Kinetic determination of 1,3-propanediamine-N,N′-diacetic-N,N′-di-3-propionic acid and in a mixture with ethylenediaminetetra-acetic acid

A kinetic method is proposed for the determination of propanediamine-N,N′-diacetic-N,N′-di-3-propionic acid, based on its inhibitory effect on the acetonitrile-catalysed oxidation of Pyrocatechol Violet by hydrogen peroxide. The concentrations of 1,3-propanediamine-N,N′-diacetic-N,N′-di-3-propionic acid determined ranged from 5.0 × 10^?7 to 4.0 × 10^?6 M with a relative standard deviation of up to 3.3%. The same indicator reaction can be applied to the determination of 1,3-propanediamine-N,N′-diacetic-N,N′-di-3-propionic acid and ethylenediaminetetra-acetic acid in mixtures. Mixtures of these acids in molar ratios from 1 ∶ 4.5 to 10 ∶ 1 have been analysed. Concentrations of 1,3-propanediamine-N,N′-diacetic-N,N′-di-3-propionic acid from 2.0 × 10^?7 to 1.0 × 10^?6 M and ethylenediaminetetra-acetic acid from 1.0 × 10^?7 to 9.0 × 10^?7 M were determined with relative standard deviations of up to 4.3 and 5.7%, respectively. The effect of foreign ions on the accuracy of these determinations was also investigated.     

The electrochemical stripping determination of tin in aqueous and nonaqueous media after its extraction

The anodic stripping voltammetric and chronopotentiometric determination of tin(IV) in aqueous and nonaqueous medium after its extraction using the rotating disc electrode made of glassy carbon with the mercury film was studied. The optimum composition of nonaqueous medium for the determination of tin is 0.2 M NaBr+5×10^?5M Hg²⁺ in 20 ml of the extract +30 ml of methanol. Tin(IV) was determined by anodic stripping voltammetry or chronopotentiometry down to the concentration 10^?7M. The selective determination of tin was studied. 10^?6M of tin(IV) was determined with an error ±4–5% even in the presence of metals: Co²⁺, Ni²⁺, Cd²⁺, Zn²⁺ (5×10^?3M), Ag⁺ and Pb²⁺ (5×10^?4M), Cu²⁺ (1.5×10^?4M), Sb³⁺ and Bi³⁺ (5×10^?5M).     

The electrochemical stripping determination of bismuth in aqueous and nonaqueous media after its extraction

The cyclic voltammetry of bismuth in aqueous media and electrochemical stripping determination of bismuth in aqueous and nonaqueous media after its extraction using a rotating disc electrode of glassy carbon was studied. To raise the conductivity of the organic medium and for the preparation of a convenients medium for the determination of bismuth, an alcoholic (methanol) solution of NH₄SCN+HClO₄ was employed. In non-aqueous medium bismuth can be determined down to concentrations 10^?8M by anodic stripping voltammetry and to 5×10^?8M by anodic stripping chronopotentiometry. The selectivity of the determination of bismuth after its extraction was studied. Electrochemical determination of 10^?6M Bi³⁺ with error ±3–4% was not interfered with by these elements: Co²⁺, Ni²⁺, Zn²⁺, Cd²⁺, As³⁺ in the concentration 8×10^?3M, Fe³⁺, In³⁺, Sn²⁺ and Sn⁴⁺ (5× 10^?3M), Cu²⁺ (10^?3M), Sb³⁺ (1.5×10^?4M) and Hg²⁺ (2×10^?5M). The reproducibility of the electrochemical determination of bismuth according to the recommended procedure is very good.     

The stepwise formation of complexes in the uranyl/azide system in aqueous medium

The use of an indirect potentiometric method with the glass electrode in a ₃?/HN₃/UO₂2+ solution leads to ligand number $\text{n}\text{?}$, at several azide concentrations, at 2.0M ionic strength (NaClO₄), aqueous medium and 25.0±0.1°C. The analysis of data under conditions where hydrolysis is avoided leads to the six overall stepwise constants: β₁ = 1.39 × 10²M^?1; β₂ = 8.26 × 10³M^?2; β₃ = 4.9 × 10⁵M^?3; β₄ = 7.1 × 10⁵M^?4; β₅ = 2.3 × 10⁶M^?5; β₆ = 1.2 × 10⁷M^?6.     

