Highly selective thiocyanate membrane electrode based on butane-2,3-dione bis(salicylhydrazonato)zinc(II) complex

A highly selective poly(vinyl chloride) (PVC) membrane electrode based on butane -2,3-dione bis(salicylhydrazonato) zinc(II) [Zn (BDSH)] complex as carrier for thiocyanate-selective electrode is reported. The influence of membrane composition, pH and possible interfering anions were investigated on the response properties of the electrode. The sensor responds to thiocyanate in linear range from 1.0 × 10⁻⁶ to 1.0 × 10⁻¹ M with a slope −56.5 ± 1.1 mV decade⁻¹, over a wide pH range of 3.5-8.5. The limit of detection of the electrode was 7.0 × 10⁻⁷ M SCN⁻. Selectivity coefficients determined with fixed interference method (FIM) indicate a good discriminating ability towards SCN⁻ ion in comparison to other anions. The proposed sensor has a fast response time of about 5-15 s and can be used for at least 3 months without any considerable divergence in potential. It was applied as indicator electrode in titration of thiocyanate with Ag⁺ and in potentiometric determination of thiocyanate in saliva and urine samples.     

The first use of a Rh(III) complex as a novel ionophore for thiocyanate-selective polymeric membrane electrodes

The feasibility of a newly synthesized Rh(III) complex, Rh[(trpy)(bpy)Cl](PF₆)₂, as a novel ionophore for the preparation of anion-selective polymeric membrane electrodes was tested. The ionophore exhibited anti-Hofmeister behavior with enhanced potentiometric selectivity toward thiocyanate ion compared to other anions. The influence of some experimental parameters such as membrane composition, nature and amount of plasticizer and additive and concentration of internal solution on the potential response of the SCN⁻ sensor were investigated. The electrode exhibits a Nernstian response for SCN⁻ over a wide concentration range (1.0 × 10⁻⁵ to 1.0 × 10⁻¹ M) with a slope −58.7 ± 0.5 mV per decade and a detection limit of 4.0 × 10⁻⁶ M (0.23 ppm). It could be used in a pH range of 3.0-8.0 and has a fast response time of about 15 s. The proposed sensor was used for the determination of thiocyanate ions in real samples such as urine and saliva of smokers and nonsmokers and, as an indicator electrode, in potentiometric titrations of SCN⁻ ion.     

Highly selective and sensitive thiocyanate membrane electrode based on nickel(II)-1,4,8,11,15,18,22,25-octabutoxyphthalocyanine

A highly selective membrane electrode based on nickel(II)-1,4,8,11,15,18,22,25-octabutoxyphthalocyanine (NOBP) is presented. The proposed electrode shows very good selectivity for thiocyanate ions over a wide variety of common inorganic and organic anions. The sensor displays a near Nernstian slope of −58.7 ± 0.6 mV per decade. The working concentration range of the electrode is 1.0 × 10⁻⁶ to −1.0 × 10⁻¹ M with a detection limit of 5.7 × 10⁻⁷ M (33.06 ng/mL). The response time of the sensor in whole concentration ranges is very short (<10 s). The response of the sensor is independent on the pH range of 4.3-9.8. The best performance was obtained with a membrane composition of 30% PVC, 65% dibutyl phthalate, 3% NOBP and 2% hexadecyltrimethylammonium bromide. It was successfully applied to direct determination of thiocyanate in biological samples, and as an indicator electrode for titration of thiocyanate ions with AgNO₃ solution.     

A selective modified carbon paste electrode for determination of cyanide using tetra-3,4-pyridinoporphyrazinatocobalt(II)

A chemically modified carbon paste electrode with 3,4-tetra pyridinoporphirazinatocobalt(II) (Co(3,4 tppa) was applied to the determination of free cyanide ion. The electrode has a linear range between 1.5 × 10⁻⁵ M and 1.0 × 10⁻² M with a Nernstian slope of 60 ± 1.5 mV/decade and its detection limit is 9 × 10⁻⁶ M. The response time of electrode is 5 min. The proposed electrode was applied successfully for the determination of cyanide in commercially available spring water. Some anions, such as SCN⁻, I⁻, Cl⁻, Br⁻ and oxalate that are usually serious interfering species for most of cyanide selective electrodes, did not have any interfering effect for this proposed electrode.     

