Quantitative determination of fucoidan using polyion-sensitive membrane electrodes

The use of polyanion and polycation-sensitive membrane electrodes to detect five different preparations of fucoidan is described. Unlike linear polyanionic molecules previously measured with polymer membrane-based electrochemical sensors, fucoidans from marine brown algae are all highly branched, sulfated polysaccharides with varying charge densities and structures, depending on the species of seaweed, method of extraction used and extent of purification. When tridodecylmethylammonium (TDMA) was used as the ion-exchanger, a large, non-equilibrium EMF response was observed over a concentration range of 0.5–50 μg mL⁻¹ fucoidan. Fucoidan was also measured by titration with polycationic protamine, using a dinonylnaphthalene sulfonate (DNNS)-doped membrane electrode as the potentiometric endpoint detector. Potentiometric titration was used to determine the binding ratio between protamine and fucoidan at the neutralization endpoint for each fucoidan preparation. This binding ratio was then used to successfully determine the fucoidan content of commercially available nutritional supplements. Fucoidan was also measured in undiluted blood serum, demonstrating that this method may be applicable for measuring fucoidan for clinical applications.     

Potentiometric flow injection sensing system for determination of heparin based on current-controlled release of protamine

A flow injection system incorporated with a polycation-sensitive polymeric membrane electrode in the flow cell is proposed for potentiometric determination of heparin. An external current in nano-ampere scale is continuously applied across the polymeric membrane for controlled release of protamine from the inner filling solution to the sample solution, which makes the electrode membrane regenerate quickly after each measurement. The protamine released at membrane–sample interface is consumed by heparin injected into the flow cell via their strong electrostatic interaction, thus decreasing the measured potential, by which heparin can be detected. Under optimized conditions, a linear relationship between the potential peak height and the concentration of heparin in the sample solution can be obtained in the range of 0.1–2.0 U mL⁻¹, and the detection limit is 0.06 U mL⁻¹. The proposed potentiometric sensing system has been successfully applied to the determination of heparin in undiluted sheep whole blood.     

Chromium(III)-Selective Electrodes Based on Titanium Dichalcogenides Intercalated with Chromium

Solid-contact chromium-selective film electrodes were prepared on the basis of titanium diselenide and titanium ditelluride intercalated with chromium. It was found that the titanium diselenide–based electrode with the lowest concentration of the intercalant (Cr_0.1TiSe₂) exhibits the best properties and provides the determination of 5 × 10^–5–1 × 10⁰M chromium(III) in the pH range 2.75–4.7. The slope of the electrode function for all chromium-selective electrodes depends on the pH of the solution and is close to the theoretical slope for the singly charged Cr(OH)⁺ ₂ ion. It was demonstrated that chromium-selective electrodes can be used as indicator electrodes in determining chromium(III) by direct titration with the potentiometric detection of the titration end-point using EDTA and KMnO₄as titrants.     

Some observations on catalytic conductometric titrations

Conductometric and high-frequency conductometric methods for the determination of the endpoint of catalytic titrations were developed. Titrations of sodium acetate were made in a mixture of acetic anhydride and acetic acid (7:3–11:3) which was 0.05–0.1 mol dm⁻³ in sodium perchlorate. Integral and derivative titration curves were recorded in both coulometric and volumetric titrations. Different acylation reactions, as well as dehydration of formic acid, were used as the indicator reactions. The optimal conditions of determination—choice of volume ratio of acetic anhydride to acetic acid, rate of the titrating reagent addition, concentration of sodium perchlorate, and concentration of several alcohols, water, and formic acid as components of the indicator reactions—were determined. Using the catalytic conductometric method, amounts of 0.04–11 mg of sodium acetate were determined with a relative standard deviation of less than 0.8 and 1.6% in volumetric and coulometric addition, respectively. Using the catalytic high-frequency conductometric method, amounts of 1–11 mg of sodium acetate were determined with relative standard deviation less than 0.5% (volumetrically) or less than 1.4% (coulometrically). The obtained results were compared with those of potentiometric and catalytic thermometric titrations.     

