The aggregation in dodecyltrimethylammonium hydroxide aqueous solutions

The aggregation of dodecyltrimethylammonium hydroxide (DTAOH) aqueous solutions has been studied by several methods. It is stepwise and four critical points were found. AtC _T=(2.51±0.10)×10^–4 mol · dm^–3 the surface excess becomes zero, atC _T=(1.300±0.041)×10^–3 mol · dm^–3 small aggregates from, which grow with concentration. AtC _T=(1.108±0.010)×10^–2 mol · dm^–3 true micelles form (CMC) and at (3.02±0.28)×10^–2 mol · dm^–3 the structure of micelles probably changes affecting their properties. The DTAOH micelles are highly ionized (=0.8) at the CMC, and decreases to reach very small values when the total concentration increases.     

Determination of traces of iron with the catalytic maximum wave in differential pulse polarography

Summary A differential pulse polarographic method for the determination of iron employing the catalytic maximum wave has been studied. A well-defined differential pulse polarographic peak for iron(III) in Britton-Robinson buffer solution containing 50 mol/l N-(2-hydroxyethyl) ethylenediamine N,N,N-triacetic acid (HEDTA) and 5 mmol/l KBrO₃ is observed in the potential range from +0.2 to –0.3 V vs. SCE. The peak current is very large compared to that of the Fe(III)/EDTA complex, being proportional to the concentration of iron(III) between 1.00×10^–8 and 3.58×10^–6 mol/l under optimum conditions. The relative standard deviations for 3.58×10^–7 mol/l and 1.79×10^–6 mol/l iron(III) were 1.38 and 0.54%, respectively (n=5), and the calculated detection limit was 5.2×10^–9 mol/l iron(III). The method has been applied to the determination of iron in fresh snow and rain waters.

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Spurenbestimmung von Eisen mit Hilfe der katalytischen Maximumsstufe in der Differential-Puls-Polarographie

Zusammenfassung Das Verfahren beruht auf der Tatsache, daß in Britton-Robinson-Puffer (mit 50 mol/l HEDTA und 5 mmol/l KBrO₃) im Potentialbereich von +0,2 bis –0,3 V gegen SKE ein gut definierter puls-polarographischer Peak für Eisen(III) auftritt. Der Peakstrom ist im Vergleich zu dem des Fe(III)/EDTA-Komplexes sehr groß und ist unter optimalen Bedingungen im Konzentrationsbereich von 1,00·10^–8 bis 3,58·10^–6 mol/l der Eisen(III)-Konzentration proportional. Die relative Standardabweichung beträgt 1,38% bzw. 0,54% (n=5) für 3,58·10^–7 mol/l bzw. 1,79·10^–6 mol/l Fe(III). Die berechnete Nachweisgrenze liegt bei 5,2·10^–9 mol/l Fe(III). Das Verfahren wurde zur Eisenbestimmung in Schnee- und Regenwasser eingesetzt.

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This work was supported in part by a Grant-in-Aid for Scientific Research from Hokkaido-prefecture, 1982.     

The viscoelasticity of spinnable solutions of alkyltrimethylammonium salicylates

The viscoelasticity has been measured for aqueous solutions of tetradecyl-and hexadecyltrimethylammonium salicylates (C₁₄TASal, C₁₆TASal). The aqueous solutions of C₁₄TASal without salt displayed the gel-like behavior at 10.0×10^–2 g cm^–3, but those more dilute than 3.2×10^–2 g cm^–3 presented the viscoelasticity similar to that of a Maxwell liquid. The Maxwell-like behavior was converted to the polymer-like one on the addition of (0.1–0.2) M NaBr or (0.02–0.2) M NaSal. The gel-like viscoelasticity can be connected with the spinnability of cohesive fracture failure, and the Maxwell-like and polymer-like viscoelasticities are concerned with the spinnability of ductile failure. The gel-like and Maxwell-like viscoelasticities originate in the pseudo-network formed by the pseudo-linkages between rodlike micelles, while the polymer-like viscoelasticity is caused by the entanglement of long rodlike micelles in semidilute and concentrated solutions. The aqueous solutions of C₁₆TASal behaved very similar to those of C₁₄TASal.     

