Milk samples preparation

[gruby]

I have a pig`s milk - so the problem occurs with high content of lipids, tommorow I will have some results from HPLC.

I think it is hard to compare tetracyclines and hyperforin becouse it is very unstable and I have only DAD detector so I will never reach degradation products. I tried a method described by Steffen Bauer but it is for plasma samples - is based on extraction of samples with hexane and ethyl acetate (9:1), centrifugation, evaporation and dissolving in mobile phase - but after evaporation of milk extract lipids were present in different quantities and are only partly soluble in mobile phase - results were varying, calibration curve was completly curved ..

When I checked the freezeng of pigs lipids in hexane it looked promisingly. But due to lack of information concerning partitioning coefficient hexane-lipids for hyperforin in low temperature ( in any temperature ) I have to check it out

[HW Mueller]

Thanks, SIELC_Tech, OK, hyperforin has a hydroxyl in conjugation with a carbonyl (ascorbic acid also has this group) so my guess is that one could do what Uwe suggests but use a less acidic (maybe pH ~7 or slightly above, ... could be unstable at higher pH?) extractant.
SILC_Tech, it could be interesting to see a comparison of one of your RP with + charge (what was that?) columns with a "normal" RP on cow´s milk (with the fat and proteins removed first).

[HW Mueller]

Sorry gruby, I didn´t see the 2nd page before. If you want to stick with extractions then something like this seems more promising now: Make sure the milk has a pH as high as your hyperforin allows, centrifuge out as much of the lipids as you can, extract the aqu. part with MeOH or ACN (most proteins will precipitate), remove most of the organics and inject.