Fixed-bed adsorption kinetics study of plant total flavonoids based on a flow-injection online spectrophotometric method

Effective evaluation of the fixed-bed adsorption kinetics of plant total flavonoids is important for the design of adsorption separation of bioactive compounds. In this paper, a new merging-zone flow-injection analysis (FIA) method using Al(III) as the colorimetric agent was developed for automatic determination of total flavonoid concentration in the effluent of fixed-bed adsorption, to address the poor reproducibility of the conventional method. This method has a high sample throughput of 58 h −1 , reflecting adsorption change in each minute. The fixed-bed experimental parameters were optimized using a univariate experimental design based on the FIA method. The optimum condition for the adsorption of pomegranate peel total flavonoids were determined to be 0.5 g polyamide resin with size of 74–149 μm as adsorbent, with the initial concentration of 627.11 mg/L, the flow rate of 2.0 mL/min. Under the condition, breakthrough curves were precisely established for the adsorption of pomegranate peel total flavonoids, and the breakthrough time and adsorption capacity were determined to be 20.45 min and 60.17 mg/g, respectively. It’s found that Yoon-Nelson, Thomas and Bohart-Adams kinetic models were all able to fit the breakthrough curves well. The 80 % methanol aqueous solution was selected as the desorption solvent, and the optimal desorption flow rate was 2.5 mL/min. The FIA method can monitor the whole process of fixed-bed adsorption online and is suitable for different fixed-bed adsorption systems. The results obtained with the automatic flow method showed good agreement with the conventional method. The FIA method holds significant promise for studying and monitoring adsorption processes, due to its automatic on-line nature, high precision, low consumption of reagent and sample, and the ability to generate large quantities of highly accurate adsorption data.