Density,viscosity, and excess properties of aqueous solution of diethylenetriamine (DETA)

Densities and viscosities of aqueous DETA solutions were measured for the entire concentration range and for the temperature range between (293.15 and 363.15) K. The excess molar volume was determined from the experimental density data whereas the excess Gibbs free energy and the excess entropy of flow were determined from the experimental viscosity data by implementing the theory of rate processes of Eyring. A Redlich–Kister equation was applied to correlate the excess properties such as: the excess molar volume and the excess Gibbs free energy of flow as functions of the DETA mole fraction and temperature. The results showed that the model agree very well with the experimental data. In comparison with AEEA and DEA, the excess properties of DETA are higher than these amines.     

An infrared spectroscopic based method for mercury(II) detection in aqueous solutions

A new method that uses solid phase extraction (SPE) coupled with FTIR spectroscopy to detect Hg(II) in aqueous samples is described. The technique is envisioned for on-site, field evaluation rather than lab-based techniques. This paper presents the “proof of principle” of this new approach toward measurements of Hg(II) in water and identifies mass transport issues that would need to be overcome in order to migrate from a lab based method to field operation. The SPE material supported on a Si wafer is derivatized with an acylthiosemicarbazide, which undergoes a reaction in the presence of aqueous Hg(II) to form an oxadiazole ring. The progress of the reaction is monitored by IR spectroscopy. Following EPA guidelines, the method of detection limit (MDL) for the SPE/IR was 5 μg of Hg(II) cm⁻². In a 1 L sample and a 1 cm² Si wafer, this translates to a detection limit of 5 ppb. This system shows a high selectivity toward aqueous Hg(II) over other thiophilic heavy metal ions such as Pb(II), Cd(II), Fe(III), and Zn(II) and other metal ions such as Ni(II), Mn(II), Co(II), Cu(II), In(III), Ru(III), Na(I), and Ag(I) in aqueous solutions.     

Atomic absorption spectroscopic determination of molybdenum in aqueous tetrathiomolybdate solutions

The flame atomic absorption spectroscopic determination of molybdenum, in aqueous solutions of tetrathiomolybdate (MoS ₄ ^2– , TTM) and paramolybdate species (Mo₇O ₂₄ ^2– , PM) has been investigated. A serious signal decrease occurred, if molybdenum has been present as tetrathiomolybdate species, and the sensitivity loss has been 85%. To improve the sensitivity, the solutions of TTM have been digested by wet-acid treatment, and made 0.14 mol·l^–1 ammonia. Finally, Mo has been determined by AAS using a nitrous oxide-acetylene flame. The range of the calibration was 0–100 mg·l^–1 and the relative standard deviation of the slope was less than 1%.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday     

Raman spectroscopic determination of oxoanions in aqueous polysulfide electrolyte solutions

The equilibrium distribution of aqueous sodium polysulfide solutions is investigated over a wide concentration range using Raman spectroscopy technique. A total of eighteen bands were determined in the spectra recorded for aqueous electrolyte solutions of different S:Na ratios. Beyond the presence of four polysulfide (S_n²⁻) species, where “n” varied between 2 and 5 as reported in previous literature, the originality of this study is to show the presence of oxidised sulfur species in these aqueous polysulfide solutions. A detailed comparison of all the bands for polysulfide and oxoanion species determined in this study with those cited in literature is summarised.     

Photometric method for the determination of nitrite in aqueous solutions and in blood

Summary The sensitivity of the hitherto known determinations of nitrite by formation of azo dyes and photometric measurement in aqueous solution is limited by the concentration of nitrite. In the method described here the azo compound formed is extracted into toluene and trichloroacetic acid is added to the extract. Immediately after addition of the latter the colour intensity reaches its maximum and is measured at 560 nm. In this way the sensitivity is made independent of the nitrite concentration in the aqueous solution and is limited only by the sample volume available.This study was supported by Deutsche Forschungsgemeinschaft.     

Cd(II) determination in the presence of aqueous micellar solutions

The equilibrium constants and molar absorptivities for the fast formation of a 1:3 complex between cadmium(II) (Cd(II)) and dithizonate anion, in the presence of cationic and non-ionic surfactants, allowed a simple and fast spectrophotometric determination of total cadmium. Indeed, the molar absorptivities of the Cd(II)-dithizone (Dz) complex formed in the presence of the neutral Triton X-100 and cationic cetyltrimethylammonium bromide (CTAB) surfactants are almost twice the value observed in the standard method and the maxima of absorption are shifted by about 40 nm when compared with the standard method. Clearly, the use of neutral and cationic surfactants promotes a higher value of the molar absorptivities of the complex, resulting in an increase in the sensitivity of the method. Application of the method to the desorption of Cd(II) ions from clays is illustrated.     

