DETERMINATION OF THE AGING TIME OF COGNACS USING A LUMINESCENT SENSOR BASED ON THE TERBIUM(ІІІ) COMPLEX

Abstract

The possibility of identification of the maturation time (age) marker of cognac – gallic acid – in cognac using a terbium ion-based (III) luminescent sensor is shown. Gallic acid was isolated from cognac by thin layer chromatography on Sorbfil plates; the sample volume applied onto the plate was 1 µL. It was found that acidic systems, such as ethyl acetate : acetic acid in a ratio of 95: 5 and benzene : methanol : acetic acid (100: 5: 1) are best eluting; the latter was selected for the test. A solid-phase sensitized terbium ion luminescence (III) with gallic acid was used as an analytical response. It was established that surface active, as well as a number of donator active substances do not affect the intensity of the luminescence of the complex. An increased intensity of luminescence of the sorbate complex is recorded in the presence of a donor-active additive, trioctylphosphine oxide (TOPO). Analysis of the luminescence spectra and the excitation of the sorbates of the complex in the presence of TOPO allowed concluding that its molecule is not part of the internal sphere of the complex, but play a role of water repellent, protecting from water molecules which deactivate luminescence, which increases the intensity of luminescence. The maximum concentration of terbium ions (ІІІ) and TOPO in the developing solution is 10-3 mol/l. A 4% aqueous hexamine solution was used to achieve the optimal pH value (6.5-7.8) in a developing solution. The luminescence is excited at λ excit. = 365 nm, the intensity of luminescence of terbium ions (III) is recorded at λ em. = 545 nm. Gallic acid is identified according to the calibration curve. A simple and reliable technique has been developed for identification of the age marker of cognac – gallic acid – in different brands and various maturation periods of cognac. The correctness of the results obtained was verified by the spike test. The relative standard deviation is (Sr) 5.2–7.0%. The detection limit of gallic acid is 0.002 μg/ml.