Slurry sampling for determination of lead in marine plankton by electrothermal atomic absorption spectrometry

A slurry sampling method has been developed for the determination of Pb in marine plankton by ETAAS using a freshwater plankton certified reference material (CRM 414). Slurries were prepared in 1–3% m/v range with 1% v/v HNO₃ by ultrasonic agitation for 5 min. The effects of several chemical modifiers, including Ir(NO₃)₂, Mg(NO₃)₂, Pd(NO₃)₂, Pd(NO₃)₂ + Mg(NO₃)₂, and Mg(NO₃)₂ + NH₄H₂PO₄, were investigated for the stabilization of Pb during thermal pretreatment. Lead in slurries was effectively stabilized up to 1000 °C with Ir, Pd and Pd + Mg modifiers among which Pd + Mg provided the best results with complete atomization at 1850 °C. Firings in the presence of Ir were, problematic due to ash formation inside the atomizer. Water, dilute HNO₃ and HF were examined as suspension medium. Dilute HNO₃ (1–2% v/v) proved to be advantageous over water as it afforded extraction of Pb from plankton almost quantitatively in 5 min agitation. Hydrofluoric acid was the least suitable medium. Increasing HF concentration up to 5% v/v resulted in inaccuracy and substantial background absorption. Fast-heating furnace method provided comparable accuracy and precision to that of conventional-heating in slurries of CRM 414. Detection limits and characteristic masses were, respectively, 0.49 μg L^− 1 and 32 pg for the conventional method and 0.62 μg L^− 1 and 37 pg for the fast-heating method. However, fast-heating approach suffered from distorted peaks at high temperatures and incomplete pyrolysis of matrix at lower temperatures. Analysis of marine plankton samples for Pb was performed by using the conventional furnace program. The results showed a high correlation with those obtained by solution ICP-MS. Differences were statistically insignificant within 95% confidence interval.     

Molybdenum, Mo-Ir and Mo-Ru coatings as permanent chemical modifiers for the determination of cadmium and lead in sediments and soil samples by electrothermal atomic absorption spectrometry

Molybdenum, Ir, Ru, Mo-Ir, Mo-Ru thermally coated on to platforms inserted in pyrolytic graphite tubes as permanent modifiers and Pd + Mg(NO₃)₂ conventional modifier mixture have been employed for the determination of cadmium and lead in dissolved sediments and soil samples by electrothermal atomic absorption spectrometry (ETAAS). Optimum masses and mass ratios of permanent modifiers for the analysis of Cd and Pb in sample solutions have been investigated. The 280 μg of Mo, 200 μg of Ir, 200 μg of Ru, 280 μg of Mo + 200 μg of Ir or 280 μg of Mo + 200 μg of Ru has been found as efficient as 5 μg of Pd + 3 μg of Mg(NO₃)₂ for increasing thermal stabilization of analytes and for decreasing the most serious interferences. Pyrolysis and atomization temperatures, atomization and background signal shapes, characteristic masses and detection limits of analytes in dissolved samples with or without permanent and conventional modifiers have been compared. The detection limits and characteristic masses obtained with Mo-Ir coated platform are 0.01 μg g⁻¹ and 1.1 pg for Cd and 0.09 μg g⁻¹ and 19 pg for Pb, respectively. Long-term stabilities for analytes in samples with Mo, Mo-Ir, Mo-Ru and Pd + Mg(NO₃)₂ have been studied. Cadmium and lead contents have been determined in certified and standard reference materials by using optimum conditions investigated and the results obtained with Mo-Ir or Mo-Ru were in agreement with the values of certified reference materials.     

Thermodynamics of ternary salts in dioxane—water mixtures from conductance measurements

Studies of electrolytic conductance in dioxane—water mixtures of varying dioxane content were initiated in 1978 [1]. In the present communication, an attempt has been made to evaluate the thermodynamic function ΔG⁰_t for the transfer of Mg(ClO₄)⁺, Mg(NO₃)⁺, BaCl⁺, BaBr⁺, Ba(ClO₄⁺, Ba(NO₃)⁺, SrCl⁺, Sr(NO₃)⁺, CaCl⁺ and Ca(NO₃)⁺ from water to dioxane—water media, which would give some information regarding ionic solvation.     

