I have a mixed solvent of acetone: water: ammonia (90:7:10), can I replace the acetone with ethyl acetate as an eluent and purify my alkaloid which is a polar compound?
Of course not, first they have different solvent polarities and then I am not sure that ethyl acetate and water are miscible in your mixture proportions, especially in the presence of ammonia
The main reason for not replacing acetone with ethyl acetate in that particular solvent system is that the ethyl acetate is not miscible with water at those proportions. Assuming "ammonia" really means "ammonium hydroxide", that is about 84-85% acetone : aqueous solution.
In other applications, such as hexane/ethyl acetate purification , acetone may be generally substituted. Please see this application note: https://www.teledyneisco.com/en-us/liquidChromatography/Chromatography%20Documents/Application%20Notes/Acetone%20as%20an%20Alternative%20to%20Ethyl%20Acetate%20in%20Flash%20Chromatography%20App%20Note.pdf
Note that you probably don't want to use a more polar solvent system with ammonia (or ammonium hydroxide) than you are currently using because silica does dissolve in basic polar solvent systems. Keep it below 15% water, although we have observed noise from light scattering detectors above 10% ammoniated methanol in dichloromethane solvent systems.
Acetonitrile might be substituted for acetone, but it is more expensive.
Christopher Dumalasa , It won't be a good idea to substitute acetone for ethyl acetate (going from a polar system to a relatively less polar system, despite having a polar alkaloid to purify?) due to some reasons already highlighted above, though it is not exactly clear why you want to do so. Can you tell us the challenges you are presently facing with your current system, perhaps, we might suggest a better alternative.
Regards.
No. Acetone (polar solvent) cannot be replaced by ethyl acetate due to its non polarity.Again your mobile phase contain water and ammonia it will be immiscible with ethyl acetate. Why you want to change this system?.
Yes you can but it will increase your retention time and this may affect peak broadening, decreasing the overall efficiency of the method.
Although Acetone is highly polar and EtAc is weakly polar, I wonder how it will affect overall solubility of your compound. You may not achieve desired separation and efficiency will be poor. Try to replace acetone by another polar solvent may be ethyl methyl ketone or something similar.
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