Use of SPE—TLC for Quality Control of Rhodiola rosea Extracts

SPE and TLC have been used for qualitative and quantitative analysis of salidroside, rosavin, rosarin, and rosin in commercially available dry extracts from Rhodiola rosea roots. The best separation of all the compounds was achieved on silica gel TLC plates with ethyl acetate—methanol—water, 77 + 13 + 10 (v/v), as mobile phase. UV detection was performed at λ = 215 nm for salidroside and at λ= 245 nm for the rosavins (rosavin, rosarin, and rosin). Detection limits for salidroside and the rosavins were 90 ng and 60 ng per spot, respectively. Results from quantitative analysis confirmed the manufacturer’s declaration of the amounts of salidroside and the rosavins in the extracts.

     

Defect concentration in Ti-substituted YIG from TG curves

The article discusses theory and experiment about the measurement of defect concentration in Ti-substituted yttrium iron garnet by means of thermogravimetry techniques. The two possible cases arising from oxygen interchange with atmosphere, oxygen vacancies and interstitial cations, may be analyzed quantitatively from the derived expressions. The possibility of another type of defects being present in the samples, not associated to oxygen evolution, is not excluded. Measurements were carried out in air and CO₂ for different Ti contents. The substitution tends to increase slightly the defect parameter θ in YIG, while a CO₂ reducing atmosphere is much more effective than the Ti substitution for increasing θ. Calculations for a given single-phased sample sintered in air show two possibilities: a deficit of one oxygen atom for every 2.5 unit cells of 96 atoms, or one excess cation for every 3.5 cells. Other samples show very similar results. The accuracy involved in the measurements is about 2–3%.     

The Role of γ -Aminopropyltriethoxysilane (γ -APS) on Thermal Stability of TEOS-PDMS Ormosils

The degradation process of TEOS-PDMS Ormosils containing different amounts of γ -APS has been studied by means of DTA, TG, FTIR and ²⁹Si-NMR measurements. It has been found that the amount of γ -APS improved the thermal properties of Ormosil materials. The increase in γ -APS content causes the increment on the decomposition temperatures and activation energies of the studied Ormosils. These results have been attributed to the favourable effect of γ -APS in the copolymerisation reaction between TEOS and PDMS molecules. ²⁹Si-NMR analyses have shown that the incorporation of γ -APS increases the concentration of D(Q) units in the Ormosil structure, i.e., increases the number of TEOS molecules bonded to PDMS ones. Initial decomposition temperature (IDT), temperature of maximum weight loss rate (T_max), integral procedure decomposition temperature (IPDT) and activation energy values (E) were calculated from different equations which described the degradation of these materials. Addition of 10 wt% γ -APS produced an increase of 63^∘C in the IDT and of 115 and 110^∘C, respectively, for T_max and IPDT (up to 478 and 610^∘C) compared to the free γ -APS Ormosil. Activation energy values also rise up to 69.4 kJ⋅ mol⁻¹ by introducing 10 wt% of γ -APS.     

Evaluation of a purge-and-trap injection system for capillary gas chromatography-microwave induced plasma-atomic emission spectrometry for the determination of volatile selenium compounds in water

A method is presented for the selective determination of the volatile selenium species dimethylselenide and dimethyldiselenide, using a commercially available purge-and-trap injection system coupled to capillary gas chromatography-microwave induced plasma-atomic emission spectrometry. The efficiency of the purging step was evaluated and the parameters affecting the purge and trap processes were optimized. The method was applied to the determination of volatile selenium compounds in lake water. Relative detection limits of 2ng/l for dimethylselenide and dimethyldiselenide, corresponding to an absolute detection limit of 10 pg, were achieved.     

Conductance in homomorphous solvents: Tetrabutylammonium salts and alkali picrates in butyrolactone-sulfolane mixtures

Conductance measurements are reported for LiPi, NaPi, KPi, RbPi, CsPi, Bu₄NPi, Bu₄NBr, Bu₄NClO₄, Bu₄NNO₃, and Bu₄NBBu₄ at 25°C in -butyrolactone-sulfolane mixtures. In these mixtures of solvents that are practically homomorphous, isodielectic and with comparable dipole moments, the ion pair association and ionic mobilities of large ions conform to the expectations of the primitive model. Electrolytes containing lithium or sodium ions show anomalies indicating that other factors besides shape, dipole moment, and polarizability of the solvent molecules are involved in the association and transport processes of these ions.     

Study on the stability of noradrenaline and on the determination of its acidity constants

Noradrenaline is a catecholamine which has been largely recognised to play a very important role in biological systems. In view of the neurotransmitter's alleged importance, this work aimed at showing the influence of time on its spectral behaviour using different analytical methods and determining its acidity constants through spectrophotometric titration and by the so-called point-by-point analysis, where the samples are freshly prepared for each pH value investigated at the instant required. Because the catecholamines are light-sensitive and likely to react with the oxygen in the surrounding air, both methods used preclude its incidence onto the samples being analysed under the presence of a nitrogen atmosphere maintained over the solutions. The constants obtained through point-by-point analysis were log beta1 = 30.71+/-0.16, log beta2 = 22.00+/-0.15 and log beta3 = 11.69+/-0.16.     

Determination of six metals in galician red wines (in northwestern Spain) by capillary electrophoresis

A simple technique is described for the routine simultaneous capillary electrophoretic determination of 6 cations in wine. Separation was achieved on a fused silica capillary column with a UV-Cat-1, alpha-hydroxysobutyric acid and 18-crown-6-ether buffer at pH 4.5 and indirect UV detection at 214 nm. The content of magnesium, sodium, potassium, calcium, manganese, and lithium was determined. The method is quantitative, with recoveries in the 92-102% range, and linear over more than one order of magnitude. The precision is better than 2.5-3.4%. The method is sensible, with detection limits between 0.01 and 0.06 mg/L. Twenty-five red wines with a Certified Brand of Origin from Galicia (north-western Spain) were analyzed by the proposed method. Various wines showed very similar electrophoretic profiles, but significant quantitative differences were observed.     

Molybdenum(VI) and molybdenum(V) mononuclear and dinuclear complexes with 1,3-diphenyl-1,3-propanedione

Summary The synthesis and the dinuclear or mononuclear nature of several molybdenum(VI) and molybdenum(V) oxocomplexes derived from 1,3-diphenyl-1,3-propanedione (HLL) are described. These complexes were identified by i.r. and electronic spectra, magnetic susceptibility and analytical data, and are assigned the following formulae: [MoO₂(LL)₂], [Mo₂O₅(LL)₂], [Mo₂O₄(LL)₂], [MoOCl(LL)₂], [MoCl₂(LL)] and [MoO(OH)(LL)₂)]. The low magnetic moments of the dinuclear complexes are due, in part, to intramolecular interactions. The i.r. data show that the dionate is bound by two oxygen atoms forming a chelate six-membered ring.