Highly selective and sensitive monohydrogen phosphate membrane sensor based on molybdenum acetylacetonate

In this work, a highly selective and sensitive monohydrogen phosphate membrane sensor based on a molybdenum bis(2-hydroxyanil) acetylacetonate complex (MAA) is reported. The sensor shows a linear dynamic range between 1.0 × 10⁻¹ and 1.0 × 10⁻⁷ M, with a nice Nernstian behavior (−29.5 ± 0.3 mV decade⁻¹) in pH of 8.2. The detection limit of the electrode is 6.0 × 10⁻⁸ M (∼6 ppb). The best performance was obtained with a membrane composition of 32% poly(vinyl chloride), 58% benzyl acetate, 2% hexadecyltrimethylammonium bromide and 8% MAA. The sensor possesses the advantages of short response time, low detection limit and especially, very good selectivity towards a large number of organic and inorganic anions including salicylate, citrate, tartarate, acetate, oxalate, fluoride, chloride, bromide, iodide, sulfite, sulfate, nitrate, nitrite, cyanide, thiocyanate, perchlorate, metavanadate, and bicarbonate ions. The electrode can be used for at least 10 weeks without any considerable divergence in its slope and detection limit. It was used as an indicator electrode in potentiometric titration of monohydrogenphosphate ion with barium chloride. The proposed sensor was successfully applied to direct determination of monohydrogenphosphate in two fertilizer samples (NPK).     

A cerium(III) selective polyvinyl chloride membrane sensor based on a Schiff base complex of N,N'-bis[2-(salicylideneamino)ethyl]ethane-1,2-diamine

A polyvinyl chloride (PVC) based membrane sensor for cerium ions was prepared by employing N,N′-bis[2-(salicylideneamino)ethyl]ethane-1,2-diamine as an ionophore, oleic acid (OA) as anion excluder and o-nitrophenyloctyl ether (o-NPOE) as plasticizer. The plasticized membrane sensor exhibits a Nernstian response for Ce(III) ions over a wide concentration range (1.41 × 10⁻⁷ to 1.0 × 10⁻² M) with a limit of detection as low as 8.91 × 10⁻⁸ M. It has a fast response time (<10 s) and can be used for 4 months. The sensor revealed a very good selectivity with respect to common alkali, alkaline earth and heavy metal ions. The response of the proposed sensor is independent of pH between 3.0 and 8.0. It was used as an indicator electrode in potentiometric titration of fluoride, carbonate and oxalate anions and determination of cerium in simulated mixtures.     

Copper(I)-bathocuproine complex as carrier in iodide-selective electrode

A PVC membrane electrode for iodide ions based on Cu(I)-bathocuproine as ionophore in membrane composition is prepared. The electrode exhibits a linear response over a wide concentration range 5.0×10⁻⁶ to 2.0×10⁻¹ mol l⁻¹ with a detection limit 1.0×10⁻⁶ mol l⁻¹. The proposed membrane electrode shows Nernstian behavior with a slope of −56.8 mV/decade, a fast response time 10 s and a lifetime at least 3 months. Iodide-selective electrode reveals good selectivities for iodide ion over a wide variety of the other anions and can be used in pH range of 3-9. It can also be used as an indicator electrode in potentiometric titration of iodide ion.     

Novel monohydrogenphosphate sensor based on vanadyl salophen

A novel PVC-based membrane sensor based on vanadyl salophen (VNSP) for determination of trace amounts of monohydrogenphosphate (MHP) ions is introduced. The electrode revealed Nernstian response towards monohydrogenphosphate over the wide concentration range from 1.0×10⁻¹ to 1.0×10⁻⁶ M at the pH of 8.2. The effect of solvent mediator, cationic additives and amount of ion-carrier on the behavior of the sensor was investigated. The sensor shows a short response time (<20 s) in the whole concentration ranges. The selectivity of the electrode is very high, and it can be used for detection of trace amounts of monohydrogenphosphate in the presence of large amounts of other anions. The detection limit of the electrode was 5.0×10⁻⁷ M (48 ng/ml) and it could be used for 14 weeks without any measurable changes in the slope. The potentiometric selectivity coefficients data revealed negligible interference from 16 common anions. It was successfully applied for the direct determination of monohydrogenphosphate in fertilizer samples and, as an indicator electrode, in potentiometric titration of HPO₄²⁻ ion with barium nitrate.     

