[CrimpJiggler]

I did an experiment in which we had to determine the concentration of carboxylic acids present in pharmaceutical mixtures. In each case, we converted the carboxylic acids into their methyl esters using methanol-BF3 complex then analysed the derivatised samples with capillary GC. What I don't understand is why we converted the acids into esters, why didn't we just analyse the carboxylic acids? We dissolved the esters in n-hexane before injecting into the GC machine and the 1st peak that came up was the hexane peak so the stationary phase was obviously polar. The carboxylic acids wouldn't be very soluble in hexane but why not just dissolve the acid in polar solvent and use a non polar stationary phase?

[voidSetup]

The boiling point of the carboxylic acids might be too high due to hydrogen bonding so sometimes a derivative is used to make the compounds more volatile. I think silyl ethers are more commonly used though so I'm not sure if that's necessarily the case here.

[marquis]

The method is called FAME (Fatty Acid Methyl Ester) analysis.

Its used when the boiling point of the fatty acid is too high for normal GC analysis.

If you have access to an instrument, you might try using an HP-5 column and set the injector to the highest temp. Usually, this is 350 C for the injector. The column temperature should ramp up and end at the max temp (usually 325 C).

A lot of fatty acids showed up with this method (i.e. stearic, linolenic and linoleic), even though the technical people didn't think they would.