Coralyne cation, a fluorescent probe for general detection in planar chromatography

A large number of analytes, including non-fluorescent ones, can be sensitively detected by fluorescence scanning densitometry using silica gel HPTLC plates impregnated with a solution of coralyne cation. This is carried out by the variation, increase or decrease, that the corresponding analyte induces on native coralyne emission at a given excitation wavelength. A similar phenomenon was previously described for berberine cation, and Reichardt's dye probes. However, the sensitivity of coralyne in HPTLC detection of non-fluorescent, structurally different analytes (e.g., long-chain alkanes, alcohols, alkylbromides, neutral lipids) is superior to that of the above-mentioned probes. In this work, the analytical viability of this phenomenon for HPTLC detection using coralyne as a probe is explored, and fluorescent responses of a number of analytes on the coralyne system are rationalized in the light of a previously proposed model. This establishes that the resulting intensity for a probe in the presence of a given compound can be explained as a balance between radiative (contribution of non-specific interactions) and non-radiative processes (specific interactions), the latter producing fluorescence quenching. Experimental results and proposed model suggest that this phenomenon may be general for practically all kinds of analytes.