Ultra-High-Performance Micellar Liquid Chromatography Comparing Tween 20 and Tween 40 for the Determination of Hydroxycinnamic Acids

A simple and green ultra-high-performance micellar liquid chromatography (MLC) method was developed here, comparing Tween 20 and Tween 40 for the first time as the only mobile phase modifiers with a C18 column. Its application to the separation of nine hydroxycinnamic acid (HCA) derivatives (cinnamic, caffeic, ferulic, sinapic, o-, m-, p-coumaric, 3,4-dihydroxyhydrocinnamic, and chlorogenic acids) was made, due to their importance as antioxidants in a variety of natural beverages such as wine and coffee. The optimal conditions of 45 °C temperature (T), 1% surfactant in the mobile phase, and pH control with 2.5 mM sulfuric acid were determined and used to elucidate the analytical figures of merit. Although the effect of these conditions was insignificant between the two surfactants, the nine-component HCA mixture was separated faster—in about 15 min—and with less peak tailing using Tween 20 than with Tween 40. The linearity of the Van’t Hoff (lnk versus 1/T) plots was evident for Tween 20, indicating a single retention mechanism—but less so for Tween 40. The equilibrium constants of the analytes with the micelles and the stationary phase were calculated. The developed method was successfully used to analyze organic red wine, spiked organic red wine, and green coffee diet pills. The percent recoveries of the nine HCA compounds spiked in the organic red wine ranged from 90% to 107%. The green coffee extract diet pills showed the presence of a significant amount of chlorogenic acid.

Comparison of Phenolic Compound Separations by HPTLC and PPEC with SDS as the Mobile Phase Component

The application of the surfactant (sodium dodecyl sulphate, SDS) as the component of the water-organic mobile phase in thin-layer chromatography and pressurized planar electrochromatography is presented. The influence of various variables on the separation of various phenolic compounds (flavonoids and phenolic acids) as model compounds with systems containing surfactant is discussed. The effect of concentration of butanol and SDS as well as pH of the mobile phase buffer on migration distance of the solute zones is investigated. The presence of SDS in the eluent affects the butanol solubility in the mobile phase. It allows using higher organic solvent concentration systems compared with the mode without surfactant. The amount of SDS in the eluent has the effect on the solute retention, whereas the eluent buffer pH affects the migration distances of ionisable phenolic acids both in HPTLC and PPEC. The migration distances of flavonoid glycosides are considerably longer than those of pure flavonoids. Considering second group of investigated solutes, derivatives of the benzoic acid migrate longer distances in comparison with the cinnamic acid ones. In addition, in the majority of experiments, ionisable compounds (phenolic acids) migrate longer distances in PPEC than nonionisable compounds (flavonoids). Additionally, the order of solutes differs in the PPEC and HPTLC system.