1. Introduction It is well known that the non-fluorescent furanone reagents fluorescamine (4-phenylspiro- (furan-2-(3H)-1 -phthalan)-3,3 -dione) and MDPF (2-methoxy-2,4-diphenyl-3(2H)-furanone) do react directly and selectively with primary amines (R-NH2) in aqueous media at al-...