Disposable screen-printed ring disk carbon electrode coupled with wall-jet electrogenerated iodine for flow injection analysis of arsenic(III)

We report here a wall-jet electrogenerated iodine approach for sensitive detection of arsenite (As^III) by using a disposable screen-printed ring disk carbon electrode. Iodide (I⁻) is first oxidized to iodine (I₂) at the disk electrode; the electrogenerated I₂ can be effectively reduced back to I⁻ in the presence of As^III. The inhibited reduction current of I₂ to I⁻ can thus be monitored at the ring electrode and used for As^III analysis. Various factors influencing the flow injection analysis (FIA) of As^III were thoroughly investigated in this study. Under the optimized conditions, a linear calibration plot up to 10 μM with a detection limit (S/N = 3) of 70 nM was obtained by using 50 μM KI as the mobile phase in FIA. Practical utility of the proposed method was demonstrated to detect As^III in “Blackfoot” disease endemic village groundwater from southwestern coast area of Taiwan (Pei-Men).     

Determination of Cd levels in smoke condensate of Brazilian and Paraguayan cigarettes by Thermospray Flame Furnace Atomic Absorption Spectrometry (TS-FF-AAS)

In this study, the concentrations of Cd in smoke condensate of Paraguayan and Brazilian full flavor normal size cigarettes were determined. A “fishtail” chimney was used to confine and direct cigarette smoke to an impaction trap followed by 3 MCE (mixed cellulose ester) filters for smoke collection. The smoke condensate collected at the first two collection stages (chimney and impactor) was prepared as Triton X-100 slurry samples and the 3 MCE filters (third collection stage) used to collect smoke were microwave digested. Samples were analyzed by Thermospray Flame Furnace Atomic Absorption Spectrometry (TS-FF-AAS) for Cd and the results obtained were compared with Graphite Furnace Atomic Absorption Spectrometry (GFAAS). No significant differences were found between the values obtained with TS-FF-AAS and GFAAS at a 95% confidence level. The total concentration of Cd in the smoke of Brazilian and Paraguayan cigarettes tested ranged from 187 to 281 ng/cigarette and from 176 to 271 ng/cigarette, respectively. The LODs for Cd using TS-FF-AAS and GFAAS, were 5.8 and 1.5 ng/cigarette, respectively, for the analysis of smoke condensate from 1 cigarette. The main advantages of using the simple TS-FF-AAS system are its low running costs and the analysis time when compared to GFAAS.     

Determination of As in tobacco by using electrochemical hydride generation at a Nafion® solid polymer electrolyte cell hyphenated with atomic fluorescence spectrometry

In the present work, a novel solid polymer electrolyte hydride generation (SPE-HG) cell was developed. The home-made SPE-HG cell, mainly composed of three components (Nafion®117 membrane for separating and H⁺ exchanging, a soft graphite felt cathode and a Ti mesh modified by Ir anode), was employed for detecting As by coupling to atomic fluorescence spectrometry (AFS). The H⁺ generated by electrolysis of pure water in anode chamber transferred to cathode chamber through SPE, and immediately reacted with As^3 + to generate AsH₃. The relative mechanisms and operation conditions for hydride generation of As were investigated in detail. The developed cell employed water as an alternative of acid anolyte, with virtues of low-cost, more than 6 months lifetime and environment friendly compared with the conventional cell. Under the optimized conditions, the limit of determination of As^3 + for sample blank solution was 0.12 μg L^? 1, the RSD was 2.9% for 10 consecutive measurements of 5 μg L^? 1 As^3 + standard solution. The accuracy of the method was verified by the determination of As in the reference Tea (GBW07605) and the developed method was successfully applied to determine trace amounts of As in tobacco samples with recovery from 97% to 103%.     

Spin transition in heptanuclear star-shaped iron(III)–antimony(V) NCS- and CN-bridged compounds

The precursor [Fe^III(L)Cl] (LH₂ = N,N′-bis(2′-hydroxy-benzyliden)-1,6-diamino-3-azahexane) has been prepared and Mössbauer spectroscopy assigned a high-spin (S = 5/2) state at room temperature. The precursor is combined with the bridging units [Sb^V(X)₆]^? (X = CN^?, NCS^?) to yield star-shaped heptanuclear clusters [(LFe^III–X)₆Sb^V]Cl₅. The star-shaped compounds are in general high-spin systems at room temperature. On cooling to 20 K some of the iron(III) centers switch to the low-spin state as indicated by Mössbauer spectroscopy, i.e. multiple electronic transitions. While the cyano-bridged complex performs a multiple spin transition the thiocyanate-compound shows no significant population at both temperatures.     