Parameter optimization of electrothermal vaporization inductively coupled plasma mass spectrometry for oligoelement determination in standard reference materials

The operational parameters of the graphite furnace for electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS), i.e. the internal carrier gas flow rate, the total carrier gas flow rate, the sample pretreatment temperature and the volatilization temperature, are optimized for oligoelement determinations (⁷⁵As, ⁹Be, ¹¹²Cd, ⁵⁰Cr, ⁶⁵Cu, ¹⁰³Rh, ¹²³Sb). The volatilization temperatures of As and Cr are compared to those obtained by graphite furnace atomic absorption spectrometry (GFAAS). Several modifiers Mg(NO₃)₂, Pd(NO₃)₂, Mg(NO₃)₂/Pd(NO₃)₂, Ni(NO₃)₂, KI, (NH₄)H₂PO₄ have been tested using the concentrations recommended for GFAAS. The concentration of Mg(NO₃)₂ alone and in combination with NaCl has been varied to find the optimal modifier conditions. ETV-ICP-MS signal enhancements by a factor of 10 to 130 respective to those of conventional nebulization have been obtained. The optimized parameters are evaluated by analyzing the water standard reference NIST 1643c and the aqua regia solution of the lake sediment reference material BCR 280.     

Parameter optimization of electrothermal vaporization inductively coupled plasma mass spectrometry for oligoelement determination in standard reference materials

The operational parameters of the graphite furnace for electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS), i.e. the internal carrier gas flow rate, the total carrier gas flow rate, the sample pretreatment temperature and the volatilization temperature, are optimized for oligoelement determinations (⁷⁵As, ⁹Be, ¹¹²Cd, ⁵⁰Cr, ⁶⁵Cu, ¹⁰³Rh, ¹²³Sb). The volatilization temperatures of As and Cr are compared to those obtained by graphite furnace atomic absorption spectrometry (GFAAS). Several modifiers Mg(NO₃)₂, Pd(NO₃)₂, Mg(NO₃)₂/Pd(NO₃)₂, Ni(NO₃)₂, KI, (NH₄)H₂PO₄ have been tested using the concentrations recommended for GFAAS. The concentration of Mg(NO₃)₂ alone and in combination with NaCl has been varied to find the optimal modifier conditions. ETV-ICP-MS signal enhancements by a factor of 10 to 130 respective to those of conventional nebulization have been obtained. The optimized parameters are evaluated by analyzing the water standard reference NIST 1643c and the aqua regia solution of the lake sediment reference material BCR 280.     

Effect of nitric acid for equal stabilization and sensitivity of different selenium species in electrothermal atomic absorption spectrometry

Determination of selenium by electrothermal atomic absorption spectrometry (ETAAS) is complicated by the presence of different species of this analyte. The presence of different oxidation states (−II, IV and VI) may result in different sensitivities obtained for each species rendering impossible the use of a single species for calibration. These species also exhibit different behaviours regarding thermal stabilities; the temperature program must be provided to conform to this problem. Chemical modifiers are commonly used for thermal stabilization of selenium species. In this study, experiments were carried out to demonstrate the effect of nitric acid in the presence of chemical modifiers. Nickel and palladium + magnesium were selected as the most commonly used chemical modifiers. Using both aqueous and human serum solutions it has been demonstrated that although chemical modifiers provide thermal stabilization of species so that higher ashing temperatures can be used, equal sensitivities cannot be achieved unless nitric acid is also present. Selenite, selenate, selenomethionine and selenocystine were used in experiments. When equal sensitivities for all these species are achieved, determination of total selenium by ETAAS can be performed by using a single species as the standard; selenite was used in this study. Precision was 5.0% or better using peak height signals. There was no significant difference in detection limits (3s) when Ni or Pd + Mg(NO₃)₂ was used as chemical modifier; 37 and 35 pg of selenium were found to be the detection limits for Ni and Pd + Mg(NO₃)₂ chemical modifiers, respectively. For chemical modifications, either 5 μg of Ni or 0.5 μg of Pd and 5 μg of Mg(NO₃)₂ were used; final solutions contained 2.5% HNO₃. In serum analyses, 10 μg of Ni was used in presence of 2.5% HNO₃.     

