Electromembrane Extraction and Dual-Channel Nanoelectrospray Ionization Coupled with a Miniature Mass Spectrometer: Incorporation of a Dicationic Ionic Liquid-Induced Charge Inversion Strategy

Green analytical chemistry aims at developing analytical methods with minimum use and generation of hazardous substances for the protection of human health and the environment. To address this need, a green analytical protocol has been developed for the analysis of anionic compounds integrating electromembrane extraction (EME), dual-channel nanoelectrospray ionization (nanoESI), and a miniature mass spectrometer. Haloacetic acids (HAAs) have attracted considerable public concern due to their adverse effects on human health and were selected as model analytes for method development. A flat membrane EME device was developed and assembled in-house. Optimization of fundamental operational parameters was performed using single-factor test and response surface methodology. Both the EME acceptor phase and an imidazolium-based dicationic ionic liquid (DIL), 1,1-bis(3-methylimidazolium-1-yl) butylene difluoride (C4(MIM)2F2), were subjected to dual-channel nanoESI and miniature mass spectrometry analysis based on a charge inversion strategy, where positively charged complexes were formed. Enhancement in signal intensity by as much as 2 magnitudes was achieved in the positive-ion mode compared to the negative-ion mode in the absence of the dicationic ion-pairing agent. The developed protocol was validated, obtaining good recoveries ranging from 82.7 to 109.9% and satisfactory sensitivity with limits of detection (LODs) and quantitation (LOQs) in the ranges of 1-5 and 2-10 μg/L, respectively. The greenness of the analytical procedure was assessed with a calculated score of 0.71, indicating a high degree of greenness. The developed method was applied to the analysis of real environmental or municipal water samples (n = 16), exhibiting appealing potential for outside-the-laboratory applications.