Kinetic fluorometric methods for the determination of phosphates at the nanogram level using a lead(II)-catalyzed pyridoxal 2-pyridylhydrazone-hydrogen peroxide reaction

Fluorometric methods for the determination of phosphate (1.5 × 10^?6–3.1 × 10^?6M), diphosphate (7.0 × 10^?7–2.0 × 10^?6M), and triphosphate (2.0 × 10^?7–2.7 × 10^?6M) are described. The analytical procedure is based on the inhibition of polyphosphate ions on the oxidation of pyridoxal 2-pyridylhydrazone (PPH) by hydrogen peroxide, catalyzed by low concentrations of lead(II) ions. The reactions are followed by means of the rate of appearance of the fluorescence (λ_ex = 355 nm, λ_em = 425 nm). The effect of the variables is studied. The kinetic parameters of the reactions are reported and rate equations are suggested. The results are interpreted according to the discernment of the chemistry of complex formations.     

A multivariate calibration procedure for the tensammetric determination of detergents

A multivariate calibration procedure based on singular value decomposition (SVD) and the Ho-Kashyap algorithm is used for the tensammetric determination of the cationic detergents Hyamine 1622, benzalkonium chloride (BACl), N-cetyl-N,N,N-trimethylammonium bromide (CTABr) and mixtures of CTABr and BACl. The sensitivity and accuracy depend strongly on the nature of the detergent. Acceptable accuracy is obtained with a two-step calculation procedure in which calibration constants for the total concentration range of interest are used to guide the choice of a more specific set of calibration constants which are valid for a much smaller concentration span. For Hyamine 1622, concentrations in the range 5 × 10^?6?2 × 10^?4 M could be determined with an accuracy of ± 10^?6 M. For CTABr, these numbers were 3 × 10^?6?2 × 10^?4 M and ± 5 × 10^?7 M; for BACl, they were 2 × 10^?3?9 × 10^?2 g l^?1 and ± 1 × 10^?3 g l^?1. In the mixtures of CTABr and BACl, the accuracies were ± 3 × 10^?6 M and × 1 × 10^?3 g l^?1, respectively.     

Consecutive determination of rutin and quercetin by spectrophotometric measurements

The consecutive determination of rutin and quercetin without any pretreatment for separation was examined in methanol solutions by a conventional and a two-wavelength spectrophotometry. Based the tendency of quercetin to form more stable metal complexes compared to rutin, quercetin can be determined through the tin(II) complex formation without interference from rutin. The method was applied to the determination of quercetin in the concentration range of 3.0 × 10^?6 to 2.0 × 10^?5M.Quercetin is apt to be oxidized by oxygen rather than rutin, especially in the presence of copper(II), whereas rutin is not decomposed under such a condition. After removal of quercetin through copper(II)-catalyzed oxidation, rutin ranging in concentration from 2.0 × 10^?6 to 2.0 × 10^?M was determined by the absorbance measurement of rutin-copper(II) complex in slightly alkaline methanol media.Both rutin and quercetin were determined directly by two-wavelength spectrophotometry, without adding any complex forming metals; the lower limit of detection was about 1.0 × 10^?5M. The method was extended to the determination of a smaller amounts of rutin and quercetin using the absorption peaks of their zirconium(IV) complexes, and the determination of both components in the range of 5.0 × 10^?6 to 3.0 × 10^?5M was made with a relative error of within ±4%.     

Dipyrrolylquinoxaline-bridged hydrazones: a new class of chemosensors for copper(II)

Novel 2,3-bis(1H-pyrrol-2-yl)quinoxaline-functionalized hydrazones were prepared and characterized as new chemosensors for copper(II) ion. The binding properties of the compounds 4, 5, 6 and 7 for cations were examined by UV–vis, fluorescence spectroscopy, and linear sweep voltammetric experiments (LSV). The results indicate that a 1:1 stoichiometric complex is formed between compound 4 (or 5, 6, 7) and copper(II) ion, and the association constant is 1.3?×?10⁵ M^?1 for 4, 2.1?×?10⁶ M^?1 for 5, 4.1?×?10⁵ M^?1 for 6 and 8.0?×?10⁵ M^?1 for 7, respectively. The recognition mechanism between compound 4 (or 5, 6, 7) and metal ion was discussed based on their electrochemical properties, absorbance changes, and the fluorescence quenching effect when they interact with each other. Control experiments revealed that compound 4 (or 5, 6, 7) has a highly selective response to copper (II) ion.     

