I am getting peaks in the aliphatic region always in NMR after doing column. It has grease peaks. I do not get a clean NMR and washing with pentane does not effect much,
Savio, grease can be washed with pentane, but if it is not working in you case Perhaps the grease present In the solvent. Have you recorded the NMR to the solvent alone? Maybe the solvent was contaminated with grease in which case no matter the purity of the sample. f You want shut me a message and I can give more alternatives to minimize these signals?
Use redistilled Hexane for column chromatography! If compound is solid, after purification you should recrystallize this compound from polar solvents such as ethyl acetate methanol. before preparing your NMR sample dry your compound under high vacuum for 30 minutes.
Avoid use of grease or use grease less teflon valves .
OR These days Solvent peak suppression techniques are available in modern NMR instruments . find attached article of NMR Chemical Shifts of Common Laboratory Solvents as Trace Impurities
You can wash the solid (20-30 mg) after column by hplc grade hexane, then give sample.
Dear Vikas by simply washing with hplc grade hexane, grease peaks in aliphatic region can not be removed. I think re crystallization from more polar solvents followed by washing with hplc grade hexane and high vaccume drying is much better option. this method can greatly reduce the intensity of unwanted signals of hexane and grease . alternatively we can use re distilled or dried hexane( dried over anhyd CaCl2 and redistlation) for column chromatography.
We have done it kamil many times and it worked well after high vacuum drying.
This is unavoidable if you are using n-hexane as eluent but you can suppress them by using solvent peak suppression techniques
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