Conductivities of the Ternary Systems Y(NO3)3+La(NO3)3+H2O, La(NO3)3+Ce(NO3)3+H2O, La(NO3)3+Nd(NO3)3+H2O and Their Binary Subsystems at Different Temperatures

Electrical conductivities were measured for the ternary systems Y(NO₃)₃+La(NO₃)₃+H₂O, La(NO₃)₃+Ce(NO₃)₃+H₂O, La(NO₃)₃+Nd(NO₃)₃+H₂O, and their binary subsystems Y(NO₃)₃+H₂O, La(NO₃)₃+H₂O, Ce(NO₃)₃+H₂O, and Nd(NO₃)₃+H₂O at (293.15, 298.15 and 308.15) K. The measured conductivities were used to test the generalized Young’s rule and the semi-ideal solution theory. The comparison results show that the generalized Young’s rule and the semi-ideal solution theory can yield good predictions for the conductivities of the ternary electrolyte solutions, implying that the conductivities of aqueous solutions of (1:3 + 1:3) electrolyte mixtures can be well predicted from those of their constituent binary solutions by the simple equations.     

Thermodynamics of Sr(NO3)2 and Cd(NO3)2 in aquo-organic solvents from conductance data

The ion-solvent interaction of Sr(NO₃)₂ and Cd(NO₃)₂ in 10, 20 and 30 wt.% organic solvent (dioxane, glycol, methyl alcohol)-water mixtures at different temperatures has been studied using electrolytic conductivity data. The dissociation constant of the ion-pair Sr(NO₃)⁺ and Cd(NO₃)⁺ has been calculated along with ΔG⁰_t, ΔG⁰_t(cl) and ΔG⁰_t(ch). The ion pairs interact with the solvents and the interaction is of the order dioxane+water>methyl alcohol+water>glycol+water.     

Semi-permanent lutetium modifier for the determination of beryllium in urine by electrothermal atomic absorption spectrometry

The determination of beryllium using electrothermal atomic absorption spectrometry with deuterium background correction in the presence of various isomorphous metals and Mg(NO₃)₂ was studied. While, Eu, Ir and Sm had no effect on the transient signals, the addition of Lu and Mg(NO₃)₂ improved the sensitivity of the beryllium signal with respect to that obtained in the absence of modifier. Although, Mg(NO₃)₂ has improved the signal with respect to its sensitivity, it also increased the tail and the background (BG) signals, specially when urine samples are under study. Whereas, when Lu was used the analytical signal is virtually free of BG interference indicating that the urine matrix interference was almost eliminated. Besides, the addition of 6 μg of Lu ensured that the signals were effectively constant for five firings following the furnace program, which included: three drying, and the pyrolysis, atomization, cleaning and cooling steps. The effect of some components, likely to interfere in the accurate determination of beryllium (such as: Al, Ca, Cl, Co, Cr, Fe, Mg and Mn) were investigated. At the physiological levels, most of these elements had no effect, except in the case of chloride when Mg(NO₃)₂ was used as modifier. In this case, the tolerance limit was of 3000 mg Cl⁻ l⁻¹. The characteristic masses were 1.19, 0.45 and 0.48 pg, when integrated absorbance was measured for beryllium without the addition of any modifier and in the presence of Lu and Mg(NO₃)₂, respectively. The limits of detection (3σ) were 85, 19 and 58 fg, respectively. The accuracy and precision with the use of Lu and Mg(NO₃)₂ was tested for the direct determination of beryllium in urine samples. Quantification was performed with aqueous standards. The results obtained for the determination of beryllium in reference materials (Trace Elements in Urine), together with good recovery of spiked analyte, using either Lu or Mg(NO₃)₂ modification demonstrate the applicability of the procedure to the analysis of real samples. However, Lu provided the most accurate results. Also, the addition of Lu enhanced the precision of the measurements to levels of 1.8% relative standard deviation instead of 5.6 and 3.3% for the case of beryllium alone and with the addition of Mg(NO₃)₂.     

