Usually in preparative chromatography one needs to know when the desired substance to be separated is coming down the pike. Often this required some sophisticated instrumentation. But, it occurred to me that another way would be to two find dyes that (1) won't combine with anything in the mixture to be separated, (2) have Rf values that bracket the Rf value of the desired compound w/o including any others. Then one can simply visually inspect the chromo column (assuming it is glass)to tell where the product is and when it is about to come out. So, if this has been done then really my question is: is a table of dyes, and what kinds of functional groups they are safe with, and their Rf values.
In answer to comments below: I know a TLC is relatively fast. I was thinking of preparative chromatography.
Even approximate Rf values of dyes, run with maybe 2-3 different, pure solvents, in dry silica, would be useful. One could then guess which dyes would be useful, run test TCLs to find dyes that are either just above or below the desired substance X on the TLC plate.
Ideally the dye spots would not overlap the X spot at all so no separation would be required after.
Then in the preparative step I don't need to auto-sample or use a UV detector: just glance over at the column (thinking of low pressure flash chromo in a glass column) to see if the first dye is approaching the bottom - while doing other stuff. When the first dye just runs out, then I change the collection flask until the post-X dye starts showing up. Sounds easy! But I know there would be complications.