Calibration of titration calorimeters is an ongoing problem, particularly with calorimeters with reaction vessel volumes < 10 mL in which an electrical calibration heater is positioned outside the ...calorimetric vessel. Consequently, a chemical reaction with a known enthalpy change must be used to accurately calibrate these calorimeters. This work proposes the use of standard solutions of potassium acid phthalate (KHP) titrated into solutions of excess sodium hydroxide (NaOH) or excess tris(hydroxymethyl)aminomethane (TRIS) as standard reactions to determine the collective accuracy of the relevant variables in a determination of the molar enthalpy change for a reaction. KHP is readily available in high purity, weighable for easy preparation of solutions with accurately known concentrations, stable in solution, not compromised by side reactions with common contaminants such as atmospheric CO
2
, and non-corrosive to materials used in calorimeter construction. Molar enthalpy changes for these reactions were calculated from 0 to 60 °C from reliable literature data for the p
K
a
of KHP, the molar enthalpy change for protonation of TRIS, and the molar enthalpy change for ionization of water. The feasibility of using these reactions as enthalpic standards was tested in several calorimeters; a 50 mL CSC 4300, a 185 μL NanoITC, a 1.4 mL VP-ITC, and a TAM III with 1 mL reaction vessels. The results from the 50 mL CSC 4300, which was accurately calibrated with an electric heater, verified the accuracy of the calculated standard values for the molar enthalpy changes of the proposed reactions.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Virgin olive oil represents the main fat source of the diet in the Mediterranean countries where the production of olive oil is concentrated. It has an important role in cardiovascular disease ...protection, because of its high bioactive components. The healthful effects are attributed to olive oil's high unsaturated fatty acids content which greatly varies in quantity according to the impact of geographic origin. This research aims to characterize local Syrian olive oils by determining their fatty acid composition, and compare the results with fatty acid composition in olive oil samples obtained from some exterior regions of the Mediterranean basin which are famous for olive cultivation. Twelve olive oil samples produced in four agricultural areas (coastal region, northern region, interior region, and southern region), available in local Syrian market were analyzed for its fatty acid composition by GC-MS, and the results were compared with fatty acid composition of six samples from several exterior regions ( Lebanon, Spain, and Greece). All the values of the fatty acid compositions are in compliance with the regulations of the International Olive Oil Council (IOC) and Codex Alimentarius. Among the evaluated oils the highest percentages of total saturated fatty acids were found in the Spanish samples and the southern Syrian oil samples that showed above of (18%) of saturated fatty acids, The highest percentage of MUFA and MUFA/PUFA index were found in the Greek oil sample up to(82%) and (29.09) respectively. Also, the results showed that the highest percentage of Linoleic acid (omega 6) was found in the southern Syrian oil samples up to (14%). In addition, the northern Syrian samples, in the same way the Greek oil samples showed the highest total unsaturated fatty acids percentages up to(85%), the highest Oleic acid percentages up to (80%), which makes them the most suitable for consumption.
...the formation of trans fatty acid in oils during heating to several temperatures (180°C, 200°C, 210°C, 220°C) was examined, then the effect of repeated frying process during frying at 180°C, fat ...and moisture content in fried food, and the effect of pressure cooker on the fatty acid composition of the oils and the oils extracted from the fried food samples were investigated by gas chromatography (G.C) equipped with a Mass spectroscopy (MS). Many chemical reactions such as hydrolysis and oxidative or thermal degradation occur in the structure of the oil. Because of some physiochemical changes, new compounds arise in the oil depending on the frying conditions such as heating temperature, heating period, pressure, and the content of fat and moisture in food. According to several studies, The majority of Elaidic acid can be found in partially hydrogenated oils, shortening, margarine, cookies, snack food, and fried food as a result of heat treatments such as deodorization, cooking, frying depending on different parameters such as temperature and length of treatment (10-12) In contrast to the effect of cis and essential fatty acids that have significant benefits in human body(13,14), high contents of trans fatty acid in foods are of concern for human health, due to their ability to promote several chronic diseases such as coronary heart disease, insulin resistance and allergic reactions. Gas chromatography (GC) equipped with a Mass spectroscopy (MS) was used for the specific analysis of the trans fatty acids in the extract Samples: For the present study, three kinds of Syrian edible oils (corn oil, sunflower oil, and soybean oil) produced in Syria, were collected from local supermarkets.
Taurine has many physiological functions as an antioxidant, neurotransmitter, toxinicide, modulation of the levels of intracellular ions (e.g. Ca+, K+, Na+), membrane stabilization, osmosis and in ...conjugation of bile acids and plays an important role in prenatal development especially in neural development. ...some energy drinks contain taurine in high levels between 800-4000 ppm and this is greater than the highest estimated intake of 400 mg/day from naturally occurring taurine in diets. Because of the consumption of energy drinks which contain taurine in high levels, and increasing of the cases with undesired side effects1, a simple new analytical method has been developed to determine the taurine in energy drinks. Taurine is in fact an amino sulphonic acid and it doesn't contain a carboxy group, therefore it doesn't have the same structure of known amino acids (NH2-R-COOH)8. Since taurine doesn't have a chromophore group and it shows maximum absorption at 284 nm using water as a solvent, ninhydrin was used to form a stable colored complex with taurine, which is the most popular reagent to detect aminoacids. ...when the reaction has applied on samples, the detected amount of taurine was insignificant. ...extraction procedure has been developed to improve the recovery and obtain precise results which express about the correct concentration in samples.
