Phosphonium based anion exchange resin for enrichment of phenolic acids.

The aim of this work is to investigate the efficiency of a phosphonium-based strong anion exchange sorbent for the extraction of some selected phenolic acids. The material was synthesized through chloromethylation of a porous poly(styrene-divinylbenzene) substrate with high degree of crosslinking, followed by quaternarization with tributyl phosphine. The parameters affecting the solid phase extraction of five phenolic acids, namely chlorogenic acid, caffeic acid, dihydroxybenzoic acid, ferulic acid and rosmarinic acid were optimized. The sample pH and the type, volume and concentration of the eluting solutions were investigated. The analysis of the phenolic acids after extraction was performed using HPLC with diode array detection. Limit of detection, limit of quantitation, linear range, correlation coefficient and reproducibility for the determination of the phenolic acids were estimated. The retention of the phenolic acids on the developed phase was studied using breakthrough analysis. The experimental breakthrough curves were fitted by Boltzmann's function, and the regression parameters were utilized for the determination of the breakthrough parameters. The results obtained using the developed phase were compared with those obtained by the commercially available Oasis MAX sorbent. The proposed approach was successfully applied for the extraction and pre-concentration of rosmarinic acid from rosemary leaf (Rosmarini folium) alcoholic extract.

Does the emulsification procedure influence freezing and thawing of aqueous droplets?

Here we investigate the freezing and thawing properties of aqueous solutions in oil emulsions, with a particular focus on investigating the influence of the oil and surfactant and the stirring time of the emulsion. Specifically, we employ optical cryomicroscopy in combination with differential scanning calorimetry to study the phase behavior of emulsified 25 wt. % ammonium sulfate droplets in the temperature range down to 93 K. We conclude that the nucleation temperature does not vary with oil-surfactant combination, that is, homogeneous nucleation is probed. However, incomplete emulsification and non-unimodal size distribution of dispersed droplets very often result in heterogeneous nucleation. This in turn affects the distribution of freeze-concentrated solution and the concentration of the solid ice/ammonium sulfate mixture and, thus, the phase behavior at sub-freezing temperatures. For instance, the formation of letovicite at 183 K critically depends on whether the droplets have frozen heterogeneously or homogeneously. Hence, the emulsification technique can be a very strong technique, but it must be ensured that emulsification is complete, i.e., a unimodal size distribution of droplets near 15 µm has been reached. Furthermore, phase separation within the matrix itself or uptake of water from the air may impede the experiments.