Selective extraction and preconcentration of melatonin mediated by hydrophobic natural deep eutectic systems

Abstract

Background: Sample preparation is the key to achieve the goals of Green Chemistry and represents the highest source of the total negative impact of analytical methodologies on the environment. Therefore, assessing the greenness of analytical procedures and, if possible, reducing their impact on the environment and workers is necessary. In this sense, the alternative analytical techniques must be cost-effective, eco-friendly, and sustainable, to focus these issues and ensure efficient extraction, preconcentration, and analysis of the targeted compounds.Results: The selective extraction and preconcentration of melatonin (MEL) mediated by hydrophobic natural deep eutectic systems (HPB-NADES) from three native plant growth-promoting rhizobacteria (PGPR) cultures was studied and performed. The HPB-NADES based on menthol:thymol showed excellent selectivity for MEL, evaluated through the 3-indole acetic acid and tryptophan recovery and the matrix effect values. The extraction recovery of MEL was 97.9 to 100.3%, with an RSD of less than 3% and an interesting enrichment factor of 14.7–15.2. Finally, the LOD and LOQ for MEL were 23.4 and 71.4 ng/L, with a linear range of 71.4–5000 ng/Lshowing good linearity (F less than 1.16). The sustainability of the methodology showed scores of 0.71 and 0.66, and a chemical risk corresponding to the use of 0.812 g of chloroform per extracted and analyzed sample.Conclusions: The present study introduced, for the first time, a green analytical method for selectively extracting and quantifying MEL from three PGPR cultures using HPB-NADES. The methodology exhibited favorable linearity, LOD, LOQ, and extraction recoveries with negligible matrix effects. The use of environmentally friendly solvents and sample preparation techniques ensures the sustainability of the approach. Additionally, the present work highlighted the potential of PGPR in improving plant adaptation to abiotic stress under low MEL concentrations.