Abstract
Homogeneous liquid–liquid extraction (HLLE) has attracted considerable interest in the sample preparation of multi-analyte analysis. In this study, HLLEs of multiple phenolic compounds in propolis, a polyphenol-enriched resinous substance collected by honeybees, were performed for improving the understanding of the differences in partition efficiencies in four acetonitrile–water-based HLLE methods, including salting-out assisted liquid–liquid extraction (SALLE), sugaring-out assisted liquid–liquid extraction (SULLE), hydrophobic-solvent assisted liquid–liquid extraction (HSLLE), and subzero-temperature assisted liquid–liquid extraction (STLLE). Phenolic compounds were separated in reversed-phase HPLC, and the partition efficiencies in different experimental conditions were evaluated. Results showed that less-polar phenolic compounds (kaempferol and caffeic acid phenethyl ester) were highly efficiently partitioned into the upper acetonitrile (ACN) phase in all four HLLE methods. For more-polar phenolic compounds (caffeic acid, p-coumaric acid, isoferulic acid, dimethoxycinnamic acid, and cinnamic acid), increasing the concentration of ACN in the ACN–H2O mixture could dramatically improve the partition efficiency. Moreover, results indicated that NaCl-based SALLE, HSLLE, and STLLE with ACN concentrations of 50:50 (ACN:H2O, v/v) could be used for the selective extraction of low-polarity phenolic compounds. MgSO4-based SALLE in the 50:50 ACN–H2O mixture (ACN:H2O, v/v) and the NaCl-based SALLE, SULLE, and STLLE with ACN concentrations of 70:30 (ACN:H2O, v/v) could be used as general extraction methods for multiple phenolic compounds.
Highlights
Increasing demands on monitoring a large number of target compounds have promoted the development of multi-analyte analytical methods
For NaCl-based salting-out assisted liquid–liquid extraction (SALLE), shown in Figure 2a, extraction yields (EYs) of phenolic compounds increased as the salt concentration increased from
As the salt isoferulic acid, dimethoxycinnamic acid, cinnamic acid, kaempferol, and caffeic acid phenethyl ester concentration further increased to 125 g/L, slight growth in EYs was observed
Summary
Increasing demands on monitoring a large number of target compounds have promoted the development of multi-analyte analytical methods. To assess a broad spectrum of possible metabolites, metabolomics requires multi-analyte methods to analyze the entire metabolome [1,2]. As another example, improper usage and the cross-contamination of chemicals in agricultural practice may lead to multi-residues of contaminants in agricultural products. Especially the chromatography tandem mass spectrometry techniques, are capable of analyzing a large number of target compounds in a single analysis [5] Fingerprint profiles based on multi-analyte analysis of phytochemical compounds or volatile fractions in foods have been applied in foodomics for the issue of food quality [4].
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