Determination of antifungal caspofungin in RPMI-1640 cell culture medium by column-switching HPLC-FLD

The actual scenario in the fight against fungal infections forces researchers to carry through with resistance studies to improve the therapies. These studies, which are performed in cell culture media, need accurate and sensitive analytical methodologies. That is why, in this work, an analytical method for caspofungin (CSF) concentration determination in RPMI-1640 cell culture medium with on-line sample treatment was developed and validated. CSF concentration was determined by HPLC-FLD using a column-switching procedure. The chromatographic analysis was carried out in less than 10 min using a C8 column (4 × 4 mm, 5 μm) as extraction stationary phase and a HSS T3 column (4.6 × 100 mm, 5 μm) as the analytical column. The used mobile phases were mixtures of phase A: pH 2 (adjusted with TFA) aqueous phase and phase B: ACN. For the extraction, the composition was (95:5, A:B v/v) and for the analysis (60:40, A:B v/v), both done in isocratic elution mode. These chromatographic conditions allowed reaching a limit of quantification of 10 μg/L, using 100 μL of sample with an injected volume of 40 μL. The proposed method was successfully validated in terms of selectivity, carryover, linear concentration range, accuracy and precision according to the criteria established by the Food and Drug Administration. Available amount of CSF in RPMI-1640 solution was found critical. CSF concentrations remained stable up to 2 h at room temperature. The developed method was applied for the direct analysis of CSF concentrations from in vitro experiments in presence of C. glabrata (CAGL18). The results highlight the decrease of cell proliferation even if the CSF amount decreases too, which asks question about the real value of the efficient concentration for CSF antifungal activity.