Use of hydrogen for the elimination of matrix interferences in the determination of lead by graphite furnace atomic absorption spectrometry

Summary Comparatively high sulphur contents in brown algae (Fucus vesiculosus) cause interferences in the determination of lead by Graphite Furnace Atomic Absorption Spectrometry (GFAAS). These cannot always be eliminated by the application of the L'vov platform, matrix modifiers recommended for lead as (NH₄)₂HPO₄ and Mg(NO₃)₂, Zeeman-effect background correction and peak area evaluation.The behaviour of the lead absorbance signal obtained from the L'vov platform inserted into an uncoated as well as a pyrolytically coated graphite tube was examined in the presence of sodium and magnesium sulphate and (NH₄)₂HPO₄ and Mg(NO₃)₂ matrix modifiers.Accurate lead determinations could only be performed if hydrogen was used as alternate gas during drying and charring steps since this eliminated the interferences caused by sulphates.

---

Verwendung von Wasserstoff zur Eliminierung von Matrixstörungen bei der Bleibestimmung durch Graphitofen-AAS

Zusammenfassung Vergleichsweise hohe Schwefelgehalte in Braunalgen (Fucus vesiculosus) verursachen Störungen bei der Bestimmung von Blei mit Grahitrohrofen-AAS. Diese können nicht immer durch Anwendung der L'vov-Plattform und den für Blei empfohlenen Matrix-Modifizierer (NH₄)₂HPO₄ und Mg(NO₃)₂, Zeeman-Effekt-Untergrundkorrektur und Peakflächenauswertung behoben werden.Das Verhalten des Blei-Absorbance-Signals, das von einer L'vov-Plattform, die sowohl in ein unbeschichtetes wie in ein mit Pyrokohlenstoff beschichtetes Graphitrohr eingebracht wurde, erzeugt wird, wurde in Gegenwart von Natrium- und Magnesiumsulfat sowie (NH₄)₂HPO₄ und Mg(NO₃)₂-Matrix-Modifizierern untersucht.Richtige Bleibestimmungen konnten nur durchgeführt werden, wenn Wasserstoff als Alternativgas während des Trocknens und der thermischen Zersetzung verwendet wurde, was die durch Sulfat hervorgerufenen Störungen eliminierte.

     

Diagramme polythermique du systeme ternaire H2O—Al(NO3)3—Mg(NO3)2

The solid—liquid equilibria of the ternary system H₂O—Al(NO₃)₃—Mg(NO₃)₂ were studied at –30, –20, –10 and 0°C by using a synthetic method which allows to detemine all the characteristic points of isothermal sections. The stable solid phases which appear are respectively: ice, Al(NO₃)₃·9H₂O, Mg(NO₃)₂·9H₂O and Mg(NO₃)₂·6H₂O. Neither double salts nor mixed crystals are observed in the temperature and composition field studied. Polytherm diagram layout show two invariant transformations correspond with an eutectic point and a peritectic point.This revised version was published online in November 2005 with corrections to the Cover Date.     

