A1
Q1：How soon will a sample be eluted after starting a sample run and how much solvent will be used?
A1：The eluting time and the amount of solvent to be used can be predicted pretty accurately, when a sample is correctly run on TLC and get the Rf value of the target compound. The eluting position is given by the formula of CV (Column Volume) = 1/Rf. If the target compound reads Rf 0.25 on the TLC, it will be eluted at 4-CV position as shown in Fig.1. And the amount of solvent used is 4-CV. (Note: CV means the void volume in a column. 1-CV is the amount of solvent required to fill up the void volume. Non-absorbing matter will elute at 1-CV.). Then, the eluting time is given by 4-CV/Flow Rate. The eluting time of the open-column chromatography and that of the flash chromatography differ as shown in Fig.2. Gradient method on flash chromatography increases the sample resolution as shown in Fig.3.





Q2：The sample dissolved in highly polar solvent such as methanol, DMSO, ethyl acetate, etc. is not well absorbed by the solid phase of the flash column and is often washed out without being separated.
Q3：In purifying and separating compounds, which column achieve a better performance, a fat and short column or a slim and long one?
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