Aqueous polymerization of methacrylamide initiated by potassiumpersulfate-L-cystein hydrochloride redox system

The aqueous polymerization of methacrylamide initiated by potassiumpersulfate-L-cystein hydrochloride redox system has been studied at 35±0.01 C under nitrogen atmosphere. The initial rate of polymerization has been found to be directly proportional to the monomer and activator concentration, in the range of 1.0 × 10^–1 to 4.0 × 10^–1 mol dm^–3 and 1.25 × 10^–3 to 5.0 × 10^–3 mol dm^–3 respectively. The order with respect to initiator has been found to be 0.5, indicating thereby that the termination takes place by bimolecular process. The overall energy of activation has been found to be 53±1 KJ/mol.     

Untersuchung der Ionengleichgewichte in Tetrahydrofuranlösungen des 2-Naphthonitril-Natriums

With the aid of conductometric measurements the ion equilibria inTHF solutions of 2-naphthonitrile sodium were studied. It was established that in the concentration interval of 10^–4–10^–5 mol/l the equilibrium ion pairs—free ions is predominant . The ion pairs are contact (average interion distance about 4.1 Å). In the temperature interval of 25 to 40° the heat of dissociation –H=3.1 kcal/mol, whereas between –40 and –70°–H is 1.26 kcal/mol. At higher concentrations (10^–2–10^–3 mol/l) triple ion formation is observed.     

Determination of traces of vanadium with the catalytic maximum wave in differential pulse polarography

Summary A differential pulse-polarographic method has been studied for the determination of vanadium employing the catalytic maximum wave. A well-defined differential pulse polarographic peak is observed in the potential range from –0.2 to –0.7 V vs. SCE for vanadium(V) in 10 mmol 1^–1 NaCl containing 10 mmol 1^–1 acetic acid, 40 mmol 1^–1 pyrocatechol, and 2.5 mmol 1^–1 KBrO₃. The peak current is very large and proportional to the concentration of vanadium(V) between 1×10^–7 and 1×10^–6 mol 1^–1. The relative standard deviation at 0.5 mol l^–1 vanadium(V) was 2.06% (n=7). This method has been successfully applied to the determination of vanadium in standard materials such as pond sediment.

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Spurenbestimmung von Vanadium mit Hilfe der katalytischen Maximumsstufe in der Differential-Puls-Polarographie

Zusammenfassung Ein gut definierter differentialpuls-polarographischer Peak wurde für Vanadium(V) in 10 mmol/l NaCl-Lösung, die 10 mmol/l Essigsäure, 40 mmol/l Brenzcatechin und 2,5 mmol/l KBrO₃ enthielt, beobachtet (Potentialbereich –0,2 bis –0,7 V gegen SCE). Der Peakstrom ist sehr groß und die Vanadiumkonzentration im Bereich von 1×10^–7 bis 1×10^–6 mol/l proportional. Die relative Standardabweichung betrug 2,06% (n=7) bei 0,5 mol/l Vanadium(V). Das Verfahren wurde mit gutem Erfolg zur Vanadiumbestimmung in Standardproben (z.B. Teichsediment) eingesetzt.

     

Nitrogen Trioxide in Irradiated Aqueous Nitric Acid Solutions of Hydrazine

The rate constants of reactions of the NO₃ radical with hydrazoic acid (7.6 × 10⁶l mol^–1s^–1) and the hydrazonium ion (2.3 × 10⁶l mol^–1s^–1) in 6 M nitric acid at 290 ± 2 K were measured by a pulse radiolysis technique. The reaction scheme was refined by the computer simulation of the -radiolysis of aqueous nitric acid solutions of hydrazine with the use of the measured rate constants and published data on the reactivity of intermediates. The results of computations were compared with experimental data on the continuous radiolytic degradation of hydrazine in aqueous 2 M nitric acid solutions at 313 K.     

Flow Analysis of Transition Metals by Thermal Lensing

The conditions for the flow determination of Al(III), Bi(III), Cd(II), Co(II), Cr(III), Cu(II), Fe(III), Mn(II), Nd(III), Ni(II), Pb(II), Pr(III), and Zn(II) by reaction with Xylenol Orange in aqueous solutions at pH 4.5 and the determination of Cd(II), Co(II), Cu(II), Fe(II), Ni(II), Pb(II), and Zn(II) by reaction with 4-(2-thiazolylazo)resorcinol in water–ethanol mixtures (5 : 1) at pH 5.0 using an injected sample volume of 80 L were proposed. The limits of detection were n × 10^–8–n × 10^–7 mol/L; the linearity ranges in the calibration graphs were of about three orders of magnitude; the relative standard deviation was of 3–7%.     

