This study aimed to determine the quality of bark willow raw material available in different pharmaceutical preparations. The comparative analysis by Thin Layer Chromatography (TLC) was the base for determination of taxonomical origin of examined raw materials. Salix alba L. was provided from Wroclaw surroundings and Salix purpurea L. was collected in Bieszczady region. A quality evaluation was established by determination of salicin content by HPLC method. The results indicated that salicin content in Salix purpurea from natural environment was 2%. This value increased into 4% after alkaline hydrolysis. This fact is connected with decomposition of salicortin as an influence of alkaline environment of reaction. Moreover, these results were confirmed by comparative TLC analysis of samples prepared in cold extraction, in hot extraction and in hot extraction with alkaline hydrolysis.

The content of salicin in Salix alba from natural environment and in pharmaceutical preparation was 1%. Simultaneously, the presence of derivative with similar retention time to salicin (RRT=1,1) was detected. The different chemical structure was confirmed by UV-VIS analysis with DAD detector. TLC analysis confirmed in all samples, identified as Salix alba, a slight amount of salicin (RT=0,38) and non-identified derivative (RT=0,42), which gives a yellow colour of solution of vanillin.
This derivative was not a result of incorrect samples preparations or thermal decomposition of salicin, which is evidenced by simplified kinetics analysis of hydrolyzate and was not a metabolism product of salicin as well.
Our study demonstrates that it is possible to misinterpret the content of salicin in Salix alba due to the incorrect interpretation of HPLC profiling patterns.
To eliminate possible mistake in calculation, it is suggested to perform a comparative analysis of UV-VIS spectrum or addition a salicin standard into examinated sample.

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