Determination of thallium in the presence of large excess of lead by anodic stripping voltammetry

The paper is concerned with the determination of traces of thallium, as T1(I), in the presence of very large amounts of lead, by d.c. anodic stripping voltammetry, by adding both a complexing agent and anionic surfactant. The supporting complexing agent was 0.1M solution of EDTA (pH 4.4). The influence of the several surfactants on the signals of lead and thallium was investigated.In 0.1M EDTA at pH 4.4 at the absence of a surfactant, lead does not interfere at concentrations below 10^–4 M. When the electrolyte contains also an anionic surfactant, lead can be tolerated at concentrations up to 2 × 10^–3–6 × 10^–3 M (depending on the type of the surfactant), and the height of the thallium peak remains unaffected. This makes the determination of 10^–8 M T1(I) possible when the molar excess of lead is 2–6 × 10⁵ fold. The method has been tested by determining the thallium content of soil extracts.     

Polarographic behaviour of 2-benzilidenimino-benzohydroxamic acid (2-BIBH) and 2-BIBH-Mo(VI) system

The polarographic behaviour of 2-benzilideniminobenzohydroxamic acid (2-BIBH) solutions and of 2-BIBH solutions in the presence of Mo(VI) have been studied by using differential pulse polarography and cyclic voltammetry. The polarographic characteristics of the resulting waves have been studied and possible mechanisms of the processes involved have been proposed. A linear relationship has been observed betweenI _p and Mo(VI) concentration in the range 2×10^–6 to 1.6×10^–5 M when using 3×10^–4 M 2-BIBH. Standard deviations of 5.6×10^–8 and 1.2×10^–8 M were found for 3×10^–6 and 8 × 10^–6 M Mo(VI), respectively.     

Spectrophotometric determination of micro amounts of tetrathionate via its oxidation with permanganate

The reaction conditions of tetrathionate with permanganate were investigated by varying reaction time, temperature and amounts of sulphuric acid and permanganate. Under the optimal conditions for the reaction of tetrathionate with permanganate, both penta- and hexathionate were also oxidised; each one mol of polythionates (S _x O ₆ ^2– x=4, 5 and 6) reacts with (x–1.5) mol of permanganate. The proposed method is based on the reaction of tetrathionate with a given excess amount of permanganate in a sulphuric acid medium and on the spectrophotometric measurement of the iodine as triiodide formed by the oxidation of iodide with the excess of permanganate. This method could be successfully applied to the determinations of tetrathionate (4 × 10^–7 to 2 × 10^–5 M), pentathionate (3 × 10^–7 to 1.43 × 10^–5 M) and hexathionate (2 × 10^–7 to 1.11 × 10^–5 M), and gave a higher sensitivity than any previous methods without solvent extraction.     

Spectrophotometric determination of cationic and anionic surfactants with anionic dyes in the presence of nonionic surfactants,part II: Development of batch and flow injection methods

On the basis of the changes in absorption spectra of azo dyes on the addition of an organic onium ion, spectrophotometric methods for the determination of organic onium salts and anionic surfactants were developed, and applied to flow injection method. Propyl orange (PO^–) was used for the determination of organic onium ions. Pairs of PO^– and Zeph⁺ (tetradecyldimethyl-benzylammonium ion) or PO^– and nC₁₈TMA⁺ (n-octadecyltrimethylammonium ion) were used for the determination of anionic surfactants. The determination range of organic onium ions were (0–3) × 10^–5 M by a batch method and were (0–2) × 10^–5 M by a flow injection method. The determination ranges of anionic surfactants were (0–2) × 10^–5 M by the batch method, and were (0–5) × 10^–5 M by the flow injection method, and the detection limit corresponding toS/N = 3 was 3 × 10^–7 M by the flow injection method. By the proposed flow injection method, anionic surfactants in water samples were determined.     

