As for the thin-layer chromatographic identification,
the methanolic extract showed the presence of
oxyresveratrol as the major component, appearing as a
dark spot at 254 nm and fluorescing at 365 nm with an
Rf value of 0.27 on the TLC plate. The compound also
developed a pink spot with vanillin-sulfuric acid reagent
on the TLC plate (Figure 4).
For analysis of the oxyresveratrol content in the
samples, a capillary zone electrophoretic method was
developed. Standard solutions of oxyresveratrol with
benzoic acid as internal standard were prepared and
analyzed (Figure 5). The ratio of the area under peak of
oxyresveratrol to that of benzoic acid was then calculated
for each concentration of oxyresveratrol. A standard
curve was obtained from the plot of the ratio against the
concentration (Figure 6) and then used for determining
the oxyresveratrol content of each sample (Table 1).
This analytical method was validated for its accuracy and
precision, and the results are shown in Table 2. In this
study, it appears that the oxyresveratrol content in A.
lakoocha heartwood varied from one sample to another,
in the range of 0.44 – 2.35 % (Table 1). These values
are, however, greatly different from those earlier reported
by Sambhandharaksa et al5, which were described as 11
– 13 %. A possible explanation for this discrepancy is
that samples from different sources may contain different
amounts of oxyresveratrol. It should be noted that in the
study by Sambhandharaksa et al5 , the plant materials
were collected from the wild, whereas the samples in this
investigation were obtained from drugstores. This may
suggest that for some reason, the quality of the
commercial products is much lower than that of the
samples collected from the wild, in terms of
oxyresveratrol content. Neverthelsess, it should also be
kept in mind that the analytical method used in this
investigation is different from that in the previous report.5
It is clear that a chemical study properly designed for
comparing the oxyresveratrol content in the commercial
and the wild samples is needed before any conclusion
can be drawn.