I have noticed a significant discrepancy in the effect of oil-in-water emulsions prepared in two different ways:
1. I first add oil in DMSO to solubilise it and then make up the volume of the stock with PBS. Viability assays done with this stock using 3T3 fibroblasts have shown that concentrations of oil greater than 500 microg/ml are highly toxic and incompatible for the study.
2. I first prepare a co-solvent mixture by mixing PBS and DMSO together and subsequently add the oil. 3T3 fibroblasts are found to be almost 100% viable even at concentrations as large as 800 and 1000 microg/ml.
Concentrations and volumes in both cases are the same. What could be a plausible explanation? I am thinking that the oil has not dissolved in the second scenario and is mostly PBS and DMSO (0.5% in the stock) that I am working with.
Any help is highly appreciated!
I agree that the first approach is better one to prepare this emulsion.
However, if you check the link below, people have reported that cells can easily tolerate 0.1% (1000 ug/mL) DMSO and even more depending on the type of cells.
-https://www.researchgate.net/post/Until_what_percentage_does_DMSO_remain_not_toxic_to_cells
So, I think that the variability in your different results could be due to human variability if you have not repeated your experiments 3-4 times.
And, if your results are mean of different experiments, then probably you are right with the solubility theory.
There is another way to check your theory. Dissolve a drug/chemical in the two solutions. Test for homogeneity, by analysing concentration of top/middle/bottom layers.
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