Novel thiocyanate-selective membrane sensors based on di-, tetra-, and hexa-imidepyridine ionophores

Potentiometric thiocyanate-selective sensors based on the use of three synthesized di-, tetra-, and hexa-imidepyridine derivatives as novel anionic neutral ionophores in plasticized poly(vinyl chloride) (PVC) membranes are described. The sensors exhibit significantly enhanced response towards thiocyanate ions over the concentration range 5×10⁻⁶ to 1.0×10⁻² M with a lower detection limit of 0.3 μg ml⁻¹ and slopes ranging from −55.6 to −58.3 mV per decade. Fast and stable response, good reproducibility, long-term stability, applicability over a wide pH range (2-8) and high selectivity for SCN⁻ ion in the presence of 18 common anions are demonstrated. The sensors are used for direct potentiometric measurements of thiocyanate ions over the concentration range 0.2-580 μg ml⁻¹ and for monitoring sequential titration of some metal ions (e.g. Ag⁺, Tl⁺, Cu²⁺, Pb²⁺) in binary and ternary mixtures. Sequential binding of these metal ions with SCN⁻ ensures share stepwise titration curves with consecutive end point breaks at the equivalent points. Recoveries of 98.5-99.1±0.3% are obtained for metal ion concentrations of 0.06-4 mg ml⁻¹.     

Nickel pyrazolyl borate complexes: Synthesis, structure and analytical application in biological and environmental samples as anion selective sensors

A [{hydrotris(3-phenyl-5-methyl-1-pyrazolyl)borate}(3-phenyl-5-methyl-pyrazole) nickel chloride] [Tp^Ph,MeNi(Cl)Pz^Ph,MeH] (I) has been synthesized and explored as ionophores for the preparation of a poly (vinyl chloride) (PVC) membrane sensor for azide and thiocyanate anions. The compounds [Tp^Ph,MeNi(N₃)Pz^Ph,MeH] (II) and [Tp^Ph,MeNi(SCN)Pz^Ph,MeH] (III) were characterized by their crystal structures and proved to be bonded as monodentate through nitrogen atom of azide and thiocyanate anion. Potentiometric investigations also indicate high affinity of this receptor for thiocyanate and azide ions. PVC based membranes of I using as hexadecyltrimethylammonium bromide (HTAB) cation discriminator and o-nitrophenyloctyl ether (o-NPOE), dibutylphthalate (DBP), acetophenone (AP) and tributylphosphate (TBP) as plasticizing solvent mediators were prepared and investigated as SCN⁻ and N₃⁻ selective sensors. The best performance was shown by the membrane of thiocyanate with composition (w/w) of (I) (7%):PVC (31%):DBP (60%):HTAB (2%). This sensor works well over a wide concentration range 5.3 × 10⁻⁷ to 1.0 × 10⁻² M with Nernstian compliance (59.2 mV decade⁻¹ of activity) within pH range 2.5-9.0 with a response time of 11 s and showed good selectivity for thiocyanate ion over a number of anions. The sensor exhibits adequate life (3 months) and could be used successfully for the determination of thiocyanate content in human urine, saliva and river water samples. While the membrane of [Tp^Ph,MeNi(Cl)Pz^Ph,MeH] ionophore with composition (I) (6%):HTAB (4%):PVC (31%):TBP (59%) showed highest sensitivity and widest linear range for azide ion. These sensors exhibit the maximum working concentration range of 8.1 × 10⁻⁶ to 1.0 × 10⁻² M with Nernstian slope of 59.3 mV decade⁻¹ of activity. It can be applied for the monitoring of the azide ions concentration in aqueous black tea and orange juice samples.     

Copper(II)-selective electrode based on dithioacetal

A PVC membrane electrode for copper ion based on 1,3-dithiane,2-(4-methoxy phenyl) as ionophore and o-nitrophenyl octyl ether as a plasticizer is demonstrated. The electrode exhibits a Nernstian slope of 29.5±1 mV per decade in a linear range of 3.0×10⁻⁶ to 5.0×10⁻² M for Cu²⁺ ion. The detection limit of this electrode is 1.0×10⁻⁶ mol/l. This sensor has a very short response time of about 5 s and could be used in a pH range of 4.0-7.0. High selectivity was obtained over a wide variety of metal ions. The proposed electrode was successfully applied as an indicator electrode for the potentiometric titration of copper ion with EDTA and for the direct determination of copper in river water.     

