Characterization of "unsaponifiables"

[cms12]

Hello!

I've been here before asking questions about this class of molecules and have always gotten informative response, so hopefully you all will be able to lend some insight once again.

I am working to isolate the "neutral" or "unsaponifiable" content from a resin acid product. In the past, we have isolated the neutral components of different rosin types (gum rosin, tall oil rosin) by using a alumina-based column chromatography, which retained the acidic resin acids and allowed the neutral components (rosin alcohols, residual terpenes, etc) to be isolated.

I am now trying to isolate these same neutral components from the "rosin triglyceride"; I have reacted rosin with glycerol and I would like to characterize the product fully. I can somewhat determine the amounts of rosin products by SEC, but this only gives me an estimate of the mono-,di-, and tri- esters.

I was thinking that perhaps there is a technique that might allow me to seperate the ester products from the smaller molecules followed by GC analysis. Or perhaps HPLC would be the preferred route; however, I am still at a loss for what type of column would allow adequate seperation for this class of molecules.

Any insight will be greatly appreciated! Thanks in advance!

[KDF]

You may want to consider packed column Supercritical Fluid Chromatography (pSFC) as a means. SFC is similar to HPLC except it uses CO2 as the major component of the mobile phase. CO2 has approximately the solvating power of hexane. Modern pSFC allows binary gradients with organic solvents which are typically fully miscible at pressures over 150 bar up to polarities of about methanol. This is normal phase chromatography as you have been doing, but with a much higher performance. Spherical Silica at 3 or 5 um in a 4.5 x 250mm column is a good starting point. You can use a nonpolar co-solvent with a small amount of TFA to provide acidity or small amounts of amine to provide basicity. I'm not sure of your scale or budget, but semiprep to prep systems are available if you are looking for large scale recovery. If a few mg will do for NMR id you can probably use an analytical system with manual collections of multiple injections. After depressurization by the SFC backpressure regulator, most of the mobile phase converts to CO2 gas with just a small liquid residue. SFC handles a wide range of compounds from GC volatiles to peptides depending on the mode. Pure CO2 separations can use FID detectors,but once you start using significant organics the detector is swamped. You would need to dissolve the material in solvent of equal or lesser polarity that the co-solvent used.

Both Waters and Agilent are getting into the SFC business as of the last few years.

Full disclosure: I am part of a small company that designs SFC equipment, but I would invite your objective comparison.