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We have investigated the use of pressurized planar electrochromatography (PPEC) and planar chromatography (TLC) for reversed-phase separation of a mixture of acetylsalicylic acid, caffeine, and acetaminophen. The mixture was separated on C18 plates; the mobile phase was prepared from acetonitrile (ACN), buffer, and bidistilled water. The effects of operating conditions such as mobile phase composition, type of the stationary phase, and mobile phase buffer pH on migration distance, separation selectivity, and separation time in TLC and PPEC were compared. The results showed that pressurized planar electrochromatography of these drugs is characterized by faster separation, better performance, and different separation selectivity. In conclusion, PPEC is a very promising mode for future application in pharmaceutical analysis.

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Summary

We present a planar chromatographic separation method for the compounds caffeine, artemisinin, and equol, separated on high-performance thin-layer chromatography (HPTLC) silica gel plates. As solvents for separation, methyl t-butyl ether and cyclohexane (1:1, V/V) have been used for equol, cyclohexane and ethyl acetate (7:3, V/V) for artemisinin, and ethyl acetate and acetone (7:3, V/V) for caffeine. After separation, the plate was scanned with a very specific time of flight-direct analysis in real time-mass spectrometry (TOF-DART-MS) system using the (M + 1)+ signals of equol, artemisinin, and caffeine. The (M + 1) peak of artemisinin at 283.13 m/z is clearly detectable, which is the proof that DART-MS is applicable for the quantitative determination of rather instable molecules. The planar set-up of DART source, HPTLC plate and detector inlet in a line showed higher sensitivities compared to desorption at an angle. The optimal detector voltage increases with the molar mass of the analyte, thus an individual determination of optimal detector voltage setting for the different analyte is recommended to achieve the best possible measurement conditions. In conclusion, DART-MS detection in combination with an HPTLC separation allows very specific quantification of all three compounds.

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Journal of Thermal Analysis and Calorimetry
Authors: Lenka Findoráková, Katarína Győryová, Jana Kovářová, V. Balek, F. Nour El-Dien, and L. Halás

Abstract  

Novel zinc(II) complex compounds of general formula Zn(C6H5COO)2·L2 (where L=caffeine (caf) and urea (u)) were synthesized and characterized by elemental analysis and IR spectroscopy. The thermal behaviour of the complexes was studied during heating in air by thermogravimetry. It was found that the thermal decomposition of the anhydrous Zn(II) benzoate compounds with bioactive ligands was initiated by the release of organic ligands at various temperatures. On further heating of the compounds up to 400°C the thermal degradation of the benzoate anions took place. Zinc oxide was found as the final product of the thermal decomposition of all zinc(II) benzoate complex compounds heated to 600°C. Results of elemental analysis, infrared spectroscopy, mass spectroscopy and thermogravimetry are presented.

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Caffeine has been found to display a low-temperatureβ- and a high-temperatureα-modification. By quantitative DTA the following data were determined: transformation temperature 141±2°; enthalpy of transition 4.03±0.1 kJ·mole−1; enthalpy of fusion 21.6±0.5 kJ·mole−1; molar heat capacity
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\begin{array}{*{20}c} {{\vartheta \mathord{\left/ {\vphantom {\vartheta {^\circ C}}} \right. \kern-\nulldelimiterspace} {^\circ C}}} & {100(\beta )} & {100(\alpha )} & {150(\alpha )} & {100(\alpha )} \\ {{{C^\circ _\mathfrak{p} } \mathord{\left/ {\vphantom {{C^\circ _\mathfrak{p} } {J \cdot K^{ - 1} \cdot mole^{ - 1} }}} \right. \kern-\nulldelimiterspace} {J \cdot K^{ - 1} \cdot mole^{ - 1} }}} & {271 \pm 9} & {287 \pm 10} & {309 \pm 11} & {338 \pm 10} \\ \end{array}$$ \end{document}
in good accord with drop-calorimetric data. For the constants of the equation log (p/Pa)=−A/T+B, static vapour pressure measurements on liquid and solidα-caffeine, and effusion measurements on solidβ-caffeine yielded:
\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $$\begin{array}{*{20}c} {A = 3918 \pm 37; 5223 \pm 28; 5781 \pm 35K^{ - 1} } \\ {B = 11.143 \pm 0.072; 13.697 \pm 0.057; 15.031 \pm 0.113} \\ \end{array}$$ \end{document}
. The evaporation coefficient ofβ-caffeine is 0.17±0.03.
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, and minimize the development of resistance to antibiotics [ 2 ]. The fixed-dose combination of paracetamol (PCM) and caffeine (CF) is primarily employed in conditions such as a migraine headache [ 4 ], which is a chronic and common disorder

