294, chromoionophore I) and 9-(diethylamino)-5-[(2-octyldecyl)imino]benzo[a]phenoxazine (ETH 5350, chromoionophore III) are used as H⁺-selective fluoroionophores that also act as reference ionophores. The resulting optode-based sensors are compared with their ion-selective electrode (ISE) counterparts, and it is revealed that optodes are better suited for operation at physiological pH. The best optode performance was found for the two component optode sensors doped with ETH 5350 and phosphate ionophore(I). The linear range of these sensor was log a = −6.0 to −2.6. Dihydrogen phosphate-selective optode sensors of optimized composition are fabricated in microsphere format and preliminary measurements in diluted sheep blood samples are presented.     

Determination of copper(II) in wastewater by electroplating samples using a PVC-membrane copper(II)-selective electrode

A PVC membrane containing 4-amino-6-methyl-1,2,4-triazin-3,5-dithione (AMTD) as a suitable ionophore, exhibits a Nernstian response for Cu²⁺ ions over a wide concentration range up to 1 × 10⁻¹ and 1 × 10⁻⁶ M, with a detection limit of 7.5 × 10⁻⁷ M in the pH range 3.0–7.5. It has a fast response time (<15 s) and can be used for at least 12 weeks without any major deviation in the potential. The electrode revealed a very good selectivity with respect to all common alkali, alkaline-earth, transition, and heavy-metal ions. It was successfully applied to the recovery of copper ions from wastewater. The electrode was also used as an indicator electrode in the potentiometric titration of Cu(II) ions with EDTA. The text was submitted by the authors in English.     

A PVC plasticized sensor for Ni(II) ion based on a simple ethylenediamine derivative.

A new PVC membrane ion selective electrode which is highly selective towards Ni(II) ions was constructed using a Schiff base containing a binaphthyl moiety as the ionophore. The sensor exhibited a good Nernstian response for nickel ions over the concentration range 1.0x10(-1)-5.0x10(-6) M with a lower limit of detection of 1.3x10(-6) M. It has a fast response time and can be used for a period of 4 months with a good reproducibility. The sensor is suitable for use in aqueous solutions in a wide pH range of 3.6-7.4 and works satisfactorily in the presence of 25% (v/v) methanol or ethanol. The sensor shows high selectivity to nickel ions over a wide variety of cations. It has been successfully used as an indicator electrode in the potentiometric titration of nickel ions against EDTA and also for the direct determination of nickel content in real samples: effluent samples, chocolates and hydrogenated oils.     

Novel PVC-based copper(II) membrane sensor based on 2-(1'-(4'-(1'-hydroxy-2'-naphthyl)methyleneamino)butyl iminomethyl)-1-naphthol.

A copper(II) ion-selective PVC membrane sensor based on 2-(1'-(4'-(1'-hydroxy-2'-naphthyl)methyleneamino)butyl iminomethyl)-1-naphthol (BHNB) as a novel Schiff base containing a sensing material has been successfully developed. The sensor exhibits a good linear response of 29 mV per decade within the concentration range of 10(-1)-10(-6) M of Cu2+. The sensor shows good selectivity for copper(II) ion in comparison with alkali, alkaline earth, transition and heavy metal ions. The BHNB-based sensor is suitable for use with aqueous solutions of pH 3.5-7.0 and displays minimal interference by Sr(II), Cd(II), Hg(II), Zn(II) and Pb(II), which are known to interfere with other previously suggested electrodes. The proposed membrane electrode was used as a sensor for determining the Cu(II) content in black tea samples. It was also applied as an indicator electrode in the potentiometric titration of Cu2+ ions with EDTA.     

Mercury(II) ion-selective electrodes based on p-tert-butyl calix[4]crowns with imine units.