Flow injection determination of ketotifen fumarate using PVC membrane selective electrodes

In this study a PVC membrane electrode for determination of ketotifen fumarate is reported, where ketotifen tetraphenylborate (Keto-TPB) was used as ion exchanger. The electrode has linear range of 5.6 × 10^− 6–1.0 × 10^− 2 and 1.0 × 10^− 5–1.0 × 10^− 2 mol/L, with detection limits 2.37 × 10^− 6and 4.60 × 10^− 6 mol/L in batch and flow injection analysis (FIA), respectively. The electrodes show a Nernstian slope value (58.40 and 61.50 mV/decade in batch and FIA, respectively), and the response time is very short (≤ 10 s). The potential is nearly stable over the pH range 2.0–8.0. Selectivity coefficient values towards different inorganic cations, sugars and amino acids reflect high selectivity of the prepared electrodes. These are used for determination of Ketotifen using potentiometric titration and standard addition methods in pure samples and its pharmaceutical preparations (Zaditen tablets and syrup). The average recovery values are 99.5 and 99.2% with RSD 1.4 and 1.2% for potentiometric titrations and standard addition methods, respectively. The electrode response at different temperatures was also studied.     

Bestimmung von Palladium in Katalysatoren durch potentiometrische Titration mit ionensensitiver Endpunktsanzeige

Zusammenfassung Zur Bestimmung von Milligramm-Mengen Palladium in Katalysatormassen wird die Fällungstitration mit Jodid herangezogen. Zur Indikation des Titrationsendpunktes wird eine Meßkette aus einer Silberjodid/Sulfidelektrode und einer Referenzelektrode mit Zwischenelektrolyten verwendet. Die potentio-metrische Indikation vereinfacht das Verfahren bezüglich der üblichen Trübungsmessung und bringt gegenüber der Redoxindikation eine weitgehende Unabhängigkeit von der Säurekonzentration. Palladiummengen von 1–20 mg können so mit einer relativen Standardabweichung von 0,4% bestimmt werden.

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Determination of palladium in catalysts by means of potentiometric titration with ion-sensitive endpoint indication

The determination of milligram amounts of palladium in catalysts is performed by iodide titration. The endpoint of the titration is indicated by a silver iodide — silver sulphide electrode together with a double junction reference electrode. Potentiometric indication facilitates the procedure considerably in comparison to the turbidimetric endpoint method. The indication is independent of the acid concentration of the solution, which gives also a major advantage over the redox indication technique. Palladium amounts of 1–20 mg can be determined with a relative standard deviation of 0.4 %.

     

Cobalt-Selective Electrode Based on Titanium Ditelluride Intercalated with Cobalt

A cobalt-selective solid-contact electrode was prepared on the basis of titanium ditelluride. The electrode exhibits the slope of the electrode function –(29 ± 1) mV/pC and provides the determination of 1 × 10^–5–1 × 10^–1 M cobalt(II) in the pH range 4.5–6.5. The electrode was used for the potentiometric indication of the titration end point in the determination of cobalt(II) in lanthanum–strontium cobaltite La_0.5Sr_0.5CoO₃. The intercalant concentration range providing optimal ion-selective properties was determined.     

A copper ion-selective electrode with high selectivity prepared by sol-gel and coated wire techniques

A sol-gel electrode and a coated wire ion-selective poly(vinyl chloride) membrane, based on thiosemicarbazone as a neutral carrier, were successfully developed for the detection of Cu (II) in aqueous solutions. The sol-gel electrode and coated electrode exhibited linear response with Nernstian slopes of 29.2 and 28.1 mV per decade respectively, within the copper ion concentration ranges 1.0×10^–5–1.0×10^–1 M and 6.0×10^–6–1.0×10^–1 M for coated and sol-gel sensors. The coated and sol-gel electrodes show detection limits of 3.0×10^–6 and 6.0×10^–6 M respectively. The electrodes exhibited good selectivities for a number of alkali, alkaline earth, transition and heavy metal ions. The proposed electrodes have response times ranging from 10–50 s to achieve a 95% steady potential for Cu²⁺ concentration. The electrodes are suitable for use in aqueous solutions over a wide pH range (4–7.5). Applications of these electrodes for the determination of copper in real samples, and as an indicator electrode for potentiometric titration of Cu²⁺ ion using EDTA, are reported. The lifetimes of the electrodes were tested over a period of six months to investigate their stability. No significant change in the performance of the sol-gel electrode was observed over this period, but after two months the coated wire copper-selective electrode exhibited a gradual decrease in the slope. The selectivity of the sol-gel electrode was found to be better than that of the coated wire copper-selective electrode. Based on these results, a novel sol-gel copper-selective electrode is proposed for the determination of copper, and applied to real sample assays.     