Electrochemical sensor of nitrite based on an inorganic film modified glassy carbon electrode

The electrocatalysis of nitrite in solutions at an inorganic film modified glassy carbon electrode was studied. The modifier was an electrodeposited thin inorganic film of the copper-heptacyanonitrosylferrate (CuHNF). Cyclic voltammetry of the modified electrode in a nitrite solution revealed that both oxidation and reduction of nitrite were catalyzed and the electrocatalytic currents were controlled by the diffusion of nitrite. Voltammetric and amperometric responses were investigated. When applied as an amperometric sensor in a flow injection system, the modified electrode permitted detection at — 0.55 V, over 500 mV lower than at the naked electrode surface. A linear response range extending from 1 × 10^–6 to 1 × 10^–3 M nitrite was obtained, with a detection limit of 3 × 10^–7 M. The relative standard deviation for 50 repetitive injections with a 5 × 10^–5 M nitrite solution was less than 4%. The procedure was applied to the determination of nitrite in saliva and nitrate.     

Fibre optic sensor with bio-membrane supported immobilized morin for aluminium determination

A new type of fibre optic sensor based on the use of bio-membrane is proposed for the determination of aluminium. Morin is immobilized on mutton membrane pre-treated with formaldehyde and attached to the fibre optic. Fluorescence response is linear from 8 × 10^–7 to 3 × 10–5M. The detection limit is 6 × 10^–7 M. Response time is 30—60 s.     

Differential pulse polarographic determination of salicylaldehyde as its Girard-P derivative

A method for the determination of salicylaldehyde (2 × 10^–6–10^–4 M) by differential-pulse polarography, based on the in situ formation of its Girard-P derivative in aqueous solution at pH 2.5, is proposed. The relative standard deviation was 1.5% (ten determinations of 4 × 10^–5 M level). The applicability of this method was checked in synthetic samples containing salicyl alcohol,o-aminophenol, 2-methylphenol, salicylic acid and 4-aminobenzoic acid.     

Determination of tantalum with hexafluorotantalate(V)-selective coated graphite electrode

A hexafluorotantalate(V)-selective coated-graphite electrode was prepared by coating a graphite rod with brilliant green-hexafluorotantalate(V) extract in 1-chloronaphthalene in a PVC matrix. Potential measurements were made against an HF-resistant plastic sleeve (Ag/AgCl) external reference electrode. The concentrations of sulfuric and hydrofluoric acids, for the optimum response of the electrode to hexafluorotantalate(V), were found to be 1M each in the test solutions. The electrode responded to hexafluorotantalate(V) in the linear range 5.0 × 10^–6-5.0 × 10^–3 M, with a slope of -58 mV per decade and detection limit of 8.0 × 10^–7 M within 5–15s. The relative standard deviation for six determinations of 1.0 × 10^–4 M tantalum(V) was 2%. The life-time of the electrode was 60 days. The effects of forty diverse ions on the electrode response to the hexafluorotantalate(V) were studied and the electrode was found to be highly selective to hexafluorotantalate(V). Niobium, the element that commonly occurs with tantalum ores, showed a very low level of interference. The newly developed coated-graphite electrode has been applied to the determination of tantalum in tantalite-columbite ores and several synthetic matrices by direct, sample addition, standard addition, and Gran's plot potentiometric techniques with reasonable precision (2–4%) and accuracy.     

Potentiometric study using chemically modified silica gel with pyridinium as membrane for ClO 4 − ions

A potentiometric sensor for the perchlorate anion was developed by mixing chemically modified silicagel with pyridinium perchlorate, with an epoxy polymer and graphite. The electrode showed Nernstian response between 1.0 × 10^–2 and 1.0 × 10^–3 M perchlorate concentrations. The electrode showed high selectivity to this ion at solutions pH between 5.5 and 8.0. The presence of IO ₄ ^– , NO ₃ ^– ,Br^–, IO ₃ ^– , Cl^– and SO ₄ ^2– ions in the solutions, had only small interference in the electrode response in the range mentioned.     

Preconcentration and voltammetric determination of the herbicide metamitron with a silica-modified carbon paste electrode

A carbon paste electrode incorporating silica (Si-MCPE) was fabricated to accumulate Metamitron at the electrode surface. Several electroanalytical techniques were used to explore its reductive behaviour. The results indicate that the system is irreversible and fundamentally controlled by adsorption. The adsorptive stripping response has been evaluated with respect to accumulation time, deposition potential, scan rate, pH and other variables, using differential pulse voltammetry (DPV) and square wave voltammetry (SWV) as redissolution techniques. In both cases a voltammetric peak is obtained, at –0.542 V (DPV) and –0.421 V (SWV) in Britton-Robinson buffer (pH 1.9). The detection limits were 3.66 × 10^–1 M and 4.22 × 10^–9 M for AdS-DPV and AdS-SWV, respectively. Under optimum conditions the Metamitron reduction peak gave two linear regions in the range from 4.0 × 10^–9 M to 8.0 × 10^–8 M by means of AdS-DPV, with a coefficient of variation of 2.19% (n = 10) for 1 × 10^–8 M herbicide solution. A method was developed for determination of Metamitron in soils, with a recovery of 98.8% and a coefficient of variation of 5.26% (0.01 g/g of soil).     

