Have you compared the FT-IR trace of pure biodiesel and pure Glycerol. What % of Glycerol are you looking for? I would have thought GC would be a more sensitive method to detect Glycerol. What is the Purpose of the analysis, What are you trying to achieve?

Free glycerol only, poly -ol groups found near 3464 cm^-1 , thanks anyway...!

i think ,may it will form ester by linkage of 1st & 3rd -OH. see if u observe peak at 1730-1750cm-1....

otherwise free -OH will mostly observe abv 3500...

What % of free glycerol do you think may be there?

Have you thought of doing an extraction with water. Free glycerol will go into the water, then evaporate off the water or RI may work. Still need to know what % you are looking for before choosing best method. FT-IR not likely to be very sensitive.

@robert taylor yes it is not sensitive, i need to analyse in GC only, then my biodiesel is partially converted, leaving mono glycerides, biodiesel is getting dissolved in MeOH, but glycerol was not separated out, i'm working with lipase mediated transesterification, it needs more time, i just used 5hr reaction time, but it needs 20 hrs i think.

@Yogesh Gawale yes i have a long peak @1742 cm-1, but i'm confused with both the esters(ester in mono glycerides and ester in ME), GC only can give the accurate results.

Hi Mozhi, are you trying to monitor the extent of the reaction of your biodiesel with methanol to replace the glycerol? Try using Acetonitrile as your GC solvent. Maybe also take you reaction mixture and get rid of any methanol by vacuum in a rotary evaporator or similar. You need to get rid of the methanol (without heating) before you do the GC or you will get misleading results. Hope that helps :-)

@robert taylor thanks for your help, then why methanol should not be evaporated by heating????

It will react preferentially to form the methyl ester of your biodiesel.

Oh you mean, yet another methyl group will bond with it ?????

Mozhi, I am have difficulties because I do not know what you are trying to achieve. Answer this question that I asked previously:

Are you trying to monitor the extent of the reaction of your biodiesel with methanol to replace the glycerol?

If so then :

Do you want to follow the amount of methyl ester as it increases and the amount of glyceryl ester as it decreases?

Yes absolutely.... i'm trying to monitor extent of the reaction

Then you need to remove excess methanol without heating before you put the mixture in the GC. The injection port of the GC is very hot and so you will get more reaction in the injection port and hence the wrong result. Do not use methanol as the solvent for GC either or any alcohol. I previously suggested you use MeCN as the solvent.

Okay.. Thanks a lot....!