The role of nitrogen gas in FAME preparation is just to prevent the oxidation of fatty acids by reducing the oxygen level in the surrounding environment. You can use low grade oxygen for this purpose but ensure the purity has to be more than 60%. However, the purity of nitrogen gas used as carrier gas should be 99.99%.  

Hello Rayudika,

I am not clear in understanding your question. Could you please explain the purpose of drying FAME?

Anyway, I agree with the opinion of Mr. Jannathullah. 

There is a step of evaporating organic solvent to condense the FAME during sample preparation. That only he is mentioning as drying. 

Thanks Mr Jannathulla and Monjurul,

if purity nitrogen 99.9%, is it nearly to Ultra High Purity (UHP) nitrogen ? I just worry, some fatty acid is volatile and using low grade of nitrogen can impact to that

I guess you can as long as there is no oxygen contamination

thanks for your suggestion Mr Adnan