Lead atomization in the presence of aluminum matrices by electrothermal atomic absorption spectrometry. A comparative study of slurry vs solution sample introduction

The atomization behaviour of Pb introduced to the electrothermal atomizer in a slurry of Al₂O₃ and in a solution of Al(NO₃)₃ has been studied. The characteristics of the absorbance vs time profiles are highly dependent on the way in which Pb is incorporated in the matrix. In particular, Pb adsorbed on the surface of Al₂O₃ particles behaves differently from Pb entrapped within the particles. Atomization using platform and wall atomization from both pyrolytic and non-pyrolytic graphite surfaces is described. Pyrolytic platforms do not always provide complete recovery and better results are obtained with atomization from a non-pyrolytic platform surface within a pyrolytically coated tube. With wall atomization, large differences in the absorbance vs time profiles precludes its use for quantitative determinations. However, wall atomization should be useful for future studies of the kinetic and thermodynamic processes of Pb release. Finally, the feasibility of using the non-resonance Pb line at 261.4 nm to reduce the analytical sensitivity is examined. The strong dependence of the lower energy level population on temperature makes this difficult, but the absorbance profiles with non-pyrolytic platform atomization show that all forms of Pb can be made to atomize at similar temperatures.     

Thermogravimetry of the analytical precipitates M2Pb[Co(NO2)6] AND MPb[Co(NO2)6]

Thermogravimetric studies are reported for analytical precipitates of the types MPb[Co(NO₂)₆] and M₂Pb[Co(NO₂)₆], where M represents the univalent cations NH⁺₄, K⁺, Rb⁺, Cs⁺, and Tl⁺. Compounds of the latter series are consitently more stable to higher temperatures. For either series increasing the radius of M increases thermal stability. Decomposition to temperatures approaching 500°C involves some four separate processes.     

Preparation of Forsterite (Mg2SiO4) Powders Via an Aqueous Route Using Magnesium Salts and Silicon Tetrachloride (SiCl4)

Forsterite (Mg₂SiO₄) powders were prepared by mixing SiCl₄ with aqueous solutions of either Mg(CH₃COO)₂·4H₂O or Mg(NO₃)₂·6H₂O and heating the powdered gel. The powders were characterised using thermal analysis (DTA and TGA), X-ray diffraction (XRD), nitrogen adsorption surface area analysis (BET) and transmission electron microscopy (TEM). On heating, MgO and enstatite (MgSiO₃) were observed in addition to forsterite. On heating to 1200°C, forsterite was the dominant phase in the powders produced from Mg(NO₃)₂·6H₂O, and MgO was the dominant phase in the powders produced from Mg(CH₃COO)₂·4H₂O. The primary particle sizes of these powders were between 100 and 500 nm, which remained the same on heat treatment. However, higher temperatures gave rise to an increase in the size and densities of the agglomerates of primary particles.     

Die thermische Zersetzung einiger Wismut-Doppelnitrate

Zusammenfassung Die Zersetzung von CsNO₃, Bi(NO₃)₃, Bi(NO₃)₃·5H₂O, BiONO₃, 2CsNO₃·Bi(NO₃)₃ und 3M(NO₃)₂·2Bi(NO₃)₃·24H₂O (M=Mg, Mn, Co, Ni, Zn) wurde thermogravimetrisch untersucht. Es wurde festgestellt, daß 2CsNO₃·Bi(NO₃)₃ über eine beständige Zwischenstufe 2CsNO₃+1/2Bi₂O₃, die Doppelnitrate 3M(NO₃)₂·2Bi(NO₃)₃·24H₂) über 3M(NO₃)₂+2BiONO₃ zerfallen. Eine Herabsetzung der thermischen Stabilität des CsNO₃ wegen der Anwesenheit von Bi₂O₃, und der NitrateM(NO₃)₂ wegen der Anwesenheit von BiONO₃ wurde beobachtet. Zugleich ist BiONO₃ von zweiwertigen Nitraten stabilisiert.

