Retention Of Phenolic Acids Research Articles

Mobility and retention of phenolic acids through a goethite-coated quartz sand column

In the present work, a natural mineral, such as quartz sand (NQS), was modified with a small amount of goethite to yield a goethite-coated quartz sand (GCQS) adsorbent that was used for depolluting water contaminated with a series of phenolic acids that have various numbers and positions of hydroxyl groups in the benzene ring. Thus, the transport and retention of gallic acid and its derivatives from water onto GCQS column were carried out at ambient temperature. Prior to the column adsorption experiments, the GCQS adsorbent was characterized with various methods such as X-ray diffraction, X-ray fluorescence, and scanning electron microscopy (SEM) coupled with X-ray microanalysis and zeta potential. The amount of adsorbed phenolic acid at the GCQS-water interface was found to be controlled by hydrogen bonding and electrostatic interactions, and it was tuned by varying parameters such as the aqueous phase pH, the ionic strength and the nature of inorganic ions. In addition, the effect of the number and the positions of hydroxyl groups (OH) on the benzoic acid mobility was also examined. The data indicate that adding no more than 2.5 wt% of goethite to NQS shifts the solid Isoelectrical Point from 2.5 for pure NQS to 5.7 for GCQS and leads to a 16-fold increase in the maximum adsorbed amount of gallic acid. Moreover, the adsorbed amount of gallic acid was also found to decrease in the presence of inorganic anions in the order Cl− > NO3− > SO42− > H2PO4−, and to decrease as the ionic strength of the aqueous phase increases. This study brings new insight to the role of colloid and interface science for mineral processing and the environment.

Simultaneous isocratic separation of phenolic acids and flavonoids using micellar liquid chromatography

The simultaneous isocratic separation of a mixture of five phenolic acids and four flavonoids (two important groups of natural polyphenolic compounds with very different polarities) was investigated in three different RPLC modes using a hydro-organic mobile phase, and mobile phases containing SDS at concentrations below and above the critical micellar concentration (submicellar LC and micellar LC (MLC), respectively). In the hydro-organic mode, methanol and acetonitrile; in the submicellar mode methanol; and in the micellar mode, methanol and 1-propanol were examined individually as organic modifiers. Regarding the other modes, MLC provided more appropriate resolutions and analysis time and was preferred for the separation of the selected compounds. Optimization of separation in MLC was performed using an interpretative approach for each alcohol. In this way, the retention of phenolic acids and flavonoids were modeled using the retention factors obtained from five different mobile phases, then the Pareto optimality method was applied to find the best compatibility between analysis time and quality of separation. The results of this study showed some promising advantages of MLC for the simultaneous separation of phenolic acids and flavonoids, including low consumption of organic solvent, good resolution, short analysis time, and no requirement of gradient elution.

Fast separation of phenolic acids in normal-phase partition chromatography

Normal-phase partition chromatography on CN-bonded silica column was investigated for a fast separation of a number of benzoic and cinnamic phenolic acids. Various partition systems involving formic, acetic and phosphoric acids were used; the capacity factors and selectivities of the solutes calculated in the different chromatographic conditions are compared. The results obtained show that the partition system based on the use of formic acid exhibits excellent performance. In addition, small changes in the content of the alcoholic and aqueous acid parts of the mobile phase can cause a significant change in retention of phenolic acids.