I am wondering if there is anyone out there who can help me. I am trying to find a method for to quantify the amount of Oleic Acid in a drug formulation. Does anyone have any ideas on where to start?

there are numerous methods for analyzing fatty acids. They usually involve conversion to methyl esters and analysis by GC. I am sure that if you contact Restek or Supelco, they will be able to supply you with methodologies. I think that one of them used to sell kits to perform these derivitizations.

Good luck

You can also derivatize them with a chromophore and run them via reversed phase or if high sensitivity isn't an issue, you can even assay for them without derivatizing them via reversed phase with UV detection (205 nm) or RI detection. RI might give better sensitivity. It's not too hard to do, but I would suggest the use of an acetonitrile based mobile phase and a relatively short column (50-100mm)with a small particale size if you're not going to derivatize. You'll enhance sensitivity by reducing the total dilution.

If you'd like to speak further, e-mail me at christopher.judd@collabo.com and I'll give more info.

CJ

I have analyzed fatty acids (including oleic acid) on a Water's free fatty acid column with a RI detector. This did not require any derivatization. The fatty acids eluted in order of increasing # of carbon atoms. However, this order was altered by introducing unsaturated fatty acids.

Donīt forget that resolution is much higher in GC. If you donīt need to resolve other FA then HPLC may indeed be good enough.

An ELS detector will give you much better sensitivity than RI. It will also allow use of gradient elution to enhance the separation and does not require derivatization. As Mueller points out, resolution can be a problem in HPLC if you have "critical pairs". A critical pair with oleic acid (18:1) is palmitic acid (16:0). This separation is difficult at best, but it can be done. Other critical pairs for oleic acid would be 20:2, 22:3, 24:4 (sorry, don't know the names). Elution order is by increasing carbon#, and each double bond reduces the carbon # by 2, so 18:1 is the same as 16:0. As long as you don't have these pairs, separation from other FA's is no problemo.