Flow injection analysis of sulfite ion with a potentiometric titanium phosphate-epoxy based membrane sensor

A novel pH sensor suitable for use in both aqueous and non-aqueous mediums is reported. The sensor is derived from polymer modified electrode obtained from electrochemical polymerisation of aniline in dry acetonitrile containing 0.5 M tetraphenyl borate at 2.0 V versus Ag/AgCl. The light yellow colour polymer modified electrode obtained under the present experimental condition has been characterised by scanning electron microscopy (SEM). The pH sensing of polymer modified electrode in both aqueous and non-aqueous mediums is examined and reported. As the typical examples, we used weak acid (acetic acid) and weak base (ammonium hydroxide) as analytes. The acetic acid is analysed in both aqueous and dry acetonitrile whereas ammonium hydroxide is analysed only in aqueous medium. The analysis in aqueous medium is conducted in 1 mM Tris-HCl buffer pH 7.0 and also in 0.1 M KCl. The slope of pH sensing is calculated from the data recorded in typical buffers and found to be approximately 86 mV per pH. The application of polymer modified electrode for the construction of urea biosensor is described based on immobilised urease within poly vinyl alcohol (PVA) matrix and also within organically modified sol-gel glass on the surface of polymer-modified electrode. The new urea sensor has shown maximum response of 160 mV at 25 degrees C with a lowest detection limit of 20 muM. The performance of new pH sensor and urea sensor has been studied and reported in this communication.     

Determination of diclofenac in pharmaceuticals and urine samples using a membrane sensor based on the ion associate of diclofenac with Rhodamine B

The potentiometric response characteristics of a diclofenac selective electrode, based on ion association in different plasticizers, were compared. The sensitivity, working range, detection limit and selectivity of membrane sensors demonstrated significant dependence on the type of plasticizers. The potentiometric unit presented a linear response toward diclofenac concentrations between 1 × 10⁻⁵ − 5 × 10⁻² mol L⁻¹, with slopes of approximately 60 mV dec⁻¹, and exhibited a response time of 3 s. The potentiometric analysis of sodium diclofenac in pharmaceutical formulations was perfomed by the membrane electrode proposed and compared with the results of potentiometric titration given by the Pharmacopoeia of Ukraine.      

Determination of sodium ion diffusion coefficients in sodium vanadium phosphate

Carbon-coated Na₃V₂(PO₄)₃ (NVP) was prepared by a standard sol–gel procedure. The apparent diffusion coefficients of sodium ions in the rhombohedral NVP have been determined by different techniques such as galvanostatic intermittent titration technique (GITT) and cyclic voltammetry (CV). It was found that the apparent diffusion coefficients range from 6?×?10^?13 cm² s^?1 to 2?×?10^?15 cm² s^-1. These sodium ion apparent diffusion coefficients follow a similar trend as observed for lithium ions in the closely related monoclinic modification of Li₃V₂(PO₄)₃, demonstrating a minimum at the potential where the ion extraction/insertion occurs.     

Liquid membrane potentiometric sensor for determination of Fe3+ ion

Solution studies showed a selective interaction between the new synthesized ionophore, 2-[(thiophen-2-yl)methyleneamino]isoindoline-1,3-dione (TMID) and Fe(III) ion. Therefore, TMID was used as an iron selective ion-carrier in a plasticized liquid membrane sensor. The linear response range of the proposed electrode was 1.0 × 10^?6–1.0 × 10^?2 M. The Nernstian slope of 20.1 ± 0.3 mV/decade, and a detection limit of 5 × 10^?7 M was obtained. The sensor could be used in the pH range of 2.3–4.8, and the response time was about 10 s. The lifetime of the electrode was at least 7 weeks. The sensor accuracy was investigated in two ways: (i) with the potentiometric titration of a Fe³⁺ solution with EDTA and (ii) with Fe(III) monitoring in some cationic mixtures. Finally, the newly fabricated electrode was effectively applied as an indicator electrode for the direct Fe³⁺ determination in real samples.     