Zur automatisch-potentiometrischen Titration von Halogeniden mit Quecksilber(II)-nitrat

Zusammenfassung Die bei potentiometrischen Titrationen mit Quecksilber(II)-salzen auftretenden Elektrodenschwierigkeiten lassen sich durch Verwendung einer Silberamalgamelektrode beseitigen. Ein registrierendes Verfahren wird beschrieben, welches noch 10^–2 mVal Chlorid, 2 · 10^–3 mVal Bromid und 10^–4 mVal Jodid in 100 ml zu titrieren erlaubt. Jodid/Bromid und Jodid/Chlorid können nebeneinander bestimmt werden.

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Summary The electrode problems involved in potentiometric titrations of halides with mercury(II) salts can be avoided by the use of a silver amalgam electrode. A recording method is described, which allows the determination of 10^–2 mval of chloride, 2×10^–3 mval of bromide and 10^–4 mval of iodide. Iodide/bromide and iodide/chloride can be determined in presence of each other.

     

Potentiometric Determination of Nitrilotriacetate in Water and Sewage

Abstract

A potentiometric titration of nitrilotriacetate in wastewater and sewage samples and a procedure of sample treatment to eliminate the interferences are described. T1³⁺ and Cu²⁺ solutions were the titrants and the potentiometric titrations were monitored with a platinum redox electrode. T1³⁺ :2NTA complex formation was found. The lower detection limit was 0. 1 ppm of NTA. The relative standard deviation in sewage samples was 5% and the recovery varied from 90–110%.     

Determination of the protonation constant and partition coefficient of 4-methylpyridine in KNO3-toluene at 25°C

The protonation constant in 1.0 mol-dm^–3 KNO₃, and partition coefficient of 4-methylpyridine (B) between 1.0 mol-dm^–3 KNO₃, and toluene have been determined at 25°C by measuring the H₃O⁺ ion concentration with a glass electrode. The experimental work consisted of two sets of potentiometric titrations. In the first case, the titrations were carried out in an aqueous system of constant ionic strength and in the second, two-phase titrations using toluene as organic phase were performed. All the titrations were conducted automatically by the use of a computer controlled potentiometric system. The results were treated using graphical and numerical methods and the systematic erros were also considered. The formation constant of the protonated 4-methylpyridine was correlated with the composition of the aqueous phase by means of Bromley's theory.Recently deceased. This paper is dedicated to the memory of Dr. José Maria Castresana.     

Novel potentiometric immunosensor for determination of diphtheria antigen based on compound nanoparticles and bilayer two-dimensional sol–gel as matrices

A novel method for fabrication of a diphtheria potentiometric immunosensor has been developed by means of self-assembling compound nanoparticles to a thiol-containing sol–gel network. A cleaned gold electrode was first immersed in a 3-mercaptopropyltrimethoxysilane (MPS) sol–gel solution to assemble a silica sol–gel monolayer. The silane entities were then polymerized into a two-dimensional sol–gel network (2D network) by dipping into aqueous NaOH. The second silane layer was formed by re-immersion in the MPS sol–gel solution overnight. The compound nanoparticles (nanocompounds) containing gold nanoparticles and silver nanoparticles were then chemisorbed on to the thiol groups of the second silane layer. Finally, diphtheria antibody (anti-Diph) was adsorbed on to the surface of the compound nanoparticles. The modified process was characterized by cyclic voltammetry (CV). Detection is based on the change in the potentiometric response before and after the antigen–antibody reaction. A direct potentiometric response to diphtheria antigen (Diph) was obtained from the immobilized diphtheria antibody. The potentiometric response of the resulting immunosensor was rapid and the linear range was from 22 to 800 ng mL^–1 with the linear regression equation E=–79.5+69.4 log [Diph] and a detection limit of 3.7 ng mL^–1 (at 3). Up to 19 successive assay cycles with retention of sensitivity were achieved for probes regenerated with 0.2 mol L^–1 glycine–hydrochloric acid (Gly–HCl) buffer solution. Moreover, analytical results from several serum samples obtained using the developed technique were in satisfactory agreement with those given by the ELISA method, implying a promising alternative approach for detecting diphtheria antigen in clinical diagnosis.     