Analysis of various very slightly water soluble drugs in micellar medium

A potentiometric and/or visual method for the determination of sulphamethoxazole (SULF) in pure form in the range of 5.3 × 10^–5 to 5.0 × 10^–4 mol/L is proposed. To enhance the solubility, the determination has been carried out in a micellar medium formed by an aqueous 5.0 × 10^–2 mol/L N-hexadecyl-N,N,N-trimethyl ammonium bromide (CTAB) solution which increases the dissociation constant K of SULF about tenfold. The titration is performed with NaOH (2.5 × 10^–3 or 5.0 × 10^–2 mol/L) and the end-point is determined by the second derivative graph. The results agree with those obtained by the official method of the USP XXIII. The method is simple, accurate, economical and can successfully replace the more complicated, more expensive and time-consuming existent procedures which are carried out in a non-aqueous medium.     

Mechanism of the oxidation of L-ascorbic acid by the bis(pyridine-2,6-dicarboxylate)cobaltate(III) ion in aqueous solution

A detailed investigation of the oxidation of L-ascorbic acid (H₂A) by the title complex has been carried out using conventional spectrophotometry at 510 nm, over the ranges: 0.010 [ascorbate] _T 0.045 mol dm^–3, 3.62 pH 5.34, and 12.0 30.0 °C, 0.50 I 1.00 mol dm^–3, and at ionic strength 0.60 mol dm^–3 (NaClO₄). The main reaction products are the bis(pyridine-2,6-dicarboxylate)cobaltate(II) ion and l-dehydroascorbic acid. The reaction rate is dependent on pH and the total ascorbate concentration in a complex manner, i.e., k _obs = (k ₁ K ₁)[ascorbate] _T /(K ₁ + [H⁺]). The second order rate constant, k ₁ [rate constant for the reaction of the cobalt(III) complex and HA^–] at 25.0 °C is 2.31 ± 0.13 mol^–1 dm³ s^–1. H = 30 ± 4 kJ mol^–1 and S = –138 ± 13 J mol^–1 K^–1. K ₁, the dissociation constant for H₂A, was determined as 1.58 × 10^–4 mol dm^–3 at an ionic strength of 0.60 mol dm^–3, while the self exchange rate constant, k ₁₁ for the title complex, was determined as 1.28 × 10^–5 dm³ mol^–1 s^–1. An outer-sphere electron transfer mechanism has been proposed.     

Spectrofluorimetric determination of trace amounts of Tb(III) using acetylacetone in ethanol solution

Summary The spectrofluorimetric determination of terbium(III) in ethanol (95%) solution of acetylacetone (3×10^–4 mol/l) was studied. Intensive fluorescence of terbium(III) (=545 nm) was observed after excitation of the system (=310 nm). The method proposed is satisfactory for the determination of terbium(III) in the range of 4 to 40 ng/ml (2.5×10^–8 to 2.5×10^–7 mol/l). The effect of other rare earths, common metal ions and anions upon the intensity of the fluorescence emitted by terbium(III) is discussed.

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Spektrofluorimetrische Bestimmung von Tb(III)-Spuren mit Acetylaceton in Ethanollösung

     

Association-Assisted Kinetics of Pentanol-1 and Heptanol-1 Oxyethylation: Kinetic Parameters of Reactions and Association Parameters of Alcohols in the Series Butanol-1–Heptanol-1

The kinetics of pentanol-1 and heptanol-1 oxyethylation in the absence and in the presence of solvents (dodecane, p-xylene, and 1,4-dioxane) is studied under the conditions of base catalysis at 80–150°C and the concentrations of the catalyst (the corresponding sodium alkoxide) and ethylene oxide in the starting mixture of 1 and 10^–3–10^–1 mol/l, respectively. The experimental results are adequately described by the rate law that takes into account the association of alcohol molecules via hydrogen bonds. A hypothesis is advanced that an associate consisting of n alcohol molecules acts as a kinetically independent species in this reaction. The kinetic and association parameters for alcohols in the C₄–C₇ series are compared with the published data.     

