external std and unknown smaple are not in the same solvent

[jiangds06]

unknown sample are in aqueous emulsion, while external std are in ethanol solution. Does solvent difference affect accuracy of quantitative result?
For example, different volume can be inject into the column because of viscosity difference between external stds and unknown samples? How can address this problem?

[Consumer Products Guy]

For one of our most frequently run cGMP-validated assays we dissolve samples in one solvent and the external standard in another. And different solvent as organic in the mobile phase. One injects volume, so the same number of molecules get injected onto the column.

In general, we like to keep solvents the same for standard and samples, but one cannot always do this for reasons of solubility, etc.

As long as you don't inject too-large a volume of the one that's in the stronger organic solvent (in your case, the standard in ethanol) you should have no issues. Your precision and accuracy data should confirm this if your assay is decent.

Question: what happens if you dilute your sample and your standard both 1:1 with ethanol - does the assay work? That would get get things more "aligned".

Some purists like to extract samples with the same solvent mix as will be used as mobile phase. We RARELY do that; likely that is more important for refractive index detection when the signal to noise ratio is less than desired.