Pollution of Musts and Wines: A New Method for the Determination of Petroleum By-Products Using Fluorescence

Abstract

Pollution of musts and wines by petroleum by-products may happen accidentally by mechanical machines, particularly during harvests. A new method for detecting and determining this type of pollutant, using fluorescence, has been developed in the present work. The principal pollutant investigated was diesel fuel which exhibits a characteristic fluorescence spectrum, whichever its origin. Fluorescence is principally emitted by traces of polycyclic aromatic compounds (PACs), principally polycyclic aromatic hydrocarbons (PAHs), contained in most petroleum by-products. The method involves a liquid-liquid extraction of PAHs using cyclohexane and fluorescence measurements were performed on the resulting “cyclohexane extracts.” Some natural compounds extracted from must and wine samples may also exhibit an intrinsic fluorescence emission which interferes with the characteristic fluorescence of pollutants. This is the case, in particular, of tannins contained in red wines and in wood. Thus, this prevents any reliable determination of pollutants. Natural compounds were efficiently separated from PAHs using solid phase extraction by elution of the cyclohexane solution on the florisil phase. The corresponding fluorescence was totally eliminated at the characteristic emission wavelength of pollutants. Thus, the presence of any pollution by diesel fuel could be characterized unambiguously and determined accurately. The limits of detection and quantification were determined to be around 0.3 and 1.0 μL L⁻¹, respectively. Uncertainties on determinations were estimated at less than 20% for diesel fuel, provided a reference spectrum of the pollutant is available. If not, the pollutant concentration can be estimated within a factor two. The evolution of the pollution with time was also investigated over several weeks, particularly during the time of fermentation. The method is fairly simple to implement, quick and reliable.

Key Words:

• fluorescence
• petroleum by-products
• wine pollution

The authors wish to thank M. Jobet and M. Nicolas, wine growers, who kindly provided various samples of musts and wines.