The laboratory experiments described in this work present the CMC-determination of some surfactants by following three different methods, which require the use of the very common techniques in physical chemistry laboratories, such as UV-Vis spectroscopy, luminescence spectroscopy, and electrical conductivity.In performing these experiments, the CMC of a surfactant is determined by measuring a change (i) in the UV-Vis spectra of benzoylacetone, (ii) in the fluorescence emission spectra of pyrene monomers, and (iii) in the electrical conductivity of an ionic-surfactant solution, as the concentration of the surfactant increases.The CMC values corresponding to the surfactants sodium dodecyl sulfate, tetradecyl trimethylammonium bromide and polyoxyethylene,9-dodecyl ether determined in this work following the three indicated methods and in the absence and presence of electrolytes and non-electrolytes are reported.

It is known that residential wood combustion (RWC) is an important source of fine particle emissions. The purpose of this work was to characterize the chemical composition of the particulate matter present in the Temuco urban atmosphere during winter, specifically the polycyclic aromatic hydrocarbon (PAH) profile, because PAHs are considered to be among the key compounds in particulate matter toxicity. During the 2008 winter monitoring campaign, samples of particulate matter with aerodynamic diameters of 10 (PM 10 ) and 2.5 (PM 2.5 ) mm were taken on days with contamination episodes. Sixteen U.S. Environmental Protection Agency (EPA) PAH compounds were extracted with toluene and determined by gas chromatography-mass spectrometry (GC-MS). The results show that phenantrene was the predominant compound associated with particulate matter, at a concentration range between 300 and 600 ng m À3 , 18 times higher than the second most abundant PAH compound. High-molecular-mass compounds such as dibenz [a,h]anthracene, benzo[g,h,i]perylene, and indeno[1,2,3,c,d]pyrene were also found, but they were minorities in the set. It was recognized from the PAH concentration ratios of the Temuco atmospheric aerosol that the main contamination source was in fact residential wood combustion; although not all the concentration ratios evaluated match the reported reference values, probably due to the kind of biomass used, the characteristics of Chilean heating appliances and climate.Implications: The study results suggest that if molecular markers (MMs) and concentration ratios (CRs) are dependent on the type of firewood and combustion processes specific to each location, among others factors, then the values of these indicators could be applicable with caution between different areas, although not necessarily they must be totally in accord. Moreover, having representative values of MM and CR of each place, it will achieve a better estimation of the source importance and concentrate the monitoring and the control strategies. Regulatory organizations in each country can have more reliable information and optimize financial and human resources, enabling it to reduce air pollution and improve the health of population.

The redox reaction between bromate and bromide ions in aqueous acid medium was studied in the absence and presence of cationic and anionic surfactants. The rate equation in water was found to be v ) k3 w [BrO3 -][Br -][H + ] 2 . The cationic surfactant, tetradecyltrimethylammonium bromide, catalyzes the reaction, using either HBr or HNO3 as the source of H + ; nevertheless, the observed rate constant decreases slightly, goes through a minimum, and increases again as the tetradecyltrimethylammonium nitrate concentration increases. The anionic surfactant, sodium dodecyl sulfate, strongly inhibits the reaction when its concentration is increased, reaching a leveling off at high surfactant concentration; but hydrogen dodecyl sulfate catalyzes the reaction. These micellar effects are quantitatively explained on the basis of the pseudophase ion exchange model: tetradecyltrimethylammonium bromide increases the Brconcentration, while sodium dodecyl sulfate decreases the H + concentration (through the exchange with Na + counterions) in the water phase where the reaction takes place.

