I would like to determine the void volume of a column on a HPLC system equipped with a fluorescence detector. Can anyone suggest a fluorescent compound that is not retained by a reverse phase C18 column?

David,
You might find some inorganic fluorescene compounds that C18 does not retain, e.g., rare earths. Another approach, you might try using non polar solvents, of course, the void volume will change slightly.

The literature thrashes with void volume theory. Each author argues his method works best and explains the defects of other methods. You might benefit from reading it before getting too excited about void volume determination.
Jim

Also the nomenclature is somewhat unfortunate. There have been times when I was thinking of void volume as that volume which does not have any stat phase... "Unretainedīs volume", or something similar, would be more descriptive.
Anyway, one does not necessarily need a fluorescent compound to see this, absorption differences (to mobile phase) or differences in scattering can show up. So: substances that are useful in UV detection often work here as well. Lastly, Jim seemed to hint at this: The interpretation is not trivial.

David;

I have used CeCl3 to measure dwell volumes and pump performance using fluorescence detection. This was done years ago and I need sometime to get you more details.

However if you go to any Fluorescence spectroscopy textbook it is quite likely that you will find details such as wavelengths, concentration, etc.

I will check this column in the next few days to give you additional information in case you have not found it already.

Benjamin

David;

The Ce+3 ion fluoresces at 260 Ex/350 Em. I believe a 50-100 ppm solution in water is a good point to start.

Good Luck;

Benjamin