Raman spectroscopic determination of equilibrium constants of uranyl sulphate complexes in aqueous solutions

Raman spectra are used to determine the formation constants of uranyl sulphate complexes in aqueous solutions at 20 degrees and remedy the confusion existing in this area in the available literature. Solutions with a varying total sulphate concentration and an ionic strength lower than 0.4M are analysed. The species UO(2)SO(4) and UO(2)(SO(4))(2-)(2) are characterized by a resolved Raman band at 861 cm(-1) and an unresolved one at 852 cm(-1), corresponding to the uranyl symmetrical stretching vibration. The equilibrium constants, in term of activity (standard state 1M), are found to be about 1400 and 11, respectively, for the consecutive reactions: UO(2+)(2)(aq)+SO(2-)(4)(aq)=UO(2)SO(4)(aq) and UO(2)SO(4)(aq)+SO(2-)(4)(aq)=UO(2)(SO(4))(2-)(2)(aq).     

Selective separation of Hg(II) from aqueous solutions by the precipitate flotation technique

Summary The flotation of Hg(II) ions as sulphide or iodide from aqueous solutions has been investigated, using oleic acid as surfactant. Selective separation from Cd ions has been achieved. There was no interference by Bi, Pb, Cu, Cd, Mn, Zn, Co or Ni.     

Membrane-introduced infrared spectroscopic chemical sensing method for the detection of volatile organic compounds in aqueous solutions

A novel membrane-introduced infrared (IR) chemical sensing method has been developed for the detection of volatile organic compounds (VOCs) in aqueous solutions. In this method, a porous Teflon membrane was used to eliminate the problems associated with conventional IR spectroscopic sensing methods. The porous Teflon membrane was sealed below an IR spectroscopic sensing element pre-coated with a hydrophobic film and a two-channel flow cell configuration was established. In this configuration, the aqueous sample was allowed to pass through the lower channel and the VOCs that penetrated through the membrane to the upper channel were detected by the IR sensor. In this manner, the performance of the sampling at the headspace was improved while the problems caused by the presence of water were eliminated. Meanwhile, using a purging channel allowed the sensing element to be regenerated rapidly and enabled automation of the detection process. The parameters that influenced the analytical signals were studied, such as the sampling flow rate, the pH and ionic strength of the sample solutions, the effect of the volatilities of the VOCs, and the regeneration efficiency of the sensing element. The results indicated that the analytical signals were insensitive to the sampling flow rate and to the pH and ionic strength of the sample solutions. The results obtained from the detection of seven different volatile compounds indicated that this method is highly suitable for the detection of organic compounds that have vapor pressures >1 Torr and that it is potentially usable for organic compounds that have vapor pressures between 20 mTorr and 1 Torr. The regression analysis of the standard curves indicated that a regression coefficient (R(2)) > 0.99 was obtainable in the concentration range from 1 to 100 microg mL(-1). The detection limits for the tested compounds were around a few hundred ng mL(-1).     

New spectroscopic method for aqueous solutions: Raman xi-function dispersion for NaClO4 in water

A new Raman method is exemplified by xi identical with-RT[ partial differential ln(I(omega)I(REF)) partial differentialX(1)](T,P,n(2),n(3) ) for ternary NaClO(4)D(2)OH(2)O, or by xi identical with-RT[ partial differential ln(I(omega)I(REF)) partial differentialX(2)](T,P) for binary NaClO(4)H(2)O solutions. (Fundamental differences exist between xi and the chemical potential mu.) I(omega) is the Raman intensity at omega, I(REF) is the reference intensity, e.g., at the isosbestic frequency, X(2) is the H(2)O and X(1) the small D(2)O mol fraction, and n(2) and n(3) are constant mols of H(2)O and NaClO(4), respectively. Maxima (max) and minima (min) were observed in xi versus omega (cm(-1)); xi(max)-xi(min)=Deltaxi(max). Deltaxi(max)=8050+/-100 calmol H(2)O for the coupled, binary solution OH stretch, and Deltaxi(max)=4200+/-200 calmol H bond for the decoupled, ternary solution OD stretch. The perchlorate ion breaks the H bonds in water. 8050 calmol H(2)O corresponds to the maximum tetrahedral Deltaxi(max) value for two H bonds, i.e., Deltaxi(max)=4025 calmol H bond, in agreement with the HDO Deltaxi(max)=4200+/-200 calmol H bond. [Deltaxi(max) is not the H bond enthalpy (energy).] Minima occur in xi at the peak omega values corresponding to the HDOH(2)O and H(2)O ices, and maxima in xi at 2637+/-5 cm(-1) (OD) and 3575+/-10 cm(-1) (OH) correspond to the peak OD and OH stretching omega values from dense supercritical water. Enthalpy dispersion curves were also determined for saturated, binary, and ternary NaClO(4) solutions and for D(2)O in H(2)O. The xi-function method is shown to be applicable to infrared absorbance spectra.     