---

The thermal decomposition of some bismuth double nitrates

The decomposition of CsNO₃, Bi(NO₃)₃, Bi(NO₃)₃·5H₂O, BiONO₃, 2CsNO₃·Bi(NO₃)₃, and 3M(NO₃)₂·2Bi(NO₃)₃·24H₂O (M=Mg, Mn, Co, Ni, Zn) has been studied by thermogravimetric analysis. It was found that 2CsNO₃·Bi(NO₃)₃ decomposesvia a stable intermediate, 2CsNO₃+1/2Bi₂O₃, and the double nitrates 3M(NO₃)₂·2Bi(NO₃)₃·24H₂)via 3M(NO₃)₂+2BiONO₃·Bi₂O₃ and BiONO₃ decrease the thermal stability of CsNO₃ andM(NO₃)₂, resp. Bivalent nitrates stabilize BiONO₃ to a certain degree.

---

---

Auszug aus einem Teil der Magisterarbeit vonF. Lazarini.     

FTIR-ATR <Emphasis Type="Italic">in situ</Emphasis> observation on the efflorescence and deliquescence processes of Mg(NO<Subscript>3</Subscript>)<Subscript>2</Subscript> aerosols

The efflorescence and deliquescence processes of Mg(NO₃)₂ aerosol particles deposited on ZnSe substrate have been investigated through in situ Fourier transform infrared-attenuated total reflection (FTIR-ATR) technique at the molecular level. At relative humidity (RH) of ∼3%, Mg(NO₃)₂ particles existed as amorphous states. The amorphous Mg(NO₃)₂ particles were transformed into crystalline Mg(NO₃)₂ · nH₂O (n ≤ 5) with slight increasing of RH. Thermodynamically stable Mg(NO₃)₂·6H₂O crystals were gradually formed on the particle surface and started to be dissolved at the saturation point (∼53% RH). At the same time, a continuous phase transition from Mg(NO₃)₂ · nH₂O (n≤5) to Mg(NO₃)₂·6H₂O occurred on the particle surface. This led the solid particles to completely deliquesce at 76% RH, which was much higher than the saturation point of 53% RH. In the efflorescence process, Mg(NO₃)₂ droplets entered into the supersaturated region due to the gradual evaporation of water. Finally, amorphous particles were formed when RH decreased below 5%. In the FTIR-ATR spectra of the supersaturated Mg(NO₃)₂ droplets, the absorbance of the symmetric stretching vibration of NO ₃ ⁻ (v ₁- NO ₃ ⁻ ) clearly became stronger. It resulted from the continuous formation of solvent share ion pairs (SIPs), and even the contact ion pairs (CIPs) between Mg²⁺ and NO ₃ ⁻ . Supported by the Trans-Century Program Foundation for the Talents by the Ministry of Education of China, the National Natural Science Foundation of China (Grant Nos. 20073004, 20473012, and 20673010), the 111 Project (B07012), and the State Key Laboratory of Physical Chemistry for Solid Surface of Xiamen University     

Simultaneous determination of cadmium and lead in wine by electrothermal atomic absorption spectrometry

A method has been developed for the direct simultaneous determination of Cd and Pb in white and red wine by electrothermal atomic absorption spectrometry (ET-AAS) using a transversely heated graphite tube atomizer (THGA) with longitudinal Zeeman-effect background correction. The thermal behavior of both analytes during pyrolysis and atomization stages were investigated in 0.028 mol l⁻¹ HNO₃ and in 1+1 v/v diluted wine using mixtures of Pd(NO₃)₂+Mg(NO₃)₂ and NH₄H₂PO₄+Mg(NO₃)₂ as chemical modifiers. With 5 μg Pd+3 μg Mg as the modifiers and a two-step pyrolysis (10 s at 400°C and 10 s at 600°C), the formation of carbonaceous residues inside the atomizer was avoided. For 20 μl of sample (wine+0.056 mol l⁻¹ HNO₃, 1+1, v/v) dispensed into the graphite tube, analytical curves in the 0.10–1.0 μg l⁻¹ Cd and 5.0–50 μg l⁻¹ Pb ranges were established. The characteristic mass was approximately 0.6 pg for Cd and 33 pg for Pb, and the lifetime of the tube was approximately 400 firings. The limits of detection (LOD) based on integrated absorbance (0.03 μg l⁻¹ for Cd, 0.8 μg l⁻¹ for Pb) exceeded the requirements of Brazilian Food Regulations (decree #55871 from Health Department), which establish the maximum permissible level for Cd at 200 μg l⁻¹ and for Pb at 500 μg l⁻¹. The relative standard deviations (n=12) were typically <8% for Cd and <6% for Pb. The recoveries of Cd and Pb added to wine samples varied from 88 to 107% and 93 to 103%, respectively. The accuracy of the direct determination of Cd and Pb was checked for 10 table wines by comparing the results with those obtained for digested wine using single-element ET-AAS, which were in agreement at the 95% confidence level.     

