【单选题】What should we pay attention to when maceration, dissolution, extraction, partition and concentration were used for sample preparation?
A.
Maceration, dissolution and extraction: homogenise the sample as soon as possible to facilitate a uniform and efficient extraction of analytes from the sample matrix prior to partition, beside that a degree of matrix integrity (heterogeneity) needs to be maintained;
B.
C oncentration: The definition and inclusion for essential element are not the same in plant and animal systems. Because the trace elements essential for plants are those elements which cannot be substituted by others in their specific biochemical roles and that have a direct influence on the organism so that it can neither grow nor complete some metabolic cycle.
C.
P artition: transfer of an analyte or analytes from the extractant to the partitioning solvent with high efficiency;
D.
C oncentration: do not reduce the volume of solvent by the application of too much heat, which may lead to some alteration or decomposition of the analyte. It is better to use a lower temperature, at reduced pressure if possible, to expedite rapid solvent removal. Once the solution has been reduced to a small volume, ca. 5 cm 3 , a more prudent method is to direct a stream of dry nitrogen gas onto the surface of the extract.
【简答题】You can tell the age of a tree by counting its rings, but these records of trees' life really say a lot more. Scientists are using tree rings to learn what's being happening on the sun's suce for t...
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【单选题】女婴,2个月,已按照计划免疫程序接种过疫苗,家长带其到社区卫生服务中心继续接种。按计划免疫程序,应为该婴儿接种的疫苗是
【判断题】唇膏的选用要与肤色相配,肤色较白的人选择偏红色。 ( )
【判断题】唇膏的选用要与肤色相配,肤色较白的人选择偏红色。
【判断题】唇膏的选用要与肤色相配,肤色较白的人选择偏红色。
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【多选题】实现节能降耗的“硬指标”的关键在于( )。
D.
将“绿色GDP”纳入对地方政府的考核评价体系