Novel lipoate-selective membrane sensor for the flow injection determination of alpha-lipoic acid in pharmaceutical preparations and urine

A potentiometric lipoate-selective sensor based on mercuric lipoate ion-pair as a membrane carrier is reported. The electrode was prepared by coating the membrane solution containing PVC, plasticizer, and carrier on the surface of graphite electrode. Influences of the membrane composition, pH, and possible interfering anions were investigated on the response properties of the electrode. The sensor exhibits significantly enhanced response toward lipoate ions over the concentration range 1 × 10⁻⁷ mol L⁻¹ to 1 × 10⁻² mol L⁻¹ with a lower detection limit of (LDL) of 9 × 10⁻⁸ mol L⁻¹ and a slope of −29.4 mV decade⁻¹, with S.D. of the slope is 0.214 mV. Fast and stable response, good reproducibility, long-term stability, applicability over a pH range of 8.0–9.5 is demonstrated. The sensor has a response time of ≤12 s and can be used for at least 6 weeks without any considerable divergence in its potential response. The proposed electrode shows good discrimination of lipoate from several inorganic and organic anions. The CGE was used in flow injection potentiometry (FIP) and resulted in well defined peaks for lipoate ions with stable baseline, excellent reproducibility and reasonable sampling rate of 30 injections per hour. The proposed sensor has been applied for the direct and FI potentiometric determination of LA in pharmaceutical preparations and urine; and has been also utilized as an indicator electrode for the potentiometric titration of LA.     

Determination of levodopa methyl ester and its metabolites in rat serum by CZE with amperometric detection

A reliable and reproducible method, capillary zone electrophoresis with amperometric detection (CZE–AD), has been developed for separation and quantification of levodopa methyl ester (LDME) and its biotransformation products levodopa (L-DOPA) and dopamine (DA) in rat serum. A carbon-disk electrode was used as working electrode. The optimum conditions for CZE detection were 50 mmol L^–1 phosphate solution at pH 7.0 as running buffer, 17 kV as separation voltage, 1.0 V (vs Ag/AgCl, 3.0 mol L^–1) as detection potential, and sample injection for 8 s at 17 kV. The linear ranges were from 2.4×10^–2 to 2.2 g mL^–1 for LDME, 2.9×10^–1 to 49.5 g mL^–1 for L-DOPA, and 1.4×10^–2 to 1.5 g mL^–1 for DA with correlation coefficients of 0.9997, 0.9994, and 0.9999, respectively. The detection limits for LDME, L-DOPA, and DA were 14.6, 98.0, and 9.7 ng mL^–1, respectively. Recoveries were 80.3% for LDME, 93.5% for L-DOPA, and 86.5% for DA. This method was applied to serum samples after intravenous injection of LDME and L-DOPA to rats.     

Anionic surfactant selective electrode for the titrimetric determination of anionic surfactant

The construction and characteristic performance of a PVC membrane electrode responsive for sodium dodecylsulfate (SDS) are described in this paper. The electrode based on CTA⁺DS^? ion pair as ionophore in PVC membrane displays a Nernstian slope of ?58.8 ± 0.7 mV/decade in a 1.32 × 10^?6 to 3.75 × 10^?3 mol L^?1 concentration range and a limit of detection of 1.13 × 10^?6 mol L^?1. The electrode can be used for 3 months without showing significant changes in the value of slope or working range. The electrode has been utilized as an end point indicator electrode for potentiometric titration involving Hyamine as titrant. More than 100 titrations were carried out for the evaluation of the electrode parameters: the standard deviations of the equivalent volume and the equivalent potential, the height of the potential jump and the number of faulty titrations. The behavior of the electrode was assessed with regard to their usefulness in routine analysis.     

Primary amine drug sensitive electrodes based on macrocyclic polyethers with 2,2′-dinaphthyl subunits

Dinaphthyl macrocyclic polyethers were synthesized and used as neutral carriers for preparing primary amine drug sensitive PVC membrane electrodes. Contrary to the ion-associate based electrodes, which show an excellent potentiometric response to quaternary ammonium ions and the like, but a very poor response to primary amines, the macrocyclic polyether-based electrodes showed potentiometric response characteristics with primary amines preferred. Dinaphthyl macrocyclic polyether-based electrodes are superior to those based on common macrocyclic polyethers for their potentiometric selectivity coefficients much lower than those of the latter. The main characteristics of a dinaphthyl-20-crown-6-based benzyl amine sensitive electrode are as follows: linear response range, 4.2 × 10^–5 – 1.0 ×10^–1 M; slope, 51.3 mV/decade; and detection limit, 4.6 × 10^–6 M. A mexiletine sensitive electrode was prepared using dinaphthyl-23-crown-7 with following performance features: linear response range, 2.0 × 10^–5 – 1.0 ×10^–1 M; slope, 52.1mV/decade; and detection limit, 5.0 × 10^–6 M.     

