Online Electroextraction–NanoESI–MS for Rapid Analysis of Catecholamines in Urine

The direct mass spectrometric analysis of complex biological samples is often hindered by matrix interference and the need for extensive sample preparation. In this study, an online electroextraction method based on nano-electrospray mass spectrometry (OEE–nESI–MS) was proposed for the high-sensitivity and rapid analysis of urine samples. Compared with other methods, OEE–nESI–MS requires only 5 μL of sample and 35 μL of extraction solvent to achieve the migration and simultaneous ionization of the target from the sample solution to the extraction solvent in the nano tip, and online extraction and simultaneous analysis can be achieved within 8 min, while maintaining comparable sensitivity to other detection methods. The OEE–nESI–MS showed good linearity (R² > 0.995) in the range of 1–600 ng mL^–1 for the five catecholamines (CAs) in urine, with detection limits as low as 0.39–0.89 ng mL^–1 with recoveries of 91.9–104.9% (RSD ≤ 8.9%). Exploration of the OEE–nESI mechanism emphasized the electric field applied as a key factor facilitating online electroextraction. The OEE–nESI–MS was successfully applied to the analysis of five CAs in real urine samples. This advancement provides a very simplified solution for the online rapid, highly sensitive, and quantitative determination of complex samples.