Kinetics and Isotherms of Cationic Polyelectrolyte Adsorption on Quartz

The kinetics of the formation of quartz surface charge in the solutions of a cationic polyelectrolyte, poly(styrene-co-dimethyl aminopropylmaleimide) with the molecular mass M = 20000 is studied in the concentration range from 10^–5 to 0.5 g/l in 10^–4 M KCl background solution at pH 6.5. Quartz capillaries with the radius from 5 to 10 m and molecularly smooth surface are used as model systems. Characteristic times of the formation of the surface charge at equilibrium with the solution are calculated from the data on the kinetics of adsorption; these times are equal to 40–50 min for the region of electrostatic adsorption (before the surface charge reversal) and 20–25 min, for the region of hydrophobic adsorption upon the formation of the second adlayer. Based on the steady values of the surface charge, the isotherms and potentials of adsorption of cationic polyelectrolyte are calculated. Electrostatic adsorption isotherm is described by the Langmuir equation with the energy of molecular adsorption of 25.4kT. It is shown that, at polymer concentration above 10^–2 g/l, the conformation of adsorbed molecules ceases to be planar. However, even in this case, we succeed in calculating the surface charge using the Helmholtz and Gouy equations and applying the pressure drops at the capillary ends higher than 10 atm, when under the loading of increasing shear stress in the surface layer the conformation of adsorbed molecules approaches the planar shape. Based on the two-layer model of the formation of surface charge developed earlier, it is shown that the energy of hydrophobic adsorption is smaller than that of electrostatic adsorption and is equal to 17.7kT. Possible physical mechanisms of electrostatic and hydrophobic adsorption of cationic polyelectrolyte molecules on quartz are discussed.     

Spectrophotometric behaviour of quinolinium oxime-palladium(II) complexes

Summary It has been established that 1-(2-phenyl-2-hydroxyiminoethyl)-1-quinolinium chloride, 1-(2-phenyl-2-hydroxyiminoethyl)-1-isoqui-nolinium chloride, 1-(2-phenyl-2-hydroxyiminoethyl)-1-(4-methyl)-quinolinium chloride and 1-(2-phenyl-2-hydroxyiminoethyl)-1-(6-methyl)quinolinium chloride react with palladium(II) chloride in the pH range 3.3–7.1 and form yellow water-soluble 11 complexes with maximum absorbance at 413 nm. The conditional stability constants of the complexes at the optimum pH of 6.5 are all about 10^4.7, and the molar absorptivities are in the range 2.2–2.6×10³ l·l mole^–1·cm^–1 at pH 6.5 and 413 nm. Beer's law is obeyed up to 3–4×10^–4 M oxime concentration, depending on the oxime determined.     

Acid–Base Zeta-Metric Titration of Quartz Dispersions in Ethanol Solutions of Electrolytes

The conductivity of dilute quartz suspensions and electrophoretic mobility of quartz particles in solutions with the concentration C = 10^–5–10^–2 M XBr (X = H, Cs, Na, and Li) and NaOH, as well as in mixed solutions of 10^–4 M XBr (X = Cs, Na, and Li) + 10^–4–10^–2 M HBr and 10^–4 M XBr + 10^–4–10^–2 M XOH (X = Cs, Na, and Li) in ethanol containing 6 vol % of water were measured using conductometry and microelectrophoresis. The values of surface conductivity of quartz were calculated by the Wagner formula and used to calculate zeta potential by the Henry–Booth formula. The resultant dependences (logC) suggest that the value and sign of zeta potential are determined not only by the adsorption of potential-determining ions ⁺ and ^–, but also by the competitive specific adsorption of all ions of the aforementioned electrolytes, the adsorption values increasing in a cation series Li⁺ < Na⁺ < Cs⁺ < H⁺ and an anion series Br^– < OH^–. In particular, it is found that the titration of the above suspensions with XOH bases results in the reversal of zeta potential sign from negative to positive at a concentration depending on the adsorption capacity of alkali cation.     

