An existing method HPLC method (ISO 14502) was applied and validated for the matrix of coffee leaf tea (genus Coffea). This method is usually used to measure conventional Camellia sinensis teas with high-performance liquid chromatography (HPLC). For the purposes of method validation, robustness, applicability, measurement precision and linearity were investigated. The focus was kept on the ingredients epigallocatechin gallate (EGCG), caffeine and chlorogenic acid.

It was possible to determine a high level of robustness, applicability, and measurement precision of this method by the measurement of caffeine and chlorogenic acid in authentic sample matrices. The repeatability standard deviation of caffeine was lower than ±0.09 g/100 g and that of chlorogenic acid was lower than ±0.08 g/100g. The repeatability coefficient of variation (CV) of caffeine ranged between ±0.93% and ±4.52% and that of chlorogenic acid was between ±1.20% and ± 21.10%. The reproducibility standard deviation of caffeine was lower than ±0,03g/100g and that of chlorogenic acid is lower than 0.03 g/100 g. The reproducibility CV of caffeine was between ±0.68% and ±2.92% and that of chlorogenic acid is between ±0,91% and ±5,36%. These results show a high level of robustness, and measurement precision in each case. However, the used samples were unsuitable for determining the robustness, applicability, and measurement precision of EGCG because its amount in coffee leaves was too low or even undetectable. A detection limit (LOD) for EGCG in coffee leaf of 0.02 g/100g and a quantification limit (LOQ) of 0.04 g/100g were determined.

All in all, this method was judged as being suitable for the analysis of coffee leaf tea. Specifically, the ingredients EGCG, caffeine and chlorogenic acid can be reliably determined.