[Hend Yamani]

I need to determine two drugs simultaneously by spectrofluorimetry.  One of them has natural fluorescence. The highest fluorescence intensity is obtained in pure methanol. Using other solvents or addition of any buffer or surfactant result in significant decrease in fluorescence intensity.

The other drug doesn’t exhibit natural fluorescence. It is a quaternary ammonium compound. So a fluorogenic agent is needed to enhance its fluorescence.
 
I searched a lot and found different reagents mainly anionic dyes as eosin Y or alizarin red S, that form ion pair complex with quaternary ammonium compounds. But all of them are used in water and form water soluble ion pair or water insoluble ion pair that needs another extraction step by dichloromethane or chloroform.

Can anyone help me to find a regent that forms with quaternary ammonium compounds a fluorescent product that is methanol soluble? (as I said the first drug must be measured in methanol).