A PVC membrane incorporating p-tert-butyl calix[4]crown with imine units as an ionophore was prepared and used in an ion-selective electrode for the determination of mercury(II) ions. An electrode based on this ionophore showed a good potentiometric response for mercury(II) ions over a wide concentration range of 5.0 x 10(-5) - 1.0 x 10(-1) M with a near-Nernstian slope of 27.3 mV per decade. The detection limit of the electrode was 2.24 x 10(-5) M and the electrode worked well in the pH range of 1.3 - 4.0. The electrode showed a short response time of less than 20 s. The electrode also showed better selectivity for mercury(II) ions over many of the alkali (Na+, -1.69; K+, -1.54), alkaline-earth (Ca2+, -3.30; Ba2+, -3.32), and heavy metal ions (Co2+, -3.67; Ni2+, -3.43; Pb2+, -3.31; Fe3+, -1.82). Ag+ ion was found to be the strongest interfering ion. Also, sharp end points were obtained when the sensor was used as an indicator electrode for the potentiometric titration of mercury(II) ions with iodide and dichromate ions.     

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.     

Silver(I)-selective coated-wire electrode based on an octahydroxycalix[4]arene derivative.

The performance of octahydroxycalix[4]arene derivative used as a neutral carrier for silver polymeric membrane electrode was studied. The sensor gave a good Nernstian response of 58 +/- 1 mV per decade for silver ion in the activity range 3.3 x 10(-6) to 3.3 x 10(-2) M Ag+. The limit of detection reached 2.1 x 10(-6) M Ag+ and exhibited high selectivity for silver ion against the alkali, alkaline earth and transition metal ions. The sensor can be used in wide pH range from 1.5 to 6.5. The response time of the sensor is less than 20 s. The potentiometric sensor was used as the indicator electrode in the titration of Ag+ ions by sodium chloride solution.     

New polymeric membrane cadmium(II)-selective electrodes using tripodal amine based ionophores

Fabrication of PVC membrane electrodes incorporating selective neutral carriers for Cd(2+) was reported. The ionophores were designed to have different topologies, donor atoms and lipophilicity by attaching tripodal amine (TPA) units to the lipophilic anthracene (ionophore I) and p-tert-butylcalix[4]arene (ionophores II, III and IV). The synthesized ionophores were incorporated to the plasticized PVC membranes to prepare Cd(II) ion selective electrodes (ISEs). The membrane electrodes were optimized by changing types and amounts of ionic sites and plasticizers. The selectivity of the membranes fabricated from the synthesized ionophores was evaluated, the relationship between structures of ionophores and membrane characteristics were explored. The ionophore IV which composed of two opposites TPA units on the calix[4]arene compartment showed the best selectivity toward Cd(2+). The best membrane electrode was fabricated from ionophore IV (10.2 mmol kg(-1)) with KTpClPB (50.1 mol% related to the ionophore) as an ion exchanger incorporated in the DOS plasticized PVC membrane (1:2; PVC:DOS). The Cd-ISE fabricated from ionophore IV exhibited good properties with a Nernstian response of 29.4±0.6 mV decade(-1) of activity for Cd(2+) ions and a working concentration range of 1.6×10(-6)-1.0×10(-2)M. The sensor has a fast response time of 10s and can be used for at least 1 week without any divergence in potential. The electrode can be used in the pH range of 6.0-9.0. The proposed electrodes using ionophores III and IV were employed as a probe for determining Cd(2+) from the oxidation of CdS QDs solution and the real treatment waste water sample with excellent results.     

A mercury(II) ion-selective electrode based on N,N-dimethylformamide-salicylacylhydrazone as a neutral carrier.

A new PVC membrane mercury(II) ion electrode based on N,N-dimethylformamide-salicylacylhydrazone (DMFAS) as an ionophore is described, which shows excellent potentiometric response characteristics and displays a linear log[Hg(2+)] versus EMF response over a wide concentration range between 6.2 x 10(-7) and 8.0 x 10(-2) M with a Nerstian slope of 29.6 mV per decade and a detection limit of 5.0 x 10(-7) M. The response time for the electrode is less than 30 s and the electrode can be used for more than 2 months with less than a 2 mV observed divergence in a potentials. The proposed electrode exhibits very good selectivity for mercury(II) ions over many cations in a wide pH range (pH 1 - 4). The electrode was also applied to the determination of a mercury(II) ion in vegetables and in Azolla filiculoides.