A new diclofenac membrane sensor based on its ion associate with crystal violet. Application to diclofenac determination in urine and pharmaceuticals

A novel diclofenac ion-selective electrode has been prepared and used in pharmaceutical analysis. The ion-associate of diclofenac with basic dye (crystal violet) was used as the membrane carrier. Among the four different solvent mediators tested, dibutylphthalate (DBP) exhibited proper behavior including the Nernstian slope of the calibration curve, fast response time and good reproducibility of the emf values. The electrode exhibits a Nernstian slope of 59 ± 1 mV decade^?1 for diclofenac in the concentration range 5.0 × 10^?5-5.0 × 10^?2 M with the limit of detection of 2.5 × 10^?5 M. The electrode displays good sensitivity with the respect to a number of common inorganic and organic species. It can be used in a pH range of 6–11. The membrane sensor was successfully applied to the determination of diclofenac in capsules and for its recovery from urine samples.     

Novel membrane potentiometric sulfate ion sensor based on zinc-phthalocyanine for the quick determination of trace amounts of sulfate.

Poly(vinyl chloride) (PVC) based membranes of zinc-phthalocyanine (ZPC) with hexadecyltrimethylammonium bromide (HTAB) as a cation excluder, and dibutyl phthalate (DBP) and benzyl acetate (BA) as plasticizing solvent mediators were prepared and investigated as a SO4(2-) selective electrode. The best performance was observed with a membrane having a composition of ZPC-PVC-HTAB-BA in a ratio of 5%:32%:3%:60%, which works well over a wide concentration range (1.0 x 10(-2) - 1.0 x 10(-6) M) with a Nemstian slope of -29.2 mV per decade of activity, between the pH values of 2.0 to 7.0. This sensor shows a very fast response time of 10 s, and can be used over a period of 2 months with good reproducibility. The proposed sensor displays excellent selectivity for SO4(2-) over a large number of common inorganic anions. The sensor has been successfully applied for the direct and indirect determination of sulfate and zinc in zinc sulfate tablets, respectively. It was also used as an indicator electrode in the potentiometric titration of sulfate ions with barium ions.     

Lead-selective membrane potentiometric sensor based on an 18-membered thiacrown derivative.

A PVC-based membrane electrode for lead ions based on hexathia-18-crown-6-tetraone as membrane carrier was prepared. The influence of membrane composition, pH of test solution and foreign ions on the electrode performance were investigated. The electrode showed a Nernstian response over a lead concentration range from 1.0 x 10(-6) to 8.0 x 10(-3) M at 25 degrees C, and was found to be very selective, precise and usable within the pH range 3.0-6.0. The electrode was successfully used as an indicator electrode in potentiometric titration of lead ions and in direct determination of lead in water samples.     

Serine-selective membrane probe based on immobilized anaerobic bacteria and a potentiometric ammonia gas sensor

A new class of bioselective membrane probes using anaerobic bacteria is introduced with the successful construction of a L-serine-selective probe consisting of Clostridium acidiurici cells coupled to a potentiometric ammonia gas sensor. The intact cells containing the enzyme serine dehydratase are physically immobilized at the electrode surface in conjunction with iron(II) stearate, which is shown to enhance response characteristics. The potential vs. log concentration plot is linear from 1.6 × 10^-2 to 1.8 × 10^-4M serine with an average slope of 54 mV/decade and response times of 3–5 min. Optimal behavior of the probe is retained even in non-deaerated media for at least three days, and significant interference is posed only by L-glutamine. Quantitative conversion of serine is demonstrated over the linear concentration range, suggesting possible analytical or clinical applications for these probes utilizing anaerobic bacteria     

Determination of l-carnitine using enantioselective, potentiometric membrane electrodes based on macrocyclic antibiotics

In order to determine the enantiopurity of l-carnitine three enantioselective, potentiometric membrane electrodes were proposed for the assay of l-carnitine. The electrodes were designed using macrocyclic glycopeptide antibiotics—vancomycin and teicoplanin. Acetonitrile was added to the teicoplanine to design a modified teicoplanine based electrode. The linear concentration ranges for the proposed enantioselective membrane electrodes were 10⁻⁴ to 10⁻² mol l⁻¹ for electrodes based on vancomycin and teicoplanin and 10⁻⁵ to 10⁻² mol l⁻¹ for electrode based on teicoplanin modified with acetonitrile. The slopes of the electrodes were 56.5 mV per pl-carnitine; 54.5 mV per pl-carnitine and 58.3 mV per pl-carnitine for vancomycin-, teicoplanin- and teicoplanin modified with acetonitrile-based electrodes, respectively. The enantioselectivity was determined over d-carnitine. The proposed electrodes could be employed reliably for the assay of l-carnitine raw material and its pharmaceutical formulation, Carnilean^® capsules. The surfaces of the electrodes are stable and easily renewable by polishing on alumina paper.     

