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.     

A novel optical sensor for uranium determination

A metal ion indicator, Alizarin Red S, was tested for its potential use in uranium selective optode membrane. The water-soluble indicator was lipophilized in the form of an ion pair with tetraoctylammonium bromide, and subsequently immobilized on a triacetyl cellulose membrane. The membrane responds to uranium ions, giving a color change from yellow to violet in acetate buffer pH 5. This optode has a linear range of (1.70-18.7) × 10⁻⁵ M of UO₂²⁺ ions with a limit of detection of 5 × 10⁻⁶ M. The response time of optode was within 6 min depending on the concentration of UO₂²⁺ ions. The sensor can readily be regenerated with hydrochloric acid solution (0.01 M). The optode is fully reversible.     

A new sensitive optical bulk test-system for thallium based on pyridylazo resorcinol

A color changeable optode for thallium(III) ions in aqueous solutions was prepared by physical inclusion of 4-(2-pyridylazo)-resorcinol into a plasticized PVC film. The increase in the absorbance of the optode at 524 nm is proportional to thallium(III) concentration. Different parameters effecting the sensitivity such as sample parameters and composition of the membrane were optimized. The response times of the prepared test-system are found to be 230, 210, and 180 s for 4.8 × 10^?6, 4.8 × 10^?5, and 4.8 × 10^?4 M Tl(III), respectively. The analytical performance of the optode was evaluated, obtaining a linear concentration range of two decades of concentration, 3.1 × 10^?6 ? 4.7 × 10^?4 M Tl(III), with a limit of detection of 1.8 × 10^?6 M Tl(III). Selectivity of the optode is also studied. Application of the optode to the determination of Tl(III) in some aqueous samples yields good results.     

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.     

An optode sensor for Cu2+ with high selectivity based on porphyrin derivative appended with bipyridine.

A porphyrin derivative (fluorophore) appended with bipyridine (ionophore) has been applied for preparation of a Cu2+-sensitive optical chemical sensor, which is based on fluorescence quenching of porphyrin derivative entrapped in a poly(vinyl chloride) membrane by the energy transfer process. The sensor exhibits a linear response toward Cu2+ in the concentration range 2.0 x 10(-8) - 1.0 x 10(-5) M, with a working pH range from 6.0 to 8.0 and a high selectivity. The detection limit is 5 x 10(-9) M. The response time for Cu2+ is less than 5 min with concentrations lower than 5 x 10(-6) M. The optode can be regenerated using 0.3 M EDTA (pH 9) and acetate buffer solution. The effect of the composition of the sensor membrane was studied, and the experimental conditions were optimized. The sensor has been used for direct determination of Cu2+ in water samples with satisfied results.     

Constructing a new optical sensor for monitoring ammonia in water samples using bis(acetylacetoneethylendiamine)-tributylphosphin cobalt(III) tetraphenylborate complex-coated triacetylcellulose.

A new ammonia optical sensor was designed using bis(acetylacetoneethylendiamine)tributylphosphin cobalt(III) tetraphenylborate complex, coated on transparent triacetylcellulose film as membrane. The change in the absorbance of the optode at the maximum wavelength of 408 nm was related to ammonia concentration in aqueous samples. A buffer solution with a pH of 9 (sodium borate-HCl) was used. The optode was fully regenerated in pH 2. The linear dynamic range for determination of ammonia was 3.3 x 10(-4) to 6.9 x 10(-3) mol l(-1) with a detection limit of 5.0 x 10(-5) mol l(-1) and a response time range of 4 - 6 min. This membrane was successfully applied for determination of ammonia in drinking water.     

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.     