Chromatographic separation was conducted in the reversed phase operating mode, with a mobile phase consists of aqueous solution contains chiral selector Mβ-CD (1.5 g/l)/methanol with the volumetric ...ratio of 86:14 respectively , (aqueous solution :add to one liter of HPLC water 3.3 ml TEA the adjust the pH on 3.1 using glacial acetic acid), The final pH value of mobile phase was adjusted by using glacial acetic acid. The measurements were carried out in an isocratic elution mode at ambient temperature with a flow rate of 0.5 mL/min, an injection volume of 20 pL and UV detection at 274 nm. The most suitable mobile phase composition for enantiomeric resolution of metoprolol tartrate is (aqueous solution :add to one liter of HPLC water 3.3 ml TEA the adjust the pH on 3.1 using glacial acetic acid) 86%: methanol 16%) and the other conditions are (M-ßCD 1.5 g/l ,pH of 3.1, flow rate 0.5 ml/min, detection wavelength at 274nm, at room temperature) as shown in table 1. Tables 3 shows the effect on the USP resolution(Rs) of variation in final pH value of mobile phase and the other conditions are (M -ß-CD 1.5 g/l, flow rate 0.5 ml/min, detection wavelength at 274nm, at room temperature).
The reported inconsistencies between calorimetry and the van't Hoff equation hinder the utility of thermodynamics in pharmaceutical research. In ligand binding or adsorption assays, it is believed ...that the van't Hoff equation falls short because of the lack of stoichiometric treatment in the equilibrium constant. A new modified Langmuir-Like equation that accounts for the stoichiometry of solute adsorption and solvent displacement is proposed in this work. The performance of the model was evaluated by studying the adsorption of phenobarbital from aqueous solutions by commercial activated carbon. The amount of water occupying the adsorption sites was estimated by graphical analysis of the 'knee point' of water-vapor adsorption isotherms and was found to correlate well with the relative percentage of hydroxyl and carbonyl surface groups. It was found that one phenobarbital molecule displaces 2-6 water molecules from the adsorption site. It is shown that adsorption enthalpy was not affected by the adjustment for stoichiometry, supporting the notion that the van't Hoff enthalpy is intrinsic and is independent of the stoichiometry of solvent displacement in Langmuir-based binding. The widely reported disparities between the van't Hoff and calorimetric enthalpies are unlikely to be from a stoichiometric origin.
The reported inconsistencies between the van't Hoff equation and calorimetry hinder the utility of thermodynamics in biochemical and pharmaceutical research. A novel thermodynamic approach is ...developed herein for ligand adsorption with a focus on the interpretation of calorimetric data in the presence of concurrent proton exchange reactions. Such exchange reactions typically result in a pH-dependence of calorimetric measurements that obscures intrinsic binding enthalpies. It is shown that for the adsorption of phenobarbital to activated carbon, the measured calorimetric enthalpy is a result of three linked acid/base equilibria. A model was established to predict the intrinsic binding enthalpy using 1) the adsorbate's pKa and 2) the adsorbate's enthalpy of protonation. The observed calorimetric enthalpy of binding exhibited both pH and buffer-dependence and was between -5 and -42 kJ/mol. Meanwhile, the predicted intrinsic enthalpy (-25.1 kJ/mol) of binding was in excellent agreement with the measured intrinsic enthalpy (-25.6 kJ/mol). Corrections to the observed calorimetric enthalpies allowed comparisons with enthalpies obtained from the van't Hoff method. It is shown that the predicted intrinsic calorimetric enthalpy agrees well with the van't Hoff enthalpies in instances where observed enthalpies significantly deviated. This treatment is general and is not specific to phenobarbital or activated carbon.
This paper reports a rapid reversed-phase high-performance liquid chromatography (RP-HPLC) method for the determination of seven volatile N-nitrosamines namely N-nitrosodimethylamine (NDMA), ...N-nitrosomethylethylamine (NMEA), N-nitrosodiethylamine (NDEA), N-nitrosodiproylamine (NDPA), N-nitrosodi butylamine (NDBA), N-nitrosopiperidine (NPIP) and N-nitrosopyrrolidine (NPYR) for monitoring food safety. A strategic experimental approach was implemented for the method development. The desired chromatographic separation was achieved on a Symmetry C18 column using gradient elution. The optimized mobile phase consisted of the 10 mM ammonium hydroxide pH = 8.9 and acetonitrile. The eluted compounds were monitored at 231 nm wavelength using spectrophotometric detector. The developed method separated seven compounds from each other within a run time of 10 minutes. The method is effective for the determination of presence of these carcinogenic compounds. The average extraction recovery of seven nitrosamines was found 84.5%; the precision of method was found less than 2.7% and accuracy was found between 95%-102.5%. The assay could be applied in food monitoring safety.
In this study, various fast food samples, including raw meat, cured meat, grilled meat, fried meat, smoked meat and canned meat products, were analyzed for the determination of the seven volatile ...N-nitrosamines. The samples were treated with an aqueous sodium hydroxide by autoclaving at 121 degree Celsius for 10 min and extracted by liquid-liquid extraction with dichloromethane, and then the nitrosamines were pre-concentrated, by using activated silica. Then, gas chromatography coupled with flame ionization detector was used for the separation and determination of the different nitrosamines contained in a real sample. The applied method allowed the determination of nitrosamine compounds at trace levels with limit of detection ranging from 0.077 to 0.18 ppb, and quantitation limits were from 0.26 to 0.60 ppb for all nitrosamines. The total concentrations of the seven nitro-samines in the studied meat samples ranged from 2.60 to 13.28 mu g/kg.
PDF
