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This research article describes a simple and sensitive thin-layer chromatographic (TLC)-densitometric method for simultaneous determination of guaifenesin (GUF) and pseudoephedrine HCl (PSH) in their binary mixtures and in the presence of guaifenesin impurity and related substance, guaiacol. The proposed chromatographic method has been developed using silica gel plates 60 F254 as a stationary phase with hexane-acetone-ethyl acetate-triethylamine-water (3:4:3:0.1:0.3, by volume) as a developing system followed by densitometric measurements at 208 (for pseudoephedrine HCl and guaifenesin) and 278 nm (for guaiacol). Experimental conditions have been optimized to get the desired separation and sensitivity. Calibration curves for the three studied components were constructed using polynomial equation which was superior to linear equation with respect to correlation coefficients and quantified ranges (14–25, 2–12, and 0.1–1.1 μg band−1) for pseudoephedrine HCl, guaifenesin and guaiacol, respectively. The developed method has been successfully applied for determination of pseudoephedrine HCl and guaifenesin in Triaminic® Chest Congestion syrup where no interference from syrup additives has been found. The data obtained from method validation confirm the specificity, sensitivity and accuracy of the method. Statistical comparison of the results obtained by the proposed chromatographic method and of those obtained by the reported chemometric technique showed no significant difference at 95% confidence limit.

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Nitration of acetyl guaiacol, one typical aromatic nitration, is highly exothermic and extremely fast. Better control and high efficiency can be achieved in the microreactor due to its enhanced mixing and heat transfer rates. In this study, nitration of acetyl guaiacol was carried out in a microreactor using nitric acid—acetic acid as nitrating agent. The nitration kinetics was first investigated, and a kinetic model was established and revealed good prediction of experimental results at higher temperatures. Effects of molar ratio of nitric acid—acetyl guaiacol, residence time, temperature, and nitric acid concentration on the reaction were studied in detail. Under optimized condition, 90.7% yield of desired product, 5-nitroguaiacol, was achieved with 40% of nitric acid concentration, nitric acid—acetyl guaiacol molar ratio of 2.6, reaction temperature of 120 °C, and residence time of 2 min. Compared to traditional batch reactor, microreactor showed the advantages of higher yield and selectivity, much shorter reaction time, and less use of nitric acid.

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Abstract  

Guiacol, i.e. o-hydroxyanisole, gives a distinct color reaction with U(VI) suitable for spectrophotometric determination of the metal. The complex formed in the reaction has an absorption maximum at 352 nm. Optimum pH for the color development ranges from 6.5 to 8.5. The molar absorptivity and Sandell's sensitivity of the method were found to be 3.75×103 l·mol–1·cm–1 and 0.063 g·cm–2, respectively. Many anions and cations do not interfere up to 100 ppm. The method has been made very specific by selective extraction of U(VI) with TBP from a mixture of different cations and anions in the presence of 60% NH4NO3 as salting out agent followed by developing the color in the non-aqueous phase by adding quaiacol in methanol at pH 6.5 to 8.5 An amount as low as 30 g of uranium (VI) per 10 ml of the solution could be satisfactorily determined with an RSD of ±2.0%. The method was applied to rock samples after U(VI) had been extracted from a sample solution into 25% TBP in hexane. Results obtained by the new method compare very well with those of conventional fluorimetric and radiometric assays. The features of the method include excellent precision, rapidity, good selectivity, and ease of performance.

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Abstract  

Eugenol is an allyl chain-substituted guaiacol in the biosynthesized phenylpropanoid compound class derived from Syzygium aromaticum L. and widely used in folk medicine. Nonetheless, its pharmacological use is limited by some problems, such as instability when exposed to light and high temperature. In order to enhance stability, the eugenol molecule was structurally modified, resulting in eugenyl acetate. The eugenyl acetate’s thermal behavior and crystal structure was then characterized by differential scanning calorimetry (DSC) and X-ray diffraction (XRD) and compared to a commercial sample.