Simultaneous determination of dopamine and serotonin by use of covalent modification of 5-hydroxytryptophan on glassy carbon electrode

An electrochemical biosensor was fabricated by covalent modification of 5-hydroxytryptophan (5-HTP) on the surface of glassy carbon electrode (GCE). The electrode, denoted as 5-HTP/GCE, was characterized by X-ray photoelectron spectroscopy, cyclic voltammetry and differential pulse voltammetry. For comparison, tryptophan modified GCE (TRP/GCE) and serotonin modified GCE (5-HT/GCE) were prepared by the same method. It was found that electrocatalytic ability of these electrodes was in the order of 5-HTP/GCE?>?TRP/GCE?>?5-HT/GCE for the oxidation of dopamine (DA) and 5-HT. The sensor was effective to simultaneously determine DA and 5-HT in a mixture. It can resolve the overlapping anodic peaks into two well-defined voltammetric peaks at 0.24 and 0.39 V (versus SCE). The linear response is in the range of 5.0?×?10^?7–3.5?×?10^?5 mol L^?1 with a detection limit of 3.1?×?10^?7 mol L^?1 for DA, and in the range of 5.0?×?10^?6–3.5?×?10^?5 mol L^?1 with a detection limit of 1.7?×?10^?6 mol L^?1 for 5-HT (s/n?=?3), respectively.     

Direct potentiometric titration of thiosulfate,thiourea, and ascorbic acid with lodate using an iodide ion-selective electrode

A potentiometric method has been developed for the semi-automatic direct titration of thiourea, thiosulfate, and ascorbic acid with potassium iodate in strongly acidic solutions using an iodide ion-selective electrode to monitor the reaction and locate the endpoint. The method is simple, fast, precise, and accurate. Amounts ranging from 0.15–1.5 mg of thiourea (3.9 × 10^?4–3.9 × 10^?3, M), 0.3–3.0 mg of thiosulfate (5.4 × 10^?4–5.4 × 10^?3, M), and 0.5–5.0 mg of ascorbic acid (5.7 × 10^?4–5.7 × 10^?3, M) have been determined with an average error of about 1%. The method has been applied to the determination of ascorbic acid in tablets. Results checked closely with those obtained with a standard titrimetric method.     

Kinetic study of the reaction of meso-tetrakis (p-trimethylammoniumphenyl)porphinatodiaquorhodate(II) with chloride,bromide, iodide,hexacyanocobaltate(III) and thiocyanate ions in aqueous solution

The reaction of Cl^?, Br^?, I^?, Co(CN)₆^3? and NCS^? with meso-tetrakis (p-trimethylammoniumphenyl)porphinatodiaquorhodate(III), [RhTAPP(H₂O)₂]⁵⁺, has been studied at 15, 25 and 35°C in 0.1 M [H⁺] with μ = 1.00 M (NaNO₃). The value of the acidity constant, K_al, at 25°C is 4.39 × 10^?9 M. The reactions are first order in anion concentration up to 0.9 M. The values of the stability constants, K₁, and the second order rate constants, k₁, for the reaction with Cl^?, Br^?, I^?, Co(CN)₆^3? and NCS^? are respectively 0.23 M^?1 and 2.5 × 10^?3 M^?1 s^?1, 1.1 M^?1 and 6.92 × 10^?3 M^?1 s^?1, 40.0 M^?1 and 17.0 × 10^?3 M^?1 s^?1, 550 M^?1 and 20.0 × 10^?3 M^?1 s^?1, 3400 M^?1 and 20.9 × 10^?3 M^?1 s^?1. The porphine greatly labilizes the Rh(III). There has been about a 500-fold increase in the rate constant for substitution compared to that of [Rh(NH₃)₅H₂O]³⁺. The substitution rates are however about the same as for [Rh(TPPS)(H₂O)₂]^3?, indicating that the overall charge on the complex plays only a minor role. The kinetic results indicate that dissociative activation is occurring in these reactions.     