Sensitive Determination of DNA by Resonance Light Scattering with Pentamethoxyl Red

A novel sensitive method for the determination of nucleic acid (DNA) using the resonance light scattering (RLS) spectra of pentamethoxyl red has been developed. It is based on the effects on the resonance light scattering of Pentamethoxyl Red. The effective factors and the optimum conditions were studied, and the enhanced intensity of RLS is in proportion to the concentration of nucleic acids in the range of 0–2.54 µg mL⁻¹ for ct-DNA, 0–4.54 µg mL⁻¹ for hs-DNA. The limits of detection are 1.1 and 2.1 ng mL⁻¹, respectively. Most foreign substances do not interfere in the determination, and the method has good selectivity and high sensitivity. It has been applied to the determination of DNA in synthetic samples and in real samples with satisfactory results.     

Coulometric determination of organic substances using electrogenerated dipositive silver

Summary Conditions are described for the efficient generation of silver(II) and the titration of organic compounds by electrogenerated silver(II). An electrolyte of 0.1 M silver nitrate and 5 M nitric acid at –10°C is used, with a gold generating anode and a current density of 1.5–5 mA/cm². A potentiometric (platinum-S.C.E. pair) or biamperometric (platinum electrodes, 200 mV) end point detection is used. For potentiometric detection, the platinum electrode is preconditioned with AgO in nitric or by anodization. The compounds isoniazid, oxalyldihydrazide, hydroquinone, and resorcinol were titrated down to sub-milligram quantities with errors of 1–2%.

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Coulometrische Bestimmung von organischen Substanzen mit Hilfe von elektrolytisch erzeugtem zweiwertigem Silber

Zusammenfassung Der verwendete Elektrolyt besteht aus 0,1 M Silbernitrat in 5 M Salpetersäure bei –10°C. Die Generatoranode besteht aus Gold (Stromdichte 1,5–5 mA/cm²). Die Bestimmung des Endpunkts erfolgt potentiometrisch (Pt/SKE) oder biamperometrisch (Pt-Elektroden, 200 mV). Für die potentiometrische Bestimmung wird die Indicatorelektrode mit einer Lösung von AgO in Salpetersäure oder durch elektrochemische Anodisierung vorbehandelt. Folgende Substanzen wurden bis herab in den sub-Milligramm-Bereich mit Fehlern von 1–2% titriert: Isoniazid, Oxalyldihydrazid, Hydrochinon, Resorcin.

     

Potentiometric determination of mercury(II) and thiourea in strong acid solution using an ion-selective electrode with AgI-based membrane hydrophobised by PTFE

Summary The potentiometric determination of mercury(II) and thiourea (TU) in strong acid solution (pH 0–1) by using an all-solid-state ion-selective electrode with (Ag₂S 25%, AgI 25% and PTFE 50% m/m)-membrane is described. The linear response, 43 mV(pHg)^–1 and 80 mV(pTU)^–1, has been obtained in the concentration range from 10^–2 to under 10^–5 mol/l. By direct potentiometry at pH 0 mercury(II) can be determined in the presence of up to 10^–3 mol/l of iron(III). The change in potential in the tested concentration range of thiourea indicates the formation of Ag(TU) _1.4 ⁺ at the exposed surface of the membrane. This stoichiometry is in good agreement with that calculated from the average Ag/TU ratio in the potentiometric titration. The investigated electrode can be used as a good sensor for mercury(II) and thiourea in strong acid media and a wide variety of practical analytical systems.     

Microquantitative determination of hesperidin by pulse perturbation of the oscillatory reaction system

A simple and reliable kinetic method for the determination of hesperidin (Hesp) is developed. It is based on potentiometric monitoring of the concentration perturbations of the matrix reaction system which is in a stable non-equilibrium stationary state close to the bifurcation point. The Bray–Liebhafsky oscillatory reaction is used as the matrix system. The response of the matrix to perturbations by different concentrations of Hesp is followed by using a Pt electrode. A linear relationship between maximal potential shift and the logarithm of Hesp concentrations is obtained between 7.5 and 599.4 g mL^–1. The limit of detection is 0.65 g mL^–1. The described procedure has been successfully applied to the determination of Hesp from different sources (capsules, industrial and hand-squeezed orange juice, and white wine).