Rapid separation and desalination of antibiotics from highly saline seawater by mask–based paper spray ionization

Advances in mass spectrometry for antibiotic detection in marine environments are highly sought, with ambient ionization mass spectrometry (AIMS) providing a promising pathway for rapid and straightforward analysis of complex samples. However, effectively separating antibiotics in seawater using AIMS remains challenging due to high salt concentrations. Here, we introduce a technique——mask-based paper spray ionization (M–PSI)—for separating antibiotics in seawater through rapid adsorption and desorption. The response intensities of M–PSI-treated high-salinity samples were double as high as those of paper spray ionization-treated high-salinity (3.5 wt%) samples and 3−5 orders of magnitude higher than untreated medium-salinity (0.35 wt%) samples. M–PSI demonstrated compatibility with high-salinity, low-salinity, and salt-free samples, as well as biological samples like blood and urine. M–PSI enhanced spray stability, extended analysis duration, and yielded higher signal intensities compared to conventional paper spray ionization. Using M–PSI, four antibiotics (clarithromycin, azithromycin, ofloxacin, and sulfadimidine) were detected in high-salinity seawater samples, with a linear range of 1−1000 ng mL⁻¹ and limits of detection of 0.12, 0.08, 0.04, and 0.35 ng mL⁻¹, respectively. Method recoveries ranged from 93.1 % to 109.3 %, with an RSD below 8.3 %. This advancement offers a viable solution for the rapid online separation and determination of antibiotics in highly saline seawater.