PRELIMINARY TLC STUDIE S ON POSI DONIA OCEANICA SEAGRASS [610274]

PRELIMINARY TLC STUDIE S ON POSI DONIA OCEANICA SEAGRASS

Loreta -Andrea Bozin1, Mihai -Cosmin Pascariu2,3, Alina Georgescu1, Georgeta Simu1†,
Anca Dragomirescu1, Eugen Sisu1*

1“Victor Babeș” University of Medicine and Pharmacy of Timișoara, 2 Eftimie Murgu S q.,
RO-300041 Timișoara , Romania
2National Institute of Research & Development for Electrochemistry and Condensed Matter –
INCEMC Timișoara, 144 Dr. Aurel Păunescu -Podeanu, RO -300569 Timișoara, Romania
3“Vasile Goldiș” Western University of Arad, 86 Liviu Rebreanu, RO -310414 Arad, Romania
†Deceased in 2017
e-mail: [anonimizat]

Abstract
Several photosynthetic pigments , i.e. chlorophyl ls and carotenoids, belonging to Posidonia
oceanica seagrass , were separated by thin-layer chromatography (TLC) using a
hexane/acetone solvent mixture. Addit ionally, densitometric measurements and spectral
scanning of the TLC plates were performed using the Camag TLC Scanner 3 together with
the WinCATS software.

Introduction
The use of several species of marine magnoliophy tes, with the purpose of monitoring and
managing the coastal ecosystems , was frequently discussed during recent years . Because of
their wide geographical distribution, their longevity, the permanence of their populations
during the seasons, the ease of sam pling, their abundance, and their ability to concentrate a
wide range of xenobiotics, marine magnoliophytes appear as very interesting organisms in the
context of environmental monitoring. Among the many studies of magnoliophytes, Posidonia
oceanica (Fam. Posidoniaceae ) appear s of particular interest .

Figure 1. Posidonia oceanica on the Tunisian coast

In the Mediterranean Sea, the Posidonia oceanica meadow is a powerful integrator of the
overall qualit y of marine waters [1-3]. Very widely distributed throughout the coastline,
which is particularly “receptive” to pollution, and connected to the sea bottom, it indicates by
its presence and vitality (or its regression materialized by dead ecosystems) the quality of the
water that drifts above it.
This paper represents a preliminary study regarding the c hemical composition of Posidonia
oceanica leaves. We first determine the optimal thin -layer chromatography (TLC) eluent
which allows the separation of a maximum number of components, i.e. photosynthetic
pigments [4-6]. In the second step, an identification of th e isolated pigments was attempted by
using UV/Vis densitometry directly on the TLC plate.

Experimental
The sample was collected from the Tunisian coast during May 2017. After harvesting , the
sample was washed with tap water for several times, was dried an d preserved on ice ( -28 °C)
for further processing. 50 g of seagrass were processed using a blender and extract ed in
methanol for 24 h using a Soxhlet. Next, t he sample was filtered and the solvent was removed
using a rotary ev aporator. The evaporated samp le was redissolved in methanol by stirring for
a couple of minutes, a nd then placed on the TLC plate (10 by 10 cm TLC Silica gel 60F 254
from Merck). The plate was eluted in a developing chamber with a mobile phase composed of
a hexane/acetone mixture (70:3 0 v/v). After drying in an oven, the densitometric evaluation of
the TLC plate was performed using the CAMAG TLC Scanner 3.

Results and discussion
The TLC plate (Fig. 2) was scanned in the 200–700 nm spectral region . Most peaks were
revealed at 250 nm (1 1 peaks) and only a few were found at 700 nm (4 peaks) . Fig. 3a shows
the overlaid chromatograms obtained at various wavelengths , while the dens itogram at 450
nm is illustrated in Fig. 3b. The major photosynthetic pigments iden tified in Posidonia
oceanic a with the Rf and the corresponding maximum absorbance are shown in table 1.

Figure 2 . TLC plate with Table 1. The major photosynthetic pigments identified in Posidonia
the identified pigments oceanica extract
Substance Rf Spectral data (nm)
Chlorophyll
a 0.42 426, 662
Chlorophyll
b 0.32 453, 643
β-carotene 0.81 451, 478
Xantophyll 0.31 421, 667

Figure 3 . (a) O verlaid densitograms at various wavelengths of photosynthetic pigments , and
(b) densitogram of detected peaks at 450 nm

Chlorophyll s a and b (green photosynthetic pigments) are characterized by two absorption
bands, located in the blue -violet and , respe ctively, red region of the visible domain (UV
domain not shown here). Carotenoids are revealed as yellow or orange pigments. The
migration of photosynthetic pigments was compared with standard samples under the same
experimental conditions.

Conclusion
The densitometric analysis at different wavelengths , which reveal s the presence of several
peaks corresponding to various photosynthetic pigments, represents a starting point towards a
more thorough chemical analysis of components found in Posidonia oceanica .

References
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