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.     

A new ionic strength adjustor for nitrate analysis in waters,soils and plants using ion-selective electrode

A new ionic strength adjustor, ISA (ISA-Pb) composed of 0.02M Pb(CH₃COO)₂–0.01M PbO–0.02M CH₃COOK–0.01M NH₂SO₃H, was tested for the rapid nitrate analysis of waters, soil and plant extracts by means of ion-selective electrode (ISE). It was found that nitrate can be determined accurately and precisely within the concentration range of 5 × 10^–2 M to 2 × 10^–6 M. The proposed ISA-Pb, with a pH of 6.8, controlled the interferences of Cl^–, HCO ₃ ^– , NO ₂ ^– , and organic anions effectively, and gave results comparable to those obtained by the commonly used ISA with Ag₂SO₄ (ISA-Ag) and to well established chemical methods as well. ISA-Pb is much cheaper than ISA-Ag, and can therefore economically replace the latter when ISE is used for nitrate determination.Part of the senior author's doctorate thesis     

Comparative study on the determination of cephalexin in its dosage forms by spectrophotometry and HPLC with UV-vis detection

This paper discusses the spectrophotometric determination of cephalexin as the intact cephalexin or as its acid-induced degradation product. Cephalexin can be determined in the range 1 × 10^–5–18 × 10^–5 M with relative standard deviations of 5-1%. The limits of quantitation and detection were 10^–5 and 0.3 × 10^–5 M, respectively. These procedures were compared with reversed-phase HPLC determination. No interference was observed in the presence of common pharmaceutical adjuvants. The H-point standard additions method was applied in order to correct for the possible presence of the cephalexin precursor, 7-aminocephalosporanic acid; this improves the selectivity of the UV-vis spectrophotometric method.     

Tetrachloroferrate(III)-selective liquid membrane electrode based on crystal violet

An extract of crystal violet-tetrachloroferrate(III) in nitrobenzene was used to prepare a tetrachloroferrate(III)-selective liquid membrane electrode with a poly(vinyl chloride) support. The optimal conditions to determine 2.5 × 10^–5 – 5.0 × 10^–2 M iron(III) as tetrachloroferrate(III) (anionic slope 56 mV/decade, detection limit 7.9 × 10^–6 M) were found to be 4.0–5.5.M total chloride in 0.75–1.5M hydrochloric acid. The electrode was reliably applied to determine iron in human blood, haematite and mineralized vitamin syrup by direct potentiometry, standard and sample additions as well as standard subtraction techniques.     

Solubility of methane in aqueous solutions of triethylenediamine

The solubilities of methane were measured in water and aqueous solutions of triethylenediamine (TED), triethylenediamine hydrochloride (TED·HCl), and HCl at several concentrations up to 1M at 5° intervals from 5 to 25°C. Methane solubilities in solutions of TED·HCl and HCl are lower than those in water and decrease with increasing cosolute concentration. In contrast, the solubilities in TED solutions are greater than those in water and increase with increasing TED concentration. The order of methane solubilities at 25°C in water and in 0.5M aqueous solutions is TED>H₂O>HCl>TED·HCl with Ostwald coefficients of 3.57×10^–2, 3.44×10^–2, 3.26×10^–2, and 3.19×10^–2, respectively, and with an experimental precision of about ±0.2×10^–3. Thermodynamic functions for the transfer of methane from water to 0.25, 0.50, and 0.75M aqueous solutions have been calculated on the molar concentration scale. The free energies of transfer are compared with previous results for methane in aqueous solutions of tetraalkylammonium halides.     