Investigation on the Binding of Terazosin Hydrochloride and Naftopidil to an Immobilized α 1-Adrenoceptor by Zonal Elution

The interaction between drugs and receptors is particularly important in revealing the drug acting mechanism and developing new leads. In this work, α ₁-Adrenoceptor (α ₁-AR) from HEK293 cell line is purified and immobilized on the surface of macro-pore silica gel to prepare an high-performance affinity chromatography stationary phase for the pursuit of drug–receptor interactions by competition zonal elution. Naftopidil is found to have only one type of binding site to α ₁-AR with an association constant of 1.45 × 10⁶ M^?1 and a concentration of binding sites of 1.56 × 10^?6 M, while terazosin hydrochloride proves to present two kinds of binding site on the receptor at which the association constants are determined to be 1.61 × 10⁵ M^?1 and 2.06 × 10³ M^?1, and the corresponding concentrations of the binding sites are 1.56 × 10^?6 M and 1.11 × 10^?3 M, respectively. It is concluded that the stationary phase containing attached α ₁-AR can be used to realize the binding of a drug to the receptor.     

Determination of biogenic amines from electrocatalytic responses of graphite electrodes modified with metallic osmium or an osmium oxide-ruthenium cyanide film

Particles of osmium or an inorganic polymeric film of osmium oxide-ruthenium cyanide (OsO-RuCN) electrodeposited on glassy carbon (GC) electrocatalyze the oxidation of dopamine (DA), adrenaline (AD), and noradrenaline (NAD). It is found that these biogenic amines are determined with a high sensitivity by oxidation at an electrode with an OsO-RuCN film. Procedures for the voltammetric determination of DA, AD, or NAD at a composite film electrode are developed. The currents of the substrate oxidation are linear functions of the concentrations in the ranges from 5 × 10^?7 to 1 × 10^?3 M for DA and from 1 × 10^?6 to 1 × 10^?3 M for AD and NAD.     

Boron Photochemistry : XII. The role of iodine in the photocyclization of anilinodimesitylboranes

The ratio of methyl group rearrangement to methyl group elimination during the photocyclization of anilinodimesitylborane is dependent upon the concentration of iodine present. At iodine concentrations of less than 10^?3M, the major product is a demethylated borazarophenanthrene, 7,9-dimethyl-6-mesityldibenz[ce][1,2]-azaborine (IV). At concentrations of iodine above 5 × 10^?3M, the major products is a methyl-rearranged borazarophenanthrene, 7,9,10-trimethyl-6mesityldibenz[ce][1,2]-azaborine (V). The role of iodine was at least threefold: assisting in the production of a reactive cation-radical at low iodine concentrations, quenching the formation of the cation-radical at higher iodine concentrations, and actively assisting at the higher concentrations in the formation of a reactive species.     

Voltammetric and chronoamperometric investigation of germanium amalgams: Part I. Properties of the homogenous amalgam

Using cyclic voltammetry and chronoamperometry with several anodic steps the deposition and particularly the oxidation of germanium from a HMDE was investigated within pH range 4–12 at Ge (IV) concentrations ranging from 4×10^?7M to 1×10^?4M in the absence of ligands capable to form the complex compounds with Ge(IV) in a solution. It was found that the initially formed product of electrodeposition is a homogeneous, usually supersaturated amalgam. Germanium from this amalgam oxidizes at about 1 V (vs. mercury sulphate reference electrode) or after some induction period, the length of which depends on concentration of Ge(0) in mercury, it begins to crystallize forming heterogenous germanium amalgam. Germanium from this heterogenous amalgam oxidizes in a separate voltammetric peak at more positive potentials. The solubility of germanium in mercury was evaluated on the basis of the oxidation current of homogenous amalgam and the value obtained is equal to (2±0.5)×10^?7M i.e. (1.1±0.3)×10^?7 wt. %. Applying the Stevens and Shain method the diffusion coefficient of germanium in mercury was found to be (1.32±0.1)×10^?5 cm² s^?1.     

Electrochemical Responses and Sensitivities of Films Based on Multi-Walled Carbon Nanotubes in Aqueous Solutions