A highly selective thallium(I) electrode based on a thia substituted macrocyclic ionophore

A new highly Tl(I)-selective PVC membrane electrode based on tetrathia macrocycle 6,7: 14,15-dibenzo-5,8,13,16-tetraoxo-1,4,9,12-tetrathiacyclohexadecane [Bz₂O₄(16)aneS₄] (I) as membrane carrier, o-nitrophenyloctyl ether (o-NPOE) as solvent mediator and potassium tetrakis(p-chlorophenyl)borate (KTpClPB) as lipophilic additive has been developed. The best performance was given by the membrane of macrocycle (I) with composition 3:120:1.5:50 (I:o-NPOE:KTpClPB:PVC). This electrode exhibits a Nernstian response to Tl(I) ions in the concentration range 1.0 × 10⁻¹-2.23 × 10⁻⁶ M with a slope of 58.2 mV/decade of concentration and a detection limit of 1.58 × 10⁻⁶ M. The response time of the sensor is 12 s and can be used over a period of 4 months with good reproducibility. The proposed electrode revealed good selectivity over a wide variety of other cations including alkali, alkaline earth, heavy and transition metals. The electrode works well over a pH range of 3.2-11.5 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 Tl(I) ions with KI solution.     

A novel tetrachlorothallate (III)-PVC membrane sensor for the potentiometric determination of thallium (III)

A novel tetrachlorothallate (III) (TCT)-selective membrane sensor consisting of tetrachlorothallate (III)-2,3,5-triphenyl-2-H-tetrazolium ion pair dispersed in a PVC matrix plasticized with dioctylphthalate is described. The electrode shows a stable, near-Nernstian response for 1×10⁻³-4×10⁻⁶ M thallium (III) at 25 °C with an anionic slope of 56.5±0.5 over the pH range 3-6. The lower detection limit and the response time are 2×10⁻⁶ M and 30-60 s, respectively. Selectivity coefficients for Tl(III) relative to a number of interfering substances were investigated. There is negligible interference from many cations and anions; however, iodide and bromide are significantly interfere. The determination of 0.5-200 μg ml⁻¹ of Tl(III) in aqueous solutions shows an average recovery of 99.0% and a mean relative standard deviation of 1.4% at 50.0 μg ml⁻¹. The direct determination of Tl(III) in spiked wastewater gave results that compare favorably with those obtained by the atomic absorption spectrometric method. The electrode was successfully applied for the determination of thallium in zinc concentrate. Also the tetrachlorothallate electrode has been utilized as an end point indicator electrode for the determination of thallium using potentiometric titration.     

A cobalt(II)-selective PVC membrane based on a Schiff base complex of N,N′-bis(salicylidene)-3,4-diaminotoluene

A new PVC membrane electrode for Co²⁺ based on N,N′-bis(salicylidene)-3,4-diaminotoluene, an excellent neutral carrier, has been fabricated using sodium tetraphenylborate (NaTPB) as an anionic excluder and dioctylphthalte (DOP) as a solvent mediator. The electrode exhibits a linear potential response in the concentration range of 7.9 × 10⁻⁸ to 1.0 × 10⁻¹ M with a slope of 30 ± 0.2 mV per decade. The detection limit of the proposed sensor is 5.0 × 10⁻⁸ M and it can be used over a period of 5 months. The proposed sensor revealed good selectivity over a wide variety of other cations including alkali, alkaline earth, heavy and transition metals and could be used in the pH range of 2.0-9.0. This electrode was successfully applied for the determination of Co²⁺in real samples and as an indicator electrode in potentiometric titration of cobalt ions.     

