Insights on the Extraction and Analysis of Phenolic Compounds from Citrus Fruits: Green Perspectives and Current Status

Citrus fruits (CF) are highly consumed worldwide, fresh, processed, or prepared as juices and pies. To illustrate the high economic importance of CF, the global production of these commodities in 2021 was around 98 million tons. CF's composition is considered an excellent source of phenolic compounds (PC) as they have a large amount and variety. Since ancient times, PC has been highlighted to promote several benefits related to oxidative stress disorders, such as chronic diseases and cancer. Recent studies suggest that consuming citrus fruits can prevent some of these diseases. However, due to the complexity of citrus matrices, extracting compounds of interest from these types of samples, and identifying and quantifying them effectively, is not a simple task. In this context, several extractive and analytical proposals have been used. This review discusses current research involving CF, focusing mainly on PC extraction and analysis methods, regarding advantages and disadvantages from the perspective of Green Chemistry.

Advanced Development of Supercritical Fluid Chromatography in Herbal Medicine Analysis

The greatest challenge in the analysis of herbal components lies in their variety and complexity. Therefore, efficient analytical tools for the separation and qualitative and quantitative analysis of multi-components are essential. In recent years, various emerging analytical techniques have offered significant support for complicated component analysis, with breakthroughs in selectivity, sensitivity, and rapid analysis. Among these techniques, supercritical fluid chromatography (SFC) has attracted much attention because of its high column efficiency and environmental protection. SFC can be used to analyze a wide range of compounds, including non-polar and polar compounds, making it a prominent analytical platform. The applicability of SFC for the separation and determination of natural products in herbal medicines is overviewed in this article. The range of applications was expanded through the selection and optimization of stationary phases and mobile phases. We also focus on the two-dimensional SFC analysis. This paper provides new insight into SFC method development for herbal medicine analysis.

A Rapid and Sensitive Method for the Simultaneous Determination of Multipolar Compounds in Plant Tea by Supercritical Fluid Chromatography Coupled to Ion Mobility Quadrupole Time-of-Flight Mass Spectrometry

In this study, matrix solid phase dispersion (MSPD) microextraction combined with supercritical fluid chromatography-ion mobility quadrupole time-of-flight mass spectrometry (SFC/IM-QTOF-MS) was used to analyze the multipolar compounds in plant tea. The parameters of stationary phase, mobile phase, make-up solution, temperature, and back pressure were optimized. The target analytes were gradient eluted in 8 min by supercritical CO₂ on a Zorbax RX-SIL column. Collisional Cross Section (CCS) values for single and multiple fields were measured. A series of validation studies were carried out under the optimal conditions, and the linear relationship and reproducibility were good. The limits of detection were 1.4 (Scoparone (1))~70 (Naringenin (4)) ng/mL, and the limits of quantification were 4.7 (Scoparone (1))~241 (Naringenin (4)) ng/mL. The recoveries of most compounds ranged from 60.7% to 127%. As a consequence, the proposed method was used for the separation and quantitative analysis of active ingredients in caulis dendrobii.

Analysis of flavonoids with unified chromatography-electrospray ionization mass spectrometry-method development and application to compounds of pharmaceutical and cosmetic interest

In this project, we aimed at analysing flavonoid-type compounds with unified chromatography (joining supercritical fluid chromatography and enhanced fluidity liquid chromatography with carbon dioxide-methanol mobile phases covering a wide range of compositions) and diode-array and electrospray ionization mass spectrometric detection (UC-DAD-ESI-MS). First, the chromatographic method was developed for 9 standard flavonoid molecules from three different families (flavanols, flavanones and flavonols, glycosylated or not), with a strong focus on mobile phase composition to achieve the elution of a wide range of flavonoids with good chromatographic quality (efficiency and resolution). For this purpose, two stationary phases were selected (ACQUITY UPC² DEA and Diol), and five different additives (formic acid, citric acid, phosphoric acid, methanesulfonic acid and ammonium hydroxide) were successively introduced in the methanol co-solvent. The composition containing 0.1% methanesulfonic acid in methanol was retained as it provided the best chromatographic quality together with the possibility of hyphenating the chromatography to mass spectrometry. The DEA column appeared to provide the best efficiency and was retained for further method development. The gradient method was then optimized to achieve a fast analysis, which involved elution with a wide range of mobile phase composition (from 20 to 100% co-solvent in methanol) together with reversed flow rate and reversed pressure gradients at fixed temperature. The final gradient lasted 10 min, followed by 2.5 min of re-equilibration. Then, ESI-MS detection was optimized. Because the single-quadrupole mass spectrometer employed (ACQUITY UPC² QDa) allowed the variation of only a few parameters, a design of experiments was used to define the best compromise for three parameters (probe temperature, cone voltage and capillary voltage). The make-up fluid introduced before entering the MS was also varied: different compositions of methanol-water containing either formic acid, ammonium hydroxide or sodium chloride were tested. The best results in terms of signal-to-noise ratio were obtained with methanol containing 20 mM ammonium hydroxide and 2% water. The optimal UC-DAD-ESI-MS method was then applied to two different flavonoid formulation ingredients. The first one, hidrosmin (5-O-(β-hydroxyethyl)diosmin), is known for its vasoprotective properties and therefore employed in pharmaceutical formulations. The second one, α-glucosyl-hesperidin (sometimes referred to as vitamin P), is employed in cosmetic formulations. Identification of the major compounds in each sample was achieved with the help of MS detection. Graphical abstract.

Preparation of two-dimensional magnetic molecularly imprinted polymers based on boron nitride and a deep eutectic solvent for the selective recognition of flavonoids

Two-dimensional (2D) boron nitride (BN) were developed as a 2D scaffold material in preparation of magnetic molecularly imprinted polymers (MMIPs).

Polymeric stationary phases based on poly(butylene terephthalate) and poly(4-vinylpirydine) in the analysis of polyphenols using supercritical fluid chromatography. Application to bee pollen

Two new polymer-based stationary phases; DCpak PBT (poly(butylene terephthalate)) and DCpak P4VP (poly(4-vinylpirydine)) were evaluated for the analysis of polyphenols using supercritical fluid chromatography (SFC). The compounds studied included phenolic acids and flavonoids. The different variables that influence the chromatographic separation, such as type and percentage of organic modifier, additive, pressure and temperature were examined. Using the DCpak P4VP column the retention was exceptionally high, obtaining better results with the DCpak PBT column. The separation of nine polyphenols was achieved using a gradient of modifier (methanol with 0.1% trifluoroacetic acid) from 5 to 50%, a pressure of 150 bar, a temperature of 35 °C and a flow-rate of 2 mL/min. The use of additives was necessary in order to obtain good peak shapes and efficiencies, achieving the best results with trifluoroacetic acid. LODs and LOQs values were lower than 5 μg/mL in all the cases; meanwhile, the %RSD values for method repeatability and inter-day reproducibility were lower than 3% and 10% respectively. Finally, the proposed method was successfully applied to the analysis of polyphenols in commercial bee pollen; four compounds, namely cinnamic acid, p-coumaric acid, catechin and quercetin were identified and quantified.