The volatile metabolome of Vitis vinifera C.V. Carménère wines, a unique Chilean winegrape variety, was characterized in this work. After solvent extraction with dichloromethane (LLE) or head space solid phase microextraction (HS-SPME), the resulting volatile compounds were analyzed by gas chromatographymass spectrometry (GC-MS). Specific methods were carried out too for the determination of methoxypyrazines and thiols. Almost 150 compounds corresponding to aliphatic and aromatic alcohols, organic acids, acetate and ethyl esters, lactones, terpenes, norisoprenoids, pyrazines, thiols and phenolic compounds were found in these wines. Both extraction techniques were complementary; HS-SPME allowed to identify several important compounds that were not detected by liquid-liquid solvent extraction, in particular b-damascenone, nerolidol, citronellol, linalool, ethyl 2-methyl-butyrate and geranyl acetone. Several varietal volatile compounds with significant odorant properties were also identified: 3-mercaptohexyl acetate (3MHA), 3-mercaptohexan-1-ol (3MH), benzenemethanethiol (BM), 2-furanmethanethiol (2FM); and 2-isobutyl-3-methoxypyrazine (IBMP) while 2-isopropyl-3-methoxypyrazine (IPMP) and 4-mercapto-4-methylpentan-2-one (4MMP) were not detected. Twenty two of these compounds, including b-damascenone, several thiols, ethyl octanoate, 2-phenylethanol, and 2-isobutyl-3-methoxypyrazine, showed significant odor activities values (OAV), and were clearly related with the cooked fruits, berries-like and herbaceous notes characteristic of Carménère wines. Olfactometric techniques are underway to validate the sensory impact of these compounds.

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This study presents a method for teaching the subject of chemical equilibrium in which students engage in self-learning mediated by the use of a new multimedia animation (SEQ-alfa©). This method is presented together with evidence supporting its advantages. At a microscopic level, the simulator shows the mutual transformation of A molecules into B molecules and vice versa for the reversible one-step chemical reaction, A(g) ⇔ B(g). The user defines the reaction as endothermic or exothermic and sets a given reaction temperature; SEQ-alfa© then calculates the kinetic constants of the forward and reverse reactions. Based on initial given concentrations, the animation then evaluates the respective rates and concentrations, as well as the concentration quotient value, as the reaction progresses towards its equilibrium state. SEQ-alfa© also demonstrates the effects of concentration and temperature alterations on the reaction's progress and the value of the reaction quotient until equilibrium is reached, thus giving the equilibrium constant. In addition, a validation of this new approach was carried out with 27 teachers. A pre-test and post-test of students’ understanding of the basic concepts of chemical equilibrium were conducted. Tested groups attained a 50% average learning gain (nexp = 130, nctrl = 26). Those students with little or no previous knowledge acquired a better understanding of chemical equilibrium. In addition, 80% of teachers agreed that the multimedia resource and its complementary activities had positive effects.

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The detection of pesticide in tomato (Solanum lycopersicum L.) matrix using Gas Chromatography hyphenated to Mass Spectrometry detector (GC/MS) can affect the sensitivity of the analysis by enhancement or suppression of their chromatography response, the percentages of recoveries and leading to errors in the quantification of the pesticides. In this study, the matrix effect was investigated using nine pesticides, and "Quick, Easy, Cheap, Effective, Rugged and Safe" (QuEChERS)-GC/MS analytical technique was validated for pesticides multiresidue analysis. The matrix effect was determined using not statistical and statistical procedures including ANOVA, with similar results. Strong negative matrix effect was found for the pesticides trifluralin, 4,4'-DDT, and permethrin, resulting in the increment of the chromatogram background and a decrease in their detection responses. Contrary, an enhancement induced by the matrix presence was obtained for carbaryl and azinphos methyl, showing a positive medium matrix effect. While, dimethoate, simazine, 4,4'-DDE, and iprodione did not exhibit matrix effect. The detection limits (LOD) obtained, varied from 0.003 to 0.1 mg kg -1 . Reproducibility was less than 20% for each pesticide. Recoveries were found to be between 71% and 121%, except for dimethoate, carbaryl, and azinphos methyl which reached values lower than 70%. Recoveries relative standard deviations were less than 22%. Quechers-GC/MS technique was used for evaluation of fresh commercial tomatoes samples, detecting carbaryl in all of them, but in concentration levels lower than the maximum residue limits according to regulations of Codex.