wherein R is above-defined and W is a hydrogen bonded to a reactive nitrogen (primary or secondary amine) or to a hydroxy oxygen; with chlorosulfonylisocyanate to yield a chlorosulfonamidocarbonyl-ligand-analog derivative of the formula ##STR18## The chlorosulfonamidocarbonyl-ligand-analog derivative is reacted with an aminofluorescein of formula (IV) to yield the tracers of the present invention