Recent applications of supercritical fluid chromatography in the analysis of polyphenols.

Polyphenols are a large group of plant secondary metabolites, synthesized mostly through the phenylpropanoid pathway, and they comprise flavonoids, stilbenes, lignans, and simple phenolic acids. The characterization of these natural compounds is challenging, due to the complexity of plant extracts, the variety of polyphenols forms in the various plant organs, and the limited availability of authentic standards. The analysis of polyphenols is mostly achieved by reversed-phase liquid chromatography (LC), but poor retention and resolution are often observed for the polar ones. Supercritical fluid chromatography (SFC) represents a versatile chromatographic technique, and a valid and greener alternative to traditional LC, suitable for a heterogeneous class of compounds as polyphenols, where very polar or chiral compound separation is requested. The advancements in instrumental technology allowed the coupling with mass spectrometry (MS) and the introduction of sub-2 µm stationary phases, and paved the way to the use of SFC for the analysis of these compounds. The present review provides an overview of the latest SFC methods for the characterization of polyphenols, over the period 2019-2024. Coupling with MS and applications in plants are mostly discussed in this review, along with other selected applications suitable to critically describe the state-of-the-art and potential of this technique in the field of polyphenol characterization. The survey indicated that SFC is still underutilized in this field, particularly in combination with MS, mainly because of the need for extensive optimization of several critical parameters. Most of the described works are quantitative targeted studies, and only a few reports use metabolomics approaches for large-scale analysis of polyphenols. As a result, SFC applications have been limited to a small range of polyphenols rather than complex mixtures, making this technique still not competitive with LC. Nonetheless, SFC has potential, especially in filling the existing gap of LC for analysis, as better characterizations can be obtained for polar and chiral polyphenols.