A simple, effective and highly sensitive analytical method used for the determination of caffeine in tea and energy drink samples, and method optimization using a central composite design

Abstract

A rapid, simple and highly sensitive analytical method based on a microextraction method, followed by high-performance liquid chromatography was developed for the determination of caffeine in different tea and energy drink samples. Important factors in the microextraction process, including salt, pH, volume of extraction solvent and volume of disperser solvent, were optimized using response surface methodology (RSM) based on central composite design (CCD). Under the optimum conditions, the calibration curves showed high levels of linearity (R² > 0.9805) for caffeine in the range of 1–200 ng mL⁻¹. The limit of detection (LOD) and limit of quantitation (LOQ) were obtained to be 0.9 ng mL⁻¹ and 2.9 ng mL⁻¹, respectively. The relative standard deviations (RSD) for seven analyses were 3.8%, and the recovery was 97%. A clean separation and good chromatogram were readily achieved without the presence of matrix interference. A comparison of this method with other methods showed that the proposed method is an accurate, rapid and reliable sample pre-treatment method that gives a very good enrichment factor and detection limit for determining caffeine in different tea and energy drink samples.