Thermodynamic properties and solution equilibria of aqueous bivalent transition metal nitrates and magnesium nitrate

Osmotic coefficients for Mn(NO₃)₂, Co(NO₃)₂, Ni(NO₃)₂, Cu(NO₃)₂, Zn(NO₃)₂, and Mg(NO₃)₂ in aqueous solution have been determined by the isopiestic method at 25°C, and activity coefficients have been derived. The results agree with the literature data for Zn(NO₃)₂, while they are significantly different for Co(NO₃)₂, Cu(NO₃)₂, and Mg(NO₃)₂, and those for Mn(NO₃)₂ and Ni(NO₃)₂ are new. The concentration dependence of the osmotic coefficients for the bivalent metal nitrates is similar to that for the trifluoroacetates, while it differs from those for the other salts of the same series of metals. The results are discussed in terms of the inner-sphere and outer-sphere association of ions, auxiliary information being derived from the concentration effects in the visible spectra of the coloured metal nitrates.     

Synthesis of Mg–Al–Fe–NO3 layered double hydroxides via a mechano-hydrothermal route

Mg–Al–Fe–NO₃ layered double hydroxides (LDHs) with a constant Mg²⁺/(Al³⁺ + Fe³⁺) molar ratio but varying Al³⁺/Fe³⁺ molar ratios were successfully synthesized by a mechano-hydrothermal (MHT) method from Mg(OH)₂, Al(OH)₃ and Fe(NO₃)₃·9H₂O or Mg(NO₃)₂·6H₂O as starting materials. The resulting LDHs (MHT-LDHs) were characterized by XRD, TEM, SEM, FT-IR, and zeta potential, size distribution and specific surface area analyses. It was found that pre-milling played a key role in the LDH formation during subsequent hydrothermal treatment. The MHT route is advantageous in terms of low reaction temperature compared with the conventional hydrothermal method, and the target products are of high crystallinity and good dispersion compared with the conventional mechanochemical (MC) method. The MHT-LDHs had higher specific surface area and zeta potential, and lower hydrodynamic diameter than LDHs obtained by MC method (MC-LDHs). Furthermore, the removal of Cr(VI) from aqueous solutions using the LDHs was examined, showing that the MHT-LDHs are of higher removal efficiency than MC-LDHs for the heavy metal pollutant.     

Determination of thermodynamic properties of aqueous mixtures of MgCl2 and Mg(NO3)2 by the potentiometric method at T = 298.15

In this research, thermodynamic properties of the ternary electrolyte system (MgCl₂ + Mg(NO₃)₂ + H₂O) were investigated using a potentiometric method. The galvanic cell used had no liquid junction of type: Mg-ISE|MgCl₂ (m_A), Mg(NO₃)₂ (m_B), H₂O|Ag/AgCl. The measurements were performed at T = 298.15 K and at total ionic strengths from 0.001 to 8.000 mol/kg for different series of salt ratios r=mMgCl₂/mMg₂(NO₃) =1.00, 2.50, 5.00, 7.50, 10.00 and 15.00. The PVC based magnesium ion-selective electrode (Mg-ISE) and the Ag/AgCl electrode used in this work were prepared in our laboratory and showed a reasonably good Nernst response. The Pitzer ion interaction model and Harned rule were used to illustrate the ternary electrolyte system investigated. The experimental results showed that both Pitzer model and Harned rule were suitable to be used satisfactorily to describe this ternary system.