Kinetics and mechanism of the chromic oxidation of 3-O-methyl-d-glucopyranose

The oxidation of 3-O-methyl-d-glucopyranose (Glc3Me) by Cr^VI in acid medium yields Cr^III, formic acid and 2-O-methyl-d-arabinose as final products when a 50-times or higher excess of Glc3Me over Cr^VI is used. The redox reaction takes place through the combination of Cr^VI → Cr^IV → Cr^II and Cr^VI → Cr^IV → Cr^III pathways. Intermediacy of free radicals and Cr^II in the reaction was demonstrated by the observation of induced polymerization of acrylamide and detection of CrO₂²⁺ formed by reaction of Cr^II with O₂. Intermediate oxo-Cr^V–Glc3Me species were detected by EPR spectroscopy. In 0.3–0.5 mol/L HClO₄, intermediate Cr^V rapidly decompose to the reaction products, while, at pH 5.5–7.5, where the redox processes are very slow, five-coordinate Cr^V bis-chelates of the pyranose and furanose forms of Glc3Me remain more than 15 h in solution. The C1–C2 bond cleavage of Glc3Me upon reaction with Cr^VI distinguishes this derivative from glucose, which is oxidized to gluconic acid.     

Non-aqueous chromium acetylacetonate electrolyte for redox flow batteries

A single-metal redox flow battery employing chromium(III) acetylacetonate in tetraethylammonium tetrafluoroborate and acetonitrile has been investigated using electrochemical techniques. Cyclic voltammetry was used to evaluate electrode kinetics. Four redox couples were observed in the stable potential window. The Cr^II/Cr^III, Cr^I/Cr^II, Cr^III/Cr^IV and Cr^IV/Cr^V redox couples all appeared to be quasi-reversible, with the Cr^III/Cr^IV couple exhibiting comparatively slow kinetics. A cell potential of 3.4 V was measured for the one-electron disproportionation of the neutral Cr^III complex. The diffusion coefficient for chromium acetylacetonate in the supporting electrolyte solution was estimated to be in the range of 5.0–6.2 × 10^?7 cm² s^?1 at room temperature. The charge–discharge characteristics of this system were evaluated in an H-type glass cell, and coulombic and energy efficiencies of approximately 55% and 20%, respectively, were obtained.     

X-ray absorption LIII and MV edges of hexavalent lower actinides

X-ray absorption spectroscopy is used to probe the electronic and structural features of the actinides. To better understand the effect of the effective charge and polyhedron on the edge structure, we discuss the L_III and M_V edges in AnO₂(NO₃)₂(TBP)₂ (where the actinide is shortly linked to the ‘yl’ oxygens) and in the perovskite Ba₂ZnAnO₆ (where the hexavalent actinide is in the cubic structure as An⁶⁺), An=U, Np, Pu. Using FEFF8 simulations, both features and position of the L_III and M_V edges are explained within a crystal field splitting of the orbitals picture and a multiple scattering picture. © 2000 Académie des sciences / Éditions scientifiques et médicales Elsevier SASXANES / uranium / neptunium / plutonium / perovskite     

A family of dodecanuclear Mn11Ln single-molecule magnets

A series of four isostructural dodecanuclear complexes [Mn^III₉Mn^II₂Ln^III(O)₈(OH)(piv)₁₆(NO₃)(CH₃CN)]·xCH₃CN·yC₇H₁₆ (piv = pivalate; x = ½, y = ¾, Ln = Tb (1); x = 2, y = ½, Ln = Dy (2), Ho (3), and Y (4)) has been prepared for which the structural motif described as ‘a lanthanide ion nested in a large manganese shell’ is observed. All compounds show out-of-phase signals in their ac susceptibilities, and their single-molecule magnet behaviour was confirmed by single-crystal micro-SQUID studies of 1-3 which show hysteresis loops of molecular origin at T < 1.0 K. The SMM behaviour observed in compounds 1-3 is more pronounced than that for 4, which contains the diamagnetic Y^III ion. This is principally the result of ferromagnetic coupling between the paramagnetic anisotropic Ln^III ions (Tb^III, Dy^III and Ho^III) and the manganese shell, which enhances the total spin ground state of the complexes.     