Effect of using mixed ion-pairs on PVC-membrane electrodes for ephedrine

Mixed ion-pairs based on the use of ephedrinium (EPH)-TPB plus EPH-reineckate (II) and phenylephrine-TPB plus EPH-reineckate (III) were tried for use in plastic membranes. The results were compared to those of an EPH-reineckate (I) single ion-pair electrode. The Nernstian slopes were 50, 49 and 55 mV decade^–1 for membranes I, II and III, respectively. The linear concentration ranges were 10^–5–10^–1, 4.0 × 10^–5–10^–1 and 6.3 ×^–5–10^–1 M ephedrine. The detection limits were 4 ×^–6,10^–5 and 1.2 × 10^–5 M ephedrine for membranes I, II and III, respectively. The pH ranges were 4–9, 3–9 and 2–8 for I, II and III-membranes, respectively. Selectivity coefficient values for membrane II were better than those for membranes I and III. The effects of increasing KC1 concentration and temperature changes were explained for the three electrodes. The isothermal temperature coefficients were 0.00145, 0.0007 and 0.00055 V/ °C for electrodes I, II and III. Electrode III was applied for the determination of ephedrine in its pharmeaceutical preparations with an overall relative standard deviation range of 1.3–2.4% and an overall mean recovery value of 98.1%.     

A kinetic method for the determination of zinc(II) in presence of a large excess of cadmium(II) by the different dissociation rate of their complexes with 5,10,15,20-tetrakis(4-sulfonatophenyl)porphine

Summary Acid-dissociation reaction of the cadmium(II) complex of 5,10,15,20-tetrakis(4-sulfonatophenyl)porphme (H₂tspp) proceeds about 10¹² times as fast as that of the zinc(II) complex. This provides the basis for a kinetic determination of zinc(II) in presence of a large excess of cadmium (II). The absorbance at soret-band (421 nm) of Zn(II)(tspp) was used to monitor the reaction. At 5.0×10^–2 M hydrogen ion concentration, Cd(II)(tspp) dissociates completely to Cd²⁺ in 1 s and only the reaction associated with Zn(II)(tspp) is observed during the reaction time from 30 s to 5 min. Zinc(II) concentration <10^–6 M is determined in the presence of 10^–2 M cadmium(II). The molar absorption coefficient is 2.7×10⁵ M ^–1 cm^–1. Iron(III), aluminum(III) and cobalt(II) being masked sodium tartrate, this method is highly selective and is free from interferences of most substances usually encountered. The method was applied to determine zinc(II) in tap water and in cadmium(II) sulfate.     

Preparation and characterization of a codeine responsive electrode

Summary The behaviour of codeine reineckate and codeine tetraphenylborate membrane electrodes has been observed with a respectiveNernstian response of 58 and 56 mV/decade for 9.3×10^–5–1.3×10^–3 M codeine sulfate solutions. The workingpH ranges were 5–8 and 4–8, respectively. The selectivity towards sugars, amines, amino acids, cations, and some pharmaceutical compounds was found to be satisfactory. The isothermal temperature coefficient was 0.0014 V/°C. The electrodes were applied successfully for the determination of codeine in some pharmaceutical dosage forms with a relative standard deviation range of 0.16–0.30% and an average recovery of 98.6±0.6%.

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Herstellung und Charakterisierung einer codeinselektiven Elektrode

Zusammenfassung Das Verhalten von Codeinreineckat- und Codeintetraphenylboratmembranelektroden in 9.3×10^–5–1.3×10^–3 M Codeinsulfatlösungen wurde untersucht (Nernstscher Response: 58 bzw. 56 mV/Dekade). Der verwendetepH-Bereich für die beiden Elektroden war 5–8 bzw. 4–8. Ihre Selektivität gegenüber Zuckern, Aminen, Aminosäuren, Kationen und einigen pharmazeutisch aktiven Verbindungen ist zufriedenstellend. Der isotherme Temperaturkoeffizient beträgt 0.0014V/°C. Die Elektroden wurden erfolgreich zur Bestimmung von Codein in einigen pharmazeutischen Präparaten eingesetzt (relative Standardabweichung: 0.16–0.30%).