The Effect of Water Addition on the Electrosurface Properties of Quartz in Solutions of Alkali Metal Bromides in Ethanol

Electrosurface properties (the -potential and surface conductivity) of quartz particles in water–ethanol solutions of CsBr, NaBr, and LiBr with concentrations C = 10^–5–10^–2 M are studied. The (log C) dependences plotted from the results of electrophoretic measurements with allowance made for the particle surface conductivity demonstrate that, when water content in the aforementioned solutions increases from 4 to 40 vol %, the -potential of quartz becomes more negative and the isoelectric point shifts toward higher electrolyte concentrations, which increase in the following series: CsBr < NaBr < LiBr. This shift of the isoelectric point is explained by a decrease in the specific interaction of the alkali metal cations with the quartz surface because of a rise in the degree of their hydration (supersolvation).     

Formation of uniform silver particles from bis (1,2-ethanediamine)silver(I) complex

Uniform spherical silver particles were produced by decomposing the bis(1,2-ethanediamine)silver(I) complex, by aging a solution of 1.0×10^–3 mole dm^–3 in silver (I) nitrate, 1.0 mole dm^–3 in 1,2-ethanediamine, and 2.5×10^–1 mole dm^–3 in nitric acid (basic solution) at 100°C for 42 min. The average modal diameter was estimated to be 0.52 m with a relative standard deviation of 0.10. A moderately oxygenrich layer, 40 Å thick, on the surface of the particles was detected by means of photoelectron surface microanalysis (XPS). The silver particles grew through a polynuclear-layer mechanism, as judged from the concentration change in soluble silver(I) species in the supernatant solution. The particles' point of zero charge (PZC) was estimated at pH 6.5 by potentiometric titration.     

Propionyl promazine phosphate as a new reagent for the spectrophotometric determination of rhodium(III)

Summary PPP forms an orange-red coloured complex with rhodium(III) at room temperature (27°) in the presence of sodium acetate-hydrochloric acid buffer of pH 1.0–3.0 containing copper(II) and ascorbic acid. The complex exhibits absorption maximum at 470 nm. Beer's law is valid over the rhodium concentration range 0.1–18g/ml. Sandell's sensitivity of the reaction is 1.8·10^–3 g Rh/cm² and the molar extinction coefficient is 5.68×10³ l·mol^–1cm^–1 at 470 nm. The composition of the complex is 11 and the apparent stability constant of the complex at pH 2.5 and 27° has the logK value of 4.0. The proposed method has been used for the determination of rhodium in thermocouple wires and in synthetic mixtures containing palladium, ruthenium, osmium, uranium or iridium.

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Propionylpromazinphosphat (PPP), ein neues Reagens für die spektrophotometrische Bestimmung von Rhodium(III)

Zusammenfassung PPP bildet mit Rh(III) bei Zimmertemperatur (27°) in Gegenwart von Natriumacetat-Salzsäure (pH 1,0–3,0), Cu(II) und Ascorbinsäure eine orange-rote Komplexverbindung mit einem Absorptionsmaximum bei 470 nm. Das Beersche Gesetz gilt für Konzentrationen von 0,1 bis 18g/ml. Die Empfindlichkeit nach Sandell beträgt 1,8×10^–3 g Rh/cm²; der molare Extinktionskoeffizient bei 470 nm ist 5,68×10³ l·mol^–1·cm^–1. Die Zusammensetzung der Komplexverbindung entspricht dem Verhältnis 11, die scheinbare Stabilitätskonstante bei pH 2,5 und 27° entspricht log K=4,0. Das vorgeschlagene Verfahren diente zur Rh-Bestimmung in Thermoelementdraht sowie in synthetischen Gemischen aus Pd, Ru, Os, U und Ir.

     

Fulfillment of the Conditions of Thermodynamic Equilibrium in an Ice/Electrolyte Solution System with Constrained Geometry

For small volumes of a NaCl solution (10^–6 cm³) with concentrations of 0.1 and 1 M, temperature dependences of the length lof solution columns frozen in thin quartz capillaries (5–10 m in radius) are obtained. At the temperatures t above –4 and –8°C (for 0.1 and 1 M solutions, respectively), the l(t) dependences are reversible, independent of the direction of changes in temperature, and, hence, correspond to the equilibrium conditions of ice/solution system. From the constant mass condition of the solute, an expression for l(t) is derived that includes only one thermodynamic characteristic, namely, the temperature dependence of the solution concentration in equilibrium with ice. Deviations from the calculated l(t) dependences are observed at a temperatures below –2 and –5°C (for 0.1 and 1 M solutions, respectively), which can be explained by the adhesion of frozen solution to the capillary walls. The arising internal stresses lead to the deviations from the thermodynamic equilibrium conditions known for the bulk systems. On approaching the melting zone, the adhesion is failed because of the formation of thin nonfreezing water interlayers on the quartz surface.     