Determination of the Interaction of Arsenic and Human Serum Albumin by Online Microdialysis Coupled to LC with Hydride Generation Atomic Fluorescence Spectroscopy

Study on the stoichiometry and affinity of the arsenicals bound to HSA is an important step toward a better understanding of arsenic toxic effects. After incubation of As^III or As^V with HSA at the physiological conditions (pH 7.43 and 37 °C), the free arsenicals and arsenic-HSA complexes were separated and detected by the combined techniques of microdialysis and liquid chromatography with hydride generation atomic fluorescence spectroscopy (MD–LC–HGAFS). The decrease of As^III peak response rather than As^V indicated that HSA reacted with As^III but not As^V. The binding plots indicated that the binding between HSA and As^III was in Scatchard pattern when the concentration ratios of As^III to HSA were ≤1:1. The strong binding sites (n ₁) were 1.6 and the stability constant (K ₁) was 1.54 × 10⁶ M^?1. When the concentration ratios of As^III to HSA were >1:1, the binding was in Plasvento pattern with the stability constant K ₂ ? 0 and no specific binding of As^III with HSA. On the contrary, As^V did not show binding with HSA. The results showed that As^III reacted with HSA more readily than As^V, which provides a chemical basis for arsenic toxicity.     

Electrochemical immunoassay of cotinine in serum based on nanoparticle probe and immunochromatographic strip

A disposable sensor for the determination of cotinine in human serum was developed based on immunochromatographic test strip and quantum dot label. In this assay, cotinine linked with quantum dot competes with cotinine in sample to bind to anti-cotinine antibody in the test strip and the quantum dots serve as signal vehicles for electrochemical readout. Some parameters governing the performance of the sensor were optimized. The sensor shows a wide linear range from 1 ng mL^?1 to 100 ng mL^?1 cotinine with a detection limit of 1.0 ng mL^?1. The sensor was validated with spiked human serum samples and it was found that this method was reliable in measuring cotinine in human serum. The results demonstrate that this sensor is rapid, accurate, and less expensive and has the potential for point of care (POC) detection of cotinine and fast screening of tobacco smoke exposure.     

Determination of the Interaction of Arsenic and Human Serum Albumin by Online Microdialysis Coupled to LC with Hydride Generation Atomic Fluorescence Spectroscopy

Study on the stoichiometry and affinity of the arsenicals bound to HSA is an important step toward a better understanding of arsenic toxic effects. After incubation of As^III or As^V with HSA at the physiological conditions (pH 7.43 and 37 °C), the free arsenicals and arsenic-HSA complexes were separated and detected by the combined techniques of microdialysis and liquid chromatography with hydride generation atomic fluorescence spectroscopy (MD–LC–HGAFS). The decrease of As^III peak response rather than As^V indicated that HSA reacted with As^III but not As^V. The binding plots indicated that the binding between HSA and As^III was in Scatchard pattern when the concentration ratios of As^III to HSA were ≤1:1. The strong binding sites (n ₁) were 1.6 and the stability constant (K ₁) was 1.54 × 10⁶ M⁻¹. When the concentration ratios of As^III to HSA were >1:1, the binding was in Plasvento pattern with the stability constant K ₂ ≅ 0 and no specific binding of As^III with HSA. On the contrary, As^V did not show binding with HSA. The results showed that As^III reacted with HSA more readily than As^V, which provides a chemical basis for arsenic toxicity.

     

Co-deposition of arsenic and arsine on Pt,Cu, and Fe electrodes

An electrochemical investigation of arsenic in aqueous solutions was carried out in order to assess the possibility of removing it by reduction from As(III) to its elemental form. Arsine evolution was significant at potentials below −0.650 V_SCE on Cu, and below −0.728 V_SCE on Pt. As(V) could also be removed on Cu, with a larger evolution of arsine. When a potential equal to −0.560 V_SCE was applied to an iron electrode, arsenic deposition took place simultaneously with iron dissolution, and arsine evolution was negligible.     

