Fluorescence quenching and measurement of glutathione in fresh vegetables

A new method for the determination of glutathione was established based on the principle of fluorescence quenching. The reaction mechanism has been studied by the measurement of fluorescence lifetime and based on the Stern–Volmer plot. The binding constant, K = 9.86 × 105 J mol−1 and the number of binding sites n = 1.12 were obtained against this reaction. The thermodynamic parameters were estimated. The data, ΔG = −34.19 KJ mol−1, ΔH = −182.2 KJ mol−1, and ΔS = −496.8 J K−1 mol−1 showed that the reaction was spontaneous and exothermic. The calibration curve was found to be linear between the fluorescence quenching (F 0 /F) and the concentration of glutathione with the range of 3.0 × 10−5–3.6 × 10−3 g/L. The detection limit was 4.5 μg/L and the relative standard derivative was 3.32% for 11 replicate determination of 6.0 × 10−4 g/L glutathione. This method can be used for the determination of glutathione in fresh vegetables with satisfactory results.