I am making liposomes in phosphate buffer and need to quantify my lipid concentration after extrusion.
You may try HPLC methods with ELSD detector, or LC/MS system. Both are good reliable techniques
If you are using phosphatidylcholine (PC) as the lipid or as one component, you can use a PC assay kit. Several are available commercially. If your liposomes contain cholesterol, there are also kits for cholesterol quantitation.
There are also methods of measuring the amount of phosphate in the phospholipids. These involve complete oxidation of the lipids with strong acid at high temperature, reaction with peroxide, and detection of inorganic phosphate with a molybdate-based reagent. Personally, I would avoid this method if possible.
Easy and cheap way, Stewart assay. You can argue it is not really quantitative, but it gives you a pretty good estimation of the lipid concentration in your sample. It takes some time to get it right, but once you get a grasp on it it becomes routine.
You can also go for other methods, including those mentioned above, but it is really down to how accurate and how "routine" your measure has to be.
I'm having some problems implementing the Stewart assay to measure the concentration of phosphate. Can you send Stewart assay protocol for liposomal suspensions?
The concentration of the lipids in the liposomes can be measured by spectrophotometric methods. There are two methods that are used in many research labs.
1) The Bartlett assay 2) The Stewart assay
What kind of Phosphate buffer use for Bartlett assay is good?
For me i use KH2PO4.
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