Simple and rapid HPLC method for the determination of quinine in soft drinks using fluorescence detection

A simple and rapid reversed-phase high performance liquid chromatographic (RP-HPLC) method was developed for the routine determination of quinine in soft drinks, which is added when a bitter taste is required. The analytical column, an MZ Kromasil, C-18, 5 mum, 250 x 4 mm(2), was operated at ambient temperature with backpressure of 230 kg/cm(2). The mobile phase consisted of CH3OH-CH3CN-CH3COONH4 0.1 M, (45: 15: 40 %v/v/v) and was delivered at a flow rate of 1.0 mL/min. Fluorescence detection was performed at 325 nm (excitation) and 375 nm (emission). For the quantitative determination of quinine, salicylic acid was used as internal standard at a concentration of 0.5 ng/muL, resulting in a detection limit (signal-to-noise ratio 3: 1) of 0.3 ng, while the upper limit of linear range was 0.7 ng/muL. Analysis time was less than 5 min. The statistical evaluation of the method was examined performing intraday (n = 8) and inter-day calibration (n = 8) and was found to be satisfactory, with high accuracy and precision results. The method was applied to the analysis of soft drinks containing quinine, such as tonic water and bitter lemon. No interferences from other food additives were observed.