Lab-in-syringe automated supramolecular solvent-based electrolyte-assisted microextraction coupled on-line to liquid...

For the determination of capsaicinoids in chili spices, an automated lab-in-syringe procedure coupled on-line with liquid chromatography was developed for the first time. It involves the micelle-mediated isolation of capsaicinoids from the sample matrix followed by the pre-concentration of the analytes into the supramolecular solvent that was obtained in-situ due to coacervation induced by the fatty acid-based deep eutectic solvent. The 10 % aqueous solution of bio-based surfactant alkyl polyglucoside C_8-C₁₀ was used for analytes isolation. No toxic organic solvents were required for sample preparation. The supramolecular solvent precursors include alkyl polyglucoside C_8-C₁₀ as an amphiphile and heptanoic acid-based deep eutectic solvent as a coacervation agent. Individual components of deep eutectic solvent are tetrapropylammonium bromide, heptanoic acid, and formic acid in a molar ratio of 1:3:1. The phase separation was facilitated using 10 % aqueous solution of sodium chloride as electrolyte, which additionally increases the ionic strength promoting a salting-out effect. The linear ranges were of 0.1 ̶ 20 mg L^-1 with a regression coefficient of 0.9997 for nordihydrocapsaicin, capsaicin and dihydrocapsaicin. The limits of detection and quantification, calculated from a blank test based on 3 σ and 10 σ were 0.03 mg L^-1 and 0.1 mg L^-1, respectively. The intra-day repeatability values were <5.1 % while inter-day repeatability was <6.1 %. Relative recovery values were in the range of 80 ̶ 108 %. The developed method does not require centrifugation and has been easily coupled online with liquid chromatography, allowing full automation of the preconcentration and determination steps.