Determination of dopamine in synthetic cerebrospinal fluid by SWV with a graphite–polyurethane composite electrode

This work describes an electroanalytical investigation of dopamine using cyclic voltammetry (CV) and the graphite–polyurethane composite electrode (GPU). In CV studies, well-defined redox peaks characterize the oxidation process at the GPU electrode, which is indicative of electrocatalytic effects associated with active sites on the GPU electrode surface. A new analytical methodology was developed using the GPU electrode and square wave voltammetry (SWV) in BR buffer solution (0.1 mol L^–1; pH 7.4). Analytical curves were constructed under optimized conditions (f=60s^–1, E_a=50 mV, E_I=2 mV) and detection and quantification limits of 6.4×10^–8 mol L^–1 (12.1 g L^–1) and 5.2×10^–6 mol L^–1 (0.9 mg L^–1), respectively, were achieved. The precision of the method was checked by performing ten successive measurements for a 9.9×10^–6 mol L^–1 dopamine solution. For intra-assay and inter-assay precisions, the relative standard deviations were 1.9 and 2.3%, respectively. In order to evaluate the developed methodology, the determination of dopamine was performed with good sensitivity and selectivity, without the interference of ascorbic acid in synthetic cerebrospinal fluid, which indicates that the new methodology enables reliable analysis of dopamine.     

Electrochemical behavior of a covalently modified glassy carbon electrode with aspartic acid and its use for voltammetric differentiation of dopamine and ascorbic acid

Aspartic acid was covalently grafted on to a glassy carbon electrode (GCE) by amine cation radical formation in the electrooxidation of the amino-containing compound. X-ray photoelectron spectroscopic (XPS) measurement and cyclic voltammetric experiments proved the aspartic acid was immobilized as a monolayer on the GCE. Electron transfer to Fe(CN)₆^4– in solution of different pH was studied by cyclic voltammetry. Changes in solution pH resulted in the variation of the charge state of the terminal group; surface pK_a values were estimated on the basis of these results. Because of electrostatic interactions between the negatively charged groups on the electrode surface and dopamine (DA) and ascorbic acid (AA), the modified electrode was used for electrochemical differentiation between DA and AA. The peak current for DA at the modified electrode was greatly enhanced and that for AA was significantly reduced, which enabled determination of DA in the presence of AA. The differential pulse voltammetric (DPV) peak current was linearly dependent on DA concentration over the range 1.8×10^–6–4.6×10^–4 mol L^–1 with slope (nA mol^–1 L) and intercept (nA) of 47.6 and 49.2, respectively. The detection limit (3) was 1.2×10^–6 mol L^–1. The high selectivity and sensitivity for dopamine was attributed to charge discrimination and analyte accumulation. The modified electrode has been used for determination of DA in samples, in the presence of AA, with satisfactory results.     

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).     

Kinetics and mechanism of the copper(II) promoted hydrolysis of the methyl ester of ethylenediaminemonoacetate

Summary Base hydrolysis of methyl ethylenediaminemonoacetate has been studied at I=0.1 mol dm^–3 (NaClO₄) over the pH range 7.4–8.8 at 25 °C. The proton equilibria of the ligand can be represented by the equations, where E is the free unprotonated ester species. Values of pK₁ and pK₂ are 4.69 andca. 7.5 at 25° (I=0.1 mol dm^–3). For base hydrolysis of EH⁺, k_OH=1.1×10³ dm³ mol^–1 s^–1 at 25 °C. The species E is shown to undergo lactamisation to give 2-oxopiperazine (k_lact ca. 1×10^–3 s^–1) at 25 °C. Formation of the lactam is indicated both by u.v. measurements and by isolation and characterisation of the compound.Base hydrolysis of the ester ligand in the complex [CuE]²⁺ has been studied over a range of pH and temperature, k _OH ²⁵ =9.3×10⁴ dm³ mol^–1 s^–1 with H=107 kJ mol^–1 and S ₂₉₈ =209 JK^–1 mol^–1. Base hydrolysis of [CuE]²⁺ is estimated to be some 10⁵5 fold faster than that of the free ester ligand. The results suggest that base hydrolysis occursvia a chelate ester species in which the methoxycarbonyl group of the ligand is bonded to copper(II).     