A novel potassium ion membrane sensor based on rifamycin neutral ionophore

A novel potentiometric membrane sensor for potassium ion based on the use of rifamycin as a neutral ionophore is described. The sensing membrane is formulated with 2 wt.% rifamycin-SV, 69 wt.% dibutylsebacate plasticizer and 29 wt.% PVC. Linear and stable potential response with near-Nernstian slope of 56.7 +/- 0.2 mV decade(-1) are obtained over the concentration range 1 x 10(-1)-3 x 10(-5) M K(+). The detection limit is 0.3 microg ml(-1) K(+), the response time is 10-30 s and the working pH range is 4-11. Responses of the sensor toward alkali and alkaline earth metal ions are in the order K(+) > Rb(+) > Cs(+) > Na(+) > NH(4)(+) > Ba(2+) > Mg(2+) > Ca(2+) > Sr(2+) > Li(+). The selectivity coefficient data reveal negligible interference from transition metal ions. Direct potentiometric determination of K(+) in the presence of 10-50-fold excess of alkali and alkaline earth metals gives results with an average recovery of 99.1%, and a mean standard deviation of 1.2%. The data agree fairly well with those obtained by flame photometry.     

Effect of anionic additive type on ion pair formation constants of basic pharmaceuticals

Due to their beneficial effect on selectivity, peak shape, and sample loading, the use of mobile phase anionic additives, such as formate (HCOO-), chloride (Cl-), and trifluoroacetate (CF3COO-), is increasing in both reversed-phase chromatography (RPLC) and liquid chromatography-mass spectrometry (LC/MS). Similarly, perchlorate is a common "ion pair" agent in reversed-phase separation of peptides. Although many studies have suggested that anions effect in chromatography is due to the formation of ion pairs in the mobile phase between the anions and cationic analytes, there has been no independent verification that ion pairs are, in fact, responsible for these observations. In order to understand the mechanisms by which anionic additives influence retention in chromatography and ionization efficiency in electrospray mass spectrometry, we studied the formation of ion pairs between a number of prototypical basic drugs and various additives by measuring the effect of anionic additives on the electrophoretic mobility of the probe drugs under solvent conditions commonly used in chromatography. For the first time, ion pair formation between basic drugs and anionic additives under conditions commonly used in reversed-phase liquid chromatography has been confirmed independently with all anions (i.e. hexafluorophosphate, perchlorate, trifluoroacetate, and chloride) used in this study. We measured ion pair formation constants (Kip) for different anionic additives using capillary electrophoresis (CE) and obtained quantitative estimates for the extent of ion pairing in buffered acetonitrile-water. The data clearly indicate that different anionic additives ion pair with cationic drugs to quite different extents. The ion pair formation constants show a clear trend with the order being: PF6- > ClO4- > CF3COO- > Cl-. However, the extent of ion pairing is not large. At a typical RPLC mobile phase additive concentration of 20mM, the percentages of the analytes that are present as ion pairs are about 15%, 6%, and 3% for hexafluorophosphate, perchlorate, and trifluoroacetate, respectively. The fraction of the analytes present as a chloride pair is even smaller.     

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.     

Determination of inorganic anions in mushrooms by ion chromatography with potentiometric detection

A simple method for determination of common inorganic anions in mushroom samples has been developed by using suppressed ion chromatography with a pH detection unit. The detection unit which was constructed in such a way that practically no additional dispersion occurred consisted of a flow-through quinhydrone pH sensor and a small reference electrode. Chromatographic separation was performed in the order F⁻, Cl⁻, NO₂⁻, Br⁻, PO₄³⁻, ClO₃⁻, NO₃⁻, and SO₄²⁻, at room temperature by using Ion Pac AS 9-HC anion exchange column. Anion extracts from dried mushroom samples at room temperature were homogenized and filtered before injection. Under optimized analytical conditions, the detection limits of the method were between 2 × 10⁻⁶ and 3 × 10⁻⁴ M, depending on the anion studied. The results showed that the concentrations of fluoride and bromide in all mushroom samples were below their limit of detection. Nitrite was found to be the lowest abundant ion, while the most abundant ion was sulfate in all the mushroom samples studied.     

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).     

