Hand-Held Ultrasonic–Arc Discharge Ionization Enables Rapid On-Site Detection of Sulfur-Fumigated Wolfberries

Rapid on-site chemical analysis is increasingly important for food safety and agricultural quality control, yet many ambient ionization methods fail to combine portability with strong and informative ionization performance. Here, we present a hand-held ionization platform that integrates ultrasonic spray with arc discharge to achieve efficient sample nebulization and energetic ionization within a single device. This hybrid mode yields higher signal intensity than either technique alone and produces characteristic oxidation products that enable localization of double-bond positions in unsaturated fatty acids, surpassing the capabilities of nanoESI. Applied to sulfur-fumigated wolfberries, the device rapidly distinguished samples and revealed pronounced metabolic alterations associated with increasing fumigation levels; classification of 150 specimens using an AdaBoost model achieved 95% accuracy. Field tests further demonstrated seamless compatibility with portable mass spectrometers. Together, these results establish the ultrasonic-arc discharge platform as a compact and effective solution for real-time, on-site mass spectrometric analysis.