A flow-injection ultrafiltration sampling chemiluminescence system for on-line determination of drug–protein interaction

A flow-injection ultrafiltration sampling chemiluminescence system for on-line determination of cimetidine–bovine serum albumin (BSA) interaction is proposed in this paper. Cimetidine can be oxidized by N-bromosuccinimide (NBS) and sensitized by fluorescein to produce high chemiluminescence emission in basic media. The concentration of cimetidine is linear with the CL intensity in the range 3×10^–7–1×10^–4 mol L^–1 with a detection limit of 1×10^–7 mol L^–1 (3). The drug and protein were mixed in different molar ratios in 0.067 mol L^–1 phosphate buffer, pH 7.4, and incubated at 37 °C in a water bath. The ultrafiltration probe was utilized to sample the mixed solution at a flow rate of 5 µL min^–1. The data obtained by the proposed ultrafiltration flow-injection chemiluminescence method was analyzed with Scrathard analysis and a Klotz plot. The estimated association constant (K) and the number of the binding site (n) on one molecule of BSA by Scrathard analysis and Klotz plot were 3.15×10⁴ L mol^–1 and 0.95, 3.25×10⁴ L mol^–1 and 0.92, respectively. The proposed system proved that flow-injection chemiluminescence analysis coupled with on-line ultrafiltration sampling is a simple and reliable technique for the study of drug–protein interaction.     

Amperometric nitrite sensor based on hemoglobin/colloidal gold nanoparticles immobilized on a glassy carbon electrode by a titania sol-gel film

A novel amperometric nitrite sensor was developed based on the immobilization of hemoglobin/colloidal gold nanoparticles on a glassy carbon electrode by a titania sol-gel film. The sensor shows a pair of well-defined and nearly reversible cyclic voltammogram peaks for Hb Fe(III)/Fe(II) with a formal potential (E°) of –0.370 V, and the peak-to-peak separation at 100 mV s^–1 was 66 mV vs. Ag/AgCl (3.0 M KCl) in a pH 6.9 phosphate buffer solution. The formal potential of the Hb Fe(III)/Fe(II) couple shifted linearly with pH with a slope of –50.0 mV/pH, indicating that electron transfer accompanies single-proton transportation. The sensor exhibited an excellent electrocatalytic response to the reduction of nitrite. The reduction overpotential was 0.45 V below that obtained at a colloidal gold nanoparticles/TiO₂ sol-gel film-modified GCE. The linear range for nitrite determination for the sensor was 4.0×10^–6 to 3.5×10^–4 M, with a detection limit of 1.2×10^–6 M. The stability, repeatability and selectivity of the sensor were also evaluated.     

Determination of traces of bismuth by quenching of solid-substrate room-temperature phosphorescence from morin-labeled silicon dioxide nano-particles

Silicon dioxide nano-particles, diameter 50 nm, containing morin (morin–SiO₂) have been synthesized by the sol–gel method. They emit strong and stable room-temperature phosphorescence (SS-RTP) on filter paper as substrate, and bismuth can quench the intensity of the SS-RTP. On this basis a new morin–SiO₂ solid-substrate room-temperature phosphorescence-quenching method has been established for determination of traces of bismuth. Reduction of phosphorescence intensity (I_p) is directly proportional to the concentration of bismuth in the working range 0.16–14.4 ag spot^–1 (sample volume 0.40 L spot^–1, corresponding to the concentration range 0.40–36.0 fg mL^–1). The regression equation of the working curve is I_p=14.86+5.279×[Bi³⁺] (ag spot^–1) (n=6, r=0.9982). The detection limit of this method is 0.026 ag spot^–1 (corresponding to a concentration of 6.5×10^–17 g mL^–1).This sensitive, reproducible and accurate method has been used for successful analysis of real samples.     

