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Abstract  

Experimental results of positron annihilation experiments in solutions of n-butanol in three diols are compared to those of ultrasonic velocity and absorption. Variations of the annihilation parameters with composition show that the effect of the hydrophobic solute on the original diol structure is rather limited and occurs only in the system where ethylene glycol is the solvent. Subtle similarities were found when compared it to the respective results for similar aqueous systems, suggesting that crystalline-like solvates are forming in ethylene glycol. However, no such evidences were found for the systems where butanediols are the solvents. Ultrasonic investigations do not confirm formation of any specific structures. This is caused, most possibly, by the fact that compressibility of solvates is close to those of the pure components and/or that of unstructured medium (regular solution).

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Abstract  

The results of positron annihilation experiments of solutions of n-hexanol in diols are compared to those of ultrasonic velocity and absorption. Variations of the annihilation parameters with composition allow the conclusion that the effect of hydrophobic solute on the original diol structure is limited. There are, however, significant similarities with the results known for aqueous systems, suggesting that clathrate-like solvates are forming in ethylene glycol, the phenomenon called here is a hydrophobic-like solvation. No evidences for it were found for the systems containing butanediols as solvents. Unfortunately, ultrasonic investigations do not confirm the formation of any specific structures, most possibly because the compressibilities of solvates are close to those of the pure components.

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This paper reviews our findings on the susceptibility of the organic chemically bonded ligands to hydrolytic cleavage from the silica matrix for the most common TLC-type stationary phases, i.e. RP-18, RP-8, CN, and Diol. In our experiments this process was induced by repeated (i.e. one-, two-, four-, and eightfold) development of these phases with mixed mobile phases comprising methanol, water, and buffers of different pH.Quantification of the extent of hydrolytic cleavage of octadecyl, octyl, 3-cyanopropyl, and diol ligands from the silica surface was basically achieved by means of Raman spectroscopy, although other supplementary analytical techniques were also employed-namely elemental (combustion) analysis, thermogravimetry (TG), and differential scanning calorimetry (DSC).

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Conditions have been established for TLC analysis and determination of the flavonol truxinic esters daglesiosides I and II in species of the family Pinaceae . Optimization of the separation of eleven flavonoids, including daglesiosides I, II, III, and IV, trans -tiliroside, trans -ditiliroside, kaempferol, quercetin, isorhamnetin, hyperoside, and astragalin, which are present in the methanol extract of Pseudotsuga menziesii , was performed on two types of layer — glass plates coated with RP-18F 254S and diol F 254S . Good resolution was achieved on diol F 254S layers by use of multiple gradient development with a mixture of chloroform and ethyl acetate. Under these conditions the presence of daglesioside I was demonstrated in two other species of Pinaceae — Cedrus atlantica and Cedrus atlantica var. glauca — and the flavonoid complex occurring in Pseudotsuga menziesii was completely separated by use of 2D TLC on coupled silica gel and RP-18 layers.

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Separation selectivity has been optimized in two-dimensional thin-layer chromatography (2D TLC) by connecting diol or silica plates (on which NP chromatograms were developed) to RP-18W plates (on which reversed-phase chromatograms were developed). Retention of test substances was investigated to select optimum chromatographic systems for separation of selected phenolic compounds by 2D TLC. Selection of optimal mobile phases was performed on the basis of plots of retention against mobile phase composition. The next step of the optimization was calculation of statistical data for correlation of R M values for pairs of chromatographic systems — NP diol-RP C 18 or silica-RP C 18 . Orthogonal chromatographic systems were selected on the basis of these correlations and used to separate phenolic compounds present in plant extracts. For example, extracts from Polygonum sp. and Verbascum sp. were separated by use of optimum 2D TLC systems.