A simple optical sensor for cadmium ions assay in water samples using spectrophotometry

A new simple and inexpensive optical chemical sensor for cadmium(II) ions is presented. The cadmium sensing system was prepared by incorporating 2-amino-cyclopentene-1-dithiocarboxylic acid (ACDA) on a triacetylcellulose membrane. The absorption spectra of the optical sensor membrane in Cd(II) solution showed a maximum peak at 430 nm. The proportionality in intensity of the membrane color on the optode to varying amounts of Cd(II) suggests its potential applications for screening Cd(II) in aqueous samples by visual colorimetry. The sensor provided a wide concentration range of 3.0 × 10⁻⁶–3.4 × 10⁻⁴ M of Cd(II) ions with a detection limit of 1.0 × 10⁻⁶ M (0.2 μg/mL). The relative standard deviations for eight replicate measurements of 8.0 × 10⁻⁶ and 5.0 × 10⁻⁵ M Cd(II) were 2.7 and 2.3%, respectively. The response time of the optode was 6 min. The influence of interfering ions on the determination of 1.0 × 10⁻⁵ M Cd(II) was studied and the main interferences were removed by extraction method. The sensor was applied to the determination of Cd(II) in water samples.     

Design of a Novel Gadolinium Optical Sensor Based on Immobilization of (Z)-N′-((Pyridine-2-yl) Methylene) Thiophene-2-carbohydrazide on a Triacetylcellulose Membrane and Its Application to the Urine Samples

Abstract

In this work, for the first time we report a highly selective and sensitive Gd(III) optical sensor based on immobilization of (Z)-N′-((pyridine-2-yl) methylene) thiophene-2-carbohydrazide (PMTC) on a triacetylcellulose membrane. This optode exhibits a linear range 5.0 × 10^?8 to 2.0 × 10^?5 M of Gd(III) ion concentration with a detection limit of 1.1 × 10^?8 M. The response time of the newly designed optode was within 1–2 min, depending on the Gd(III) ion concentration. The response of the sensor is independent of the pH solution in the range of 2.0–9.0. It manifests advantages of low detection limit, fast response time, and most significant, very good selectivity with respect to a number of lanthanide ions (La, Ce, Sm, and Eu ions). The proposed sensor could be successfully regenerated with a thiourea solution. Its response was reversible and reproducible (RSD less than 1.3%). This optode was applied to the determination of Gd(III) in synthetic and real samples.     

A reversible optode membrane for picric acid based on the fluorescence quenching of pyrene

Pyrene immobilized in plasticized poly(vinyl chloride) (PVC) membrane is able to extract selectively picric acid from the sample solution into the organic membrane phase. Since this extraction equilibrium is accompanied by a change in the fluorescence spectrum of pyrene, the chemical recognition process can be directly translated into an optical signal. With the optode membrane described, picric acid in sample solutions from 8.7 x 10(-6) to 4.3 x 10(-3)M can be determined. The calibration curve of the optode membrane for picric acid shows a good correlation with the mathematically derived formalism and thus confirms the theoretically expected behaviour. Besides a high reproducibility of the optical signals, the very short response times less than 35 sec are realized. The optode membrane presented exhibits good selectivity for picric acid over many other usual hydrophobic anions.     

Development of a new flow-through bulk optode for the determination of manganese(III)

A flow-through bulk optode based on the use of 1-(2-pyridylazo)-2-naphthol (PAN) immobilized in a plasticized poly(vinyl chloride) membrane entrapped in a cellulose support, in conjuntion with the flow injection analysis technique, is proposed for the determination of manganese(II). The calibration graph obtained at 570 nm was linear in the range 0.27-27.5 mg L(-1) (5 x 10(-6)-5 x 10(-4) M) Mn(II) with a detection limit of 0.18 mg L(-1). The coefficients of variation of the sensor response for 5.5 mg L(-1) of Mn(II) were +/-0.22% for consecutive measurements (n = 10), +/-0.48% between days (n = 5) and +/-0.38% between different membranes (n = 6). The sensor was readily regenerated with the carrier acetic acid/acetate buffer of pH 4.5. The method was applied to the determination of manganese in steels, waters and lemon tree leaves.     

A sensitive optode membrane for berberine using conjugated polymer as sensing material.

