Efficient and Wide Chemical-Space Ionization of Organic Contaminants Using LC-MS with a Miniaturized Plasma Source...

Dielectric barrier discharge ionization has gained significant interest due to its versatility and broad chemical coverage. Although electrospray ionization (ESI) is the most commonly used ionization source for organic contaminant analysis by liquid chromatography-mass spectrometry (LC-MS), it has limitations such as low ionization efficiency for nonpolar compounds and matrix effects. This study investigates the potential of flexible microtube plasma (FμTP) as an alternative ionization source for the LC-MS determination of multiclass pesticides comprising ESI-amenable and organochlorine contaminants. The analytical performance of FμTP was assessed in terms of limits of quantification, reproducibility, linearity, and matrix effects, comparing the results to those obtained with ESI and atmospheric pressure chemical ionization (APCI) sources. Sensitivity assessment based on calibration slopes showed that 70% of the pesticides had higher sensitivity with FμTP than with ESI. Regarding the matrix effects, between 76 and 86% of the pesticides showed negligible matrix effects for FμTP, compared to 35-67% for ESI and 55-75% for APCI across the different matrices evaluated. The study further explored the use of argon and argon-propane mixtures as alternatives to helium as discharge gases. Results showed similar LOQs for nearly 90% of the pesticides in the positive mode and 80% of the organochlorines in the negative mode. Notably, some ion species differed when using argon-based gases for certain organochlorine pesticides, suggesting the discharge gas influences the ionization mechanism, especially in the negative mode. Overall, FμTP proves to be a sensitive and robust miniaturized ionization source, expanding the chemical space and making it useful for both target and nontarget screening applications.