I am working on Vitamin D analysis now, attempting to extract it from Dried Plum Powder. Vitamin D is soluble in Acetonitrile, Ethyl Acetate and Methanol, so if any of those would work to extract the Vitamin D from the oil, it could then be diluted into Methanol for injection into the RP analysis.
I was having a terrible time with my extractions. My first simple test extract work great, so to bring up the concentration I decided to try 4g/20ml in each solvent instead of 2g/20ml and I seemed to get worse results. Thinking maybe it was the plastic centrifuge tubes, I tried glass. With glass I got almost no recovery, even on blank spikes. After that I thought maybe it was UV light causing my problems so I tried using 40ml Amber vials, first run gave lower than expected results, second gave almost no recovery at all. Difference was second run was extracted for a longer time. It would appear from this that Vitamin D can adhere to glass.
In frustration, and after reading another paper, I decided to try the Quad Solvent we use for broccoli seed extractions which is equal parts DI water, Acetonitrile, DMF an DMSO. A quickie extraction in plastic centrifuge tubes gave similar results to my very first quickie extraction, but matrix spike was about 50% recovery. Today I am running the test again with a blank, blank spike, sample, sample duplicate and spiked sample to see it the result was a fluke or something genuine. If so this may be some interesting research in that I am finding Vitamin D2 and D3 in fruits and finding that glass can interfere with recovery of Vitamin D.
I wonder if on the oil, you could extract with a mixture of water and acetonitrile, which should not dissolve the oil completely. Then dilute with more water and pass it through a C18 SPE, then elute with acetonitrile or methanol to make an extract for injection?