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 ( C W ), the liquid to solid ratio ( R L/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.