Disposable barrel plating nickel electrodes for use in flow injection analysis of trivalent chromium

We report a disposable barrel plating nickel electrode (Ni-BPE) coupled with a specifically designed electrochemical cell for use in flow injection analysis for the determination of trivalent chromium (Cr^III). The response of the activated Ni-BPE was found very sensitive under alkaline condition with a systematic increase in current signal upon successive addition of Cr^III. Under optimized conditions, the calibration curve showed a linear range up to 1 mM with a detection limit (S/N = 3) of 0.30 μM. Continuous hydrodynamic flow of 0.1 M NaOH at regular Cr^III injections verify the reproducibility of the present system. The proposed method was successfully used to detect the amount of Cr^III in environmental water to show its potential use in real applications.     

Synthèse et étude structurale du polyanion [AsIII 4Mo6W14O72(H2O)2]12– isomorphe de [AsIII 4W20O72(H2O)2]12–

Synthesis and X-ray study of the polyanion [As^III ₄Mo₆W₁₄O₇₂(H₂O)₂]^12– isomorphous of [As^III ₄W₂₀O₇₂(H₂O)₂]^12–. The addition of an excess of MoO₄^2– to a solution of [As^III₂W₈O₃₀(OH)]^7– led at pH=4 to a new polyanion [As^III ₄Mo₆W₁₄O₇₂(H₂O)₂]^12– isostructural of [As^III ₄W₂₀O₇₂(H₂O)₂]^12–. The structure of this compound was determined by X-ray diffraction: a=11.183(4) Å, b=13.432(3) Å, c=19.626(5) Å, α=77.87(2), β=73.57(3), γ=67.44(3)°, V=2 594(1) ų, P1̄. Reliability factors are R=7.89 and R_w=9.97. The starting compound underwent an isomerisation β→α and one tungsten was formally substituted by one molybdenum atom; two other molybdenum atoms were incorporated. The polyanion is formed of two units αB–As^IIIMo₂W₇O₃₃ connected by a double chain As^IIIOMo₂O₂(H₂O). Arsenic and molybdenum are both bound to two octahedrons WO₆ of one unit As^IIIOMoO₂W₇O₃₃, both molybdenum atoms of which are contiguous. © 2000 Académie des sciences / Éditions scientifiques et médicales Elsevier SASpolymolybdotungstate / arsenomolybdotungstate / crystal structure / (hexamolybdenumtetradecatungsten)ate / synthesis of a new mixed polytungstate     

Continuous flow hydride generation-atomic fluorescence spectrometric determination and speciation of arsenic in wine

Methods for the atomic fluorescence spectrometric (AFS) determination of total arsenic and arsenic species in wines based on continuous flow hydride generation (HG) with atomization in miniature diffusion flame (MDF) are described. For hydride-forming arsenic, l-cysteine is used as reagent for pre-reduction and complexation of arsenite, arsenate, monomethylarsonate and dimethylarsinate. Concentrations of hydrochloric acid and tetrahydroborate are optimized in order to minimize interference by ethanol. Procedure permits determination of the sum of these four species in 5–10-fold diluted samples with limit of detection (LOD) 0.3 and 0.6 μg l^− 1 As in white and red wines, respectively, with precision between 2% and 8% RSD at As levels within 0.5–10 μg l^− 1.Selective arsine generation from different reaction media is used for non-chromatographic determination of arsenic species in wines: citrate buffer at pH 5.1 for As(III); 0.2 mol l^− 1 acetic acid for arsenite + dimethylarsinate (DMA); 8 mol l^− 1 HCl for total inorganic arsenic [As(III) + As(V)]; and monomethylarsonate (MMA) calculated by difference. Calibration with aqueous and ethanol-matched standard solutions of As(III) is used for 10- and 5-fold diluted samples, respectively. The LODs are 0.4 μg l^− 1 for As(III) and 0.3 μg l^− 1 for the other three As species and precision is within 4–8% RSDs.Arsenic species in wine were also determined by coupling of ion chromatographic separation on an anion exchange column and HG-flame AFS detection. Methods were validated by means of recovery studies and comparative analyses by HG-AFS and electrothermal atomic absorption spectrometry after microwave digestion. The LODs were 0.12, 0.27, 0.15 and 0.13 μg l^− 1 (as As) and RSDs were 2–6%, 5–9%, 3–7% and 2–5% for As(III), As(V), MMA and DMA arsenic species, respectively. Bottled red and white wines from Bulgaria, Republic of Macedonia and Italy were analyzed by non-chromatographic and chromatographic procedures and the As(III), arsenite, has been confirmed as major arsenic species.     