     

Catalytic determination of ultratrace amounts of Cu(II) by the oxidative coupling reaction of 3-methyl-2-benzothiazolinone hydrazone with N,N-dimethylaniline

Summary Copper (II) catalyzes the coupling reaction of 3-methyl-2-benzothiazolinone hydrazone (MBTH) with N,N-dimethylaniline (DMA) to form an intensely colored dye (_max=590 nm) in the presence of hydrogen peroxide and ammonia as an activator. On the basis of this reaction, a highly sensitive and selective catalytic method for Cu(II) has been developed. As little as 10^–9 M Cu(II) can be determined by measuring the absorbance of the reaction product at a fixed time (20 min at 40°C). Sandell's sensitivity calculated from the working curve is 1.3×10^–3 ng cm^–2. The method was applied to water analysis and some comments on the analysis of copper in river water were added.Presented at the 1st International Symposium on Kinetics in Analytical Chemistry, Córdoba, Spain, September 28th, 1983.     

New effective and selective extractants for separation and determination of silver

Summary Isopropyl-N-alkylthiocarbamates have been studied as extractants for preconcentration of silver trace amounts and for separation of silver macroquantities. It has been shown that the 0.05M reagents in chloroform extract trace amounts of silver with high distribution coefficients from HNO₃, H₂SO₄, HClO₄ and HCl solutions in wide range of their concentrations. The highest selectivity is obtained when HNO₃, H₂SO₄ or HClO₄ solutions are used. Besides silver only mercury and palladium are extracted. When HC1 solutions are used, gold is also transferred into organic phase. Isopropyl-N-alkylthiocarbamates are effective for extraction of silver from its concentrated (up to 1M) solutions, particularly from HNO₃ solutions: more than 99.9% of silver is extracted even at 2-fold reagent excess. Some characteristics of reagents themselfes have been investigated, such as dissociation, protonation, distribution between organic and aqueous phases and association in organic solvents. The thion forms are found to be predominant. Silver is extracted as coordination solvated compounds Ag(HL) _n X, where X=Cl, Br, J, NO₃. Sulfur serves as a donor atom for their formation.The procedures for silver determination in geological samples by flame atomic absorption (3×10^–7%) and atomic emission (1×10^–7%) have been developed. The procedures for atomic emission determination of 23 trace elements (5×10^–8–1×10^–5%) and for electrothermal atomic absorption determination of 17 trace elements (4×10^–9–8×10^–6%) in high purity silver have also been developed.

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Neue wirksame und selektive Extraktionsmittel für die Trennung und Bestimmung von Silber

Zusammenfassung Isopropyl-N-alkylthiocarbamate wurden als Extraktionsmittel für die Anreicherung von Silberspuren und für die Abtrennung von Makromengen Silber geprüft. Es ergab sich, daß solche 0,05M, in Chloroform gelöste Reagenzien Silberspuren mit hohen Verteilungskoeffizienten aus HNO₃, H₂SO₄, HClO₄ und HCl extrahieren. Die beste Selektivität wurde mit HNO₃, H₂SO₄ oder HClO₄erzielt. Neben Silber werden nur Quecksilber und Palladium extrahiert. Verwendet man HCl, so geht auch Gold in die organische Phase. Isopropyl-N-alkylthiocarbamate eignen sich für die Extraktion von Silber aus konzentrierten (bis zu 1M) Lösungen, besonders aus HNO₃: mehr als 99,9% Silber werden mit zweifachem Reagensüberschuß extrahiert. Einige charakteristische Eigenschaften der in Rede stehenden Reagenzien wurden untersucht: z. B. die Dissoziation, die Protonation, die Verteilung zwischen organischer und wäßriger Phase und die Assoziation in organischen Lösungsmitteln. Hauptsächlich liegen diese Reagenzien in Thionform vor. Silber wird als Ag(HL) _n X extrahiert, worin X für Cl, Br, J oder NO₃ steht. Schwefel fungiert als Donatoratom für deren Bildung.Verfahren zur Silberbestimmung in geologischen Proben mit Hilfe der Flammen-Atomabsorption (3×10^–7%) bzw. der atomaren Emission (l×10^–7) wurden ausgearbeitet. Außerdem wurden auch Verfahren zur Bestimmung von 23 Spurenelementen mittels atomarer Emission (5×10^–8 bis 1×10^–5%) und von 17 Spurenelementen mittels elektrothermaler Atomabsorption (4×10^–9 bis 8×10^–6%) in hochgereinigtem Silber entwickelt.

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The paper has been presented at the Fifth European Conference on Analytical Chemistry (Euroanalysis V), Cracow, August 26–31, 1984.