Extração de lipídios da microalga Scenedesmus sp. Com diferentes mistura de solventes orgânicos Lipid extraction of the microalga Scenedesmus sp. with different mixture of organic solvents Extracción de lípidos de la microalga Scenedesmus sp. con diferentes mezclas de solventes orgánicos JOSÉ JOVANNY BERMUDEZ-SIERRA 1 RESUMO As microalgas são fontes de lipídeos com potencial para produção de biocombustíveis e suplementos alimentares em grande escala. O presente estudo avalia o papel dos solventes orgânicos de tipos apolares e próticos polares (razão 1:2) na extração e quantificação de lipídios totais e ácidos graxos metil-ésteres (FAMEs sigla em inglês) da micro-alga Scenedesmus. sp. As amostras da microalga liofilizadas foram quantificados os lipídios por Bligh & Dyer (B&D) modificado e pré-tratadas com acido clorídrico 3 mol•L -1 (com e sem HCl). O clorofórmio foi substituído pelo acetato de etila, éter de petróleo e éter etílico e o metanol por etanol, Isopropanol e terc-butanol. Os FAMEs dos óleos de cada tratamento, com ou sem adição de HCl, foram quantificados por cromatografia gasosa. Os resultados evidenciaram que a maior extração de li-
The solubility at 25°C of p-nitroaniline in aqueous alcohols at concentrations of up to 40 % v/v is reported and activity coefficients are calculated. The rate of increase of the indicator solubility with alcohol concentration diminishes in the order cyclohexanol > n-propanol > isopropanol > ethanol >methanol, and this effect of the alcohol is sufficient to account for the behaviour of the indicator in dilute acid solutions without the assumption of the protonation of the alcohols themselves. Attention is drawn to some weaknesses in the protonation argument.Since changes in the activity coefficient of the base form of an indicator may be as important as proton hydration changes in the interpretation of salt effects,l it seemed that the determination of the solubility of p-nitroaniline in aqueous solutions might throw a different light upon the conclusion, drawn from studies with this indicator, that alcohols and other oxygen-containing molecules are protonated in dilute acid solutions.
EXPERIMENTALSamples of p-nitroaniline (twice recrystallized from water) were shaken in 6Oml flasks with 20 ml of 5,10,20, 30, or 40 % vlv alcoholic solutions for at least 3 days in a thermostat at 25"C, after which 5 rnl samples were removed for spectrophotornetric determination of their p-nitroaniline concentrations. With cyclohexanol only 1, 2, and 3 % v/v solutions were used because of its limited miscibility with water. The other alcohols were methanol, ethanol, nand iso-propanol, all of analytical reagent quality.
RESULTS AND DISCUSSIONSolubilities axe expressed in table 1 in terms of molarity (column 4) or number of moles of p-nitroaniline per mole of solution (column 5) and the corresponding values of the logarithm of the activity coefficient, -logyB and -logf,, are recorded in columns 6 and 7 respectively : Y , and fB are calculated directly from the ratio of the solubility in pure water (4.02 x to that in the alcohol solution. Column 1 records the alcohol concentration in vol. % and columns 2 and ' H. J. Campbell and J. T. Edward, Can.
The objective of this paper is to compare the lipid content and composition ofbiomass produced by a consortium of microalgae and bacteria, cultivated under different solar radiation intensities and tropical conditions in pilot-scale high-rate ponds (HRPs) using domestic sewage as culture medium. The treatment system consisted of an upflow anaerobic sludge blanket reactor followed by UV disinfection and six HRPs covered with shading screens that blocked 9%, 18%, 30%, 60% and 80% of the solar radiation. The total lipid content does not vary significantly among the units, showing a medium value of 9.5%. The results show that blocking over 30% of the solar radiation has a negative effect on the lipid productivity. The units with no shading and with 30% and 60% of solar radiation blocking have statistically significant lipid productivities, varying from 0.92 to 0.96 gm(-2) day(-1). Besides radiation, other variables such as volatile suspended solids and chlorophyll-a are able to explain the lipid accumulation. The lipid profile has a predominance of C16, C18:1 and C18:3 acids. The unsaturation of fatty acids increases with the reduction in solar radiation. On the other hand, the effect of polyunsaturation is not observed, which is probably due to the presence of a complex and diverse biomass.
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