In Situ Liquid-Phase-Adsorption Measurement System Based on Fiber-Optic Sensing with the Aid of Membranes

At present, liquid phase adsorption (LPA) is still being quantitatively characterized in the way of manual sampling and off-line determination because of the complexity of the system comparing to gas adsorption. This paper describes a novel method for in situ, real-time measurement of LPA in general based on fiber-optic sensing (FOS) with the aid of membranes for the first time. A self-made measurement vessel was assembled from an adsorption bag, thermostatic devices with a stirrer, and a fiber-optic dipping probe. Also, macroporous adsorption resins (MARs) and rutin were chosen as model adsorbent and adsorbate to establish the FOS system. Here, in situ light absorption measurement was achieved by eliminating interference of adsorbent particles via encapsulating them with a membrane into the adsorption bag. In situ LPA measurement of rutin solution on MARs was obtained by detecting light absorption at 353 nm using dipping probe, in the broad concentration range from 0.3 to 60 mg/L with excellent linearity (R ² = 0.9996). In situ measurements of adsorption and desorption kinetics on five kinds of MARs with different polarities were systematically carried out, showing that the adsorption process obeyed the pseudo-second-model. As well as, the system was proved to be highly accurate and reproducible. More importantly, this method enabled to study the initial stage of the adsorption process, starting from the time of the first second, which is the most important part in the adsorption kinetics, and this is impossible for traditional sampling methods. The successful application of FOS to in situ measurement of LPA not only contributes to fast, automatic, and real-time monitoring of LPA process but also enriches the research connotation of adsorption.