Determination of uranyl ion by potentiometric titration using an uranyl-selective electrode

Summary A potentiometric titration of uranyl ion is described using an uranyl selective electrode based on a membrane containing a complex of UO₂-bis[di-4-(1,1,3,3-tetra-methylbutyl)phenyl phosphate] as an ion-exchanger and tritolyl phosphate as a solvent mediator. The titrations were carried out with various titrants: sodium hydroxide, potassium fluoride and sodium salts of acetate, oxalate and citrate. The equivalence points were determined by Gran's method. Good results were obtained by using sodium oxalate as a titrant for the determination of uranium in several samples of ammonium diuranate. The results were quite comparable with those obtained by X-ray fluorescence spectrometry.     

Photocatalytic degradation of betamethasone sodium phosphate in aqueous solution using ZnO nanopowder

The photocatalytic degradation of betamethasone sodium phosphate has been investigated in aqueous phase by using ultraviolet (UV) light and ZnO nanopowder. The effect of catalyst loading, irradiation time, pH, addition of oxidizers, effect of alcohol and anion presence on the reaction rate was ascertained and optimum conditions for maximum degradation were determined. The photocatalytic degradation of betamethasone sodium phosphate was strongly influenced by these parameters. The optimum amount of the photocatalyst used is 0.44 g/L. The efficiency of betamethasone sodium phosphate increases with the photo-degradation increase of the irradiation time.     

Selective potentiometric determination of nitrite ion using a novel (4-sulphophenylazo-)1-naphthylamine membrane sensor

A novel polymeric membrane sensor sensitive to (4-sulphophenylazo-)1-naphthylamine (SPAN) based on the use of tris(bathophenanthroline) Ni(II)–SPAN ion pair as an ion exchanger in plasticised PVC membrane is described. The sensor exhibits a linear calibration plot with near-Nernstian anionic slope of −55.0±0.3 mV log[SPAN]⁻¹ over the concentration range 10⁻⁶–10⁻² mol l⁻¹ at pH 7. The sensor shows working range over the pH 6–8, response time of 20 s for 10⁻⁵ mol l⁻¹ and operational lifetime of 8 weeks. The sensor is used for quantification of micro quantities of nitrite ion by a prior conversion into the more lipophilic SPAN ion, which is measured with adequate sensitivity, and high selectivity using SPAN sensor. Validation of the method according to the quality assurance standards shows good performance characteristics. The sensor is satisfactory utilised for potentiometric determination of nitrite ion in wastewater samples and meat products. The results are favourably compared with data obtained using the standard spectrophotometric procedure involving the same reaction.     

Solid-state ion selective electrode based on polypyrrole conducting polymer nanofilm as a new potentiometric sensor for Zn2+ ion

A pencil graphite electrode (PGE) electrodeposited by a polypyrrole conducting polymer doped with tartrazine (termed as PGE/PPy/Tar) was prepared and used as a zinc (II) solid-state ion-selective electrode. For the preparation of the zinc sensor electrode, electrodeposition of a polypyrrole nanofilm was carried out potentiostatically (E _app?=?0.75 V vs SCE) in a solution containing 0.010 M pyrrole and 0.001 M tartrazine trisodium salt. A pencil graphite and Pt wire were used as working and auxiliary electrodes, respectively. The introduced electrode in the current paper can be fabricated simply and was found to possess high selectivity, exhibited wide working concentration range, sufficiently rapid response, potential stability, and very good sensitivity to Zn (II) ion. The sensor electrode showed a linear Nernstian response over the range of 1.0?×?10^?5 to 1.0?×?10^?1 M with a slope of 28.23 mV per decade change in zinc ion concentration. A detection limit of 8.0?×?10^?6 M was obtained. The optimum pH working of the electrode was found to be 5.0.     

Interaction of calcium ion with sodium triphosphate determined by potentiometric and calorimetric techniques

The stoichiometry of the interaction of Ca²⁺ with sodium triphosphate was determined using a Ca²⁺ sensitive electrode, divalent ion sensitive electrode, a glass electrode and by titration calorimetry, A 2:1 and 1:1 complex of Ca²⁺ and P₃O^5?₁₀ is found when titrating calcium chloride with sodium triphosphate by the calcium ion sensitive electrode and tritation calorimetry. However, only by titration calorimetry is the 2:1 and 1:1 complex found when titrating sodium triphosphate with calcium chloride. Thermodynamic value (log K, ΔH and ΔS) are reported for the formation of CaP(in3)O^?3₁₀ and Ca₂P₃O^?₁₀ in aqueous solution.