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211.
本文采用正交实验对青海产大黄中总有机酸提取条件进行了研究,利用酸碱滴定法对总有机酸的含量进行了测定.结果表明最佳提取条件为:95%的乙醇,物料比1:20,超声时间30min,有机酸含量最高为5.09%,该测定方法简单可行,精密度高,重现性好. 相似文献
212.
Low molecular weight (LMW) organic acids are important and ubiquitous chemical constituents in the atmosphere. A comprehensive
study of the chemical composition of precipitation was carried out from June 2007 to June 2008 at a rural site in Anshun,
in the west of Guizhou Province, China. During this period, 118 rainwater samples were collected and the main LMW carboxylic
acids were determined using ion chromatography. The average pH of rainwater was 4.89 which is a typical acidic value. The
most abundant carboxylic acids were formic acid (volume weight mean concentration: 8.77 μmol L−1) and acetic acid (6.90 μmol L−1), followed by oxalic acid (2.05 μmol L−1). The seasonal variation of concentrations and wet deposition fluxes of organic acids indicated that direct vegetation emissions
were the main sources of the organic acids. Highest concentrations were observed in winter and were ascribed to the low winter
rainfall and the contribution of other air pollution sources northeast of the study area. The ratio of formic and acetic acids
in the precipitation ([F/A]
T
) was proposed as an indicator of pollution source. This suggested that the pollution resulted from direct emissions from
natural or anthropogenic sources. Comparison with acid precipitation in other urban and rural areas in Guizhou showed that
there was a decreasing contribution of LMW organic acids to free acidity and all anions in rainwater from urban to remote
rural areas. Consequently, it is necessary to control emissions of organic acids to reduce the frequency of acid rain, especially
in rural and remote areas. 相似文献