Spectrophotometric and derivative spectrophotometric determination of copper (II) with dithizone in aqueous phase

A Spectrophotometric and derivative Spectrophotometric study of Cu-dithizonate complex in aqueous phase in the presence of Triton X-100, a neutral surfactant, is reported. The system obeys Beer's law between 1.0 × 10^–6–9.0 × 10^–6 mol/l of Cu²⁺; detection limit is 12 ng/ml. The molar absorption coefficient, specific absorptivity and Sandell's sensitivity of the complex are 3.06 × 10⁴ 1 mol^–1 cm^–1, 0.4825 ml g^–1 cm^–1 and 2.1 × 10^–3 g cm^–2, respectively. The conditional stability constant of the 1 2 complex, calculated considering simultaneously existing equilibria, has been found to be 1.73 × 10¹¹ I² mol² (I = 0.07, pH 1.4, temperature = 10 °C). Absorption studies in the derivative mode have been carried out to determine the absorption maximum of the complex and to overcome interference due to the presence of certain metal ions. The method has been validated by determination of copper in beers, wines, human hair, goat liver and fly ash samples.     

Comparison of the Diffusion of Aqueous Glycine Hydrochloride and Aqueous Glycine

A Taylor dispersion tube has been used to measure mutual diffusion in aqueous solutions of glycine hydrochloride at 25°C and concentrations from 0.0005 to 0.5 M. Analysis of the dispersion profiles shows that the diffusion of glycine hydrochloride (GlyHCl) produces a subtantial additional flow of hydrochloric acid that is liberated by the dissociation: GlyH⁺ + Cl^- Gly + H⁺ + Cl^-. Diffusion in this system is, therefore, a ternary process described by the equations J ₁(GlyHCl) = – D ₁₁C ₁ – D ₁₂C ₂ and J ₂(HCl) = –D ₂₁C ₁ – D ₂₂C ₂ for the coupled fluxes of total glycine hydrochloride (1) and hydrochloric acid (2) components. The ratio D ₂₁/D ₁₁ of measured diffusion coefficients indicates that up to two moles of HCl are cotransported per mole of GlyHCl. Although protonated glycine diffuses with relatively mobile Cl^– counterions, the main diffusion coefficient of glycine hydrochloride, D ₁₁, is lower than or nearly identical to the diffusion coefficient of aqueous glycine. A model for the diffusion of protonated solutes is developed to interpret this result and the large coupled flows of HCl. Diffusion coefficients are also reported for the aqueous hydrochlorides of 3- and 4-aminobenzoic acids.     

Adsorptive stripping voltammetric determination of cobalt in the presence of dimethylglyoxime and cetyltrimethylammonium bromide

A sensitive procedure for determination of micro-traces of Co(II) by adsorptive stripping voltammetry is proposed. The procedure exploits the enhancement of the cobalt peak obtained by use of the system Co(II)–dimethylglyoxime–piperazine-1,4-bis(2-ethanesulfonic acid)–cetyltrimethylammonium bromide. Using the optimized conditions, a detection limit (based on the 3 criterion) for Co(II) of 1.2×10^–11 mol L^–1 (0.7 ng L^–1) was achieved. The calibration plot for an accumulation time of 30 s was linear from 5×10^–11 to 4×10^–9 mol L^–1. The procedure was validated by analysis of certified reference materials and natural water samples.     

Isotachophoretic analysis of the lipophilic cation tetraphenylphosphoniumbromide

Summary Tetraphenylphosphoniumbromide (TPP), a lipophilic cation used for the determination of plasma membrane potential, was quantified by isotachophoresis. The optimized leading electrolyte consisted of 10 mmol/l KOH as leading ion, supplemented with 0.5% hydroxy-ethylcellulose. The pH was adjusted to 9.5 with methionine. The terminating ion was 10 mmol/l tris(hydroxymethyl)-aminomethane (pH 9.2, adjusted with methionine). Leading ion concentrations of 10, 1 and 0.5 mmol/l respectively, showed nearly the same detection limits (2×10^–11 mol of TPP). This detection limit allowed the quantitative determination of TPP down to a concentration of 2 mol/l. Calibration curves in the range of 2×10^–11 to 1.5×10^–10 mol of TPP showed correlation coefficients greater than 0.95 (n=12; =0.01).     