Simultaneous determination of mercury and arsenic by anodic stripping voltammetry

An electrochemical method for the simultaneous determinations of Hg^II concentration and total As^III and As^V concentration has been developed. The method does not require the additional preliminary step of the chemical reduction of As^V to As^III, or oxidation of As^III to As^V before stripping analysis takes place. Also, the method for the simultaneous determination of Hg^II concentration and As^III concentration is described. Measurements were performed in 0.1 M HCl using a gold-plated graphite electrode as sensor. Detection limits for both methods are below 0.4 ppb. Relative standard deviation did not exceed 15%. The possible interference by other trace metals was investigated. Analyses of natural water and industrial solutions were made using proposed methods and AAS. The t-test demonstrates that there was no significant difference between the results obtained with these methods. Proposed methods decrease the time of analysis because concentrations of the Hg^II and arsenic ions were measured simultaneously. Also, the removal of the additional step of chemical reduction of As^V to As^III or oxidation of As^III to As^V decreases analysis time, and also reduces the chance of contamination due to the use of additional reagents.     

Cross-sections for formation of 195mPt through natPt(n,x)195mPt reaction over neutron energy range 13–15 MeV

The cross-sections for formation of metastable state of ¹⁹⁵Pt (^195mPt, 98.85 keV, 4.02 d) through ^natPt(n,x)^195mPt reaction induced by 13.5–14.6 MeV neutrons were measured. Measurements were corrected for gamma-ray attenuations, random coincidence (pile-up), dead time and fluctuation of neutron flux. The data for ^natPt(n,x)^195mPt reaction cross-sections are reported to be 438±46, 399±44 and 372±43 mb at 13.5±0.2, 14.1±0.1 and 14.6±0.2 MeV incident neutron energies, respectively.     

Jahn–Teller coupling and the influence of strain in Tg and Eg ground and excited states – A ligand field and DFT study on halide MIIIX6 model complexes [M = TiIII–CuIII; X = F−, Cl−]

In contrast to well established experimental results of vibronic coupling effects in octahedral dⁿ complexes with E_g ground states (Cu²⁺, Ag²⁺; Cr²⁺, Mn³⁺ etc.), not much useful material is available for the Jahn–Teller (JT) effect in orbital triplet ground states. The present study is concerned with this deficiency, providing data for octahedral halide model complexes with 3dⁿ cations – in particular for Ti^III, V^III and high-spin Co^III, Ni^III with T_2g and T_1g ground states, which involve, to first-order, solely splitting of the π-antibonding t_2g MOs. Besides experimental results – structural and spectroscopic, mainly from d–d spectra – data from computations are needed for a quantitative treatment of the T_g ? (?_g + τ_2g) vibronic interaction as well as in the E_g ? ?_g coupling case (Mn^III, low-spin Ni^III); DFT was the method of choice, if only critically selected outcomes are utilised. The theoretical bases of the treatment are the dⁿ ligand field matrices in O_h, extended by the inclusion of lower-symmetry distortion parameters, and the conventional theory of vibronic coupling. Caution is needed when classifying the effects of interelectronic repulsion; DFT does not reproduce the magnitudes of the Racah parameters B, C, as deduced from the d–d spectra, properly – the presumed reasons are analysed. DFT even allows one to deduce reliable vibronic coupling constants via the analysis of orbitally degenerate excited states (Cr^III, ⁴A_2g ground state). The group-theoretical analysis of the interaction with the JT-active ?_g and τ_2g modes yields D_4h, D_3d and D_2h as the possible distortion symmetries in the case of a T_g ground state. The DFT-calculations give clear evidence, that the D_4h stationary points represent the absolute minima in the T_g ? (?_g + τ_2g) potential surface – in agreement with experiment, where available. For the first time, vibronic coupling constants, characterising JT splitting of ground and excited T_g states, can be presented for trivalent 3dⁿ cations in octahedral halide ligand fields. They turn out to be smaller by a factor of almost 3 in comparison to those, which determine the coupling in σ-antibonding e_g MOs.The tetragonal splitting of T_g states is typically only small, around 0.1 eV, and suggests that strain influences from a specific ligand arrangement and/or the presence of different ligands may modify the potential surface considerably. We have studied such effects via compounds A^IM^IIIF₄, where an elastic strain induced by the host structure, and a binding strain, due to the simultaneous existence of (largely) terminal and of bridging ligands, are active. A novel strain model, in its interplay with JT coupling, is proposed and applied – using energies from the d–d spectra, structural results and data from DFT.Chloride complexes are only known for Ti^III to Fe^III; the rather small electronegativity already of Co^III suggests a reducing ligand-to-metal (3dⁿ) electron transfer for n ≥ 6. Similarly, the low-lying ligand-to-metal charge transfer bands in the d–d spectra of the Cu^IIIF₆^3? complex and the reduced T_g ? ?_g coupling strength suggest a pronounced covalency of the Cu^III–F, and, even more distinctly, of the Cu^III–O bond, which is of interest for superconductivity. The Ni^IIIF₆^3? polyhedron possesses a low-spin configuration in the elpasolite structure. The spectroscopic evidence and the DFT data indicate, that the minimum positions of the alternative _a²A_1g(_a²E_g) and _a⁴A_2g (_a⁴T_1g) potential curves are only ≤0.02 eV apart, giving rise to interesting high-spin/low-spin phenomena. It is the strong E_g ? ?_g as compared to the T_1g ? ?_g coupling, which finally stabilises a spin-doublet ground state in D_4h.We think, that the selected class of solids is unique particularly for the study of Jahn–Teller coupling in T ground states, with model character for other systems. In our overview a procedure is sketched, which uses reliable computational results (here from DFT) for supplementing incomplete experimental data, and presents – on a semiquantitative scale – convincing statements, consistent with chemical intuition. It is also a pleading for ligand field theory, which rationalises d-d spectra in terms of chemical bonding; though the latter spectra provide frequently only rather coarse information, their assistance in the energy analysis is crucial.     

