I have 4 ml of eluent from SPE and I brought the volume up to 5 ml using the solvent. The eluent was ran in UV for Quant analysis. Is the dilution factor 0.8 because it would be "4 in 5"?

Answer 1

Yes, the dilution factor is 4 in 5 or 0.8. Frankly, I don't use the factor as such but read the quantity from the graph of A vs conc, which gives you the concn in the diluted sample. Then
concn in diluted sample x 5/4 = concn in original sample

Answer 2

Wouldn't it be the concentration on the graph multipled by 4/5 rather than 5/4 for the concentration in the original sample ?

Answer 3

I don't think so and that's one reason I don't use the factor. I'm never sure we're all on the same page with dilution factor. If the graph you are reading from gives you the concn in the SAMPLE BEING MEASURED, then you KNOW that the concn in the undiluted sample MUST be more and the only way you can get a larger number is 5/4. 4/5 gives you a smaller number. If it has been diluted you know the measured sample is weaker than the initial sample.