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Journal of Thermal Analysis and Calorimetry
Authors: Katarína Győryová, J. Chomič, Erika Szunyogová, Lenka Piknová, V. Zeleňák, and Zuzana Vargová

Abstract  

Three new complex compounds of general formula Zn{4-ClC6H3-2-(OH)COO}2L 2nH2O (where L=thiourea (tu), nicotinamide (nam), caffeine (caf), n=2,3), were prepared and characterized by chemical analysis, IR spectroscopy and their thermal properties were studied by TG/DTG, DTA methods. It was found that the thermal decomposition of hydrated compounds starts with the release of water molecules. During the thermal decomposition of anhydrous compounds the release of organic ligands take place followed by the decomposition of salicylate anion. Zinc oxide was found as the final product of the thermal decomposition performed up to 650C. RTG powder diffraction method, IR spectra and chemical analysis were used for the determination of products of the thermal decomposition.

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Summary Three new complex compounds of general formula Zn[5-ClC6H3-2-(OH)COO]2·L2·nH2O (where L=thiourea (tu), nicotinamide (nam), caffeine (caf), n=2-5), were prepared and characterized by chemical analysis, IR spectroscopy and their thermal properties were studied by TG/DTG, DTA methods. It was found that the thermal decomposition of hydrated compounds starts with the release of water molecules. During the thermal decomposition of anhydrous compounds the release of organic ligands take place followed by the decomposition of salicylate anion. Zinc oxide was found as the final product of the thermal decomposition performed up to 800°C. RTG powder diffraction method, IR spectra and chemical analysis were used for the determination of products of the thermal decomposition.

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Summary  

This paper describes an analytical method using a nuclear-related technique for the detection of forbidden doping substances in the urine of race horses. The proposed method, adapted from the Méthode Alcaline Sur C-18 developed by the French Laboratoire de Contrôle Antidopage, is based on gas chromatography separation followed by mass spectrometry (GC-MS). The method was validated for caffeine, identified as the most frequent doping substance in the Brazilian horseracing activity. This validation is also a major requirement to achieve ISO/IEC 17025 laboratory accreditation. The validation has led to several metrological challenges because the decisions are largely based on qualitative results (“false-positive” and/or “false-negative”) and the degree of accuracy, as well as the traceability had to be determined in the absence of certified matrix reference materials.

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A new process, bilateral band compression has been used to increase the sensitivity of detection of minor components of a mixture. After band-shaped sample application, fully off-line OPLC separation, and drying, the separated bands were compressed bilaterally, in parallel, perpendicular to the direction of development, by use of a strong eluent and capillary driven chromatography. To introduce the eluent on to the layer for band compression a simple manual tool equipped with parallel foam strips was constructed. A mixture of xanthine standards (caffeine 0.998 mg mL −1 , theophylline 1 μg mL −1 , and theobromine 1 μg mL −1 ) and black tea leaf extract were used to test the efficiency of detection after bilateral band compression. After band compression 20 ng theophylline and theobromine could be detected by densitometry in the xanthine standard mixture at a loading of 20 μg/10 mm whereas they were not visible in the original, uncompressed chromatogram.

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Summary

A rapid and sensitive high-performance liquid chromatographic method has been developed and validated for the simultaneous determination and quantification of cephalosporins (cefpirome, cefaclor, ceftazidime, and cephradine) in pharmaceutical formulations. Separation was achieved in the presence of caffeine as internal standard on a Mediterranea C18 (5 μm, 25 × 0.46 mm) column. The mobile phase was composed of methanol and water (30:70), which was pumped at a flow rate of 1 mL min-1. Effluents were monitored at 265 nm. The assay was linear in the concentration range of 0.5–50 μg mL−1, with the correlation coefficient (r 2) greater than 0.9998. The intra-day and inter-day coefficients of variation (CV %) were less than 4% at different concentrations.

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Abstract  

Isothermal titration calorimetry (ITC) has been used to develop a method to construct the solid-liquid equilibrium line in ternary systems containing the solute to precipitate and an aqueous mixed solvent. The method consists in measuring the heat of dissolution of a solid component (the solute) during successive additions of the liquid solvent. The cumulated heat, resulting from the successive heat peaks obtained for the different injections of known volumes of solvent, plotted vs. the ratio of the numbers of moles n solvent /n solute is represented by two nearly straight lines. The intersection of the two lines gives the solubility limit and the corresponding enthalpy of dissolution of the solute in the solvent. Phase diagrams have been established at 303.15 K in binary mixed solvents ethanol-water over the whole concentration range for four components of pharmaceutical interest, namely: caffeine, nicotinamide, nicotinic acid and salicylic acid.