A novel NMR method for the determination and monitoring of evolution of hydrogen peroxide in aqueous solutions

A novel NMR method that allowed the rapid and direct quantitative analysis of hydrogen peroxide in protic solvents was developed. The method was based on the highly deshielded ¹H NMR signal of the H₂O₂ protons (δ?～?11.15 ppm at 298 K) in H₂O and the combined use of cryoprotective (antifreeze) mixtures of H₂O?DMSO-d₆, low temperatures (～260 K), and pH effects in order to achieve minimum proton exchange rate and, thus, sharp ¹H line widths. Extremely broad resonances with line widths above 550 Hz at room temperature in H₂O were observed in a wide range of pH values, which were reduced below 2 Hz with the use of the above method which resulted in a detection limit of 20.0 μmol L^?1 (in tube) even when using very short total experimental time of 10 min. The method was applied in aqueous extract of Greek oregano and in aqueous instant coffee. Line widths below 10 Hz for oregano samples and 17 Hz for instant coffee samples were obtained which resulted (i) in the unequivocal assignment of H₂O₂ with spiking experiments precluding any confusion with interferences from intrinsic phenolics in the extracts and (ii) in the quantitative investigation of the evolution of H₂O₂ in real time with parameters easily accessible experimentally.

Electrophoretic method for the determination of diffusion coefficients of ions in aqueous solutions*

The electrophoretic method was recently developed for the determination of diffusion coefficients of ions in aqueous solution. By solving the Fick's second law in the presence of unlimited media and constant quantity of diffusing species we obtain a relationship between the diffusion coefficient and the standard deviation of the distribution profile. The diffusion coefficients of Cd(II), In(III), Zr(IV), Hf(IV), Pu(VI) and [InDTPA]^2– in nitric acid solution were determined as well as the effective charge of In-DTPA complex at pH 4.50.     

Quick analytical method for the determination of iodide and iodate ions in aqueous solutions

An analytical quick-test method was developed to determine iodide and iodate ions in aqueous solutions using solid phase extraction cartridges for sample preparation. Work was focussed on finding simple, but efficient conditions for quantitative separation of iodate and iodide. Iodine amounts were then determined by standard methods. Ion-exchange absorbers in cartridge form were used. Selectivity and yield of the species separation were studied at pH value of 5-10 and various solution compositions using ¹³¹I radioactive tracer. The electrolytes used were diluted alkaline, nitrate and boric acid-borate solutions. Application to nuclear reactor cooling water analysis or environmental investigations and monitoring is proposed.     

A spectroscopic study of the mineral paceite (calcium acetate)

A comprehensive spectroscopic analysis consisting of Raman, infrared (IR) and near-infrared (NIR) spectroscopy was undertaken on two forms of calcium acetate with differing degrees of hydration. Monohydrate (Ca(CH(3)COO)(2).H(2)O) and half-hydrate (Ca(CH(3)COO)(2).0.5H(2)O) species were analysed. Assignments of vibrational bands due to the acetate anion have been made in all three forms of spectroscopy. Thermal analysis of the mineral was undertaken to follow its decomposition under a nitrogen atmosphere. Three major mass loss steps at approximately 120, 400 and 600 degrees C were revealed. These mass losses correspond very well to firstly, the loss of co-ordinated water molecules, and then the loss of water from the acetate anion, followed by finally the loss of carbon dioxide from the carbonate mineral to form a stable calcium oxide.     

Polarographic determination of uranium(VI) in aqueous tri-n-butyl phosphate solutions

The effect of TBP as well as the organic diluents on the polarographic wave of U(VI) reduction has been investigated in sulphuric and perchloric acids. It was found that the presence of TBP traces in the solution to be analyzed induced another wave which was more prominent in sulphuric acid solutions. This can be eliminated by boiling the solutions for about 5 min before their analysis for uranium. The effect of supporting electrolyte on the polarographic reduction of U(VI) was also studied and the use of 6N HClO₄ was recommended.