Kinetics of the thermal and photochemical decomposition of aquapentacyanoferrate(III) in aqueous solution

Summary The kinetics of the thermal and photochemical decomposition of aquapentacyanoferrate(III) ion in aqueous solution in the presence ofo-phenanthroline was studied spectrophotometrically. The first-order rate constant (k ) at 30° C [I=1 M(NaCl)] for the thermal reaction is (1.49±0.13)×10^–6 s^–1 with H =(158±7)kJ mol^–1 and S=(42±4) JK^–1 mol^–1. The initial quantum yield for the photochemical reaction at pH=7 is independent of the light intensity and is (1.49±0.33)×10^–2 mol einstein^–1.A communication on this subject was presented at the XVI Latinamerican Chemistry Congress held at Rio de Janeiro. Brasil, October 14–20, 1984.     

Binding constants of calcium and/or magnesium electrolytes and aggregation numbers in oil-in-water type microemulsions formed by an amphoteric surfactant

The effects of anti-symmetric electrolytes (CaCl₂, Ca(SCN)₂, MgCl₂, and/or Mg(SCN)₂) and pH on the phase behavior, the -potential, the hydrodynamic diameter and the surface charge density of an oil-inwater type (O/W-type) microemulsion formed in solutions of an amphoteric surfactant (N ,N -dimethyl-N -lauroyllysine, DMLL)/n-octane/1-pentanol/brine have been examined. The formation of the microemulsion in the presence of CaCl₂ and/or Ca(SCN)₂ is of Winsor-type with an increase in the concentration of 1-pentanol. Particularly, microemulsion is not formed by the addition of Ca(SCN)₂ in a pH region less than 2.6. The -potential and the surface charge density of the microemulsion in the presence of CaCl₂ decrease with an increase in pH and show slightly positive values in the isoelectric region (pH 5-7), while, in the presence of Ca(SCN)₂, the -potential and the surface charge density show negative values in the same region at which the net charge of DMLL molecules becomes almost zero. The hydrodynamic diameters in the presence of CaCl₂ show a maximum value around pH 2.5, whereas, in the presence of Ca(SCN)₂, the minimum value is around pH 5.5. Similar tendencies are recognized in results for the -potential, the hydrodynamic diameter and the surface charge density of the O/W-type microemulsion in the presence of MgCl₂ and Mg(SCN)₂. A new formula to estimate the binding constants (K) of Ca²⁺, Mg²⁺, Cl^–, and SCN^– to the hydrophilic groups in DMLL molecules and the adsorption density of DMLL molecules on the oil/water interface (N) in the presence of antisymmetric electrolytes has been derived.K for Ca²⁺, Mg²⁺, Cl^–, and SCN^– was found to beK _Ca=0.12M^–1,K _Mg=0.14 M^–1,K _Cl=0.0084±0.0016 M^–1, respectively.N for DMLL molecules in the presence of CaCl₂, Ca(SCN)₂, MgCl₂ and/or Mg(SCN)₂ was found to be 0.50 nm^–2, 0.38 nm^–2, 0.44 nm^–2, and 0.47 nm^–2, respectively; and the surfactant (DMLL) numbers per O/W-type microemulsion droplet change from a few hundreds to a few thousands with changing pH. The larger the hydrodynamic diameter of the O/W-type microemulsion, the greater the number of DMLL molecules adsorbed on the O/W-type microemulsion surfaces.     

Electrical properties of poly(bis(β-phenoxyethoxy)phosphazene) and its complexes

Electrical and dielectrical properties of poly(bis(-phenoxyethoxy)phosphazene) (I) and its complexes with various content ratios of AgSO₃CF₃ to monomeric unit (0.25/1 (II) and 0.5/1 (III) in molar ratio) were investigated.Dc conductivity of respective samples at 18 °C were 6.1×10^–12, 4.4×10^–9, and 7.1×10^–8 S/m.Dc conduction was considered to be due to ion hopping. Charge mobility ranged from 3×10^–12 to 6× 10^–11 m²/Vs depending on the applied field in sample II. In sample I, a tan peak was found which can be ascribed to molecular relaxation of main chains. The peak vanished upon introducing AgSO₃ CF₃. Temperature dependence of total conductivity ( _T ) measured byac method in the temperature range between –150 °C and 50 °C showed several peaks at the temperatures corresponding to the peak temperatures of tan. Total conductivities of respective samples at 100 kHz were 4.9×10^–7 (69 °C), 1.7×10^–4 (45 °C), and 1.5×10^–4(40°C)S/m.     

