Water Soluble Analyte Dilemma

Discussions about sample preparation: extraction, cleanup, derivatization, etc.

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Hey guys,

I'm doing some work on a project to analyze an analyte in a cream. The problem is that the analyte is only water soluble. I was trying to use liquid liquid extraction. The cream has some water in it (~73% but we don't know the exact amount) and I was trying to use organic solvent to dissolve the cream and then allow the water layer and organic layer to separate by centrifuging, but since the analyte goes into the water layer I'm not sure how to accurately quantify without knowing the exact amount of water. Any thoughts on a better way to do this?

Just a heads up, the solubility is very limited in all organic solvents so that's what makes this really tricky.

Thanks in advance.
If the sample intake is low compared to the amount of water for extraction, for example if you extract 1g wet cream with 50mL water, the error coming from extra dilution of water in the cream is negligible.

Alternatively, you can dry or freeze-dry the cream before liquid-liquid extraction. Record the mass of the sample before and after drying so you can quantify on the wet product.
If presented with a matrix like that I'd be very much hoping that a headspace SPME method would work. Have you considered if that extraction methodology might suit your needs using a fiber that leaned in a more polar direction?
Where's the problem if you collect the aqueos layer from the l-l extraction in a volumetric flask and fill it up to the mark?
You can even do the l-l partition multiple times and collect all aqu. layers in the same flask, therefore increase the recovery.
The initial volume of water in the cream will add to the first fraction but when you finally fill up to the mark it doesn't matter any longer.

Then proceed as you want, use an aliquote for dilution or concentrate if necessary etc. etc.

Or find a suitable internal standard to add before doing the l-l extraction but this may be more tedious to establish.
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