A novel dual ionization modality source for infrared laser ablation post-ionization mass spectrometry imaging to study fungicide metabolism and transport

We present a novel probe design for ambient laser-based mass spectrometry imaging combining electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) in a single probe, compatible with a commercial laser ablation electrospray ionization (LAESI) instrument. Here we describe the probe design considerations and features, as well as an in-house developed data processing routine designed to extract accurate mass spectrometry imaging data from ambient laser ablation post-ionization experiments. We characterize the probe performance in both APCI and ESI mode on a selection of compounds and show improved pixel-to-pixel repeatability for LA-APCI as compared to LAESI. We apply the dual ionization probe in APCI mode in a time series experiment to monitor agrochemicals on tomato plants. We investigate the translocation of fungicide isotianil and one of its metabolites, anthranilonitrile, by mass spectrometry imaging over a period of two weeks after application on a leaf surface. LA-APCI-MSI shows translocation of anthranilonitrile from treated leaves towards non-treated leaves. In summary, we demonstrate that LA-APCI imaging is a valuable addition to the ambient mass spectrometry toolbox, with particular advantages for imaging experiments across a variety of compounds