Differential pulse-polarographic determination of adenine, adenosine and mono-, di- and tri-phosphate of adenosine

Summary The application of differential pulse polarography for the quantitative trace determination of adenine, adenosine, adenosine-3-monophosphate, adenosine-5-monophosphate, adenosine-5-diphosphate and adenosine-5-triphosphate has been investigated. Optimum conditions were found (pulse amplitude 100 mV, scan rate 2 mV · s^–1, drop time 2s). The effect of pH was studied, and the optimum pH was determined to give the highest sensitivity. The detection limit for adenine, adenosine and A-5-MP is ca. 2.2 ×10^–6M, 1.5×10^–6M and 2.99×10^–6M, respectively; for the other adenosine nucleotides it is 4.45×10^–6M. The validity of this method is supported by the constancy of the i _DPP/C values.

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Bestimmung von Adenin, Adenosin sowie Adenosinmono-, -di- und -triphosphat durch Differential-Puls-Polarographie

Zusammenfassung Die Anwendbarkeit der Differential-Puls-Polarographie zur quantitativen Spurenbestimmung von Adenin, Adenosin, Adenosin-3-monophosphat, Adenosin-5-monophosphat, Adenosin-5-diphosphat und Adenosin-5-triphosphat wurde geprüft und optimale Bedingungen ausgearbeitet (Pulsamplitude 100mV, Abtastgeschwindigkeit 2 mV/s, Tropfzeit 2s). Der Einfluß des pH-Wertes wurde untersucht und der optimale pH für maximale Empfindlichkeit bestimmt. Die Nachweisgrenzen für Adenin, Adenosin und A-5-MP betragen etwa 2,2 · 10^–6M, 1,5 · 10^–6M bzw. 2,99 · 10^–6M, für die übrigen Adenosinnucleotide 4,45 · 10^–6M. Die Brauchbarkeit der Methode ergibt sich aus der Konstanz der i _DPP/C-Werte.

     

Determination of subnanomolar concentrations of cobalt by adsorptive stripping voltammetry at a bismuth film electrode

Procedures for trace cobalt determinations by adsorptive stripping voltammetry at in situ and ex situ plated bismuth film electrodes are presented. These exploit the enhancement of the cobalt peak obtained by using the Co(II)–dimethylglyoxime–cetyltrimethylammonium bromide–piperazine-N,N-bis(2-ethanesulfonic acid) system. The calibration graph for an accumulation time of 120 s was linear from 2 × 10^–10 to 2 × 10^–8 mol L^–1. The relative standard deviation from five determinations of cobalt at a concentration of 5 × 10^–9 mol L^–1 was 5.2%. The detection limit for an accumulation time of 300 s was 1.8 × 10^–11 mol L^–1. The proposed procedure was applied to cobalt determination in certified reference materials and in tap and river water samples.     

Physicochemical properties of α, ω-type bolaform surfactant in aqueous solution. Eicosane-1,20-bis(triethylammonium bromide)

The physicochemical properties of the, - type (bolaform) surfactant, eicosane-1, 20-bis(triethylammonium bromide) (C₂₀Et₆), in aqueous solution have been investigated by means of surface tension, electrical conductivity, dye solubilization, and time-resolved fluorescence quenching (determination of average micelle aggregation number). Using electrical conductivity, the critical micelle concentration of C₂₀Et₆ was found to be 6.0×10^–3 mol dm^–3 and the ionization degree of C²⁰Et₆ micelle was found to be 0.42. From surface tension measurments, the molecular area of C₂₀Et₆ at the air-water interface was about twice that of normal type surfactants such as dodecyltrimethylammonium bromide (DTAB). The solubilizing power of micellar solution of C₂₀Et₆ toward Orange OT was 1.0×10^–2 mole of dye per mole of surfactant, i. e., slightly smaller than that of DTAB. The micelle aggregation number,N, was found to be 17±2 by time-resolved fluorescence quenching. C₂₀Et₆ showed a very small temperature dependence ofN, much less than for normal surfactants.