Flash Columns Related Q&A
Since the introduction of silica gel flash column chromatography, it has been widely used in organic chemistry. Increasing the sample size results in reduced resolution. Compared with high-performance liquid chromatography (HPLC), the resolution of flash column chromatography is already at a medium level, but it is sufficient for sufficient separation, so an increase in quantity will only make the situation worse.
Second, the optimal flow rate depends on the length and width of the column and the nature of the gel. This is due to the number of plates available, for example, longer and narrower columns will provide a larger number of theoretical plates, which will affect the flow rate.
Finally, the resolution is affected by the stationary phase.
It provides a better resolution if the stationary phase or gel arranged on the column is more uniform and has a smaller particle size. The smaller the particle size, the larger the surface area and the higher the resolution. Now, we summarize the problems and methods encountered in the use of flash columns.
Q1：Could the silica-based normal-phase flash column be used repeatedly?
A：The silica-based normal-phase flash column can be used only once. However, if it is maintained properly it can be used again with good performance. The column needs to be dried by the compressed air or filled with isopropanol in order to be used again.
Q2: Could the silica-based flash column be eluted with methanol?
A: It is not recommended to use more than 25% methanol as eluent on the normal phase flash column.
Q3: What are the limitations of using polar solvents such as DMSO and DMF?
A: Generally speaking, the maximum tolerance concentration of solvents such as DMSO and DMF is 5%.
Q4: What is the suitable storage condition for a C18 reversed-phase column?
A: The correct storage condition can make C18 be used repeatedly. Do not let the column dry after using it, and use 80% methanol or acetonitrile aqueous solution of 3 times the column volume to wash the column to remove all organic solvents, and keep the column in the column cleaning solution.
Q5: How to deal with the thermal effect in the pre-equilibrium process of the flash column?
A: The thermal effect is quite obvious during the pre-equilibrium process for the flash columns with a larger size of more than 220g. Therefore, we suggest that the flow rate should be set at 50-60% of the column efficiency test speed in the pre-equilibrium process to avoid the thermal effect.
Q6: What happens to the backpressure of flash columns when using columns?
A: First of all, the backpressure of the flash column is related to the particle size of the packing. The smaller the particle size is, the higher the backpressure is. Generally speaking, the size of the pre-loaded silica gel is small. The back pressure of the flash column is high. In consequence, we should slow down the flow rate of the mobile phase in the separation process. Secondly, the backpressure of the flash column is related to the length of the column. The longer the column is, the higher the backpressure of the flash column is. In addition, the backpressure is also related to the cross-sectional area of the column. The smaller the cross-sectional area is, the higher the backpressure is. Finally, the backpressure of the flash column is related to the viscosity of the mobile phase. The higher the viscosity of the mobile phase is, the higher the backpressure of the flash column is.