Innovative combination of thermal desorption with on-line solid phase extraction reversed phase liquid chromatography applied to targeted nutrimetabolomics in human biofluids

This study proposed for the first time the use of thermal desorption in the on-line solid phase extraction coupled with reversed phase liquid chromatography (on-line SPE-RPLC) using mixed mode polymeric sorbents. This analytical strategy was applied to the on-line SPE-RP-LC targeted analysis of a model set of 34 human gut metabolites characterized by heterogeneous physicochemical properties (e.g., octanol–water partition coefficient in the range -0.3 – 3.4). The novel temperature-assisted on-line SPE approach was investigated in comparison with the conventional desorption strategies at ambient temperature based on the use of (i) an optimized elution gradient or (ii) an organic desorption followed by post-column dilution. The thermal desorption strategy has been shown to be better performing and suitable for the development of a reliable and sensitive method for the analysis of the model group of analytes in urine and serum. In more detail, under the optimized experimental conditions (Isolute ENV+ sorbent, desorption temperature 120°C, desorption time 5.5 min), the proposed method provided negligible matrix effects in both biofluids for almost all target analytes. Moreover, method quantification limits were in the ranges 0.026-7.2 μg L-1 and 0.033- 23 μg L-1 for urine and serum, respectively, i.e., comparable to or lower than those reported in methods previously published.