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Coffee, due to its common consumption, is one of the main sources of polyphenols in human diet. Coffee species and coffee-related products differ in composition and content of main components, such as chlorogenic acid and caffeine. Chemical and biological fingerprints of various Coffea arabica L. extracts were obtained in order to check and compare their antibacterial and antioxidant properties. The antibacterial activity of green and roasted coffee seeds and pomace was evaluated against Bacillus subtilis using thin-layer chromatography (TLC)-direct bioautography. TLC-2,2-diphenyl-1-picrylhydrazyl (DPPH) test was used to determine antioxidant properties of the afore-mentioned extracts. Furthermore, different solvents and several extraction methods such as simple maceration, maceration under stirring, and ultrasonic accelerated extraction were tested. The most efficient method of extraction of caffeine and chlorogenic acid was chosen based on quantitative TLC analysis. Additionally, these two main components of coffee were quantitatively determined in commercial products of green coffee.

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Abstract  

Micelle/water partition coefficients were obtained for procaine hydrochloride using micellar liquid chromatography (MLC) to illustrate the potential application of this technique to compounds of pharmaceutical interest. Experiments were conducted over a temperature range which led to calculation of a Gibbs free energy, enthalpy and entropy of transfer for procaine hydrochloride. Successful application of this technique was confirmed using a second compound over a range of temperatures, namely caffeine. Overall, this work confirms that MLC can be used to determine precise and accurate partition coefficients that possibly more closely mimic biological membranes than traditional in vitro systems, namely octanol/water.

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We report a new combination of overpressured-layer chromatography (OPLC) with near-infrared (NIR) spectroscopy for pharmaceutical analysis. Different pharmaceutical preparations containing caffeine, paracetamol, and acetylsalicylic acid as model compounds were separated by OPLC. The band density in the solid phase after OPLC was suitable for study of the separated components directly on the layer by NIR spectroscopy.We have demonstrated the applicability of rapid OPLC separation combined with UV densitometry and NIR spectroscopy for both qualitative and quantitative analysis. This OPLC-UV-NIR technique is thus suitable for rapid, nondestructive investigation of multicomponent pharmaceutical preparations and enables a different type of pharmaceutical analysis, e.g. starting-material tests, in-process control, end-product control, stability testing, etc. Another benefit of this newly developed combination of rapid off-line techniques is the possibility of simultaneous collection of qualitative and quantitative chromatographic and spectral information.

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Abstract  

Thermal behaviours of three zinc(II) benzoate complex compounds (two new with caffeine and urea), namely Zn(C6H5COO)2, Zn(C6H5COO)2·caf2, Zn(C6H5COO)2·u2, were characterized by using thermogravimetry (TG/DTG), differential thermal analysis (DTA), evolved gas analysis (EGA) with mass spectrometry (MS) detection and emanation thermal analysis (ETA). Temperature intervals of the stability of the compounds as well as the mechanisms of their thermal degradation were determined. From TG and DTA results it followed that the oxidative degradation of urea with CO2 or caffeine with CO2 from the investigated Zn(II) benzoate complex compounds takes place as the first step of their thermal degradation. In the second step of thermal degradation diphenylketone was release. The evolved gas analysis has been used to determine intermediate products of thermal degradation and temperature ranges of their evolution from the samples. From the emanation thermal analysis results it followed that changes in the surface area and microstructure accompanied the thermal degradation of the compounds studied and that no microstructure changes can be supposed in the resulting zinc oxide on heating from 650 up to 850 °C.

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A simple, rapid, cost-effective, and eco-friendly method is proposed for the simultaneous determination of some common over-the-counter drugs (aspirin, paracetamol, and caffeine [APC]) in saliva and pharmaceutical formulations based on the coupling of ultrasound-assisted emulsification microextraction (USEME) with thin-layer chromatography (TLC)‒image-processing analysis. The process involves the rapid injection of 65 μL of chloroform in diluted saliva samples (2 mL) followed by ultrasonication, which results in the formation of an emulsion. This solution is centrifuged, and 20 μL was spotted on TLC plate which was allowed to develop in mobile phase of ethyl acetate and acetic acid (95:5, v/v). The developed TLC plate was photographed, and the spots of APC were quantified by using the freely available ImageJ software (National Institute of Health [NIH], Bethesda, MD, USA). Factors which can influence the yield of USEME were screened using 27‒4 Placket–Burman design (PBD), and significant factors were optimized using central composite design (CCD). The recoveries and detection limits for all the analytes were found to be in the range of 89.2–94.1% and 0.007–0.012 mg spot−1, respectively. The assay was found to be linear in the range of 0.04–0.2 mg spot−1 with correlation of coefficient of 0.990–0.994. Intra- and inter-day precision for the assay were found to be in the range of 3.12–4.93% and 5.66–8.61%, respectively. The developed method does not require any special instrument and handling skill for the quantitative analysis of APC in saliva and pharmaceutical formulations.

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