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A modified QuEChERS method was developed and validated for determination of pesticide multi-residues in green tea by liquid chromatography tandem mass spectrometry. Lead acetate was first time used together with primary secondary amine and graphite carbon black to eliminate tannin, caffeine, and other pigments in tea and thus reduced the matrix effects. The method was compared to the original QuEChERS method as well as A.O.A.C. QuEChERS method. For accurate quantification, the matrix matched calibration technique was used. The method showed good performance in the concentration range from 0.01 to 1 mg kg–1. All pesticides could be quantified at and lower than 0.01 mg kg–1. Recoveries were from 70 to 120% and repeatabilities were <15% RSD depending on the compounds.

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Bending, twitching and quivering are different types of tentacle movements observed during olfactory orientation of the snail. Three recently discovered special muscles, spanning along the length of superior tentacles from the tip to the base, seem to be responsible for the execution of these movements. In this study we have investigated the ultrastructure, contractile properties and protein composition of these muscles. Our ultrastructural studies show that smooth muscle fibers are loosely embedded in a collagen matrix and they are coupled with long sarcolemma protrusions. The muscle fibers apparently lack organized SR and transverse tubular system. Instead subsarcolemmal vesicles and mitochondria have been shown to be possible Ca2+ pools for contraction. It was shown that external Ca2+ is required for contraction elicited by high (40 mM) K+ or 10−4 M ACh. Caffeine (5 mM) induced contraction in Ca2+-free solution suggesting the presence of a substantial intracellular Ca2+ pool. High-resolution electrophoretic analysis of columellar and tentacular muscles did not reveal differences in major contractile proteins, such as actin, myosin and paramyosin. Differences were observed however in several bands representing presumably regulatory enzymes. It is concluded that, the ultrastructural, biochemical and contractile properties of the string muscles support their special physiological function.

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The newly developed experimental OPLC separation unit 100 (OSU 100) has been used for fully on-line multiple hyphenation using the one-channel flowing eluent wall (FEW) arrangement at the inlet. OSU 100-UV and OSU 100-DAD-ESI-MS with manual injector or autosampler were used to test the connected systems (OPLC-UV; OPLC-DAD-ESI-MS), using xanthine standards (caffeine, theophylline, theobromine) and green tea leaf extract as model compounds. The mobile phase chloroform-trifluoroacetic acid-acetonitrile-methanol, 76:4:6.67:13.33 ( v / v ) is suitable for rapid and selective separation, DAD, and ESI-MS of xanthines. The detection sensitivity of OPLC-UV or OPLC-DAD was increased by hyphenation with ESI-MS coupled in series. In contrast with DAD, the extracted ion chromatogram ( m / z = 181.1 Da) after background subtraction yields readily measurable peaks from the small amounts of theophylline and theobromine in tea leaf extract. Analysis of xanthines was achieved within 10 min with less than 2 mL mobile phase. Owing to the openable adsorbent layer in OPLC the bed conditions can, moreover, be checked off-line after single or multiple fully online separations.

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Summary

A simple, rapid, and sensitive high-performance liquid chromatography method was developed and validated for the simultaneous determination and quantification of fusidic acid and steroids (prednisone, betamethasone valerate, hydrocortisone acetate, and dexamethasone sodium) from bulk drugs and human plasma. A RP-HPLC, operated at ambient temperature, was equipped with a UV detector for monitoring the effluents at 235 nm. The mobile phase consisted of methanol, acetonitrile, and 0.05 M phosphoric acid (10:60:30, v/v/v), and separation was achieved on a Medeterrane, C18 (5 μm, 12.5 × 0.46 mm) column at a flow rate of 1.7 mL min−1. Calibration curves were linear over concentration range 0.625–10 μg mL−1 with correlation coefficient (r 2) greater than 0.9999. The coefficient of variation (CV) and relative error (RE) for intra- and interassay were <2% and <1%, respectively. Interference of other already administered common medicaments, such as aspirin, paracetamol, caffeine, nicotine, and other plasma components, were not found.

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