Help with sorbitan oleate

[dkollmorgen]

Does anyone have any advice for determining the amount of sorbitan oleate in a drug product matrix (cream)? I would like to run it either by GC or HPLC (whichever is more practical) but I don't have any experience with running this type of compound. Any assistance would be appreciated. Thanks!

Diane

[AICMM]

dkollmorgen,

I would be very surprised if this were easily done by GC based on the molecular weight. Therefore, I would suggest HPLC with UV detection. There are a couple of pi bonds so it might be do-able by UV detector but I cannot say from experience. Have you tried looking at a dilution of the neat material on a UV spectrophotometer?

Regarding cream, the best I can offer is to start by diluting in water. This will help eliminate some of the water soluble matrix interferences. Then extract with a non-polar solvent to pull out the oleate. I have used this for a method for camphor, menthol, and capsacein but I was able to take advantage of their high concentration to make this method work.

Best regards.

[chromatographer1]

It may be possible to determine the amount of oleic acid present which would indirectly inform you of how much sorbitan oleate is present.

Transesterify the oleate to the methyl ester of oleic acid and then measure the amount of oleic acid methyl ester against standards (done by GC).

You can use an organic base method to transesterify or you can use an acid in methanol to transesterify the sorbitan ester.

any GC derivitization book should help you with the specifics of the reagents, the conditions, and chromatography parameters for this analysis.

best wishes,

Rod