Novel films consisting of multi-walled carbon nanotubes (MWCNTs) were fabricated by means of chemical vapor deposition with decomposition of either acetonitrile (ACN) or benzene (BZ) using ferrocene as catalyst. The electrochemical responses of MWCNT-based films towards the ferrocyanide/ferricyanide, [Fe(CN)₆]^3?/4? redox couple were probed by means of cyclic voltammetry and electrochemical impedance spectroscopy at 25.0?±?0.5?°C. Both MWCNT-based films exhibit Nernstian response towards [Fe(CN)₆]^3?/4? with some slight kinetic differences. Namely, heterogeneous electron transfer rate constants lying in ranges of 2.69?×?10^?2?C1.7?×?10^?3 and 9.0?×?10^?3?C2.6?×?10^?3?cm·s^?1 were obtained at v?=?0.05?V·s^?1 for MWCNT_ACN and MWCNT_BZ, respectively. The detection limit of MWCNT_ACN, estimated to be about 4.70?×?10^?7?mol·L^?1 at v?=?0.05?V·s^?1, tends to become slightly poorer with the increase of the scan rate, namely at v?=?0.10?V·s^?1 the detection limit of 1.70?×?10^?6?mol·L^?1 was determined. Slightly poorer response ability was exhibited by MWCNT_BZ; specifically the detection limits of 1.57?×?10^?6 and 4.35?×?10^?6?mol·L^?1 were determined at v?=?0.05 and v?=?0.10?V·s^?1, respectively. The sensitivities of MWCNT_ACN and MWCNT_BZ towards [Fe(CN)₆]^3?/4? were determined as 1.60?×?10^?7 and 1.51?×?10^?7?A·L·mol^?1·cm^?2, respectively. The excellent electrochemical performance of MWCNT_ACN is attributed to the presence of incorporated nitrogen in the nanotube??s structure.     

Selektivitätssteigerung katalytischer bestimmungsverfahren—extraktionskataly-metrische molybdänbestimmung

To increase the selectivity of catalytic methods, a solvent extraction and catalytic determination have been combined. By means of the determination of molybdenum based on the catalytic oxidation of 1-naphthylamine by bromate, it is shown that by selection of a suitable extraction system the catalyst can be determined directly in the organic extract. The catalytic activity of different complexes of molybdenum was tested and for an analytical application the extraction of molybdenum as oxinate was chosen. The method enables molybdenum to be determined down to 2.7 × 10^?9M. The relative error of the determinations is 10%. 10^?4M V, 2 × 10^?4M Cr, 5 × 10^?5M W and 10^?2M Mn, Ni, Cu, Co, Fe, Mg, Zn, Cd, Al and Pb cause no interference. The method has been used for the determination of molybdenum in sea-water.     

A catalytic method for the determination of acetonitrile

A kinetic method for the determination of micro quantities of acetonitrile, based on its catalytic activity on the oxidation of pyrocatechol violet by hydrogen peroxide, is presented. On the basis of the results obtained by kinetic investigations, a kinetic equation as well as the apparent rate constant of this reaction is given. Acetonitrile was determined by the application of the differential form of the tangent method in concentrations ranging from 1.52 × 10^?3M to 22.8 × 10^?3M, with relative standard deviation up to 6%.     

Synthesis and biological activities of substituted dihydrobenzo[h]-pyrimido[4,5-b]quinolines as tetracyclic 5-deaza nonclassical folates

Novel tetracyclic compounds 1–4 have been synthesized via a regiospecific cyclocondensation reaction between substituted 6-aminopyrimidines 5– 7 and chlorovinyl aldehydes 13 and 14 . The linear structures of these compounds were established by ¹H nmr and ¹³C nmr spectral data and also by synthesis of the compounds via an unambiguous route. The growth of Manca human lymphoma cells was inhibited 50% by 1 and 4 at 4.5 × 10^?6 M and 1.2 × 10^?6 M respectively. These compounds also inhibited human dihydrofolate reductase (DHFR)by 50% at 4.4 × 10^?6 M and 1.4 × 10^?6 irrespectively and L. casei DHFR at 1.9 × 10^?5 M and 1.1 × 10^?5 M respectively. Compound 16 , a positional isomer of 1 , was the most potent of the compounds studied, it inhibited the growth of Manca human lymphoma cells by 50% at 9 × 10^?8 M. The IC₅₀ values of 16 for the inhibition of human DHFR and L. casei DHFR were 8 × 10^?8 M and 1.9 × 10^?5 M respectively.     

Determination of ruthenium as ruthenate by stripping voltammetry

Stripping voltammetric analysis of ruthenium with a platinum RDE was studied in the concentration range from 5×10^?7 to 1.2×10^?5M RuO₄^2?, where linear dependence of the anodic peak height on the ruthenate concentration was obtained. Special attention has been paid to a simple preparation of the sample for analysis. Ruthenate can be prepared directly in the electrolytic vessel from the ruthenium compounds by oxidation with potassium persulphate in alkaline medium. As a supporting electrolyte 10^?2 to 5×10^?2M K₂S₂O₈ with 10^?1 to 1 M KOH was used.