Speciation of arsenic trioxide metabolites in blood cells and plasma of a patient with acute promyelocytic leukemia

Arsenic trioxide (As₂O₃) has been widely accepted as the second-best choice for the treatment of relapsed and refractory acute promyelocytic leukemia (APL) patients. However, a few studies have been conducted on a detailed speciation of As₂O₃ metabolites in blood samples of patients. To clarify the speciation of arsenic, the blood samples were collected at various time points from a patient with APL after remission induction therapy and during consolidation therapy. The total amounts of arsenic in blood cells and plasma, and the plasma concentrations of inorganic arsenic and methylated metabolites were determined by inductively coupled plasma mass spectrometry (ICP-MS) and high-performance liquid chromatography/ICP-MS, respectively. The total amounts of arsenic in the blood cells were 4–10 times higher than those in plasma. Among all arsenic metabolites, the pentavalent arsenate (As^V) in plasma was more readily eliminated. During the drug-withdrawal period, the initial plasma concentrations of trivalent arsenic (As^III) declined more rapidly than those of methylarsonic acid and dimethlyarsinic acid, which are known as the major methylated metabolites of As^III. On the other hand, during the consecutive administration in the consolidation therapy period, the plasma concentrations of total arsenic and arsenic metabolites increased with time. In conclusion, these results may support the idea that methylated metabolites of As₂O₃ contribute to the efficacy of arsenic in APL patients. These results also suggest that detailed studies on the pharmacokinetics as well as the pharmacodynamics of As₂O₃ in the blood cells from APL patients should be carried out to provide an effective treatment protocol. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Presented at the 4th International Conference on Trace Element Speciation in Biomedical, Nutritional and Environmental Sciences, 25–29 May 2008, Munich-Neuherberg, Germany.     

Excess enthalpies and excess volumes of (2-methoxyethanol + 1,4-dioxane) and (1,2-dimethoxyethane + benzene) at temperatures between 283.15 K and 313.15 K

The measurement of excess enthalpies, H^E, at T=298.15 K and densities at temperatures between 283.15 K and 313.15 K are reported for the (2-methoxyethanol + 1,4-dioxane) and (1,2-dimethoxyethane + benzene) systems. The values of H^E and the excess volumes, V^E, are positive, and the temperature dependence of V^E is quite small for (2-methoxyethanol + 1,4-dioxane). The (1,2-dimethoxyethane + benzene) system shows a negative H^E and sigmoid curves in V^E, which change sign from positive to negative with an increase in 1,2-dimethoxyethane. The temperature dependence of V^E for this system is negative.