determination of fat soluble vitamins by HPLC

[eli Chemist]

Hi.
I am working on determination of fat soluble vitamins contents in vitamin supplements.
I have a problem:
the amount of vitamin D is usually low while the amounts of vitamin A and E are high.in extraction step 3 vitamins extracted simultaneously.for detection vitamin D3 I have to concentrate sample solution, vitamin A,E do not need to concentration but they are cocentrated too. when I inject the concentrated sample solution to HPLC high cocentration of vitamin A,E make problem. they give bad peaks and affect the column even at sequence injections.
dear friends I want you help me with this problem by your experience or ideas in HPLC or sample preparation.

[shaun78]

What about trying an SPE cleanup to remove vitamins A and E and possibly concentrate D down for you?

[eli Chemist]

Hi shaun78
already I thought about this idea and did some search about it. those vitamins show similar trends to conventional sorbents. I found a procedure that have used several special SPE sorbents for separation vitamin D and A, but this method was time consuming and I think is expensive too(because of application of 3 sorbents for each analysis). I will search more about applicable sorbents for my purpose, I want to found a simple and rapid method, as much as possible, for rutin analysis.
any way thanks for your comment.

[James_Ball]

If you have switching valves you could use a 2D technique where you use two columns and divert the flow before and after the Vitamin D peaks to waste and allow the Vitamin D peak to pass through the second column for further separation. This would allow for an undiluted run of the concentrated extract to analyze for Vit D and then you could use an non-concentrated extract for analysis of Vit A and E.

[eli Chemist]

thanks James. your idea is interest, I think about performancing it according to my equipment.