Flower honey matrix for in situ deep eutectic solvent formation and microextraction: liquid chromatographic determination of sulfonamides after derivatization.

The honey matrix contains sugars and water, which can act as components for the in situ formation of a hydrophilic deep eutectic solvent (DES). This enables liquid-phase microextraction into polar solvents without dilution of the sample, owing to the salting-out effect of the DES precursor and the reduced viscosity of the honey. Moreover, the resulting DES can serve as a medium for the derivatization of target analytes. To demonstrate this possibility, the determination of sulfonamides (sulfadiazine, sulfamethoxazole, sulfamonomethoxine, and sulfadimidine) in flower honey by high-performance liquid chromatography with spectrophotometric detection (HPLC-UV/Vis) was chosen as an analytical task. The developed approach involves in situ formation of a DES from sugars and water of the flower honey matrix and choline chloride; derivatization of the sulfonamides in the DES medium; and liquid-phase microextraction of the derivatives into acetonitrile, with choline chloride simultaneously providing the salting-out effect. For the first time, 5,7-dichloro-4,6-dinitrobenzofuroxan was proposed as a derivatization agent for the sulfonamides determination by HPLC-UV/Vis. Validation of the procedure showed limits of detection of 5-10 μg kg-1, linear ranges of 15(30)-150 μg kg-1 and relative standard deviations below 14 %, and relative bias below 20 %. The results demonstrate that the flower honey matrix itself can be turned into the functional DES medium enabling derivatization and microextraction in a single workflow suitable for the determination of trace concentrations of sulfonamides.