Insights on the impact of deep eutectic solvents on the composition of the extracts from lemon (Citrus limon L.) peels analyzed by a novel RP-LC–QTOF-MS/MS method

Extraction of polyphenolic compounds from lemon peels using deep eutectic solvents (DES) was investigated. A choline chloride-based DES paired with glycerol was used as the extraction solvent, alternative to conventional ones. Response surface methodology (RSM) was employed to optimize the extraction parameters, namely, the water concentration (CW), the liquid to solid ratio (RL/S) and the duration of the extraction (t) in terms of total phenol content and radical scavenging activity; the conditions that can be recommended as optimum for the recovery of the phenolic compounds were 55% (w/v), 13 mL g−1 and 36 min, respectively. The composition of the obtained extracts under optimum conditions was compared with extracts prepared in ethanol and water. A novel reversed phase ultra-pressure electrospray liquid chromatographic time-of-flight mass spectrometric method (RP-UPLC–ESI–QTOF-MS) was developed and validated for the determination of individual bioactive compounds in the extracts through target, suspect, and non-target screening. The developed RP-UPLC–ESI–QTOF-MS methodology was validated and presented adequately low limits of detection (LODs) and limits of quantification (LOQs) over the ranges 8.64 (quercetin)–30.4 μg L−1 (p-coumaric acid), and 25.9 (quercetin)–91.2 μg L−1 (p-coumaric acid), respectively. The RSD% of the within-day and between-day assays were lower than 3.2, and 9.8, respectively, demonstrating good method precision. Overall, 10 compounds were determined and quantified through target screening, as well as 4 suspect, and 9 non-target compounds were tentatively identified in the extracts by means of suspect and non-target screening, respectively.