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Journal of Thermal Analysis and Calorimetry
Authors: M. Ştefănescu, M. Stoia, O. Ştefănescu, A. Popa, M. Simon, and C. Ionescu

Abstract  

Hybrid organic-inorganic materials, silica – polyols (ethylene-glycol – EG; 1,2 propane diol – 1,2PG; 1,3 propane diol – 1,3PG and glycerol – GL), were prepared by a sol-gel process starting from tetraethylorthosilicate (TEOS) and polyols, in acid catalysis. The resulting materials were studied by thermal analysis (in air and nitrogen), FTIR and solid state 29Si-NMR spectroscopy. These techniques evidenced the presence of polyols in the silica matrix both hydrogen bounded and chemically bounded in the silica network. The thermal analysis proves to be the most appropriate technique to evidence the organic chains linked in the matrix network and to follow the thermal evolution of the gels to the SiO2 matrix.

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Summary

Psychotropic drugs: desipramine, olanzapine and mitrazapine were chromatographed on cyanopropyl-silica and Diol-silica thin layers using various nonaqueous and aqueous eluents.

The best results were obtained with addition of ammonia to nonaqueous eluent on both adsorbents. On the basis of the optimization, systems for extraction from human plasma and quantitative determination of investigated drugs were selected.

RP18 encaped SPE columns conditioned and pre-eluted with acetonitrile:water:ammonium buffer at pH 8.6 (5:5:2) and eluted with methanol:water (9:1) containing 2% acetic acid were used for sample preparation with high recoveries of all investigated drugs. Diol and CN plates with mixture of 15% methanol in diisopropyl ether + 1% ammonia were used for quantitative analysis by a calibration curve method.

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The objective of this study was the use of solid-phase extraction and planar chromatography with diode-array detection for analysis of dyes in beverages. The dyes were chromatographed in normalphase systems on silica, diol, cyanopropyl, and aminopropyl layers and in reversed-phase systems on cyanopropyl, diol, aminopropyl, and octadecyl silica wettable with water. Reversed-phase chromatography was performed with different mobile phase modifiers (tetrahydrofuran, dioxane, methanol, acetonitrile, and acetone) at different concentrations, containing different amines, cationic and anionic ion-pair reagents, buffers, and ammonia, again at different concentrations. On the basis of the results obtained it was possible to choose the best systems for analysis of tartrazine and sunset yellow in beverages. Identification of the analytes was confirmed by the comparison of UV spectra of drink components with those of standards, by use of the diode-array densitometer.

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Conditions have been established for separation of six fibrate drugs by automatic multiple development (AMD). The best system was selected by using results from systematic investigation of relationships between R M values and mobile-phase composition. The drugs were separated by multiple development on diol plates with tetrahydrofuran-hexane as mobile phase. The results of multiple development analysis predicted by computer simulation were compared with experimental results.

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Relationships between R M values and mobile phase composition have been determined for the six antihyperlipidemic agents-bezafibrate, ciprofibrate, clofibrate, clofibric acid, fenofibrate, and gemfibrozil. The drugs were separated on silica gel, CN, and Diol plates using mobile phases containing n -hexane as weakly polar diluent and five polar modifiers: acetone, dioxane, ethyl methyl ketone, ethyl acetate, and tetrahydrofuran. The optimum mobile phases were also investigated on alumina, NH 2 , and polyamide phases for comparison. The linearity of relationships between R M and modifier volume fraction, molar fraction, and logarithm of molar fraction was calculated. Plates were developed in horizontal chambers, visualized under UV irradiation at λ = 254 nm, and scanned with a densitometer in the multi-wavelength scan mode. Most results fitted the Snyder-Soczewinski equation with r > 0.9; for approximately half r > 0.99. Separation of all the drugs was achieved on Diol plates with mobile phases containing 20–30% of each modifier in n -hexane, and with hexane-acetone, 9 + 1, on CN plates. Five drugs were separated using the same mobile phases on silica gel. The best separation was obtained on Diol plates with tetrahydrofuran-hexane, 2 + 8, as mobile phase.

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