Development of a solid phase extraction-high-performance liquid chromatography-ultraviolet detector method for quality control of the rosemary-pepper tincture, a phytotherapic produced by living pharmacies in Brazil.

Ensuring the accurate measurement of the active components in herbal medicine is critical in maintaining their clinical effectiveness. One quality-controlled medicine is the rosemary-pepper tincture, a hydroalcoholic extract of Lippia sidoides leaves that contains the active ingredient, thymol. It is used as an antiseptic to treat injuries. Thus, a validated method for standardizing the active component was developed to extract the thymol and eliminate polar and nonpolar interferents, thereby extending the lifespan of the chromatographic column. To evaluate the adsorption of thymol into the flow, the adsorption data were adjusted using the Thomas model to obtain the maximum amount of adsorption, 4.33 mg/g. Factorial planning revealed that the best conditions for the adsorption and desorption of thymol were 1.4 mL of tincture in an SPE-C18 column and 2 ml of methanol/water (80/20) as eluent. Subsequently, the thymol was quantified using HPLC-UV spectroscopy, and the calibration curves were linear in the working range of 0.1-1.0 mg/mL (R2 = 0.997). The limits of detection and quantification were 0.02 and 0.06 mg/mL, respectively. The precision and accuracy were 95.8-103.8% at three different concentrations. Finally, the method proved robust against multiple applied variations and yielded satisfactory results within the analysis parameters.