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Abstract  

Thermogravimetry-mass spectrometry (TG-MS) was used to study the effect of the inorganic salts (NH4)2SO4 and (NH4)2HPO4, active substances of many commercial forest fire retardants, on the pyrolysis of Pinus halepensis needles and their main components (cellulose, lignin and extractives). These salts seemed to affect the pyrolysis of cellulose by increasing significantly the char residue, decreasing the pyrolysis temperature and changing the composition of the evolved gases, that is, increasing levoglucosenone and decreasing oxygen containing volatile products. (NH4)2SO4 seemed to have negligible effect on the pyrolysis of lignin, while (NH4)2HPO4 increased the char residue and decrease the relative contribution of guaiacols in the evolved gases. No effects of the inorganic salts on the extractives were observed. Finally, the inorganic salts seemed to affect the pyrolysis of pine-needles, mainly the cellulose component, but the effects were not as intense as in the pyrolysis of cellulose.

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Abstract  

The combined analytical methods of thermal analysis and mass spectrometry have been applied in form of a newly developed prototype of a thermogravimetry — single photon ionisation time-of-flight mass spectrometer coupling (TG-SPI-TOFMS) to investigate the molecular patterns of evolved gases from several biomass samples as well as a crude oil sample. Single photon ionization (SPI) was conducted by means of a novel electron beam pumped argon excimer lamp (EBEL) as photon source. With SPI-TOFMS various lignin decomposition products such as guaiacol, syringol and coniferyl alcohol could be monitored. Furthermore, SPI allows the detection of aliphatic hydrocarbons, mainly alkenes, carbonylic compounds such as acetone, and furan derivatives such as furfuryl alcohol and hydroxymethylfurfural. More alkaline biomass such as coarse colza meal show intense signals from nitrogen containing substances such as (iso-)propylamine and pyrrole. Thermal degradation of crude oil takes place in two steps, evaporation of volatile components and pyrolysis of larger molecular structures at higher temperatures. Due to the soft ionisation, homologue rows of alkanes and alkenes could be detected on basis of their molecular ions. The obtained information from the thermal analysis/photo ionisation mass spectrometry experiments can be drawn on in comparison to the investigation of the primary products from flash pyrolysis of biomass for production of biofuels and chemicals.

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Bio-oil is produced by biomass pyrolysis. It contains hundreds of chemical compounds including alkanes, aromatic hydrocarbons, esters, ethers, ketones, aldehydes, acids, alcohols, and phenols. Phenols are compounds of increasing interest; they can be used as feedstock in many industrial applications such as the production of fuel additives, chemical synthesis, or as food antioxidants. Therefore, the valorization of phenols stemming from bio-oil can be an appropriated alternative to reduce the dependence on petro-based phenols in the chemical industry. The most important phenols in biooil from agricultural wastes are phenol, guaiacol, cresols, syringol, and xylenol. These compounds were separated by silica gel column chromatography technique, using 3 different solvents: a dichloromethane—acetone mixture, ethyl acetate, and methanol. Column elution was followed by thin-layer chromatography (TLC). Phenolic fraction was obtained and not individual phenols. This fraction was analyzed using gas chromatography–flame ionization detector (GC—FID) and gas chromatography—gas chromatography—mass spectrometry (GC—MS) with a DB-1701 column, and it was quantified using the relative response factor. Dichloromethane—acetone mixture was the best eluent to obtain this phenolic fraction, specifically during the first three elution steps.

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Journal of Thermal Analysis and Calorimetry
Authors:
F. J. González-Vila
,
F. Martin
,
C. Sáiz-Jiménez
, and
H. H. Nimz

Thermofractography (TF) has been applied to humic and fulvic acids from four different soil types. Among the thermal products, 3,5-dihydroxybenzoic acid, catechol, 5-hydroxymethylfurfural, vanillin, phenol, furfural, guaiacol and indole were identified. These are typical fragments from lignins, microbial polyphenols, polysaccharides and proteins.

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Journal of Thermal Analysis and Calorimetry
Authors:
Teresa Sebio-Puñal
,
Salvador Naya
,
Jorge López-Beceiro
,
Javier Tarrío-Saavedra
, and
Ramón Artiaga

analyzed. Guaiacol was identified along some degradation steps in all cases. This aromatic compound cannot be originated from cellulose or hemicellulose and is a typical degradation product of lignin. It means that a part of the lignins remained with

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of catechol with dimethyl carbonate. Part II. Selective synthesis of guaiacol over alumina loaded with alkali hydroxide . Appl Catal A Gen 166 : 425 – 430 10.1016/S0926-860X(97)00288-3 . 21

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