Determination of methylviologen (Paraquat) by differential pulse polarography

Summary Determination of Methylviologen (Paraquat) by Differential Pulse Polarography The second reduction wave of methylviologen (Paraquat) has been studied at pH 2 by different polarographic techniques. The limiting current is diffusion-controlled. Evidence for dimerization of the radical formed in the first reduction step has been obtained. The n values for the reduction process have been calculated at concentration levels where the dimer and the monomer predominate. Paraquat can be determined by differential pulse polarography in the 6.0×10^–5–4.0×10^–7 M concentration range, the limit of determination being 1.7×10^–7 M. The method has been applied to paraquat determination in commercial herbicides.     

Reactions of molybdate ions with polyphenol reagents: Determination of molybdenum with Pyrocatechol Violet and Alizarin Red S

Summary Molybdate forms a 11 complex with Pyrocatechol Violet in weakly acidic solutions. At the optimum pH 2.7 the apparent stability constant is (1.52±0.12)×10⁴l·mole^–1 and the molar absorptivity 2.70×10⁴l·mole^–1·cm^–1 at 540 nm. At higher and lower pH the stability of the complex decreases. In the pH range 2–5 molybdate forms a 12 complex with Alizarin Red S. The apparent stability constant is (4.8±0.6)×10⁷l·mole^–1 at the optimum pH 3.8 and the molar absorptivity (9.30±0.30)×10³l· mole^–1·cm^–1 at 480 nm. In 0.1M acid solution a less stablel: 1 complex exists, logK=4.2. Both dyes are appropriate reagents for estimation of molybdate when present in weakly or strongly acidic solutions. Near to the isoelectric point of molybdic acid (pH 1.5–2.0) accurate analysis data can be obtained only when the molybdate solution to be analysed is neutralized and boiled for 10 min to transform the less reactive polymeric molybdenum species. It is thought that hexacoordinated Mo(OH)₆ is the reactive species, forming esters with the polyphenols used.

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Reaktionen von Molybdat mit Polypbenol-Reagenzien: Bestimmung von Molybdän mit Brenzcatechinviolett und Alizarinrot S

Zusammenfassung Molybdat bildet mit Brenzcatechinviolett in schwach saurer Lösung einen 11-Komplex. Bei dem optimalen pH 2,7 beträgt die scheinbare Stabilitätskonstante (1,52 ±0,12)×10⁴l·mol^–1 und die molare Extinktion bei 540 nm 2,70×10⁴l·mol^–1·cm^–1. Bei höherem oder niedrigerem pH nimmt die Stabilität des Komplexes ab. Im pH-Gebiet 2–5 bildet Molybdat mit Alizarinrot S einen 12-Komplex. Dessen scheinbare Stabilitätskonstante beträgt (4,8±0,6)× 10⁷l·mol^–1 bei dem optimalen pH=3,8 und die molare Extinktion (9,30± 0,30)×10³l·mol^–1·cm^–1 bei 480 nm. In 0,1M saurer Lösung existiert ein weniger stabiler 11-Komplex, dessen logK=4,2. Beide Farbstoffe eignen sich für die Bestimmung von Molybdat in schwach oder stark saurer Lösung. In der Nähe des isoelektrischen Punktes der Molybdänsäure (pH 1,5-2,0) können genaue Analysenergebnisse nur erhalten werden, wenn die Molybdatlösung vorher neutralisiert und 10 min gekocht wird, um die weniger reaktionsfähigen polymeren Formen des Molybdäns abzubauen. Es wird angenommen, daß Mo(OH)₆ die hexakoordinierte reaktionsfähige Form darstellt, die mit den Polyphenolen Ester bildet.

     

Extraction-spectrophotometric determination of iron with 2-(2′-benzothiazolylazo)-4,6-dimethylphenol

An extraction-spectrophotometric method for the determination of trace amounts of iron based on its extraction into chloroform with 2-(2-benzothiazolylazo)-4,6-dimethylphenol (BTADMP) from a pH 6.5 medium has been developed. The extracted 12 FeBTADMP complex species allow the determination of 4–30gmg of iron (=3.92×10⁴1·mol^–1·cm^–1 at 790 nm). The method is highly selective and has been applied to the determination of iron in polymineral-polyvitamin pharmaceutical products.