A new optode membrane for the sensitive determination of berberine based on fluorescence quenching of a conjugated polymer, poly(2,5-dimethoxy-phenyldiacetylene) (PDPA), is proposed. Incorporated in a membrane composed of plasticized poly(vinyl chloride) (PVC), the conjugated polymer exhibits better stability than those small sensing molecules regarding its excellent optical properties and lipophilic characteristics. Moreover, upon the introduction of a negatively charged lipophilic additive (tetraphenylborate salt) into a PVC membrane, the optode displayed enhanced sensitivity. In addition, satisfactory analytical sensing characteristics for determining beberine were obtained in terms of the selectivity, reversibility and reproducibility with a detecting range of between 7.5 x 10(-7) mol l(-1) and 7.5 x 10(-4) mol l(-1). The optode membrane has been applied to determine berberine in commercial tablets. The results showed a good agreement with those obtained by the pharmacopoeial method.     

Ion-Exchange Reaction of Silver(I) and Copper(II) in Optical Sensors Based on Thiaglutaric Diamide

Bulk optode membranes based on a recently reported thiaglutaric diamide ionophore were developed for measurements of silver(I) and copper(II) ions in aqueous solutions. The response properties of optical films containing ionophore and chromoionophores with different pK(a) values were investigated at different sample pH. At certain pH the measuring range of the optode can be shifted when choosing different chromoionophores. Optode with ionophore and chromoionophore V exhibited good responses to silver ions from 10(-6) - 10(-1) M at pH 5.5. The proposed sensor showed high selectivity, good reproducibility and stability. With a different chromoionophore ETH 5418 the optode could response to copper(II) ions from 10(-6) - 10(-2) M.     

Flow-Through Bulk Optode for the Spectrophotometric Determination of Perchlorate

A flow-through spectrophotometric bulk optode for the flow-injection determination of perchlorate is described. As active constituents, the optode incorporates the lipophilic pH indicator 5-octadecanoyloxy-2-(4-nitrophenylazo) phenol and methyltridodecyl ammonium chloride, dissolved in a plasticized poly(vinyl chloride) membrane which is entrapped in a cellulose support. The optode is applied in conjunction with the flow injection technique at pH 8.2 (TRIS buffer). The sensor is readily regenerated with a 10^–2M NaOH carrier solution. The analytical characteristics of this optode with respect to response time, dynamic measurement range, reproducibility and selectivity are discussed. The proposed FI method is applied to the determination of perchlorate in waters from different sources.Received December 16, 2002; accepted May 16, 2003 Published online August 8, 2003     

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.     

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.     

Picric acid sensitive optode based on a fluorescence carrier covalently bound to membrane

An acryloyl group was attached to fluorescein through the phenol hydroxyl group to make it photopolymerizable with 2-hydroxypropyl methacrylate and covalently immobilized on an optode glass surface modified with gamma-(methacryloxy)propyltrimethoxysilane. The optode system with a plastic-clad fused silica bifurcated fiber optic bundle shows satisfactory analytical performance characteristics for determining picric acid in terms of selectivity and reproducibility with a linear range from 8.0 x 10(-7) to 4.0 x 10(-3) mol L-1. The quenching mechanism was investigated. The optode membrane can be applied to the indirect determination of cinchonine drug and the results obtained were satisfactory.     

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.     

A highly selective fluorescent sensor for Cu based on 2-(2′-hydroxyphenyl)benzoxazole in a poly(vinyl chloride) matrix

This paper describes a copper selective optical chemical sensor based on static quenching of the fluorescence of 2-(2′-hydroxyphenyl)benzoxazole entrapped in a poly(vinyl chloride) (PVC) membrane. The effect of the composition of the sensing membrane was studied, and experimental conditions were optimized. The sensors exhibit stable response over the concentration range from 4.0 × 10⁻⁸ M to 5.0 × 10⁻⁵ M Cu²⁺ at pH 4.0-6.5, and a high selectivity. The response time for Cu²⁺ with concentration ≤5 × 10⁻⁶ M is less than 7 min. The optode can be regenerated using 0.1 M HCl and acetate buffer solution. The sensor has been used for direct measurement of copper content in river water samples with a relative error less than 4% with reference to that obtained by atomic absorption spectrometry.