What are differences between the two? Of course the amount of silica may vary. As for speed of the column, I think the big column will run more time efficiently but will not produce satisfactory separation. The long column, on the other hand, will provide satisfactory separation but will be much more time consuming. Are there any other differences?
Yes, of course there are differences. In a long column the number of theoritical plates will increase and it will be more efficient for separation. Longer columns allow good separation.
It can just be compared with a short and a long TLC plate. On a short TLC plate, the spots will be very near to each other and resolution wont be clear. Whereas the same sample run on a long plate, the resolution will be more clear with distant and discrete spots.
Yes, you can achieve higher resolution with a longer column due to decrease in the multiple flow path factor and an increase in the number of theoretical plates. However, if you are processing a large sample volume a larger diameter column may be necessary.
In addition to the previous answers your question is a little confusing due to the word "flat". If you meant "fat" then usually the particle sizes will have a smaller diameter as the diameter of the column goes down. If the particle sizes are the same then the previous answers are sufficient. Smaller particles are packed more tightly. This allows for better efficiency of interaction of the molecules in the mobile phase with the stationary phase. This means that there is a better ability to resolve different peaks, e.g. more theoretical plates. With smaller particles you also have less amount of silica and that means less molecular interaction sites in general so the capacity, e.g. the amount of material that can go onto the column and be separated is less. However, the pressure increases with the inverse square of the diameter of the particle and linearly with the length of the column so that pressure can be limiting. If you want a smaller column and don't have too much material, you should use smaller diameter silica particles and pack them carefully to have increased efficiency. If the particles are not packed in a continuous slurry and you have "bands" your separating ability will also be reduced. Your question is a little unclear because I don't know if you will be using a commercial column or are doing a preparative silica purification. The question seems to indicate a preparative separation for an organic synthesis.
Thank all. specially jeane. Its a preparative column (silica normal phase) for isolation of natural products mainly.................... By flat i means a large diameter column.
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