Development of prototype heterogeneous chitosan membrane using different plasticizer for glutamate sensing

This paper describes the preparation of and experimentation undertaken by heterogeneous chitosan membrane as ion selective electrode for glutamate ion. The linearity response was obtained in the range of 1.0 × 10⁻⁵ to 1.0 × 10⁻¹ M with a detection limit of 1.0 × 10⁻⁶ M. The performance of the electrode was found in the pH range of 4.0-8.0 at temperature 25 ± 3 °C. The response time was at 5-35 s and was useful for a period of more than 4 months. The selectivity values towards some anions indicates good selectivity over a number of interfering anions. No significant improvement of membrane performance over additional of plasticizers such as 2-NPOE, BEHA and DOPP. The electrodes gave sufficient Nernstian responses with the exception of membrane with 2-NPOE.     

Solid-contact potentiometric sensor for ascorbic acid based on cobalt phthalocyanine nanoparticles as ionophore

A novel solid-contact potentiometric sensor for ascorbic acid based on cobalt phthalocyanine nanoparticles (NanoCoPc) as ionophore was fabricated without any need of auxiliary materials (such as membrane matrix, plasticizer, and other additives). The electrode was prepared by simple drop-coating NanoCoPc colloid on the surface of a glassy carbon electrode. A smooth, bright and blue thin film was strongly attached on the surface of the glassy carbon electrode. The electrode showed high selectivity for ascorbic acid, as compared with many common anions. The influences of the amount of NanoCoPc at the electrode surface and pH on the response characteristics of the electrode were investigated. To overcome the instability of the formal potential of the coated wire electrode, a novel electrochemical pretreatment method was proposed for the potentiometric sensor based on redox mechanism. This resulting sensor demonstrates potentiometric response over a wide linear range of ascorbic acid concentration (5.5 × 10⁻⁷ to 5.5 × 10⁻² M) with a fast response (<15 s), lower detection limit (ca. 1.0 × 10⁻⁷ M), and a long-term stability. Furthermore, microsensors based on different conductors (carbon fiber and Cu wire) were also successfully fabricated for the determination of practical samples.     

PVC-based dicyclohexano-18-crown-6 sensor for La(III) ions

A new ion-selective electrode (ISE) based on dicyclohexano-18-crown-6 (DC18C6) as a neutral carrier is developed for lanthanum(III) ions. The electrode comprises of dicyclohexano-18-crown-6 (6%), PVC (33%), and ortho-nitrophenyl octyl ether (o-NPOE) (61%). The electrode shows a linear dynamic response in the concentration range of 10⁻⁶ to 10⁻¹ M with a Nernstian slope of 19 mV per decade and a detection limit as 5×10⁻⁷ M. It has a response time of <30 s and can be used for at least 5 months without any significant divergence in potentials. The selectivity coefficients for mono-, di-, and trivalent cations indicate good selectivity for La(III) ions over a large number of interfering cations. The sensor has been used as an indicator electrode in the potentiometric titrations of La(III) with EDTA. The membrane is successfully applied in partially non-aqueous medium. It can be used in the pH range 4-9.     

Potentiometric membrane sensor based on 6-(4-nitrophenyl)-2,4-diphenyl-3,5-diaza-bicyclo[3.1.0]hex-2-ene for detection of Sn(II) in real samples

A Sn²⁺ ion-selective electrode which was prepared with a polymeric membrane based on 6-(4-nitrophenyl)-2,4-diphenyl-3,5-diaza-bicyclo[3.1.0]hex-2-ene (NDDBH) as a ionophore. Effects of experimental parameters such as membrane composition, nature and amount of plasticizer, the amount of additive and concentration of internal solution on the potential response of Sn²⁺ sensor were investigated. The electrode exhibited a Nernstian slope of 28.8 ± 1.1 mV/decade of Sn²⁺ over a concentration range of 1.0 × 10⁻⁵ to 1.0 × 10⁻¹ M of Sn²⁺ in an acidic solution (pH 1). The limit of detection was 4.0 × 10⁻⁶ M. The results show that this electrode can be used in ethanol media until 20% (v/v) concentration without interference. It can be used for more than 6 weeks without any considerable divergence in the potentials. The proposed membrane electrode revealed very good selectivity for Sn(II) ions over a wide variety of other cations and could be used in acidic media. The standard electrode potentials were determined at different temperatures and used to calculate the isothermal coefficient of the electrode. The stability constant (log K_s) of the Sn(II)-ionophore complex was determined at 25 °C by potentiometric titration in mixed aqueous solution. It was used as indicator electrode in potentiometric determination of Sn(II) ion in real samples.     

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 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.