Validation evaluation of the spectrophotometric determination of the sum of aromatic compounds in the herb and essential oil of thyme creeping

Introduction. Thymol and carvacrol, belonging to the class of aromatic monoterpenes, are the main biologically active components of the essential oil of the herb thyme creeping (Thymus serpyllum L.). Liquid extract of thyme creeping, which is the basis of a number of domestic preparations of expectorant action, is standardised by thymol content, determined by gas chromatography or HPLC. At the same time, thyme herb is not standardised by the Russian Pharmacopoeia even by the content of essential oil. Thyme is a polymorphic species, the chemical composition of essential oil of which can vary, there are chemotypes with almost complete absence of thymol and carvacrol.

It is expedient to supplement the standardisation of thyme herb by determination of essential oil and the sum of phenolic components in it. This will allow to carry out end-to-end standardisation of raw materials and preparations for the main active substances - thymol and carvacrol. A rapid method for the determination of the sum of aromatic monoterpenes in the essential oil of thyme creeping based on spectrophotometric measurement of the optical density of an alcoholic solution of the essential oil was proposed earlier.

The aim of the work was to validate the spectrophotometric method for the determination of the sum of aromatic compounds in terms of thymol in the essential oil of the herb thyme creeping.

Materials and Methods. UNICO 2802 spectrophotometer (Russia), ADV-200M analytical balance (Russia), thymol substance with the content of the main substance 99.9% (Fluka, Germany), herb of thyme creeping, harvested in the botanical garden of Kazan State Medical University in 2023 were used. Thymol substance was used for the preparation of standard solutions and in the method of additives. The optical density of the solutions was measured at 277 nm in cuvettes with a thickness of 10 mm.

Results. The spectrophotometric method for the determination of the sum of aromatic compounds in terms of thymol in the essential oil of thyme creeping thyme was validated. Validation of the presented method, carried out in accordance with the requirements of GFA.1.1.0012 ‘Validation of analytical methods’ of the State Pharmacopoeia XV edition, showed its specificity, linearity in the range from 22.4 to 41.7 µg/ml (r = 0.9998), precision and correctness. The results are not burdened by systematic error. The relative standard deviation (RSD) does not exceed 2.0%.

Conclusions. The developed method for the quantitative determination of the sum of aromatic compounds in terms of thymol can be used to standardize both the creeping thyme herb itself and the essential oil obtained from it.