Berberrubine: a FDIC fluorophore for determining saturated hydrocarbons with a simple calibration, via non-covalent interactions and signal amplification from a keto-enol tautomerism tion
Hydrocarbon-containing heavy products from petroleum consist of an important proportion of saturated hydrocarbons, having increasingly chain lengths with increasing boiling point. A rapid and accurate determination of these compounds as a single group (Saturates) is a challenge in petrochemistry.
Berberrubine is proposed here as a quantitative fluorescence sensor for saturated hydrocarbons that can be incorporated on HPTLC silica gel plates by adsorption, through impregnation. When n-alkanes are applied on a berberrubine-impregnated plate, and the system is excited at 365 nm, we found that fluorescent response (emission collected from 400 nm) is almost constant with the number of carbon atoms in the hydrocarbon chain. This behaviour is different to that of berberine and coralyne cations. In these cases, fluorescent responses depend on the alkane chain length, and any calibration procedure should take this into account.
Results show that berberrubine can be used as a “mass detector” for the analysis of Saturates in heavy petroleum products, simply using a pure alkane as a single calibrant. Saturates were determined in different heavy petroleum samples: one lubricating oil, 10 bitumes, 7 vacuum gas oil, 3 refining products and 2 synthetic mixtures, on berberrubine post-impregnated plates (60 ppm), and using alternatively three n-alkanes (C24, C28 and C32) as calibrants. Limits of application of this calibration are discussed
Berberrubine has two fluorescent forms in acidic and basic media, which correspond to a keto-enol tautomerism. Fluorescent signals can be rationalized from the predominance of enol form when berberrubine is adsorbed onto silicagel. OH bonds in enol form may difficult the freedom of orientation to interact with alkane molecules.
Berberrubine was obtained from berberine chloride in a simple way, either by microwave-assisted or by vacuum pyrolysis synthesis