Accurate and real-time measurement of flavonoid concentration during the adsorption process is vital for understanding its adsorption mechanism. In this study, a new merging-zone flow injection analysis (FIA) method based on the NaNO 2 -AlCl 3 -NaOH colorimetric reaction was developed for automatic determination of flavonoid concentration in plant extracts and in adsorption solution during batch adsorption process. The method parameters were optimized using a univariate experimental design, and rutin standard solutions in the concentration range of 25–800 mg/L showed good linearity (R 2 = 0.9994) with the FIA signal. The sample throughput was 40 h -1 and the limit of detection was 4.888 mg/L. The adsorption kinetics, isotherms, and thermodynamics of flavonoids from Dracocephalum Moldavia onto HPD 300 resin were investigated at varying initial concentrations and temperatures. The pseudo-first-order kinetic model was found to be suitable at 25 and 35 ℃, while the pseudo-second-order model exhibited superior performance at 45 ℃. The Freundlich model was found to be appropriate for describing the adsorption isotherm. The thermodynamic parameters ΔG and ΔH were both negative, and ΔS was positive, indicating that the adsorption process of flavonoids onto the HPD 300 resin is spontaneous and exothermic. The FIA method can effectively decrease the errors arising from the big adsorption volume change in conventional method during the batch adsorption. The developed method enables rapid and online determination of total flavonoids, reducing both time and labor costs, suitable for routine measurements as well as online monitoring of adsorption processes.
Chao Lv,Ruiyang Wang,Jia Gao,Ning Ding,Shunni Dong,Jingjing Nie,Junting Xu,Binyang Du
Enhanced phase separation and inverse order-to-order phase transition with increasing temperature was observed for a series of poly (acrylic acid)- b -poly (propylene oxide)- b -poly (acrylic acid) triblock copolymers with various block lengths by temperature-variable synchrotron small-angle X-ray scattering (SAXS). This abnormal phase behavior was attributed to the change of hydrogen (H)-bonding interaction in block copolymers upon increasing temperature and theoretically explained from thermodynamic viewpoint. The temperature-dependent FTIR analysis revealed that increasing temperature led to the weakening of overall H-bonding interactions and the increase of free C O and C–O–C groups. The Flory-Huggins interaction parameter χ of PAA and PPO blocks was positive and increased with increasing temperature as determined from the SAXS profiles of disordered block copolymer. The thermodynamic calculation indicated that the increase of Δ H was larger than the decrease of – T Δ S with increasing temperature because of the relatively large value of χ , leading to the increase of overall Δ G mix and hence the enhanced phase separation at higher temperature.
危险品化学品经营许可证（带存储）